Introduction

In indoor climbing competition, a route consists of 20–50 holds and takes 2–7 minutes to complete at intensities ranging from 71–91% of maximum heart rate [1–3]. In recent decades, climbing performance measured by the difficulty rating of routes, has greatly improved in Sport Climbing World Cup series. However, the training used to improve and develop climbing performance mostly draws on experience-based knowledge, cross-sectional studies [4, 5] and a few intervention studies conducted in climbing [6, 7]

Several cross-sectional studies have reported strength and/or endurance in the fingers, body composition and relative upper-body strength as the most important physical factors predicting climbing performance [4, 5]. Several factors have been investigated as predictors of climbing performance. The most frequently used tests (Bent-arm hang, Dead-hang and finger strength) relate to climbing-specific actions, and the relative contribution of anthropometric factors (height, weight, body fat) and climbing experience and flexibility have also been examined. Between 0.3–97% of climbing performance has been explained by these factors, singly or in combination, depending on climbing performance level and number of factors included in the analyses [1, 4], with duration in a finger grip suspension (‘dead hang’) found to be the best single predictor of performance (r² = 0.66–0.76) [4].

The difficulty level of a route is manipulated by several factors such as grip type (size and shape), distance and position between grips and gradient of the climbing wall. As a result, climbing includes dynamic and often explosive movements with short static positions before the next transition. In elite climbing routes (24–27 IRCRA), the climbers often only have two contact points in the wall (typically, an arm and the opposite foot). To be successful in maintaining positions, reaching climbing holds, clipping the rope to carabiners and moving efficiently, core stability and strength have often been proposed as key factors in elite climbing performance, and although this has never been systematically examined, Muehlbauer and colleagues demonstrated 19–22% increase in core strength (flexion and extension) among sedentary adults after training climbing twice peer week for eight weeks [8]. A strong and stable core may resist rotation of the trunk [9] and allow force generated by feet to transfer to the arms without causing a loss of energy, impairing technique or reducing range of movement of the arms.

Studies have examined core training and performance in running [10, 11], swimming [12], throwing [13], kicking [14] and golf club velocity [15], however conclusive evidence of the contribution of core strength is lacking. [16]. Studies that have demonstrated improvement have utilized progressive core-training programs and included both core strength and stability [13, 17–19]. For example Saeterbakken et al. [13] demonstrated a 4.9% improvement in throwing velocity among handball players after a core-training program. Still, several studies have demonstrated improved core and stability test results without improved performance [11, 12, 20–22].

In the majority of sports, both dynamic and isometric core movements are important [23]. Previous studies into the relationship between core training and performance have utilized isometric (10, 12, 13, 16) or dynamic (9, 11) training protocols singly or in combination (14, 17) with no conclusive evidence of the best approach. However, comparison of the effects of isometric and dynamic core training has not been undertaken and the effects of progressive core training on climbing performance are unknown. Therefore, the aim of this study was to compare dynamic and isometric core training on climbing-specific performance tests in advanced and elite climbers. We hypothesized that test scores in both groups would increase after the intervention, without significant differences resulting for either groups.

Methods

Participants

Nineteen climbers (14 males and 6 females) volunteered to participate in the study. The climbers (age 27.4 ± 6.7 years, height 1.74 ± 0.09 m, weight 70.3 ± 10.1 kg) had a mean climbing experience of 7.3 ± 5.6 years. After the pre-test, participants were first stratified (by sex) and than ranked by climbing skills (red-point on-sight climbing performance last year) into pairs (i.e. the two best males were pair one, number 3 and 4 were pair two, etc.). The climbers in each pair were then randomized by drawing into either an isometric core-training program (ICT) or a dynamic core-training program (DCT). Nineteen climbers completed pre- and post- testing (one male elite climber withdrew). There were no differences between groups in climbing experience, climbing skill or the mean anthropometric measurements at pre-test (p = 0.552–0.847). For details, see Table 1.

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Table 1. An overview of the participants.

https://doi.org/10.1371/journal.pone.0203766.t001

The inclusion criteria for participation were minimum one year of climbing experience, free of injuries for the last six months, having a climbing frequency of at least two sessions per week and the climbing skill had to be on an advanced level or better (>15) according to the IRCRA scale [24].

Training protocol

The isometric and dynamic training programs were performed twice per week for ten weeks. Each session lasted 30–40 minutes and contained four exercises. The training programs were similar in intensity (4–10 repetitions maximum), volume (3–4 sets) and rests between sets and exercises (2 minutes). The exercises were: foot-lift (S5 Fig), arm lock-off (S6 Fig), side-bridge (S7 Fig) and prone-bridge (S8 Fig). The foot-lift and arm lock-off were performed on an artificial bouldering wall. In the foot-lift exercise, the participants hung from two hand grips on a pending wall and lifted one knee or foot towards a foot stance (S5 Fig). In the arm lock-off exercise, participants used their left arm and foot or right arm and foot to maintain a position in the wall and with the free arm reached horizontally as far as possible for a hand grip, achieving a position on the wall before returning to the starting position (S6 Fig). The side-bridge (S7 Fig) and prone-bridge (S8 Fig) have been described in detail elsewhere [27].

The progression of the training programs was achieved by increasing the number of repetitions, sets, steepness of the wall, decreasing the base of support, increasing the level of the arm(s) and increasing the distance to the foot stance or hand grip. The exercises in ICT were identical, but instead of moving dynamically from a starting to a finishing position as the DCT did, the ICT performed an isometric contraction in the finishing position and maintained the position for three to five seconds, with three seconds recovery between each repetition. If a participant managed to perform the final set with the maximum number of repetitions (DCT) or for the maximum time (ICT), they progressed to a higher level at their next training session. The details of the different intensity levels are presented in Table 2 and Table 3. Numbers of climbing sessions, climbing training hours and core-training sessions were reported weekly using a login form.

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Table 2. An overview of the progression of the training for the ICT group.

https://doi.org/10.1371/journal.pone.0203766.t002

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Table 3. An overview of the progression of the training for the DCT group.

https://doi.org/10.1371/journal.pone.0203766.t003

Results

Discussion

The DCT group demonstrated improvement in three isometric core tests (trunk flexion, rotation to right and left) and in the dynamic core-strength, however, there was no improvement in two climbing-specific core tests. In comparison, the ICT group improved in isometric trunk flexion strength testing and a climbing-specific test (body-lift), involving dynamic trunk and hip activation, with no improvement in the trunk rotation or body lock-off tests. These results are not in accordance with proposals of training-specific adaptations, as the dynamically trained group in this study performed superiorly on isometric strength testing after the intervention, with some evidence of isometrically trained participants performing better on a task with dynamic trunk and hip actions.

We hypothesized there would be improvements for both groups in the climbing-specific tests: dynamic training using the exercises chosen (foot-lift and arm lock-off) requires unilateral hip flexion, either whilst the upper body supports the trunk (foot-lift) or during cross-lateral stabilization (for example, from right arm and left leg support), as the unsupported upper limb and foot reach for a hold (arm lock-off). Both exercises demand isometric trunk stiffness to provide a base of support for the limb actions, with dynamic motion produced either at the shoulder or pelvic girdle. At the volume prescribed (see Tables 1 & 2), the dose over ten weeks should have been sufficient to induce adaptation, in accordance with [29]. According to our hypothesis this protocol would be expected to increase bilateral trunk strength (as both limbs are used during training), with training in contra-lateral force transfer (opposing arm and foot reciprocally stabilized in closed chain and then engaged in open chain actions) speculated to improve transverse plane (rotational) strength, due to synergy in external and internal oblique recruitment during successful arm lock-off. In the DCT group, the outcomes were consistent with this hypothesis, with improvement recorded in isolated strength testing (sagittal and oblique biased MVC strength tests). However, the strength gains did not translate into improvement in performance of climbing-specific tests in DCT, with increase in score resulting only in the ICT trained group (significant improvement in the body-lift test). This latter finding is surprising: the body-lift test involves dynamic actions of the hip and lower spine which, according to the specificity of the training [30], should favor the DCT group, whose training included dynamic pelvis on thorax movement (bouldering arm lock-off), which has been demonstrated to evoke high EMG amplitudes in oblique abdominal muscle activation [31]. The DCT demonstrated ~34% improvement with a larger effect size 0.43 vs. 0.30 than the ICT group, which improved by 30%, however, small sample size and a large standard deviation probably resulted in a type II error for the DCT group. In addition, the body-lift test does not target the core muscles in isolation, as their actions are integrated during the test. It may be speculated that the shoulder girdle plays a significant role in assisting trunk position as the body transitions from a vertical (axial) alignment to gravity to a horizontal position, with loading of epiaxial appendicular muscles and scapulothoracic muscles. Anatomically there is contiguity and fascial interdigitation between serratus anterior and the external oblique abdominal muscles such that when the shoulder is loaded there is tensioning of surrounding myofascial.

In the other climbing specific test (body-lock), neither group demonstrated significant improvement, which is perhaps less surprising as this test is performed horizontally, a position which occurs rarely in climbing [30]. The improvements in both groups were only ⅓ of the improvements for the body-lift test. Nevertheless the test was designed to examine the ability to generate force through the entire kinetic chain, from the toes through the core and ending in the fingers [32], This is a typical pattern in climbing and is crucial for the climbers to be able to reach a new hand- or foot grip [3]. Results suggest that both approaches (ICT and DCT) had a similar impact on test result inducing a comparable magnitude of improvement in holding time, with neither group performing superiorly to the other in the post-test (mean time in test position 30 second both groups).

To our knowledge, no previous studies have compared the effect of isolated vs dynamic core training. Some, but not all previous studies have demonstrated improved performance after improved core strength and/or stability [19, 20, 22, 33]. However, there are several limitation of these studies such not using elite athletes, combining core training with general resistance training or training core stability and not core strength [10, 19, 34, 35]. Several studies have performed either dynamic, isometric interventions or combined them to examine the effects on performance [10, 11, 13, 18, 34], however as none of the abovementioned studies successfully isolated the core training modes to compare them, they are not directly comparable with the present study. Other studies have used performance measuring tests after attending a core training program, with inconclusive results: some have demonstrated no effect [11, 34] and others have demonstrated improvement in performance [13, 18, 19]. In studies which have not demonstrated an effect it has been argued that as participants were already at a high performance level, the capacity to demonstrate further improvements in performance after 8–10 weeks was minimal [11, 22, 33]. Importantly, in studies that demonstrated a positive effect [13, 18, 19], a progressive core- strengthening program was used, as has been adopted in the present study. For example Saeterbakken and colleagues showed a 4.9% improvement in throwing velocity using four levels of intensity in a core-training program, using dynamic exercises which included core stability and core strengthening [13], however as exercises were combined and not isolated into dynamic versus isometric training, as in this study, results are not directly comparable.

Core strength was measured in isolation with a dynamic test (Superman) and three isometric tests (abdominal flexion and rotation to both sides). Neither group demonstrated greater improvement than the other. However, the DCT group performed better in all tests after the intervention, while the ICT group only improved in Superman and trunk flexion. It is possible that differences in exercise performance intensity (dynamic versus isometric) could have influenced results, however, total exercise duration was matched according to previous approaches [36]. Furthermore, the improvement was between ~8–15% which is quite impressive based on baseline MVC values (94–99% of body weight) in trunk flexion pre-testing. These values are 30–50% greater than those observed in our laboratory using a comparable age-match population. Based on the pre-test results, one might conclude that climbers at a high level have a strong core as a result of climbing.

In contrast to the principle of training-specificity [30] and task-specificity [37], the isometric core-training group did not improve performance in the rotational isometric core strength tests, whereas the dynamic core training group did, which suggests the two training approaches stimulated different adaptions in soft tissue. This speculation is supported by recent evidence of mode specific training adaptations in hamstring fascicle length and muscle architecture [38, 39] and previous evidence of connecting tissue adaptations after isometric training [29].

The study has some limitations: only eighteen climbers completed the study (nine participants in each group), which increases the risk of a type II error due to low statistical power. Also as core-training was not performed in isolation, but included within participants’ overall fitness routine (i.e. climbing and bouldering), the impact of non-specific trunk loading as a result of other training activities may have had an effect on results [16]. However it is important to note that there was no difference in training status, finger hang time or climbing level between the ICT and DCT groups at baseline. Finally, as participants in this study were highly trained, these results may not be generalizable to climbers at a less elite level of participation and it may be speculated that novice or intermediate-level climbers may demonstrate greater improvements after specific core-training, as previous studies suggest [11, 12].

This study is the first of it is kind to compare the effects of dynamic and isometric core training in elite climbers and to examine whether these modes of core-training improve climbing performance. Although neither training approach demonstrated significantly greater improvement overall, the DCT improved in both sagittal and rotational core strength tests, whereas the ICT only improved in the sagittal test. Both modes of training appear equally effective in improving sagittal MVC. With regard to climbing-specific tests, only the ICT group demonstrated an improvement after the intervention, however this finding should be interpreted with caution, as a positive association between improvement in core strength and climbing performance may be harder to detect in highly trained climbers with high core strength at baseline. In summary, based on findings from this and previous comparable studies [10, 11, 13], the authors recommend that dynamic core-training should be included in climbers’ exercise regime to increase oblique muscle strength, with isometric core training adopted to maximize functional transfer of core strength gains. More research is needed to provide conclusive evidence of the transferability of improvements in core strength to performance, and to demonstrate whether dynamic or isometric protocols deliver superior performance gains.

Supporting information

Acknowledgments

This study was conducted without any funding from organization or manufacturers. The authors wish to thanks all the individuals who contributed or took part in the study, especially the participants.