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Validity and reliability of speed tests used in soccer: A systematic review

  • Stefan Altmann ,

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing

    stefan.altmann@kit.edu

    Affiliation Department for Performance Analysis, Institute of Sports and Sports Science, Karlsruhe Institute of Technology, Karlsruhe, Germany

  • Steffen Ringhof,

    Roles Conceptualization, Data curation, Methodology, Validation, Writing – review & editing

    Affiliations Department for Performance Analysis, Institute of Sports and Sports Science, Karlsruhe Institute of Technology, Karlsruhe, Germany, Department of Sport and Sport Science, University of Freiburg, Freiburg, Germany

  • Rainer Neumann,

    Roles Conceptualization, Formal analysis, Investigation, Methodology, Validation, Writing – review & editing

    Affiliation Department for Performance Analysis, Institute of Sports and Sports Science, Karlsruhe Institute of Technology, Karlsruhe, Germany

  • Alexander Woll,

    Roles Conceptualization, Funding acquisition, Methodology, Resources, Validation, Writing – review & editing

    Affiliation Department for Social and Health Sciences in Sport, Institute of Sports and Sports Science, Karlsruhe Institute of Technology, Karlsruhe, Germany

  • Michael C. Rumpf

    Roles Conceptualization, Data curation, Formal analysis, Methodology, Supervision, Validation, Writing – review & editing

    Affiliation Sport Performance Research Institute New Zealand, Auckland University of Technology, Auckland, New Zealand

Validity and reliability of speed tests used in soccer: A systematic review

  • Stefan Altmann, 
  • Steffen Ringhof, 
  • Rainer Neumann, 
  • Alexander Woll, 
  • Michael C. Rumpf
PLOS
x

Abstract

Introduction

Speed is an important prerequisite in soccer. Therefore, a large number of tests have been developed aiming to investigate several speed skills relevant to soccer. This systematic review aimed to examine the validity and reliability of speed tests used in adult soccer players.

Methods

A systematic search was performed according to the PRISMA guidelines. Studies were included if they investigated speed tests in adult soccer players and reported validity (construct and criterion) or reliability (intraday and interday) data. The tests were categorized into linear-sprint, repeated-sprint, change-of-direction sprint, agility, and tests incorporating combinations of these skills.

Results

In total, 90 studies covering 167 tests were included. Linear-sprint (n = 67) and change-of-direction sprint (n = 60) were studied most often, followed by combinations of the aforementioned (n = 21) and repeated-sprint tests (n = 15). Agility tests were examined fewest (n = 4). Mainly based on construct validity studies, acceptable validity was reported for the majority of the tests in all categories, except for agility tests, where no validity study was identified. Regarding intraday and interday reliability, ICCs>0.75 and CVs<3.0% were evident for most of the tests in all categories. These results applied for total and average times. In contrast, measures representing fatigue such as percent decrement scores indicated inconsistent validity findings. Regarding reliability, ICCs were 0.11–0.49 and CVs were 16.8–51.0%.

Conclusion

Except for agility tests, several tests for all categories with acceptable levels of validity and high levels of reliability for adult soccer players are available. Caution should be given when interpreting fatigue measures, e.g., percent decrement scores. Given the lack of accepted gold-standard tests for each category, researchers and practitioners may base their test selection on the broad database provided in this systematic review. Future research should pay attention to the criterion validity examining the relationship between test results and match parameters as well as to the development and evaluation of soccer-specific agility tests.

Introduction

The game structure of soccer has dramatically changed over the last decades towards a more and more dynamic and faster playing style [1]. Compared to years past, modern soccer is denoted by shorter ball contact times, increased passing rates, higher player density, and faster transitions [1]. The changes in game structure also place modified demands on the players. These alterations not only affect technical and tactical aspects but particularly the players’ speed requirements. From a physical perspective, the players have to perform several accelerations and sprints at maximal speed with and without changes of direction throughout a match [24]. Moreover, players are forced to possess rapid information processing and to make fast and accurate decisions in order to be successful [1]. This indicates that speed in soccer encompasses both physical and perceptual-cognitive components [5].

As indicated above, speed is widely accepted to play a crucial role in soccer [6,7]. Therefore, speed testing has become a standard component of performance assessments [2,8]. For this purpose, a multitude of running-based tests has been developed aiming to examine several speed skills and have been implemented in research and practice [2,9]. More specifically, these speed tests can be categorized into linear sprinting, change-of-direction sprinting, repeated sprinting, agility, and combinations of these categories. In this context, linear sprinting relates to straight-line sprinting over various distances, including acceleration and maximum speed phases [10]. Moreover, change-of-direction sprinting comprises preplanned whole-body changes of directions as well as rapid movements and direction changes of the limbs [11,12]. Repeated sprinting refers to short-duration sprints (< 10 s) interspersed with brief phases of recovery (< 60 s) [13]. Finally, agility is considered an open skill and has been defined as a „rapid whole-body movement with change of velocity or direction in response to a stimulus”[11]. While linear sprinting, change-of-direction sprinting, and repeated sprinting mainly represent physically-driven speed skills, agility refers to both physical and perceptual-cognitive aspects of speed [5,13]. These skills share a relatively low common variance with limited training transfer between each other being evident. Hence, they can be considered as rather independent [12,1422]. Therefore, a comprehensive examination of speed should address all test categories.

From a practical perspective, the feasibility, equipment needed, and economical aspects represent important factors whether or not to choose a test. From a scientific perspective, however, tests should possess appropriate levels of psychometric properties, including validity and reliability, in order to be used with confidence and to be able to draw meaningful conclusions from test results [23,24]. While recent reviews have been published focusing on tests of motor abilities such as endurance [25] and strength [26] with regards to soccer, no overview on the validity and reliability of tests addressing speed skills is available.

Therefore, the aim of this systematic review is to review the available literature on speed tests used in soccer with a focus on the tests’ validity and reliability. The results of this review could help both scientists and practitioners decide which test(s) to choose depending on the specific aspects of speed being of interest.

Methods

This systematic review was written according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [27]. The protocol was not registered prior to the initiation of the project.

Literature search

A systematic review of the published literature was undertaken using the electronic databases PubMed and Web of Science during April and May 2018. An updated search regarding studies published after May 2018 was not conducted. The literature search was conducted by one researcher (SA). There was no restriction on publication date.

The following keywords were used to capture psychometric properties: psychometric, measurement.

The following keywords were used to capture validity: validity, logical, construct, convergent, discrimination, match performance, gold standard, level, standard.

The following keywords were used to capture reliability: reliability, repeatability, reproducibility, measurement error, consistency, smallest worthwhile change, minimal detectable change, typical error, usefulness.

The following keywords were used to capture speed testing and the different test categories: speed, quickness, sprint, acceleration, maximum speed, linear, change of direction, repeated sprint ability, agility, reactive agility, physical, unplanned, unanticipated, test, testing.

The following keywords were used to capture soccer: soccer, football.

Reference lists of retrieved full-text articles and recent reviews were examined to identify additional articles not identified by the initial search.

Eligibility criteria for study inclusion consisted of one of the following: (i) tests performed two or more times during one occasion (intraday reliability) or on two or more separate occasions (interday reliability); (ii) compared against other standards of play (construct validity); (iii) compared against match performance (criterion validity).

Except for reviews, all types of studies relating to at least one speed-test category (linear sprinting, repeated sprinting, change-of-direction sprinting, agility, and combinations) were taken into consideration. In addition, studies must have been published in English language in a peer-reviewed journal. As the present review focuses on adult players, only populations with a mean age of 17 years or older were considered. There was no restriction on gender (female and male) and playing level (e.g., recreational, amateur, semi-professional, professional). Complex tests incorporating passing or shooting were only considered when the part relating to speed was examined separately from the total test time. Studies investigating the factorial or convergent validity of speed tests were not included.

Literature selection

The literature selection consisted of two screening phases. In phase one, duplicates, titles, and abstracts were screened. In phase two, the full papers were screened using the eligibility (inclusion) criteria noted above.

Data extraction and analyses

Data were extracted independently by four researchers (SA, SR, RN, and MR) and documented using a Microsoft Excel 2016 spreadsheet (Microsoft Corporation, Redmond, Washington, USA). Extracted data from each study included publication details, number of participants, demographic information (including gender, age, playing level, and country), test category, test name, short test description, type, outcome measures as well as results for validity or reliability, respectively, and the information required to assess the methodological quality of each study. If more than one group of players were investigated in a study, only the groups with a mean age of 17 years or older were considered.

For reliability (both intraday and interday), intraclass correlation coefficient (ICC), Pearson’s r, and coefficient of variation (CV) values were recorded. While ICC and Pearson’s r represent relative reliability, CV is a measure of absolute reliability. By reflecting the degree to which indivuduals in a specific sample maintain their position over the course of repeated trials (interindividual variability), measures of relative reliability are affected by group homogeneity. Conversely, measures of absolute reliability relate to the variation over repeated trials within individuals (intraindividual variability). Therefore, they do not depend on group homogeneity [28]. Considering the ICC, a range of different approaches exist on how to interpret these values [28]. Following the recommendations of a review with a similar objective [29], in the present review, “good” reliability was considered ICC ≥ 0.75. This value was chosen as it appears to reflect a reasonable consensus as to what can be considered good reliability. The same value was applied for Pearson’s r. While a threshold of 10% for acceptable CV values has been suggested, this number seems rather arbitrary [28]. Therefore, CV values were interpreted in relation to each other.

Relating to construct validity, where possible, the percentage difference between playing levels and the respective effect sizes (ES) were calculated and rated according to Hopkins [30]. An ES less than 0.2 was considered a trivial effect; 0.2 ≤ ES < 0.6 a small effect; 0.6 ≤ ES < 1.2 a moderate effect; 1.2 ≤ ES < 2.0 a large effect; 2.0 ≤ ES < 4.0 a very large effect; and ≥ 4.0 an extremely large effect. In terms of criterion validity, the magnitude of the correlation coefficient between speed-test results and match parameters was considered as small (0.1 ≤ r < 0.3), moderate (0.3 ≤ r < 0.5), large (0.5 ≤ r < 0.7), very large (0.7 ≤ r < 0.9), and nearly perfect (r ≥ 0.9) [30].

Data were checked and verified by SA and discrepancies were resolved through discussion. The synthesis of the results was carried out descriptively.

Assessment of methodological quality

The methodological quality of the studies included in the review was assessed through a modified version of the critical appraisal tool [31]. The modified checklist included nine items:

  1. Subject characteristics were clearly described (validity and reliability studies)
  2. Competence of the raters was clearly described (validity and reliability studies)
  3. Reference (match data) was clearly described (criterion validity studies)
  4. Raters were blinded to their own prior findings (reliability studies)
  5. Time interval between the reference (match data) was suitable (criterion validity studies)
  6. Time interval between repeated measures was suitable (reliability studies)
  7. Test execution was described in sufficient detail to permit replication of the test (validity and reliability studies)
  8. Methodological aspects (e.g., timing technology, starting position, surface) were described in sufficient detail to permit replication of the test (validity and reliability studies)
  9. Statistical methods were appropriate for the purpose of the study (validity and reliability studies)

From the original checklist, the items 6 (Variation of order of examination), 9 (Independence of reference standard from index test), and 12 (Explanation of withdrawals) were not included as they were thought to be not appropriate for the purpose of this review. Conversely, item 8 (Methodological aspects) was added to the checklist because of the considerable influence of methodological aspects on results, validity, and reliability of speed tests [32]. Due to the large absolute errors associated with manual timing through stopwatches, tests using this timing technology were excluded [32].

The score for each item was determined as follows: 2 = clearly yes; 1 = to some extent; 0 = clearly no. Consequently, the maximal possible score was 14 (criterion) and 10 (construct) for validity studies, and 14 (intraday and interday) for reliability studies. In the case of more than one test being examined in a single study, the score was calculated for each test separately. According to Barrett et al. [33], the methodological quality was rated as high when > 60% of the maximal possible score was obtained (corresponding to a score of > 6 for construct validity studies and > 8.4 for criterion validity, intraday, and interday reliability studies).

Results

Search results

A flow diagram for the selection of the studies can be found in Fig 1. 10,656 records were retrieved through the initial search in the electronic databases. The removing of duplicates yielded 8,950 studies that were screened for the title. Subsequent abstract screening (1,270 records) led to the exclusion of further 1,131 studies. Consequently, the full-texts of 139 articles were assessed for eligibility, with 49 articles being excluded. The reasons for exclusion during full-text screening were

  1. ■. no validity or reliability reported (16 studies),
  2. ■. inappropriate timing technology (manual timing) used (12 studies),
  3. ■. mean population age < 17 years (8 studies),
  4. ■. reliability reported as a range over several tests (including strength and endurance tests) (5 studies),
  5. ■. full-text not written in English language (3 studies),
  6. ■. full-text not available (3 studies), and
  7. ■. sports other than soccer included in calculations of validity or reliability (2 studies).

Ultimately, 90 studies were included in this review.

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Fig 1. Flow diagram of the search and selection process for inclusion of articles.

https://doi.org/10.1371/journal.pone.0220982.g001

Overview on studies and tests included

From the 90 studies included, 20 referred to validity only, 60 to reliability only, and 10 to both validity and reliability. An overview on the number of the tests regarding validity and reliability in each category is presented in Table 1. Ball dribbling was included in change-of-direction sprint tests (4 validity, 3 reliability) and in combinations (1 validity). A total of 3,901 participants (mean ± standard deviation 56 ± 108, median 25, range 7–939) with an average age from 17 to 33 years (mean ± standard deviation 21 ± 3 years, median 21 years) were involved. Most studies examined male players (74), while female (13) and both male and female players (3) were studied less often. The playing level covered a wide range between recreational and national team players.

Assessment of methodological quality

Construct and criterion validity were reported for 41 and 6 tests, respectively. The mean score was 6.4/10 (range 4–10) and 9.8/14 (range 9–12) leading to a high rating of methodological quality.

Intraday and interday reliability were reported for 57 and 56 tests, respectively, with reliability type being not specified for 7 tests. The mean score was 7.9/14 (range 5–11) and 7.8/14 (range 5–11), which is below the threshold for a high rating of methodological quality (Tables 26, column ‘MQ’).

Subject characteristics and test execution were clearly depicted in most of the studies. In addition, the majority of studies used appropriate statistical methods at least to some extent. Conversely, only a small amount of studies stated the competence of the raters or described methodological aspects in sufficient detail, with blinding of the raters being stated in none of the studies.

Study characteristics and main findings

Linear-sprint tests.

Linear-sprint tests were examined 67 times. The distances investigated ranged from 5 to 200 m. The most frequent studied distances were 10, 20, and 30 m. In terms of construct validity, the test results between the playing levels differed between -1.6 and 5% (ES = -0.33–1.3), whereas positive values indicate that the higher-level players performed better than the lower-level players. Negative values indicate the opposite. Regarding criterion validity, the highest correlation coefficient found between test results and match parameters was r = -0.73.

Intraday reliability ranged from 0.17 to 0.99 (ICC) and from 0.7 to 7.8% (CV), whereas interday reliability ranged from 0.77 to 0.98 (ICC) and from 0.5 to 10.9% (CV).

Study findings in relation to the validity and reliability of linear-sprint tests are illustrated in Tables 23.

Repeated-sprint tests.

Repeated-sprint tests were examined 15 times. The investigated tests incorporated 3 to 15 repetitions over distances ranging from 15 to 40 m with active and passive recovery between approximately 15 s and 1 min. The most frequent utilized tests comprised of 6 x 20-m sprints with approximately 20–25 s of active recovery (n = 3) and 7 x 30-m sprints with approximately 20–30 s of active or passive recovery (n = 3).

In terms of construct validity, the test results between the playing levels ranged from 0.3 to 2.7% (ES = 0.14–0.9) for the fastest time, between 0.4 and 2.6% (ES = 0.1–0.88) for the average time, and between 2.3 and 10.3% (ES = 0.83–5.5) for the total time. Results for the percent decrement ranged from -22.9 to 14.5% (ES = -0.4–0.39). Positive values indicate that the higher-level players performed better than the lower-level players. Negative values indicate the opposite. Regarding criterion validity, the highest correlation coefficient found between test results and match parameters was r = -0.51.

Intraday reliability was ICC = 0.75 and CV = 0.8% for the total time. Interday reliability was ICC = 0.88 and CV = 5.0% for the fastest time as well as ICC = 0.90 and CV = 5.0% for the average time. Moreover, ICCs and CVs ranged from 0.91 to 0.99 and from 0.8 to 5.0% for the total time and from 0.11 to 0.14 and from 16.8 to 46.0% for the percent decrement, respectively.

Study findings in relation to the validity and reliability of repeated-sprint tests are illustrated in Tables 45.

Change-of-direction sprint tests.

Change-of-direction sprint tests were examined 60 times. The investigated distances ranged from 10 to 60 m including 1 to 9 directional changes of 45° to 270°. The most frequent studied tests were the T Test (n = 10), 505 test (n = 4), and zig-zag tests in various modifications (n = 5).

In terms of construct validity, the test results between the playing levels differed between -5.4 and 12.2% (ES = -1.89–1.64). Positive values indicate that the higher-level players performed better than the lower-level players. Negative values indicate the opposite. Regarding criterion validity, the highest correlation coefficient found between test results and match parameters was r = -0.56.

Intraday reliability ranged from 0.37 to 0.99 (ICC) and from 1.1 to 13.0% (CV), whereas interday reliability ranged from 0.63 to 0.98 (ICC) and from 0.8 to 4.0% (CV).

Study findings in relation to the validity and reliability of change-of-direction sprint tests are illustrated in Tables 67.

Agility tests.

Agility tests were examined 4 times. The investigated distances ranged from 8 to 40 m with 1 to 9 directional changes of 45° to 180°. Flashing light, video, and human stimuli were applied to indicate the directional changes. Each test was investigated once.

There were no studies investigating the construct or criterion validity of agility tests. Intraday reliability ranged from 0.70 to 0.88 (ICC) and from 3.7 to 4.9% (CV), whereas interday reliability was 0.70 (ICC) and ranged from 0.8 to 2.3% (CV).

Study findings in relation to the reliability of agility tests are illustrated in Table 8.

Combinations.

Combinations of the other test categories were examined 21 times. The investigated tests ranged from 3 to 10 repetitions over distances from 20 to 40 m with 1 to 5 directional changes of 45° to 180°. Both active and passive recovery ranging from approximately 15 to 40 s were utilized. Light stimuli were applied in all tests. The most frequent studied tests were the Bangsbo sprint test and the repeated shuttle-sprint test.

In terms of construct validity, the test results between the playing levels differed between 0.6 and 2.4% (ES = 0.44–0.82) for the fastest time, between 0.4 and 15.4% (ES = 0.28–15.24) for the average time, and between 0.4 and 9.7% (ES = 0.16–0.60) for the total time. Results for the percent decrement ranged from -23.4 to 45.9% (ES = -0.74–1.60). Positive values indicate that the higher-level players performed better than the lower-level players. Negative values indicate the opposite. Regarding criterion validity, the highest correlation coefficient found between test results and match parameters was r = -0.74.

Intraday reliability was ICC = 0.89 for the fastest time. Interday reliability ranged from 0.15 to 0.79 (ICC) and from 1.1 to 9.0% (CV) for the fastest time as well as from 0.58 to 0.81 (ICC) and from 0.9 to 10.0% (CV) for the average time. Moreover, ICCs and CVs ranged from 0.89 to 0.94 and from 0.8 to 10.0% for the total time, and from 0.17 to 0.49 and from 29.8 to 51.0% for the percent decrement, respectively.

Study findings in relation to the validity and reliability of combinations are illustrated in Tables 910.

Discussion

Overview

This review examined the validity and reliability of different speed tests used in soccer, categorized into linear-sprint tests, repeated-sprint tests, change-of-direction sprint tests, agility tests, and combinations of these tests. In general, the high number of total studies and single tests included in this review highlights the importance of speed and speed testing in soccer. The majority of studies examined male players, which corresponds to the gender distribution of soccer players [123]. The tests were applied in a variety of performance levels, thereby allowing for both general and playing-level specific considerations.

Several different tests were identified in each category, while no accepted gold-standard tests seem to exist. The most studied tests were classified as linear-sprint tests and change-of-direction sprint tests, followed by combinations and repeated-sprint tests. Agility tests were the least studied. The amounts of tests in each category might be explained by differences relating to the complexity of the measurement set-up, test execution, and data analysis. For example, a 30-m linear sprint is relatively easy to conduct, while agility tests require the application of a stimulus which must be achieved through specific timing equipment incorporating flashing lights, life-size video clips or experienced humans [5,8].

Regardless of the test category, construct validity was investigated more frequently than criterion validity. This may be due to the additional match data needed for the same players in the latter case. Conversely, intraday and interday reliability were studied equally, although these approaches differ markedly in their organizational effort. However, in order to get a more holistic insight into the measurement properties of the tests, both types of validity and reliability should be assessed.

In the following paragraphs, the tests in each of the categories are discussed in relation to their validity and reliability. Based on this, recommendations for test selection in each category are given.

Study characteristics and main findings

Linear-sprint tests.

In terms of construct validity, the majority of studies report faster sprint times in favor of the higher-level players compared to the lower-level players. Such results have been found for both the comparison within professional players, e.g., national team vs. 1st division players (trivial to small ES) [44,45], and the comparison between professional and amateur players (trivial to large ES) [36,37,40,43]. In addition, drafted players in try outs of a professional women’s soccer league demonstrated faster sprint times than non-drafted players (small to moderate ES) [42]. In line with this, starters outperformed non-starters of the same team (trivial to moderate ES), with a tendency to larger ES over longer distances [38,39,41].

However, tendencies for larger performance differences with increasing sprinting distance were not evident when all abovementioned studies were taken into consideration. Therefore, it might be concluded that all distances investigated (from 5 to 40 m) seem to be equally important in soccer, even though short sprints and accelerations (e.g., 10 m) occur more frequently than longer sprints (e.g., 40 m) during matches [2,3,124].

Some investigations reported faster sprint times for the players assigned to the lower playing level compared to those of the higher playing levels [35,47,48]. Besides the only trivial to small ES, in two studies, this finding was only obtained for a 10-m distance [48] and for males [47] with contrary results being obtained for a 20-m distance and females, respectively. Furthermore, in the third study [35], the lower-level players consisted of young elite amateur players who were training every day. Thus, both groups of players were considered as “high-level” players by the authors of that study.

In terms of criterion validity, only two studies were identified. Djaoui et al. [35] found a large relationship between the results of a 40-m sprint test and the maximal sprinting speed during matches. In addition, moderate to large relationships were reported for 5-m and 30-m sprints on the one side and high-intensity and sprinting distances during several periods of matches on the other side [34].

Considering both intraday and interday reliability, 40 studies report ICCs > 0.75 and CVs < 3.0% [21, 34, 43, 4884]. The studies obtaining lower reliability (ICC ≥ 0.55 and CV ≤ 10.9%) integrated linear-sprint testing into complex tests [86] or match-simulation protocols [73,87] or required the players to adopt a defined running velocity at the start line [92]. In addition, it seems that the reliability decreases when considering longer terms, such as 6–12 months between measurements, with Pearson’s r and CV being 0.77–0.90 and 1.8–3.3%, respectively [44].

While more consistent reliability indices were obtained whilst utilizing established timing technologies such as timing lights and radar guns, varying results have been obtained for global positioning systems (ICC = 0.17–0.86; CV = 2.1–7.8%) [62,94]. Although not consistent over all studies, both intraday and interday reliability have been reported to be higher with increasing sprinting distance [21,45,66,67,80,88].

Given the results of the abovementioned studies, linear-sprint tests over distances up to 40 m possess acceptable construct validity and high intraday and interday reliability to assess linear-sprinting skills in soccer players.

Repeated-sprint tests.

The identified repeated-sprint tests differ in their number of repetitions (3 to 15), the distance per repetition (15 to 40 m), and the type (active and passive) and duration (approximately 15 s to 1 min) of recovery per repetition. Common parameters derived from such tests include the fastest time, average time, total time, and percent decrement. The initial sprint time was reported less frequently.

The construct validity of repeated-sprint tests has been investigated in few studies (n = 5). In the majority of the studies, the higher-level players outperformed the lower-level players for all abovementioned parameters when comparing professional vs. semi-professional, college, university or regional level players; however, with considerably varying ES (trivial to very large) [9699]. Only one study [100] found the lower-level players outperforming the higher-level players. However, this was true for percent decrement only. This result might be related to the low reliability of this parameter, which will be discussed later. Except for percent decrement, no parameter was superior to another in its ability to distinguish between playing levels. Interestingly, the largest ES between higher- and lower-level players were reported in a study with females [98]. This finding mirrors the observation that repeated-sprint bouts occur more frequent during matches of professional females in comparison with those of professional males [98,125,126].

Only one study examined the criterion validity of a repeated-sprint test (6 x 6-s sprints, 20 s passive recovery) in professional male players. A large correlation was found between percent decrement in the test and the frequency of high-intensity actions interspersed by recovery times ≤ 20 s during matches. In addition, a moderate correlation was reported between average velocity in the test and recovery time between high-intensity actions during matches [95]. Given the lack of further notable relationships between the test parameters and the frequency of repeated high-intensity bouts during matches, the authors question the criterion validity of this and similar tests. Indeed, more investigations using a similar study design are needed to confidentially draw conclusions with respect to criterion validity.

As a repeated-sprint test elicits considerable degrees of fatigue, multiple testing on one occasion (intraday reliability) appears to be rather inappropriate. Therefore, most of the studies reported interday reliability values (n = 6). Intraday reliability was examined less often (n = 2) and one study did not state the reliability type. ICCs for the average and total time exceeded 0.75 in all studies and were mostly higher than 0.90 while CVs were lower than 3.0% in 7 out of 9 studies [78, 81, 83, 97, 98, 101103]. The reliability of the fastest time was 0.88 and 5.0% for ICC and CV, respectively [97]. Conversely, the percent decrement as a measure of fatigue was markedly less reliable (ICC ≥ 0.11, CV ≤ 46.0%) [81,98]. Pacing strategies of the players throughout the sprints was stated as a possible reason [127].

No differences between different recovery durations and modes were obvious regarding validity and reliability. However, the recovery duration should be short enough (e.g., < 30 s) to provoke the occurrence of fatigue [13]. Additionally, the recovery mode should be active in order to replicate the match demands [95].

The use of repeated-sprint tests has been criticized by some authors [2,128]. Their criticism is based on the very large correlations between the fastest time, average time and total time of such tests on the one side and results of single linear-sprint tests on the other side. Additionally, the low reliability of fatigue measures such as the percent decrement questions the additional benefits derived from repeated-sprint tests compared to linear-sprint tests. Nevertheless, based on the studies included in this review, repeated-sprint tests differing in the number of repetitions, the distance per repetition, and the recovery phases possess acceptable levels of construct validity and high levels of reliability for examining repeated-sprinting skills in adult soccer players regarding all parameters, except for percent decrement.

Change-of-direction sprint tests.

A plethora of change-of-direction sprint tests has been developed and introduced into soccer. Some of these tests carry the word "agility" in their name (e.g., “Illinois agility run”, “Agility T Test”) but do not contain a response to a stimulus. Therefore, they were classified as change-of-direction sprint tests in this review. Change-of-direction sprint tests vary in their total distance (10–60 m) as well as number (1–9) and angles (45–270°) of directional changes. A frequently applied type of test involves shuttle sprints, where players sprint to a line, change the direction by 180°, and sprint back. Furthermore, test set-ups using zig-zag or slalom patterns are common. In addition, some popular tests were originally developed for sports other than soccer, such as the 505 test, Illinois test, and T Test.

The construct validity of change-of-direction sprint tests has been evaluated in a number of investigations (n = 14). As with linear-sprint tests and repeated-sprint tests, the higher-level players obtained faster times than the lower-level players in the vast majority of studies (n = 13). This applied to the comparison of starters vs. non-starters in a professional team (trivial to small ES) [41], professional vs. amateur players (small to large ES) [106], 1st division vs. regional division players (moderate ES) [43], seniors vs. juniors of the same professional club (large ES) [47] and selected vs. deselected players in talent a program (small ES) [105]. Similar results were obtained when players were required to dribble a ball, commonly in a slalom or zig-zag manner (trivial to large ES) [43,47,105107].

In contrast, the study of Keiner et al. [108] showed superior performance of U21-players of a professional soccer club compared to professional adult players. However, this was particularly evident for a group of U21-players who had performed a specific strength training program for the two proceeding years. In contrast, no detailed information was provided relating to the training contents of the professional adult players.

Only one study addressing the criterion validity of change-of-direction sprint tests met the inclusion criteria [34]. This study investigated the relationships between the results of the T Test and match parameters. Compared to 5-m and 30-m sprints, as depicted above, markedly lower relationships were evident. This finding particularly applied for the correlation between the T Test and sprinting distances during several periods of the match [34]. Therefore, it might be concluded that a high change-of-direction performance translates into sprinting behavior during matches only to a limited extent. Possibly, other match parameters that reflect change-of-direction behavior more directly might represent a more suitable alternative.

A considerable number of studies (n = 27, encompassing 45 tests) reported intraday or interday reliability of various change-of-direction sprint tests with ICCs usually exeeding 0.75 and CVs lower than 3.0% [34, 43, 49, 50, 5660, 71, 80, 82, 106, 108, 109, 111]. Similar reliability was demonstrated in the four studies that included ball dribbling into the test [43,88,107,110].

Conversely, some studies report high relative reliability (ICCs 0.92–0.99) and somewhat lower absolute reliability (CVs 2.9–5.9%) [114,115]. Lower reliability was reported for shuttle sprints over 18.2 m (ICC = 0.72) [21] and 30 m (ICC = 0.63) [14].

As with linear-sprint testing, a change-of-direction sprint test using a global positioning system was reported less reliable (ICCs 0.37–0.77; CVs 3.7–13.0%) [62], supporting the utilization of appropriate timing technologies during speed testing [32].

The high number of change-of-direction sprint tests and the large differences in test design highlight the lack of an accepted gold standard [129]. However, some popular tests have been evaluated in several studies, such as the 505 test or the T Test. Several modifications of these tests have been applied. For example, the linear-sprint phase prior to the directional change of 180° in the 505 test varies between 5 m and 15 m in the literature [21,56,66,80]. Regarding the T Test, as many as six different types of this test have been used, differing in the total distance (20–40 m), the type of locomotion (shuffling, backpedaling, and sprinting), and the inclusion or exclusion of ball dribbling [21,34,43,66,82,85,90,106,111,115]. One study even added a visual stimulus prior to changing direction, leading this modification to be classified as an agility test [83]. Despite these modifications, all types of the 505 test and the T Test have been shown to be valid (T Test: ES = 0.62–1.50 in favor of the higher-level players) and/or reliable (505 test: ICC = 0.87–0.99, CV = 2.2–3.3%; T Test: ICC = 0.70–0.95, CV = 0.8–4.0%).

While many tests, including the 505 test and the T Test, do not mimic the match demands [2], the confirmed validity and reliability of these two tests for assessing change-of-direction sprinting skills through a number of studies allow their application until more game-specific tests are thoroughly evaluated.

Agility tests.

Since the introduction of a classic agility test for invasion sports by Sheppard et al. [130], this test has been evaluated and modified for the specific demands of different sports, such as Australian football, basketball, netball or rugby [5,131].

With respect to the inclusion criteria of this review, no study was identified that evaluated the validity of an agility test in soccer players. This is somewhat surprising as agility tests have been shown to possess high levels of construct validity by discriminating between playing levels in Australian football and rugby league, while change-of-direction sprint tests did not [12]. This finding is mainly attributed to the superior anticipation and decision-making skills of higher-level players [5]. It should be noted that studies examining the construct validity of such tests in soccer exist. However, either the (sub-)sample investigated for this specific outcome was too young to be considered for this review [114] or the population also included sports other than soccer (e.g., futsal) [132]. Although more complex than capturing the number of sprints or maximum speed during matches, methods for analyzing decision-making during training and matches have already been applied to soccer and might serve as a foundation for evaluating the criterion validity of agility tests [133,134].

Conversely, the reliability of agility tests has been addressed in four studies, all of them relating to interday reliability [55,83,86,114]. Two of the tests used flashing lights as a stimulus (ICCs 0.70–0.87; CVs 0.8–4.9%) [83,114]. One study [55] adopted the classic agility test by Sheppard et al. [130], which requires the players to respond to different movements of a tester (human stimulus) by sprinting in the same direction as the tester (CV = 0.8%). The last study examined agility as a part of a complex test [86]. Here, players respond to a video of a life-size soccer player dribbling the ball towards the player by sprinting in the same direction as the video (ICC = 0.70; CV = 2.3%). The slightly lower reliability of agility tests compared to the other test categories might be attributed to the complexity of such tests, incorporating both physical and perceptual-cognitive aspects of speed. While several parameters can potentially be investigated during agility tests, such as the response time at the start, the decision-making time or the response accuracy [5], the abovementioned studies were limited to the total time to complete the test.

In terms of the applied stimuli, it has been shown in other sports (e.g., Australian rules football, field hockey) that humans or video sequences appear to be more appropriate than flashing lights when examining construct validity [5]. This seems reasonable as the latter does not allow higher-level players to utilize their anticipation and decision-making skills, but simply to react to a non-specific signal [135]. Given the small total number of investigations and the lack of studies using humans or video sequences as a stimulus, it can be concluded that the soccer-specific agility research is still in its infancy.

Combinations.

This test category combines elements of two or more of the abovementioned test categories. Most of the studies examined pre-planned repeated change-of-direction sprint tests with or without ball dribbling (10 studies encompassing 12 tests), while two studies analyzed repeated change-of-direction sprint tests in response to a stimulus. Thereby, such tests comprise elements of repeated-sprint tests and change-of-direction sprint tests, and sometimes even those of agility tests. Similar to repeated-sprint tests, the fastest time, average time, total time, and percent decrement are commonly investigated during such tests. The most utilized tests were the (modified) Bangsbo sprint test [119122] and the repeated shuttle-sprint test [116118,122].

The construct validity of combination tests was supported in the vast majority of studies for most of the parameters in question. Specifically, the higher-level players performed better than their lower-level counterparts when comparing professional vs. semi-professional players (small to very large ES) [118,119], professional vs. amateur players (trivial to very large ES) [97,117,118], 2nd team vs. U19 players of a professional club (small to moderate ES) [96] or selected vs. deselected players of a talent development program (small to moderate ES) [105]. Similarly to the results of the repeated-sprint tests, the percent decrement was not always able to discriminate between playing levels, with the lower-level players obtaining better scores in some studies (trivial to moderate ES) [96,97]. All other parameters were able to distinguish between playing levels.

The criterion validity of combination tests has been evaluated in two studies [113,116]. In the study of Rampinini et al. [116], the average time of a repeated shuttle-sprint test was largely correlated to the sprinting distance and very high-intensity running distance during professional matches. However, no notable relationships were evident between the fastest time or percent decrement and match variables. The second study analyzed a reactive repeated-sprint test involving changes of direction in response to a light stimulus [113]. The authors found large to very large correlations between the total time of the test and match parameters related to high-speed running. Small to large associations were reported for the total distance covered during matches [113].

In terms of reliability, the interday reliability of combination tests was addressed in a number of studies (5 studies encompassing 7 tests), while the intraday reliability was examined less frequent (1 study encompassing 2 tests). Varying results were obtained for different parameters. ICCs and CVs for the average time and total time were > 0.75 and < 2.0%, respectively, in most studies [104,113,118,120122]. However, high CVs of 10.0% have also been found for these parameters [97]. Moreover, one study reported low relative reliability for the fastest time (ICC = 0.15) [118], while high absolute reliability (CV = 1.1%) was evident for the same parameter in another study [113]. More consistently, percent decrement was found to not be reliable (ICC = 0.17, CV = 51.0%) [97,118]. In addition, the relative reliability in long-term (3 months between occasions) seems to be somewhat lower compared to short-terms (ICC for average time 0.58), while the absolute reliability remains high (CV for average time 0.9%) [118].

In sum, the total and average time possess the highest degree of validity and reliability. Specifically, this was confirmed for the Bangsbo sprint test and the repeated shuttle-sprint test in a number of studies. Moreover, it should be noted that although evaluated in a single study only, the validity and reliability was confirmed for the reactive repeated-sprint test, which has been designed on the basis of match analysis.

Limitations.

The findings of this systematic review should be interpreted in light of its limitations. We did not conduct an updated search that included studies published after May 2018. In addition, only studies examining soccer players with an average age of 17 years or above were considered. This automatically excludes investigations in younger age groups [9], which could have broadened the database. However, the number of included articles (n = 90) was already high in this review and results from other sports, although related, or differing age groups may not always be transferable [136].

We excluded investigations applying manual timing due to large absolute errors and issues relating to inter-rater reliability with this timing technology [32]. While this approach further reduces the available database, it ensures that an appropriate timing technology has been used in the studies, thereby accounting for adequate methodological quality in this regard.

The methodological quality of the construct and criterion validity studies was rated as high, while the scores of the intraday and interday reliability studies were somewhat lower. The latter finding might be explained by the inclusion criteria, as there was no restriction on the type of studies. Therefore, studies in which the reliability assessment was not the main aim were also included. While being well-designed for their primary aim (e.g., the evaluation of a training intervention), the necessary information for the reliability assessment were not always given.

In addition, the assessment of methodological quality itself should be viewed critically. Unfortunately, no assessment tool was applicable without modifications for the purpose of this review. In this context, another frequently used tool for the evaluation of measurement properties, the COSMIN checklist [137], seems more appropriate in relation to questionnaire-based studies [138] than for performance testing. Therefore, we made use of the critical appraisal tool by Brink & Louw [31] including some modifications, which promised a more suitable assessment of methodological quality of performance testing.

Another limitation might be position-specificity. We reported study results for all players of a team as a whole, thereby not accounting for position-specific demands which could lead to differing validity and reliability of speed tests and, therefore, specific test recommendations for each position [88,139].

Further considerations and future research

Although a test may have shown to be valid and reliable, it does not automatically guarantee that the derived results provide new and useful information to the coach and the individual players [140]. While this issue seems still to be discussed [141], methodological barriers to data collection and analysis are overcome by modern technologies. As a result, researchers can better identify crucial factors of (speed) performance in soccer and consequently to develop tests with direct impact on coaches and players [140]. One solution might be the implementation of test designs based on detailed analysis of match demands. In fact, few studies clearly stated such an approach (e.g., [98,113]). However, this seems promising for future studies. Based on this, more studies are needed examining the relationship between test results and match parameters (criterion validity) throughout all test categories.

Besides intraday and interday reliability, it is of further interest to know if small performance changes can be identified using a specific test [142,143]. In particular, this becomes a matter at a professional level, where performance gains are usually small [144]. This test property, commonly referred to as usefulness, is determined through the ratio of the intra-individual variability and the so-called smallest worthwhile change (SWC) [143]. While the intra-individual variability is usually expressed as a CV, the SWC can either be calculated as 0.2 x standard deviation of a given population, representing a small effect, or a pre-defined threshold. Given the example of a 20-m linear-sprint test, Haugen et al. [2] stated that the SWC relates to approximately 0.02 s when expressed as a small effect. Considering a real-world scenario, a gap of 30 cm to 50 cm might be decisive in a sprint duel of two players. In this case, the SWC as a pre-defined threshold corresponds to 0.04–0.06 s over a 20-m distance. These approaches might not only be applied to linear-sprint testing, but also to the other test categories. However, being reported scarcely in the identified studies, the usefulness was not included in this review. Indeed, it has been highlighted that this test property is population-specific to great extends and, therefore, should be determined for each investigation or team separately [142].

Although demonstrating good validity and reliability, the value of repeated-sprint tests has been questioned, as mentioned above. As repeated accelerations have been found to occur much more frequently during matches [3], the concept of repeated-acceleration bouts has recently been introduced [125,145]. Therefore, the development and evaluation of repeated-acceleration tests should be subject of further investigations.

Lastly, agility tests are underrepresented compared to the other test categories. Based on the promising results from related sports evaluating such tests [5] and the increasing overall game speed [1], requiring the players to make fast decisions and perform an adequate motor response, more research with respect to agility tests is recommended. Particularly, tests using scenarios close to the game and specific stimuli seem appropriate.

Conclusion

Speed is considered a crucial factor for overall performance in soccer. As most of the test categories evaluated in this review share a relatively low common variance, they represent rather independent skills. Therefore, no single test is appropriate to measure all aspects of speed concurrently, thus, a comprehensive examination of speed should cover all test categories.

Linear-sprint tests over various distances (5 to 40 m) can be used to determine acceleration and maximal speed. Thereby, such tests have been shown to be able to distinguish between playing levels, to correlate with sprint-related parameters during matches, and to possess high levels of reliability. Although criticized for not replicating the match demands, repeated-sprint tests of different number of repetitions, distances per repetition as well as types and durations of recovery have been reported to be valid in terms of discriminating playing levels and to be highly reliable. However, this specifically applies to the total time and the average time of such tests, while the use of percent decrement should be treated with caution. A high number of studies identified addressed change-of-direction sprint tests. Such tests vary dramatically in their total distance, number and angles of directional changes, and often do not mimic the match demands. Nevertheless, a number of tests, including the 505 test and T Test, possess high construct validity and reliability, thereby supporting their utilization in soccer. Conversely, agility tests have been investigated scarcely. While no information on the validity of agility tests is currently available, acceptable but slightly lower reliability compared to the other categories has been reported for tests applying flashing lights, video sequences, and humans as a stimulus. Combinations include elements of two or more test categories, commonly those of repeated-sprint and change-of-direction sprint tests and sometimes even agility tests. The total and average time possess the highest degree of validity and reliability, most frequently reported for the Bangsbo sprint test and the repeated shuttle-sprint test.

As currently stated, there is a lack of an accepted gold standard test in most of the categories. Researchers and practitioners might base their test selection on the comprehensive validity and reliability database provided in this review.

Supporting information

S1 Text. Full electronic search strategy for PubMed.

https://doi.org/10.1371/journal.pone.0220982.s002

(DOCX)

Acknowledgments

Prof. Claudio Nigg for his support in preparing the manuscript.

References

  1. 1. Wallace JL, Norton KI. Evolution of World Cup soccer final games 1966–2010. Game structure, speed and play patterns. J Sci Med Sport. 2014; 17: 223–228. pmid:23643671
  2. 2. Haugen T, Tønnessen E, Hisdal J, Seiler S. The role and development of sprinting speed in soccer. Int J Sports Physiol Perform. 2014; 9: 432–441. pmid:23982902
  3. 3. Varley MC, Aughey RJ. Acceleration profiles in elite Australian soccer. Int J Sports Med. 2013; 34: 34–39. pmid:22895869
  4. 4. Dellal A, Chamari K, Wong DP, Ahmaidi S, Keller D, Barros R, et al. Comparison of physical and technical performance in European soccer match-play. FA Premier League and La Liga. Eur J Sport Sci. 2011; 11: 51–59.
  5. 5. Paul DJ, Gabbett TJ, Nassis GP. Agility in Team Sports. Testing, Training and Factors Affecting Performance. Sports Med. 2016; 46: 421–442. pmid:26670456
  6. 6. Faude O, Koch T, Meyer T. Straight sprinting is the most frequent action in goal situations in professional football. J Sports Sci. 2012; 30: 625–631. pmid:22394328
  7. 7. Jeffreys I, Huggins S, Davies N. Delivering a Gamespeed-Focused Speed and Agility Development Program in an English Premier League Soccer Academy. Strength and Conditioning Journal. 2018; 40: 23–32.
  8. 8. Turner A, Walker S, Stembridge M, Coneyworth P, Reed G, Birdsey L, et al. A Testing Battery for the Assessment of Fitness in Soccer Players. Strength and Conditioning Journal. 2011; 33: 29–39.
  9. 9. Paul DJ, Nassis GP. Physical Fitness Testing in Youth Soccer. Issues and Considerations Regarding Reliability, Validity, and Sensitivity. Pediatric Exercise Science. 2015; 27: 301–313. pmid:26331619
  10. 10. Rumpf MC, Lockie RG, Cronin JB, Jalilvand F. Effect of Different Sprint Training Methods on Sprint Performance Over Various Distances. A Brief Review. Journal of Strength and Conditioning Research. 2016; 30: 1767–1785. pmid:26492101
  11. 11. Sheppard JM, Young WB. Agility literature review: classifications, training and testing. J Sports Sci. 2006; 24: 919–932. pmid:16882626
  12. 12. Young WB, Dawson B, Henry GJ. Agility and Change-of-Direction Speed are Independent Skills. Implications for Training for Agility in Invasion Sports. International Journal of Sports Science & Coaching. 2015; 10: 159–169.
  13. 13. Girard O. Mendez-Villanueva A., Bishop D. Repeated-sprint ability—part I. Factors contributing to fatigue. Sports Med. 2011; 41: 673–694. pmid:21780851
  14. 14. Shalfawi SA, Young M, Tønnessen E, Haugen TA, Enoksen E. The effect of repeated agility training vs. repeated sprint training on elite female soccer playsers physical performance. Kinesiologia Slovenica. 2013; 19.
  15. 15. Buttifant D, Graham K, Cross K. 55 agility and speed in soccer players are two different performance parameters. 4th ed.: Science and football IV; 2001.
  16. 16. Little T, Williams AG. Specificity of acceleration, maximum speed, and agility in professional soccer players. Journal of Strength and Conditioning Research. 2005; 19: 76–80. pmid:15705049
  17. 17. Sassi RH, Dardouri W, Yahmed MH, Gmada N, Mahfoudhi ME, Gharbi Z. Relative and absolute reliability of a modified agility T-test and its relationship with vertical jump and straight sprint. Journal of Strength and Conditioning Research. 2009; 23: 1644–1651. pmid:19675502
  18. 18. Šimonek J, Horička P, Hianik J. The differences in acceleration, maximal speed and agility between soccer, basketball, volleyball and handball players. jhse. 2017; 12.
  19. 19. Vescovi JD, McGuigan MR. Relationships between sprinting, agility, and jump ability in female athletes. J Sports Sci. 2008; 26: 97–107. pmid:17852692
  20. 20. Coh M, Vodicar J, Žvan M, Šimenko J, Stodolka J, Rauter S, et al. Are Change-of-Direction Speed and Reactive Agility Independent Skills Even When Using the Same Movement Pattern. Journal of Strength and Conditioning Research. 2018; 32: 1929–1936. pmid:29570572
  21. 21. Los Arcos A, Mendiguchia J, Yanci J. Specificity of jumping, acceleration and quick change of direction motor abilities in soccer players. Kinesiology: International journal of fundamental and applied kinesiology. 2017; 49: 22–29.
  22. 22. Pyne DB, Saunders PU, Montgomery PG, Hewitt AJ, Sheehan K. Relationships between repeated sprint testing, speed, and endurance. Journal of Strength and Conditioning Research. 2008; 22: 1633–1637. pmid:18714221
  23. 23. Robertson S, Kremer P, Aisbett B, Tran J, Cerin E. Consensus on measurement properties and feasibility of performance tests for the exercise and sport sciences. A Delphi study. Sports Med Open. 2017; 3: 2. pmid:28054257
  24. 24. Currell K, Jeukendrup AE. Validity, reliability and sensitivity of measures of sporting performance. Sports Med. 2008; 38: 297–316. pmid:18348590
  25. 25. Jemni M, Prince MS, Baker JS. Assessing Cardiorespiratory Fitness of Soccer Players: Is Test Specificity the Issue?-A Review. Sports Med Open. 2018; 4: 28. pmid:29923108
  26. 26. Paul DJ, Nassis GP. Testing strength and power in soccer players: the application of conventional and traditional methods of assessment. Journal of Strength and Conditioning Research. 2015; 29: 1748–1758. pmid:25546446
  27. 27. Moher D, Liberati A, Tetzlaff J, Altman DG. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009; 6: e1000097. pmid:19621072
  28. 28. Atkinson G, Nevill AM. Statistical methods for assessing measurement error (reliability) in variables relevant to sports medicine. Sports Med. 1998; 26: 217–238. pmid:9820922
  29. 29. McCunn R, Fünten Kad, Fullagar HHK, McKeown I, Meyer T. Reliability and Association with Injury of Movement Screens: A Critical Review. Sports Med. 2016; 46: 763–781. pmid:26721517
  30. 30. Hopkins WG. A scale of magnitudes for effect statistics. A new view of statistics. 2002: Available at: http://www.sportsci.org/resource/stats/effectmag.html.
  31. 31. Brink Y, Louw QA. Clinical instruments: reliability and validity critical appraisal. J Eval Clin Pract. 2012; 18: 1126–1132. pmid:21689217
  32. 32. Haugen T, Buchheit M. Sprint Running Performance Monitoring. Methodological and Practical Considerations. Sports Med. 2016; 46: 641–656. pmid:26660758
  33. 33. Barrett E, McCreesh K, Lewis J. Reliability and validity of non-radiographic methods of thoracic kyphosis measurement: a systematic review. Man Ther. 2014; 19: 10–17. pmid:24246907
  34. 34. Silva JR, Magalhães J, Ascensão A, Seabra AF, Rebelo AN. Training status and match activity of professional soccer players throughout a season. Journal of Strength and Conditioning Research. 2013; 27: 20–30. pmid:22344051
  35. 35. Djaoui L, Chamari K, Owen AL, Dellal A. Maximal Sprinting Speed of Elite Soccer Players During Training and Matches. Journal of Strength and Conditioning Research. 2017; 31: 1509–1517. pmid:28538299
  36. 36. Haugen TA, Tønnessen E, Seiler S. Anaerobic performance testing of professional soccer players 1995–2010. Int J Sports Physiol Perform. 2013; 8: 148–156. pmid:22868347
  37. 37. Ferro A, Villacieros J, Floría P, Graupera JL. Analysis of speed performance in soccer by a playing position and a sports level using a laser system. J Hum Kinet. 2014; 44: 143–153. pmid:25713675
  38. 38. Silvestre R, Kraemer WJ, West C, Judelson DA, Spiering BA, Vingren JL, et al. Body composition and physical performance during a National Collegiate Athletic Association Division I men’s soccer season. Journal of Strength and Conditioning Research. 2006; 20: 962–970. pmid:17149986
  39. 39. Silvestre R, West C, Maresh CM, Kraemer WJ. Body composition and physical performance in men’s soccer: a study of a National Collegiate Athletic Association Division I team. Journal of Strength and Conditioning Research. 2006; 20: 177–183. pmid:16506863
  40. 40. Cometti G, Maffiuletti NA, Pousson M, Chatard JC, Maffulli N. Isokinetic strength and anaerobic power of elite, subelite and amateur French soccer players. Int J Sports Med. 2001; 22: 45–51. pmid:11258641
  41. 41. Risso FG, Jalilvand F, Orjalo AJ, Moreno MR, Davis DL, Birmingham-Babauta SA, et al. Physiological Characteristics of Projected Starters and Non-Starters in the Field Positions from a Division I Women’s Soccer Team. Int J Exerc Sci. 2017; 10: 568–579. pmid:28674601
  42. 42. Vescovi JD. Sprint speed characteristics of high-level American female soccer players: Female Athletes in Motion (FAiM) study. J Sci Med Sport. 2012; 15: 474–478. pmid:22516691
  43. 43. Rebelo A, Brito J, Maia J, Coelho-e-Silva MJ, Figueiredo AJ, Bangsbo J, et al. Anthropometric characteristics, physical fitness and technical performance of under-19 soccer players by competitive level and field position. Int J Sports Med. 2013; 34: 312–317. pmid:23059558
  44. 44. Haugen TA, Tønnessen E, Seiler S. Speed and countermovement-jump characteristics of elite female soccer players, 1995–2010. Int J Sports Physiol Perform. 2012; 7: 340–349. pmid:22645175
  45. 45. Cotte T, Chatard JC. Isokinetic strength and sprint times in English premier league football players. Biol Sport. 2011; 28: 89–94.
  46. 46. Nikolaidis PT, Knechtle B, Clemente F, Torres-Luque G. Reference values for the sprint performance in male football players aged from 9–35 years. Biomedical Human Kinetics. 2016; 8: 103–112.
  47. 47. Mujika I, Santisteban J, Impellizzeri FM, Castagna C. Fitness determinants of success in men’s and women’s football. J Sports Sci. 2009; 27: 107–114. pmid:19058090
  48. 48. Kobal R, Loturco I, Gil S, Cal Abad CC, Cuniyochi R, Barroso R, et al. Comparison of physical performance among Brazilian elite soccer players of different age-categories. The Journal of sports medicine and physical fitness. 2016; 56: 376–382. pmid:25503710
  49. 49. Gelen E. Acute effects of different warm-up methods on sprint, slalom dribbling, and penalty kick performance in soccer players. Journal of Strength and Conditioning Research. 2010; 24: 950–956. pmid:20300033
  50. 50. Rouissi M, Chtara M, Owen A, Burnett A, Chamari K. Change of direction ability in young elite soccer players: determining factors vary with angle variation. The Journal of sports medicine and physical fitness. 2017; 57: 960–968. pmid:27391410
  51. 51. Haugen T, Tønnessen E, Seiler S. Correction Factors for Photocell Sprint Timing With Flying Start. Int J Sports Physiol Perform. 2015; 10: 1055–1057. pmid:25803102
  52. 52. López-Segovia M, Pareja-Blanco F, Jiménez-Reyes P, González-Badillo JJ. Determinant factors of repeat sprint sequences in young soccer players. Int J Sports Med. 2015; 36: 130–136. pmid:25259593
  53. 53. Pareja-Blanco F, Suarez-Arrones L, Rodríguez-Rosell D, López-Segovia M, Jiménez-Reyes P, Bachero-Mena B, et al. Evolution of Determinant Factors of Repeated Sprint Ability. J Hum Kinet. 2016; 54: 115–126. pmid:28031763
  54. 54. Sporis G, Jukic I, Ostojic SM, Milanovic D. Fitness profiling in soccer: physical and physiologic characteristics of elite players. Journal of Strength and Conditioning Research. 2009; 23: 1947–1953. pmid:19704378
  55. 55. Zois J, Bishop DJ, Ball K, Aughey RJ. High-intensity warm-ups elicit superior performance to a current soccer warm-up routine. J Sci Med Sport. 2011; 14: 522–528. pmid:21907619
  56. 56. Emmonds S, Nicholson G, Beggs C, Jones B, Bissas A. Importance of physical qualities for speed and change of direction ability in elite female soccer players. Journal of Strength and Conditioning Research. 2017. pmid:28723816
  57. 57. Mujika I, Santisteban J, Castagna C. In-season effect of short-term sprint and power training programs on elite junior soccer players. Journal of Strength and Conditioning Research. 2009; 23: 2581–2587. pmid:19910815
  58. 58. Loturco I, Kobal R, Maldonado T, Piazzi AF, Bottino A, Kitamura K, et al. Jump Squat is More Related to Sprinting and Jumping Abilities than Olympic Push Press. Int J Sports Med. 2017; 38: 604–612. pmid:26667925
  59. 59. Loturco I, Pereira LA, Kobal R, Maldonado T, Piazzi AF, Bottino A, et al. Improving Sprint Performance in Soccer: Effectiveness of Jump Squat and Olympic Push Press Exercises. PLoS ONE. 2016; 11: e0153958. pmid:27100085
  60. 60. Boone J, Vaeyens R, Steyaert A, Vanden Bossche L, Bourgois J. Physical fitness of elite Belgian soccer players by player position. Journal of Strength and Conditioning Research. 2012; 26: 2051–2057. pmid:21986697
  61. 61. Manson SA, Brughelli M, Harris NK. Physiological characteristics of international female soccer players. Journal of Strength and Conditioning Research. 2014; 28: 308–318. pmid:24476742
  62. 62. Meylan C, Trewin J, McKean K. Quantifying Explosive Actions in International Women’s Soccer. Int J Sports Physiol Perform. 2017; 12: 310–315. pmid:27295719
  63. 63. Sjökvist J, Laurent MC, Richardson M, Curtner-Smith M, Holmberg H-C, Bishop PA. Recovery from high-intensity training sessions in female soccer players. Journal of Strength and Conditioning Research. 2011; 25: 1726–1735. pmid:21386721
  64. 64. Requena B, Sáez-Sáez de Villarreal E, Gapeyeva H, Ereline J, García I, Pääsuke M. Relationship between postactivation potentiation of knee extensor muscles, sprinting and vertical jumping performance in professional soccer players. Journal of Strength and Conditioning Research. 2011; 25: 367–373. pmid:20093962
  65. 65. Ingebrigtsen J, Brochmann M, Castagna C, Bradley PS, Ade J, Krustrup P, et al. Relationships between field performance tests in high-level soccer players. Journal of Strength and Conditioning Research. 2014; 28: 942–949. pmid:23838979
  66. 66. Yanci J, Los Arcos A, Brughelli M. Relationships between sprint, agility, one- and two-leg vertical and horizonztal jump in soccer players. Kinesiology: International journal of fundamental and applied kinesiology. 2014; 46: 194–201.
  67. 67. Comfort P, Stewart A, Bloom L, Clarkson B. Relationships between strength, sprint, and jump performance in well-trained youth soccer players. Journal of Strength and Conditioning Research. 2014; 28: 173–177. pmid:23542878
  68. 68. López-Segovia M, Marques MC, van den Tillaar R, González-Badillo JJ. Relationships between vertical jump and full squat power outputs with sprint times in u21 soccer players. J Hum Kinet. 2011; 30: 135–144. pmid:23487438
  69. 69. Chelly MS, Chérif N, Amar MB, Hermassi S, Fathloun M, Bouhlel E, et al. Relationships of peak leg power, 1 maximal repetition half back squat, and leg muscle volume to 5-m sprint performance of junior soccer players. Journal of Strength and Conditioning Research. 2010; 24: 266–271. pmid:19924009
  70. 70. Spierer DK, Petersen RA, Duffy K. Response time to stimuli in division I soccer players. Journal of Strength and Conditioning Research. 2011; 25: 1134–1141. pmid:20664362
  71. 71. Caldwell BP, Peters DM. Seasonal variation in physiological fitness of a semiprofessional soccer team. Journal of Strength and Conditioning Research. 2009; 23: 1370–1377. pmid:19620929
  72. 72. Ronnestad BR, Kvamme NH, Sunde A, Raastad T. Short-term effects of strength and plyometric training on sprint and jump performance in professional soccer players. Journal of Strength and Conditioning Research. 2008; 22: 773–780. pmid:18438241
  73. 73. Small K, McNaughton LR, Greig M, Lohkamp M, Lovell R. Soccer fatigue, sprinting and hamstring injury risk. Int J Sports Med. 2009; 30: 573–578. pmid:19455478
  74. 74. Gorostiaga EM, Izquierdo M, Ruesta M, Iribarren J, González-Badillo JJ, Ibáñez J. Strength training effects on physical performance and serum hormones in young soccer players. Eur J Appl Physiol. 2004; 91: 698–707. pmid:14704801
  75. 75. Gil S, Loturco I, Tricoli V, Ugrinowitsch C, Kobal R, Abad CCC, et al. Tensiomyography parameters and jumping and sprinting performance in Brazilian elite soccer players. Sports Biomech. 2015; 14: 340–350. pmid:26271313
  76. 76. Coelho DB, Pimenta E, Rosse IC, Veneroso C, Becker LK, Carvalho MR, et al. The alpha-actinin-3 r577x polymorphism and physical performance in soccer players. The Journal of sports medicine and physical fitness. 2016; 56: 241–248. pmid:25650734
  77. 77. Boussetta N, Abedelmalek S, Aloui K, Souissi N. The effect of air pollution on diurnal variation of performance in anaerobic tests, cardiovascular and hematological parameters, and blood gases on soccer players following the Yo-Yo Intermittent Recovery Test Level-1. Chronobiol Int. 2017; 34: 903–920. pmid:28613960
  78. 78. Shalfawi SAI, Haugen T, Jakobsen TA, Enoksen E, Tønnessen E. The effect of combined resisted agility and repeated sprint training vs. strength training on female elite soccer players. Journal of Strength and Conditioning Research. 2013; 27: 2966–2972. pmid:23442286
  79. 79. Sayers AL, Farley RS, Fuller DK, Jubenville CB, Caputo JL. The effect of static stretching on phases of sprint performance in elite soccer players. Journal of Strength and Conditioning Research. 2008; 22: 1416–1421. pmid:18714249
  80. 80. Thomas K, French D, Hayes PR. The effect of two plyometric training techniques on muscular power and agility in youth soccer players. Journal of Strength and Conditioning Research. 2009; 23: 332–335. pmid:19002073
  81. 81. Iaia FM, Fiorenza M, Perri E, Alberti G, Millet GP, Bangsbo J. The Effect of Two Speed Endurance Training Regimes on Performance of Soccer Players. PLoS ONE. 2015; 10: e0138096. pmid:26394225
  82. 82. Rey E, Padrón-Cabo A, Costa PB, Barcala-Furelos R. The Effects of Foam Rolling as a Recovery Tool in Professional Soccer Players. Journal of Strength and Conditioning Research. 2017. pmid:29016479
  83. 83. McGawley K, Andersson P-I. The order of concurrent training does not affect soccer-related performance adaptations. Int J Sports Med. 2013; 34: 983–990. pmid:23700329
  84. 84. Loturco I, Pereira LA, Kobal R, Zanetti V, Kitamura K, Abad CCC, et al. Transference effect of vertical and horizontal plyometrics on sprint performance of high-level U-20 soccer players. J Sports Sci. 2015; 33: 2182–2191. pmid:26390150
  85. 85. Silva JR, Magalhães JF, Ascensão AA, Oliveira EM, Seabra AF, Rebelo AN. Individual match playing time during the season affects fitness-related parameters of male professional soccer players. Journal of Strength and Conditioning Research. 2011; 25: 2729–2739. pmid:21912284
  86. 86. Bullock W, Panchuk D, Broatch J, Christian R, Stepto NK. An integrative test of agility, speed and skill in soccer: effects of exercise. J Sci Med Sport. 2012; 15: 431–436. pmid:22521425
  87. 87. Williams JD, Abt G, Kilding AE. Ball-Sport Endurance and Sprint Test (BEAST90): validity and reliability of a 90-minute soccer performance test. Journal of Strength and Conditioning Research. 2010; 24: 3209–3218. pmid:19966581
  88. 88. Mirkov D, Nedeljkovic A, Kukolj M, Ugarkovic D, Jaric S. Evaluation of the reliability of soccer-specific field tests. Journal of Strength and Conditioning Research. 2008; 22: 1046–1050. pmid:18545209
  89. 89. Silva JR, Ascensão A, Marques F, Seabra A, Rebelo A, Magalhães J. Neuromuscular function, hormonal and redox status and muscle damage of professional soccer players after a high-level competitive match. Eur J Appl Physiol. 2013; 113: 2193–2201. pmid:23661147
  90. 90. Kutlu M, Yapici H, Yilmaz A. Reliability and Validity of a New Test of Agility and Skill for Female Amateur Soccer Players. J Hum Kinet. 2017; 56: 219–227. pmid:28469760
  91. 91. Harper LD, Hunter R, Parker P, Goodall S, Thomas K, Howatson G, et al. Test-Retest Reliability of Physiological and Performance Responses to 120 Minutes of Simulated Soccer Match Play. Journal of Strength and Conditioning Research. 2016; 30: 3178–3186. pmid:26950356
  92. 92. Sonderegger K, Tschopp M, Taube W. The Challenge of Evaluating the Intensity of Short Actions in Soccer: A New Methodological Approach Using Percentage Acceleration. PLoS ONE. 2016; 11: e0166534. pmid:27846308
  93. 93. Ispirlidis I, Fatouros IG, Jamurtas AZ, Nikolaidis MG, Michailidis I, Douroudos I, et al. Time-course of changes in inflammatory and performance responses following a soccer game. Clin J Sport Med. 2008; 18: 423–431. pmid:18806550
  94. 94. Yanci J, Calleja-Gonzalez J, Cámara J, Mejuto G, San Román J, Los Arcos A. Validity and reliability of a global positioning system to assess 20 m sprint performance in soccer players. Proceedings of the IMechE. 2017; 231: 68–71.
  95. 95. Carling C, Le Gall F, Dupont G. Analysis of repeated high-intensity running performance in professional soccer. J Sports Sci. 2012; 30: 325–336. pmid:22248291
  96. 96. Dellal A, Wong DP. Repeated sprint and change-of-direction abilities in soccer players: effects of age group. Journal of Strength and Conditioning Research. 2013; 27: 2504–2508. pmid:23238090
  97. 97. Wong DP, Chan GS, Smith AW. Repeated-sprint and change-of-direction abilities in physically active individuals and soccer players: training and testing implications. Journal of Strength and Conditioning Research. 2012; 26: 2324–2330. pmid:22067248
  98. 98. Gabbett TJ. The development of a test of repeated-sprint ability for elite women’s soccer players. Journal of Strength and Conditioning Research. 2010; 24: 1191–1194. pmid:20386127
  99. 99. Aziz AR, Mukherjee S, Chia MYH, Teh KC. Validity of the running repeated sprint ability test among playing positions and level of competitiveness in trained soccer players. Int J Sports Med. 2008; 29: 833–838. pmid:18401804
  100. 100. Ingebrigtsen J, Bendiksen M, Randers MB, Castagna C, Krustrup P, Holtermann A. Yo-Yo IR2 testing of elite and sub-elite soccer players: performance, heart rate response and correlations to other interval tests. J Sports Sci. 2012; 30: 1337–1345. pmid:22867048
  101. 101. Chaouachi A, Manzi V, Wong DP, Chaalali A, Laurencelle L. Intermittent endurance and repeated sprint ability in soccer players. Journal of Strength and Conditioning Research. 2010; 24: 2663–2669. pmid:20847706
  102. 102. Haugen T, Tonnessen E, Leirstein S, Hem E, Seiler S. Not quite so fast: effect of training at 90% sprint speed on maximal and repeated-sprint ability in soccer players. J Sports Sci. 2014; 32: 1979–1986. pmid:25385308
  103. 103. López-Segovia M, Dellal A, Chamari K, González-Badillo JJ. Importance of muscle power variables in repeated and single sprint performance in soccer players. J Hum Kinet. 2014; 40: 201–211. pmid:25031688
  104. 104. Ruscello B, Tozzo N, Briotti G, Padua E, Ponzetti F, D’Ottavio S. Influence of the number of trials and the exercise to rest ratio in repeated sprint ability, with changes of direction and orientation. Journal of Strength and Conditioning Research. 2013; 27: 1904–1919. pmid:23007490
  105. 105. Huijgen BCH, Elferink-Gemser MT, Lemmink K. A. P. M., Visscher C. Multidimensional performance characteristics in selected and deselected talented soccer players. Eur J Sport Sci. 2014; 14: 2–10. pmid:24533489
  106. 106. Kutlu M. Yapıcı H., Yoncalık O, Celik S. Comparison of a new test for agility and skill in soccer with other agility tests. J Hum Kinet. 2012; 33: 143–150. pmid:23486732
  107. 107. Russell M, Benton D, Kingsley M. Reliability and construct validity of soccer skills tests that measure passing, shooting, and dribbling. J Sports Sci. 2010; 28: 1399–1408. pmid:20967673
  108. 108. Keiner M, Sander A, Wirth K, Schmidtbleicher D. Long-term strength training effects on change-of-direction sprint performance. Journal of Strength and Conditioning Research. 2014; 28: 223–231. pmid:23588486
  109. 109. Bendiksen M, Pettersen SA, Ingebrigtsen J, Randers MB, Brito J, Mohr M, et al. Application of the Copenhagen Soccer Test in high-level women players—locomotor activities, physiological response and sprint performance. Hum Mov Sci. 2013; 32: 1430–1442. pmid:24016711
  110. 110. Currell K, St. Conway , Jeukendrup AE. Carbohydrate ingestion improves performance of a new reliable test of soccer performance. Int J Sport Nutr Exerc Metab. 2009; 19: 34–46. pmid:19403952
  111. 111. Miller DK, Kieffer HS, Kemp HE, Torres SE. Off-season physiological profiles of elite National Collegiate Athletic Association Division III male soccer players. Journal of Strength and Conditioning Research. 2011; 25: 1508–1513. pmid:21358427
  112. 112. Castillo-Rodríguez A, Fernández-García JC, Chinchilla-Minguet JL, Carnero EÁ. Relationship between muscular strength and sprints with changes of direction. Journal of Strength and Conditioning Research. 2012; 26: 725–732. pmid:22289697
  113. 113. Di Mascio M, Ade J, Bradley PS. The reliability, validity and sensitivity of a novel soccer-specific reactive repeated-sprint test (RRST). Eur J Appl Physiol. 2015; 115: 2531–2542. pmid:26335624
  114. 114. Pojskic H, Åslin E, Krolo A, Jukic I, Uljevic O, Spasic M, et al. Importance of Reactive Agility and Change of Direction Speed in Differentiating Performance Levels in Junior Soccer Players: Reliability and Validity of Newly Developed Soccer-Specific Tests. Front Physiol. 2018; 9. pmid:29867552
  115. 115. Sporis G, Jukic I, Milanovic L, Vucetic V. Reliability and factorial validity of agility tests for soccer players. Journal of Strength and Conditioning Research. 2010; 24: 679–686. pmid:20145571
  116. 116. Rampinini E, Bishop D, Marcora SM, Ferrari Bravo D, Sassi R, Impellizzeri FM. Validity of simple field tests as indicators of match-related physical performance in top-level professional soccer players. 0172–4622. 2007; 28: 228–235. pmid:17024621
  117. 117. Rampinini E, Sassi A, Morelli A, Mazzoni S, Fanchini M, Coutts AJ. Repeated-sprint ability in professional and amateur soccer players. Appl Physiol Nutr Metab. 2009; 34: 1048–1054. pmid:20029513
  118. 118. Impellizzeri FM, Rampinini E, Castagna C, Bishop D, Bravo DF, Tibaudi A, et al. Validity of a repeated-sprint test for football. Int J Sports Med. 2008; 29: 899–905. pmid:18415931
  119. 119. Abrantes C, Maçãs V, Sampaio J. Variation in football players’ sprint test performance across different ages and levels of competition. Journal of Sports Science and Medicine. 2004; 3: 44–49.
  120. 120. Kaplan T. Examination of repeated sprinting ability and fatigue index of soccer players according to their positions. Journal of Strength and Conditioning Research. 2010; 24: 1495–1501. pmid:20508450
  121. 121. Wragg CB, Maxwell NS, Doust JH. Evaluation of the reliability and validity of a soccer-specific field test of repeated sprint ability. Eur J Appl Physiol. 2000; 83: 77–83. pmid:11072777
  122. 122. Brahim MB, Mohamed A, Shalfawi SA. The evaluation of soccer playersperformance on different repeated sprint testes: Training and testing implications. Kinesiologia Slovenica. 2016; 22: 49–63.
  123. 123. FIFA. International Federation of Association Football (FIFA). FIFA Marketing Research. Retrieved from https://www.fifa.com/about-fifa/news/y=2010/m=12/news=fifa-marketing-research-1354721.html. Updated April 24, 2015.; 2015.
  124. 124. Di Salvo V, Baron R, González-Haro C, Gormasz C, Pigozzi F, Bachl N. Sprinting analysis of elite soccer players during European Champions League and UEFA Cup matches. J Sports Sci. 2010; 28: 1489–1494. pmid:21049314
  125. 125. Taylor JM, Macpherson TW, Spears IR, Weston M. Repeated Sprints: An Independent Not Dependent Variable. Int J Sports Physiol Perform. 2016; 11: 693–696. pmid:27197118
  126. 126. Schimpchen J, Skorski S, St. Nopp , Meyer T. Are “classical” tests of repeated-sprint ability in football externally valid? A new approach to determine in-game sprinting behaviour in elite football players. J Sports Sci. 2016; 34: 519–526. pmid:26580089
  127. 127. Dawson B. Repeated-Sprint Ability: Where Are We. Int J Sports Physiol Perform. 2012; 7: 285–289. pmid:22930690
  128. 128. Haugen T, Seiler S. Physical and physiological testing of soccer players: why, what and how should we measure. Sportscience. 2015: 10–26.
  129. 129. Chaouachi A, Manzi V, Chaalali A, Wong DP, Chamari K, Castagna C. Determinants analysis of change-of-direction ability in elite soccer players. Journal of Strength and Conditioning Research. 2012; 26: 2667–2676. pmid:22124358
  130. 130. Sheppard JM, Young WB, Doyle TLA, Sheppard TA, Newton RU. An evaluation of a new test of reactive agility and its relationship to sprint speed and change of direction speed. J Sci Med Sport. 2006; 9: 342–349. pmid:16844413
  131. 131. Nimphius S, Callaghan SJ, Bezodis NE, Lockie RG. Change of Direction and Agility Tests. Challenging Our Current Measures of Performance. Strength and Conditioning Journal. 2018; 40: 26–38.
  132. 132. Benvenuti C, Minganti C, Condello G, Capranica L, Tessitore A. Agility assessment in female futsal and soccer players. Medicina (Kaunas). 2010; 46: 415–420.
  133. 133. Gabbett TJ, Carius J, Mulvey M. Does improved decision-making ability reduce the physiological demands of game-based activities in field sport athletes. The Journal of Strength & Conditioning Research. 2008; 22: 2027–2035.
  134. 134. González-Víllora S, Serra-Olivares J, Pastor-Vicedo JC, Da Costa IT. Review of the tactical evaluation tools for youth players, assessing the tactics in team sports: football. Springerplus. 2015; 4: 663. pmid:26558166
  135. 135. Young W, Farrow D. The Importance of a Sport-Specific Stimulus for Training Agility. Strength and Conditioning Journal. 2013; 35: 39–43.
  136. 136. Pyne DB, Spencer M, Mujika I. Improving the value of fitness testing for football. Int J Sports Physiol Perform. 2014; 9: 511–514. pmid:24231433
  137. 137. Terwee CB, Mokkink LB, Knol DL, Ostelo RW, Bouter LM, Vet HC de. Rating the methodological quality in systematic reviews of studies on measurement properties: a scoring system for the COSMIN checklist. Qual Life Res. 2011; 21: 651–657. pmid:21732199
  138. 138. Chiwaridzo M, Oorschot S, Dambi JM, Ferguson GD, Bonney E, Mudawarima T, et al. A systematic review investigating measurement properties of physiological tests in rugby. BMC Sports Sci Med Rehabil. 2017; 9: 24. pmid:29299317
  139. 139. Slimani M, Nikolaidis PT. Anthropometric and physiological characteristics of male Soccer players according to their competitive level, playing position and age group: a systematic review. The Journal of sports medicine and physical fitness. 2017.
  140. 140. Mendez-Villanueva A, Buchheit M. Football-specific fitness testing: adding value or confirming the evidence. J Sports Sci. 2013; 31: 1503–1508. pmid:23978073
  141. 141. Simperingham KD, Cronin JB, Ross A. Advances in Sprint Acceleration Profiling for Field-Based Team-Sport Athletes: Utility, Reliability, Validity and Limitations. Sports Medicine. 2016; 46: 1619–1645. pmid:26914267
  142. 142. Darrall-Jones JD, Jones B, Roe G, Till K. Reliability and Usefulness of Linear Sprint Testing in Adolescent Rugby Union and League Players. Journal of Strength and Conditioning Research. 2016; 30: 1359–1364. pmid:26466131
  143. 143. Hopkins WG. How to interpret changes in an athletic performance test. Sport sci. 2004: 1–7.
  144. 144. Haugen TA. Sprint conditioning of elite soccer players: Worth the effort or let‘s just buy faster players. Sport Performance & Science Reports. 2017; 1: 1–2.
  145. 145. Barberó-Álvarez JC, Boullosa D, Nakamura FY, Andrín G, Weston M. Repeated Acceleration Ability (RAA). A New Concept with Reference to Top-Level Field and Assistant Soccer Referees. Asian J Sports Med. 2013; 5: 63–66. pmid:24868433