Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Open Access

Peer-reviewed

Research Article

Tyrosine supplementation is ineffective in facilitating soccer players’ physical and cognitive performance during high-intensity intermittent exercise in hot conditions

  • Kate J. Donnan ,

    Contributed equally to this work with: Kate J. Donnan, Emily L. Williams, Nicholas Stanger

    Roles Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft

    K.J.Donnan@hull.ac.uk

    Affiliation Department of Sport, Health and Exercise Science, University of Hull, Hull, United Kingdom

    ⨯
  • Emily L. Williams ,

    Contributed equally to this work with: Kate J. Donnan, Emily L. Williams, Nicholas Stanger

    Roles Conceptualization, Investigation, Methodology, Supervision, Writing – review & editing

    Affiliation Carnegie School of Sport, Leeds Beckett University, Leeds, United Kingdom

    ⨯
  • Nicholas Stanger

    Contributed equally to this work with: Kate J. Donnan, Emily L. Williams, Nicholas Stanger

    Roles Conceptualization, Investigation, Methodology, Supervision, Writing – review & editing

    Affiliation Carnegie School of Sport, Leeds Beckett University, Leeds, United Kingdom

    ⨯

Abstract

Tyrosine has been proposed to potentially provide ergogenic benefits to cognitive and physical performance in physiologically demanding environments. However research into its effectiveness on cognitive and physical performance during exercise in the heat has revealed mixed findings. This study examined the effects of a commonly employed dosage of tyrosine supplementation on soccer players’ physical and decision-making performance, cognitive appraisal, and affective states, during prolonged high-intensity intermittent exercise in hot conditions. Eight trained male soccer players completed a 92-minute high-intensity intermittent cycling sprint protocol whilst responding to soccer-specific decision-making tasks at various time points in 32°C (50%rh), in two counterbalanced conditions; tyrosine (150mg.kg-1) and placebo. No differences were found for peak power output (p = .486; 715 ± 98W vs 724 ± 98W, respectively), decision-making (p = .627; 86.9 ± 10.7% vs 88.6 ± 7.0%, respectively), cognitive appraisal (p = .693, 0.90 ± 0.42 vs 0.88 ± 0.39, respectively) nor affective states (p = .918; 1.15 ± 1.55 vs 1.14 ± 1.70, respectively) between tyrosine and placebo conditions. Also, no condition by time interaction effects were noted for these outcomes. In sum, tyrosine supplementation was ineffective for facilitating prolonged intermittent sprint (self-paced) activity, soccer-specific decision-making, and in alleviating perceptual strain, for soccer players’ exercising in the heat. However, future research may wish to consider alternative approaches for tyrosine supplementation (e.g., timing, dosage) or induce heightened physiological strain to extend on these findings.

Citation: Donnan KJ, Williams EL, Stanger N (2025) Tyrosine supplementation is ineffective in facilitating soccer players’ physical and cognitive performance during high-intensity intermittent exercise in hot conditions. PLoS ONE 20(1): e0317486. https://doi.org/10.1371/journal.pone.0317486

Editor: Ersan Arslan, Tokat Gaziosmanpasa University Tasliciftlik Campus: Tokat Gaziosmanpasa Universitesi, TÜRKIYE

Received: May 14, 2024; Accepted: December 30, 2024; Published: January 16, 2025

Copyright: © 2025 Donnan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Specifically, in our ethics application, and also importantly in our participant information sheets and consent forms, we did not request permission or gain consent from participants to share their data in an anonymised dataset with third parties or in any open data repository. Participants were informed that information stored and inputted in datasets on computers would only be accessible to the research team, and results will be presented across the whole sample to protect their identity. When the project was conceived open access data sharing was less prominent and unfortunately was not adequately incorporated into our ethical and participant documents. However, we have provided individual responses for key outcome measures to further facilitate transparency of findings in Supplementary Figures. Queries can be sent to the corresponding author at K.J.Donnan@hull.ac.uk, or the Leeds Beckett University Research Management Team at openaccess@leedsbeckett.ac.uk.

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

In competitive team sports including soccer, maintaining effective execution of a range of physical (e.g., sprinting) and cognitive (e.g., decision-making) skills is fundamental for successful performance [1]. Such skill execution can be impaired by several fatigue-related factors, such as thermal strain, depleted energy stores (i.e., glycogen), dehydration and neurochemical changes [2] occurring during match-play. These responses are further exacerbated when having to perform in hot environments due to heightened core temperature, increased cardiovascular strain and fluid loss often resulting in dehydration alongside amplified perceptual strain [3, 4]. Despite this, the need to train and compete in hot environments is becoming more frequent with global warming and the globalisation of sport (e.g., Tokyo 2020 Olympic Games, Qatar 2022 World Cup) [5, 6], which could further impair performance [7–10].

The Central Fatigue Hypothesis explains that prolonged exercise and/or exposure to extreme environments changes the activity of central monoamines (i.e., serotonin [5-HT], dopamine [DA], noradrenaline [NA], and adrenaline [AD]). For instance, a higher ratio of brain DA to 5-HT is suggested to be linked with increased motivation and reduced fatigue that can facilitate physical and cognitive performance [11–14]. Moreover, higher activity of the dopaminergic pathways in the hypothalamus is suggested to predict greater exercise tolerance in the heat. It has been suggested that high dopaminergic activity is thought to override the perceived effort costs (as described by Iodice et al., 2017) when experiencing physiological fatigue and may facilitate engagement in higher-effort and higher-value actions [15]. Indeed, research has shown that dopamine reuptake inhibitors can improve exercise performance, increasing heat storage and hyperthermia tolerance, potentially due to overriding inhibitory signals sent from the central nervous system which contribute to exercise cessation due to thermal strain [16]. As a result, some researchers have attempted to manipulate physical and cognitive performance through nutritional strategies to increase the dopamine-to-serotonin ratio when competing in thermally challenging environments; whereby one such nutritional strategy is through the use of tyrosine supplementation [13, 17].

Tyrosine is a non-essential amino acid found in protein-rich dietary sources which acts as a precursor to brain neurotransmitters (i.e., DA, NA, AD) [18], which play an important role in the functioning of the prefrontal cortex [19]. Oral tyrosine supplementation can increase the ratio of tyrosine to other large neutral amino acids (e.g., tryptophan), favouring its transport across the blood–brain-barrier and increasing cerebral uptake of DA and NA [18]. Therefore, tyrosine intake may help increase effort, positive affect, and reduce perceived and performance fatigue, during demanding exercise in the heat which may facilitate cognitive and physical performance. Despite the proposed mechanistic properties of tyrosine, existing research into the effectiveness of supplementation for performing in hot conditions is limited and conflicting. For instance, 150mg.kg-1 tyrosine supplementation consumed 1 hour before exercise was shown to improve cycling time to exhaustion by 15 ± 11% at a constant load (68 ± 5% VO2peak) [13], but did not improve self-paced cycling time trial performance following 60-min cycling at 57% ± 4% VO2peak [20] despite similar environmental heat exposure (30˚C), exercise modality, population, and tyrosine dosage and timing. The primary difference between these studies being the fixed- vs. self-paced exercise protocols included.

The research to date suggests that tyrosine supplementation may be facilitative only when participants are experiencing heightened physiological and/or psychological strain such as during demanding prolonged exercise in warm/hot conditions. Some studies have also shown that fixed-paced exercise to exhaustion could be more psychologically stressful to engage in than self-paced exercise [21], and that catecholamine synthesis is heightened in rodents who are forced to exercise compared to those which voluntarily exercise, despite similar intensities and durations being undertaken [22]. This could help to explain why the effects of tyrosine supplementation may vary across types of protocol used. Therefore, more demanding activity could increase catecholamine synthesis and thereby increase the potential effectiveness of tyrosine supplementation on physical performance.

The effects of tyrosine on cognition in hot environments are also inconsistent. Although a review by Attipoe et al. [23] observed “favourable” effects of tyrosine on cognition in military contexts within six articles that explored its use across varying stressful conditions (e.g., cold, heat, sleep deprivation), these studies possessed several methodological limitations (e.g., lack of randomisation/allocation concealment), which led the authors [23] to conclude the evidence was insufficient to confidently determine its effectiveness. Moreover, in the only previous study to investigate tyrosine supplementation in team sport players, vigilance was improved following prolonged intermittent exercise in warm (25˚C, 40%rh) conditions [13], though tyrosine had no effect on other measures of cognition (e.g., dual-task) nor exercise performance (distance covered). Research in military personnel has also revealed that tyrosine supplementation did not facilitate cognitive function or physical performance (time to completion) on a load-carriage self-paced walking in 40˚C heat [24]. Therefore, the mixed findings from rather limited research to date makes it difficult to determine the effectiveness of tyrosine on cognitive and physical performance.

It should also be noted that cognitive performance has been typically measured either during a break or on cessation of exercise in previous research, rather than during exercise. During competition, soccer players need to simultaneously maintain cognitive functioning (e.g., decision-making) and physical performance during high-intensity intermittent exercise [25], in hot environments. However, research has yet to investigate the effect of tyrosine on cognitive performance during exercise in the heat.

Purpose of the research

Despite some mechanistic propositions, research into the effects of tyrosine supplementation on physical and cognitive performance are rather equivocal. Researchers have yet to investigate the effects of tyrosine on cognitive performance in hot conditions whilst simultaneously performing high-intensity intermittent exercise reflective of the demands of team sports. The aim of the present study was to examine the effects of tyrosine on soccer players’ decision-making and physical performance in hot conditions, set at 32˚C to replicate recorded or expected temperatures for previous and upcoming major sporting competitions (e.g., Tokyo 2021 Olympic Games, 2018 and 2022 UEFA Women’s Euros, 2024 Paris Olympics). Notwithstanding the mixed findings in previous research, it was hypothesised that tyrosine supplementation would help maintain decision-making and physical performance in the heat, compared to placebo. Furthermore, we examined the effects of tyrosine on cognitive appraisal, affective states, and catecholamine responses (i.e., plasma metadrenalines). It was expected that tyrosine supplementation would help attenuate threat appraisals (or increase challenge appraisal), reduce negative affective states, and stimulate plasma metadrenaline synthesis (namely plasma metanephrine and normetanephrine as serum metabolite indicators of epinephrine and norepinephrine, respectively) during exercise in the heat.

Method

Participants

Participants were eight well-trained student male soccer players and trained a minimum of twice a week (age = 19.75 ± 0.70 years; VO2peak = 46.24 ± 4.59 mL·kg-1·min-1; body composition = 12.51 ± 3.68% body fat) who were recruited via email and social media advertisements between 24-10-2019 and 25-02-2020. Data collection took place between the months of October 2019 and March 2020. Participants had an average of 13.00 (± 1.51) years of experience competing in soccer and have competed at national (n = 1), regional (n = 3) and club (n = 4) levels. VO2peak was reported where plateau criterion for VO2max was not met. Results were lower than anticipated, potentially due to tests being conducted on the cycle ergometer to coincide with the exercise conducted in the main trials. It is worth noting that this could have potentially lowered VO2peak results by approximately 7–18% compared to being conducted on a treadmill [26].

This article is the second part of a two-part study. Part A examined how heat exposure (32˚C) affected soccer-specific decision-making and physical work output during intermittent sprint exercise, compared to 18˚C, which are reported in an already published article [7]. The current article reports Part B of this larger project within the same sample, which aims to address different research purposes by examining the effects of tyrosine supplementation on physical and cognitive performance in only hot conditions (32˚C). An estimated sample size of nine participants for the two-part study was determined by a power calculation for Part A, which is presented in the previous article [7]. Although testing had to be terminated early and could not recommence within a suitable timeframe due to the pandemic, a minimum target sample size of 8 participants for this phase of the research (Part B) was recruited, allowing for sufficient counterbalancing across tyrosine and placebo conditions, to align with the sample size in previous research that revealed some effects for tyrosine on cognitive performance in soccer players after exercise in the heat [13].

Participants refrained from supplementation of ergogenic aids (including energy drinks) during the study and had not performed strenuous exercise in >30°C for more than three months [27]. Participants were non-smokers, had no history of cardiovascular or respiratory problems and were required to standardize their food intake for the morning of each trial, abstain from alcohol and caffeine (24 hours), and strenuous exercise (48 hours), and maintain their regular sleep pattern (72 hours) before each trial [27]. Participants completed food and sleep diaries 48-hours prior to each trial and asked to limit their tyrosine-rich and protein-rich foods 24 hours prior to each trial; a list of foods to limit was provided [28]. No noticeable differences were identified between trials for any participant, facilitated also by the provision of food vouchers for participants to standardise their food intake for these trials. For each trial, participants arrived at least two hours post-prandial and were asked to consume 2-3L of water in the 24-hours prior to testing. Following approval from Leeds Beckett University research ethics committee, all eligible participants provided written informed consent before commencing this research.

Experimental design and procedure

A within-subjects 2 × experimental condition (tyrosine and placebo) double-blind, cross-over design was employed. In total, participants visited the laboratory on five occasions over a 28-day period. The first visit was for familiarisation. The second and third visit were for experimental trials one and two that formed Part A of a wider project, which were completed in a temperate (18°C; 50% rh) and hot (32°C; 50% rh) environment reported in Donnan et al. [7] to address a different purpose. The fourth and fifth visits were for experimental trials 3 and 4 (Part B of the wider project reported in the present paper) to examine the effects of tyrosine on physical and cognitive performance in the heat, whereby participants completed a Tyrosine and a Placebo condition in the heat (32°C; 50% rh). Simple randomisation was employed whereby two possible supplementation condition allocations (placebo → tyrosine; tyrosine → placebo) were randomly assigned and counterbalanced by a trained member of staff, independent from the research team. Each trial for Part B (reported in this article) was completed 7 days apart and commenced in the afternoon (~1-3pm) to allow for a suitable washout period. Testing times remained consistent to control for circadian variations [29, 30].

During the first visit, participants were familiarised with all procedures and protocols for the experimental trials alongside completion of an incremental exercise test on a cycle ergometer to determine [31] (See Donnan et al. [7]). Prior to the two experimental trials relevant to this paper, participants consumed either a 150mg.kg-1 dose of Tyrosine supplementation added to 250mL of sugar free squash in one condition, and the placebo (250mL sugar free squash only) in the control condition [13, 24]. A double-blind procedure was used, whereby a suitably qualified staff member, independent from the research team, randomly allocated and prepared, each of the drinks administered to participants. These were consumed one hour prior to the start of the exercise protocol, aligned with previous research [13, 17]. Fluid intake was standardised in the main trials (tyrosine vs placebo) to minimise confounding hydration effects [13]; informed by each respective participants’ water consumption in the heat (968.8 ± 345.5ml) from Part A of the wider project where no supplementation was administered. To incentivise effort and offer a competitive element to reflect the nature of sport, participants were informed that whoever had the highest combined average decision-making score and physical performance across trials would be awarded with £100 [28].

Cycling Intermittent Sprint Protocol (CISP)

The exercise protocol used in the present research was a slightly extended version of the CISP [32] (See Fig 1). Previous research assessing the reliability of the CISP has supported its utility as a high-intensity (or sprint) intermittent exercise protocol reflective of the demands of match play in team sport players (including soccer players) and revealed strong reliability between two trails for peak power output in team sport athletes (ICC = 0.96 [0.86–0.99]) [33]. Specifically, each half of the CISP was increased to 46-minutes (23 sprints) from the original 40-minutes (20 sprints), following a standardised CISP warm-up as reported in Donnan et al. [7]. The two halves of the CISP were, interspersed by a 15-minute “half-time” period involving passive recovery in a temperate environment (~18°C).

thumbnail
Download:
Fig 1. A schematic showing a modified version of one half (minutes displayed 0–44) of the extended cycling intermittent sprint protocol.

Figure slightly adapted from Donnan et al. [7, p.6]. T/C = threat/challenge, TC = core temperature, HR = heart rate, TSS = thermal sensation, RPE = rate of perceived exertion.

https://doi.org/10.1371/journal.pone.0317486.g001

Physical and cognitive performance measures

Peak Power Output (PPO) in Watts (W) recorded during each sprint of the CISP [27] was used to measure physical performance. These outputs were averaged per half of the CISP for analysis.

Decision-making was measured via a previously validated soccer-specific decision-making task (see Donnan et al. [7]). Specifically, participants watched 5s video clips cut from previous World Cup footage and were asked to decide what their next action would be upon the clip freezing (e.g., “pass”, “shoot”, “clear”, and “maintain possession”). Based on expert opinion (i.e., elite coaches) from the validation process (see Donnan et al. [7]), participants were awarded 3 points for the best option, 2 points for the second best, and 1 point for any other response option given from expert opinion during the validation process (see Donnan et al. [7]). Clips were implemented at the same respective time points for each half (See Fig 1). As three clips were viewed pre-CISP and nine clips during each half of the CISP, 9 points were available pre-CISP and 27 points were available for each half of the CISP. A percentage decision making score was then calculated for pre-CISP and each of half of the CISP.

Physiological measures

Core temperature (TC) was measured using a temperature sensor telemetry system (CorTemp®, HQinc, US) via a small pill ingested ~6 hours prior to exercise [34]. Heart rate (HR) (in bpm) was recorded using a polar HR monitor. Both TC and HR were recorded every 2-minutes and averaged across 10-minute time points and the last 6 minutes of each half of the CISP. Nude body mass was recorded pre-post each CISP using Tanita scales (Tanita DC-430 S MA) to determine fluid loss [35]. For measurement of plasma metadrenalines, 3ml blood samples were collected in EDTA tubes from an indwelling venous catheter located in the arm pre-CISP, at half-time, and immediately post-CISP for analysis of plasma metadrenaline (MET) and normetanephrine (NMET) [7]. These samples were frozen at -80°c until liquid chromatography–tandem mass spectrometry analysis, conducted in the Integrated Laboratory Medicine Department, Freeman Hospital.

Perceptual measures

Thermal sensation (TSS) was measured using Toner et al.’s [36] 0 (unbearably cold) to 8 (unbearably hot) Likert scale. Previous research has revealed this to be a valid measure of perceived heat stress with strong correlations (r = .72) between thermal sensation and rectal temperature [37]. Rating of perceived exertion (RPE) was recorded using the 6–20 Borg scale [38] and affective valence was measured using the Feeling Scale anchored from -5 (very bad) through 0 (neutral) to 5 (very good) [39]. Unick et al. (2015) found excellent agreement for RPE (ICC = 0.77) and for the Feeling Scale (ICC = 0.83) within subjects during exercise across three sessions in previous research. Perceived challenge and threat states were measured using the cognitive appraisal ratio [40]. All perceptual measures were reported at the same four time-points during each half of the CISP (see Fig 1).

Data analysis

After data screening and checking for normality of the data using the Shapiro-Wilk test, a series of two-way (experimental condition by time) repeated measures ANOVAs were performed using IBM SPSS statistics 24.0 (IBM Corporation) for each outcome variable. Homogeneity of variance was assessed using Mauchly’s test of Sphericity, where this was unable to be assumed, Greenhouse-Geisser corrections were applied. When significant results were identified established at p < .05, Bonferroni pairwise comparisons post-hoc tests were performed. Partial eta-squared (ηp2) and generalised eta-squared (η2G) are reported as the effect size for ANOVAs. Due to Cohen’s [41] original partial eta-squared benchmarks not being suitable for interpreting partial eta-squared for multi-factorial within-subjects designs [42], we employed the original benchmarks of .01, .06 and .14 for small, medium and large effect sizes, respectively, to generalized eta-squared as per Lakens [42]. Cohen’s d [43] was reported for any post-hoc pairwise comparisons and values of 0.2, 0.5 and 0.8 indicated small, moderate, and large effects for pairwise comparisons, respectively. As the main time effects for the same exercise protocol in the same sample were included in a previous article [7], we only focus on the main condition (tyrosine vs. placebo) and condition × time interactions in the present article. Data is reported as mean (M) ± standard deviation (SD). Supplementary figures are also available to show the individualised responses for the main outcome measures as raincloud plots (S1–S4 Figs).

Results

Performance measures

There were no condition, or condition × time interaction, effects for physical performance (i.e., peak power output) nor decision making (%) (Table 1) (with effects being reflective of small effect sizes or weaker than small effect sizes).

thumbnail
Download:
Table 1. Results from 2-way repeated-measures ANOVAs for each variable.

https://doi.org/10.1371/journal.pone.0317486.t001

Physiological measures

There were no condition, or condition × time interaction, effects for TC, HR, urine osmolality, fluid loss, or NMET (Table 1), with all effects being reflective of up to (or weaker than) small effect sizes. No main effect for condition was observed for the MET results, but a condition × time interaction was identified with a medium effect size (Table 1). Specifically, MET concentration was higher at half-time in the placebo compared to tyrosine (M difference = +94.25 ± 72.75pmol/L, p = .008, d = 1.12, 95% CI 33.43 to 155.07), but was not different between conditions pre-CISP (M difference = +10.75 ± 70.14pmol/L, p = .678, d = 0.14, 95% CI -47.89 to 69.39) or post-CISP (M difference = +28.88 ± 109.88pmol/L, p = .482, d = 0.27, 95% CI -62.99 to 120.74).

Perceptual measures

There were no condition, or condition × time interaction, effects for challenge and threat state, affective valence, RPE or TSS (Table 1). All effects were reflective of up to (or weaker than) a small effect size.

Discussion

Although tyrosine has been proposed to potentially have some ergogenic effects on physical and cognitive performance in physically demanding environments, research has yet to examine the effects of tyrosine supplementation on cognitive performance during exercise in athletes. The present study investigated the effect of a commonly employed dosage of tyrosine supplementation [13] on physical and cognitive performance in soccer players during high-intensity intermittent exercise, reflective of the physical effort demands of team sport [32], in the heat. In sum, 150mg.kg-1 tyrosine consumed 1 hour prior to exercise, elicited no physical (peak power output) or cognitive (decision-making) benefits during prolonged intermittent sprint exercise in the heat. There were also no differences in perceptual measures observed between conditions (affect, TSS, RPE, demand/resource appraisal). Further, there were no significant physiological differences between conditions, other than plasma MET concentration being lower at half-time with Tyrosine compared to placebo.

No effects on physical performance were found following tyrosine supplementation compared to a placebo. These findings align with most of the limited existing research exploring the use of tyrosine on physical performance indices [13, 20, 23, 24, 44], though contradictory results have been observed [17]. For instance, Tumilty et al. [17] observed that 150mg•kg•bm-1 of tyrosine improved cycling time to exhaustion by ∼15% in 30˚C. However, Tumilty et al. [20] later found no differences between tyrosine and placebo conditions for a self-paced cycling time-trial performance in 30˚C. It is possible that fixed-paced exercise could be more psychologically (and physiologically) stressful than self-paced exercise [21], which could partly explain these discrepancies, or could be dependent on the nature of the physical performance (such as the intensity of exertion). Future research investigating the effects of tyrosine on physical performance measures based on differing levels of physiological demands of exercise in the heat could offer deeper insights into these discrepancies.

Similarly, we found no effects on the physical indices of TC and HR during exercise in the present research. However, we did identify significantly lower metanephrine concentration in hot conditions with tyrosine compared to placebo at half-time, indicating reduced sympatho-adrenal medullary activation with tyrosine compared to placebo [45]. Tyrosine concentration has been shown to peak two hours after single-dose (150mg•kg•bodymass-1) supplementation [46, 47]. In this study, participants consumed tyrosine one hour prior to exercise, to try to facilitate performance immediately after half-time, where previous cognitive and physical decrements had been observed [48]. This may offer some explanation as to why metanephrine concentration was lower at half-time with tyrosine, but not post-CISP. Heightened epinephrine and norepinephrine levels have previously been associated with additional stress reactivity and reduced perceived control and self-efficacy [49] and these factors have also been shown to provoke more of a threat state. That said, we found no effects of tyrosine on cognitive appraisal (challenge/threat state), affective valence nor other perceptual measures in the present study (e.g., perceived exertion and thermal straight).

In the only other previous study investigating the use of tyrosine on cognitive function (albeit during a break or following exercise) using a prolonged intermittent sprint protocol in soccer players, tyrosine supplementation improved vigilance in comparison to placebo, though tyrosine failed to have an effect on more higher order cognitive functions (e.g., dual-task) [13]. Despite a lower environmental temperature used (~25˚C) than the present study, Coull et al. [13] implemented a fixed-pace, prolonged intermittent running protocol where participants experienced greater levels of physiological strain (i.e., peak TC = ~39˚C vs ~38.4˚C), likely due to running activity inducing additional metabolic heat production compared with cycling-based activity [50]. Therefore, it is possible tyrosine may be more likely to have cognitive benefits (alongside potentially having effects on appraisal and affective valence) during exercise when greater levels of physiological and psychological strain are induced (e.g., via fixed paced and running based protocols), thereby increasing the need for additional tyrosine stores.

Limitations and future research

A cycling intermittent sprint protocol was used to allow players to modulate their own high-intensity physical work output as per match-play, whilst simultaneously investigating cognitive performance. Despite this being widely employed within previous team sport literature [32, 33], the physiological stress response to the heat could have been more noticeable during running-based activity [51]. This would better replicate the demands of match-play and potentially increase the need for additional tyrosine stores. Also, although we attempted to incentive effort during the exercise protocol employed in the present study by inducing a competitive element and a financial incentive [52], this does not truly replicate the competitive nature of team sport beyond the laboratory [53]. Further, there was no formal assessment of the effectiveness of the blinding of participants in the current research, and despite using a similar placebo to that implemented in existing research, we cannot be certain whether placebo effects may have contributed to our findings [54]. Therefore, although the tyrosine dosage examined in the present study did not affect peak power output, decision making, cognitive appraisal and affective valence, these factors should be considered when interpreting these findings. Future research could investigate the use of tyrosine supplementation (potentially employing different dosages) on soccer players’ physical and decision-making performance in the heat using an unfixed, intermittent running protocol to potentially better replicate the physiological and psychological strain experienced during match-play or explore its use beyond the laboratory in competitive contexts.

Conclusion

This research was the first to examine the effects of a commonly employed dosage of tyrosine on decision making, cognitive appraisal and affective valence during exercise in the heat. We examined these effects in soccer players whilst engaging in high-intensity intermittent exercise protocol reflective of the physical demands of team sport [27], and found no effects of tyrosine on power output, decision making, cognitive appraisal nor affective valence. Although metadrenaline concentration levels were lower at half-time following tyrosine consumption, these were not found post-exercise. It is possible that the null effects found in this study for acute tyrosine supplementation could be due to the demands of the exercise protocol employed being insufficient to demonstrate the potential ergogenic benefits of tyrosine. Given the limited research in this area, further investigation is warranted to examine the effects of tyrosine on physical and cognitive performance during exercise especially employing more strenuous physical demands and heat strain (e.g., where TC reaches ~39˚C). Further examination into the dosage and timing of dosage intake would also be beneficial, such as exploring larger (and safe) doses than those previously administered in the literature (300 mg.kg-1) which has observed cognitive benefits in warm and cold conditions (respectively) where no adverse tyrosine-related supplementation side effects are noted [13, 55].

Supporting information

S1 Fig. Individual responses for mean decision-making accuracy (%) across tyrosine and placebo conditions.

https://doi.org/10.1371/journal.pone.0317486.s001

(PNG)

S2 Fig. Individual responses for mean cognitive appraisal (demand/resource) ratio [40] across tyrosine and placebo conditions.

https://doi.org/10.1371/journal.pone.0317486.s002

(PNG)

S3 Fig. Individual responses for mean peak power output (W) across tyrosine compared to placebo conditions.

https://doi.org/10.1371/journal.pone.0317486.s003

(PNG)

S4 Fig. Individual responses for mean core temperature across tyrosine compared to placebo conditions.

https://doi.org/10.1371/journal.pone.0317486.s004

(PNG)

Acknowledgments

The authors would like to thank the relevant laboratory learning support officers at Leeds Beckett University who kindly assisted in supporting the conduct of the project.

References

  1. 1. Dambroz F, Clemente FM and Teoldo I. The effect of physical fatigue on the performance of players: A systematic review. PLos One 2022; 17: e0270099.
  2. 2. Reilly T, Drust B and Clarke N. Muscle Fatigue during Football Match-Play. J Sports Med 2008; 38: 357–367. pmid:18416591
  3. 3. Meeusen R, Watson P, Hasegawa H, Roelands B and Piacentini MF. Central Fatigue. The Serotonin Hypothesis and Beyond. Sports Medicine 2006; 36: 881–909.
  4. 4. Shirreffs SM, Aragon-Varagas LF, Chamorro M, Maughan RJ, Serratosa L and Zachwieja JJ. The sweating response of elite professional soccer players to training in the heat. International Journal of Sports Medicine 2005; 26: 90–95. pmid:15726482
  5. 5. Racinais S, Alonso JM, Coutts AJ et al. Consensus recommendations on training and competing in the heat. British Journal of Sports Medicine 2015; 49: 1164–1173. pmid:26069301
  6. 6. Racinais S, Havenith G, Aylwin P, Ihsan M, Taylor L, Adami PE et al. Association between thermal responses, medical events, performance, heat acclimation and health status in male and female elite athletes during the 2019 Doha World Athletics Championships. British Journal of Sports Medicine 2022; 56: 439–445. pmid:35165084
  7. 7. Donnan KJ, Williams EL and Stanger N. The effect of exercise-induced fatigue and heat exposure on soccer-specific decision-making during high-intensity intermittent exercise. PLoS One 2022; 17(12): e0279109. pmid:36520792
  8. 8. Mohr M, Nybo L, Grantham J and Racinais S. Physiological Responses and Physical Performance during Football in the Heat. PLoS One 2012; 7. pmid:22723963
  9. 9. Lieberman HR. (2007). Hydration and cognition: a critical review and recommendations for future research. Journal of the American College of Nutrition 2007; 26: 555–561. pmid:17921465
  10. 10. Roh H-T, So W-Y, Cho S-Y and Sug S-H. Effects of Fluid Ingestion on Brain-Derived Neurotrophic Factor and Cognition During Exercise in the Heat. Journal of Human Kinetics: Section II- Exercise Physiology & Sports Medicine 2017; 58: 73–86.
  11. 11. Jongkees B, Hommel B, Kühn S and Colzato L. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands–A review. Journal of Psychiatric Research 2015; 70: 50–57. pmid:26424423
  12. 12. Meeusen R, Watson P and Dvorak J. The brain and fatigue: New opportunities for nutritional interventions? Journal of Sports Sciences 2006; 24: 773–782. pmid:16766505
  13. 13. Coull NA, Watkins SL, Aldous JWF, Warren LK, Chrismas BCR, Dascombe B. et al. Effect of tyrosine ingestion on cognitive and physical performance utilising an intermittent soccer performance test (iSPT) in a warm environment. European Journal of Applied Physiology 2015; 115: 373–386. pmid:25326727
  14. 14. Watson P. Tyrosine supplementation: can this amino acid boost brain dopamine and improve physical and mental performance? Sports Science Exchange 2016; 28: 1–6
  15. 15. Phillips P. E. M., Walton M. E. & Jhou T. C. (2007). Calculating utility: preclinical evidence for cost-benefit analysis by mesolimbic dopamine. Psychopharmacology, 191, 483–495. pmid:17119929
  16. 16. Zheng X. & Hasegawa H. (2015). Central dopaminergic neurotransmission plays an 253 important role in thermoregulation and performance during endurance exercise. European Journal of Sport Science, 16, 818–828.
  17. 17. Tumilty L, Davison G, Beckmann M and Thatcher R. Oral tyrosine supplementation improves exercise capacity in the heat. European Journal Applied Physiology 2011; 111: 2941–50. pmid:21437603
  18. 18. Fernstrom JD. Large neutral amino acids: dietary effects on brain neurochemistry and function. Amino Acids 2013; 45:419–430. pmid:22677921
  19. 19. Xing B, Li W-J and Gao W-J. Norepinephrine versus Dopamine and their Interaction in Modulating Synaptic Function in the Prefrontal Cortex. Brain Research 2016; 1641: 217–233. pmid:26790349
  20. 20. Tumilty L, Davison G, Beckmann M and Thatcher R. Failure of Oral Tyrosine Supplementation to Improve Exercise Performance in the Heat. Medicine and Science in Sports and Exercise 2014; 46. pmid:24389518
  21. 21. Lander P. J, Butterly R. J. & Edwards A. M. (2009). Self-paced exercise is less physically challenging than enforced constant pace exercise of the same intensity: influence of complex central metabolic control. British Journal of Sports Medicine, 43, 789–795. pmid:19196729
  22. 22. Ke Z., Yip S. P., Li L., Zheng X. X. & Tong K.-Y. (2011). The effects of voluntary, involuntary, and forced exercises on brain-derived neurotrophic factor and motor function recovery: a rat brain ischemia model. PLoS One, 6, e16643. pmid:21347437
  23. 23. Attipoe S, Zeno SA, Lee C, Crawford C, Khorsan R, Walter AR, et al. Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans, a Rapid Evidence Assessment of the Literature. Military Medicine 2015; 180: 754–765. pmid:26126245
  24. 24. Coull N, Chrismas B, Watson P, Horsfall R and Taylor L. Tyrosine Ingestion and Its Effects on Cognitive and Physical Performance in the Heat. Medicine and Science in Sports and Exercise 2016; 48: 277–286. pmid:26285023
  25. 25. Pompeo A, Afonso J, Cirillo ELR, et al. Impact of temperature on physical and cognitive performance in elite female football players during intermittent exercise. Scand J Med Sci Sports. 2024; 34:e14646. pmid:38700046
  26. 26. Price S, Wiecha S, Cieśliński I, Śliż D, Kasiak PS, Lach J, et al. Differences between Treadmill and Cycle Ergometer Cardiopulmonary Exercise Testing Results in Triathletes and Their Association with Body Composition and Body Mass Index. Int J Environ Res Public Health. 2022 Mar 17;19(6):3557. pmid:35329246; PMCID: PMC8955092.
  27. 27. Aldous JWF, Chrismas BCR, Akubat I, Dascombe B, Abt G and Taylor L. Hot and hypoxic environments inhibit simulated soccer performance and exacerbate performance decrements when combined. Frontiers in Physiology 2015; 6: 421. pmid:26793122
  28. 28. Hase A, Gorrie-Stone T and Freeman P. Tyrosine intake and cardiovascular responses in a motivated performance situation. Sport, Exercise and Performance Psychology 2019; 8: 80–92.
  29. 29. Drust B, Waterhouse J, Atkinson G, Edwards B and Reilly T. Circadian rhythms in sports performance—an update. Chronobiology International 2005; 22: 21–44. pmid:15865319
  30. 30. Racinais S, Mohr M, Buchheit M, Voss SC, Gaoua N, Grantham J, et al. Individual responses to short-term heat acclimatisation as predictors of football performance in a hot, dry environment. British Journal of Sports Medicine 2012; 46: 810–815. pmid:22797527
  31. 31. Gibson O, Wrightson JG and Hayes M. Intermittent sprint performance in the heat is not altered by augmenting thermal perception via L-menthol or capsaicin mouth rinses. European Journal of Applied Physiology 2019; 119:653–664. pmid:30580384
  32. 32. Castle PC, Macdonald AL, Philp A, Webborn A, Watt PW and Maxwell NS. Precooling leg muscle improves intermittent sprint exercise performance in hot, humid conditions. Journal of Applied Physiology 2006; 100: 1377–1384. pmid:16339344
  33. 33. Hayes M., Smith D., Castle P. C., Watt P. W., Ross E. Z. & Maxwell N. (2013). Peak power output provides the most reliable measure of performance in prolonged intermittent-sprint cycling. Journal of Sports Sciences. 31(5): 565–572. pmid:23176342
  34. 34. Lee SMC, Williams WJ and Schneider SM. Core Temperature Measurement During Submaximal Exercise: Esophageal, Rectal, and Intestinal Temperatures. Aviation Space and Environmental Medicine 2000; 71: 939–945.
  35. 35. Lorenzo S, Halliwill JR, Sawka MN and Minson CT. Heat acclimation improves exercise performance. Journal of Applied Physiology 2010; 109: 1140–1147. pmid:20724560
  36. 36. Toner MM, Drolet LL and Pandolf KB. Perceptual and physiological responses during exercise in cool and cold water. Perceptual and Motor Skills 1986; 62: 211–220. pmid:3960662
  37. 37. Casa D. J., Becker S.M., Ganio M. S., Brown C. M., Yeargin S. W., Roti M. W., et al. (2007). Validity of devices that assess body temperature during outdoor exercise in the heat. Journal of Athletic Training, 42, 333–342 pmid:18059987
  38. 38. Borg GA. Psychophysical bases of perceived exertion. Medicine & Science in Sports & Exercise 1982; 14: 377–381.
  39. 39. Hardy CJ and Rejeski WJ. Not what, but how one feels: The measurement of affect during exercise. Journal of Sport & Exercise Psychology 1989; 11: 304–317.
  40. 40. Moore LJ, Vine SJ, Wilson MR and Freeman P. The effect of challenge and threat states on performance: An examination of potential mechanisms. Psychophysiology 2012; 49: 1417–1425. pmid:22913339
  41. 41. Cohen J. Statistical power analysis for behavioral sciences. 2nd ed. Hillsdale, NJ: Lawrence Erlbaum Associates, 1988.
    • 42. Calculating Lakens D. and reporting effect sizes to facilitate cumulative science: a practical primer to t-tests and ANOVAs. Front Psychol 2013; 4: 863.
    • 43. Cohen J. Statistical power analysis. Curr Dir Psychol Sci 1992; 1: 98–101.
    • 44. Watson P, Enever S, Page A, Stockwell J and Maughan RJ. Tyrosine supplementation does not influence the capacity to perform prolonged exercise in a warm environment. International Journal of Sport Nutrition and Exercise Metabolism 2012; 22: 363–373. pmid:23011654
    • 45. Wright H. E., Selkirk G. A. & McLellan T. M. (2010). HPA and SAS responses to increasing core temperature during uncompensable exertional heat stress in trained and untrained males. European Journal of Applied Physiology, 108, 987–997. pmid:19967394
    • 46. Glaeser B. S., Melamed E., Growdon J. H. & Wurtman R. J. (1979). Elevation of plasma 228 tyrosine after a single oral dose of L-tyrosine. Life Sciences, 25, 265–271.
    • 47. Growdon J. H., Melamed E., Logue M., Hefti F. & Wurtman R. J. (1982). Effects of oral L‐tyrosine administration on CSF tyrosine and homovanillic acid levels in patients with Parkinson’s disease. Life Sciences, 30, 827–832. pmid:6175872
    • 48. Donnan K., Williams E. L. & Stanger N. (2020). The Effects of Heat Exposure During Intermittent Exercise on Physical and Cognitive Performance Among Team Sport Athletes. Perceptual and Motor Skills. pmid:33076764
    • 49. Bandura A., Taylor B. C., Williams L. S., Mefford I. N. & Barchas J. D. (1985). Catecholamine Secretion as a Function of Perceived Coping Self-Efficacy. Journal of Consulting and Clinical Psychology, 53, 406–414. pmid:4008724
    • 50. Özgünen KT, Kurdak SS, Maughan RJ, Zeren Ç, Korkmaz S, Yazιcι Z, et al. Effect of hot environmental conditions on physical activity patterns and temperature response of football players. Scandinavian Journal of Medicine & Science in Sports 2010; 20: 140–147.
    • 51. Junge N, Jørgensen R, Flouris AD and Nybo L. Prolonged self-paced exercise in the heat–environmental factors affecting performance. Temperature 2016; 3: 539–548. pmid:28090557
    • 52. Cooke A, Kavussanu M, McIntyre D, Boardley I and Ring C. Effects of competitive pressure on expert performance: Underlying psychological, physiological and kinematic mechanisms. Psychophysiology 2011; 48: 1146–1156. pmid:21265862
    • 53. Jones MV, Bray SR and Lavallee D. All the world’s a stage: Impact of an audience on sport performers. In Jowett S. & Lavallee D. (Eds.), Social Psychology in Sport 2007; 103–113. Champaign, IL: Human Kinetics.
      • 54. Hurst P, Schipof-Godart L, Szabo A, Raglin J, Hettinga F, Roelands B, et al. The Placebo and Nocebo effect on sports performance: A systematic review. Eur J Sport Sci. 2020 Apr;20(3):279–292. Epub 2019 Aug 20. pmid:31414966.
      • 55. Mahoney C. R., Castellani J., Kramer M., Young A. & Lieberman H. R. (2007). Tyrosine supplementation mitigates working memory decrements during cold exposure. Physiology and behaviour. 92(4): 575–582. pmid:17585971