The Effects of Plyometric Training on Neuromuscular Performance in Advanced Boulder Climbers

1. Introduction

Bouldering is characterized by solving motor problems on low walls that demand high intensity, technical precision, and intermuscular coordination, involving short bursts of effort and high neuromuscular demands [1,2]. Unlike lead climbing, where endurance plays a predominant role, bouldering requires the application of effective force within very short time intervals, frequently less than 200 milliseconds, making explosive force production a key determinant of performance [1,3]. In advanced stages of development, when climbers already possess a solid technical foundation and high levels of relative strength, progression depends less on increasing maximum strength and more on the efficiency with which it is produced within short intervals [4,5,6]. This approach aligns with the evolution of modern bouldering, characterized by problems that integrate dynamic, reactive, and time-limited actions for applying force. Various studies have indicated that, in advanced climbers, finger flexor muscles have higher oxidative capacity, relative strength (strength-to-weight ratio), and overall strength levels compared to non-climbers [7].

Performance differences are not explained solely by the magnitude of maximum force, but also by the way in which this is expressed over short time intervals [8]. In this context, rate of force development (RFD) is defined as the slope of the force-time curve during the initial phase of contraction and constitutes a sensitive indicator of neuromuscular function in explosive actions [1]. RFD is particularly critical in the short-duration actions characteristic of bouldering, such as dynamic movements, reactive blocks, and campus board sequences, where the time available to apply force is typically less than 200 ms [2]. Long dynamic movements, coordinated throws, reactive blocks on small holds, and sequences on the campus board involve brief contacts and rapid changes in the direction of the centre of mass. These actions are typically performed within narrow time windows for force application, making RFD a determining factor in competitive performance [9].

In disciplines where body weight constitutes the primary resistance to be overcome, mechanical efficiency and the optimization of the centre of mass play a decisive role[10]. Vereide et al. [9] have shown that elite climbers not only exhibit higher relative strength values but also greater efficiency in the application of that force, reducing the energy cost per movement. This efficiency is linked to more coordinated muscle activation patterns and better synchronization between the upper and lower limbs [11]. In this context, improving RFD could not only influence the ability to perform explosive movements, but also the temporal precision with which these movements are integrated into complex technical sequences [1,2,9]. Furthermore, the lower body also plays a crucial role in modern bouldering. Although historical climbing was associated primarily with upper-body strength, current literature recognizes the importance of generating momentum from the lower limbs to optimize the transfer of the centre of mass and reduce the load on the finger flexors[12,13]. Li et al. [14] observed that jump power is related to efficiency in large-range dynamic movements, whilst Vigouroux & Quaine [15] noted that coordination between leg propulsion and arm pull allows for maximizing mechanical efficiency in explosive sequences, reducing energy expenditure, and improving body stability.

Plyometric training has emerged as a promising strategy for developing RFD and explosive power in sports requiring rapid force production [16,17]. Based on the stretch-shortening cycle, plyometric exercise involves a rapid transition between eccentric loading and concentric contraction, generating adaptations in neuromuscular efficiency, motor unit recruitment, and muscular stiffness [16,18,19]. Meta-analytical evidence supports plyometrics training improves vertical jump performance and explosive force production across multiple sports contexts [17]. In upper-body dominant sports, plyometrics protocols incorporating ballistic push-ups, reactive pull-ups, and campus board- based exercises have been shown to increase peak power and RFD in pulling and pushing actions [20,21,22]. Despite this evidence, the application of plyometric training remains largely unexplored. To date, only a limited number of studies have examined explosive training intervention in climbers [22,23], and none have specifically investigated the effects of a structured plyometric program targeting both upper and lower body explosive capacity of RFD in advanced boulder climbers. Given that bouldering performance depends critically on the ability to generate force rapidly in pulling actions and dynamic sequences, there is a clear rationale for examining the efficacy of plyometrics training as a targeted approach to neuromuscular intervention in this population.

Therefore, this study aims to determine the effect of a plyometric training programme on muscle strength in advanced boulderers. Given this background, improving the ability to generate force rapidly could be a key factor in performance in advanced bouldering. Therefore, this study aims to determine the effect of a plyometric training programme on muscle strength in advanced boulderers.

2. Materials and Methods

Design

The study employed a randomized experimental design with two parallel groups and repeated measures (group × time) over ten weeks.

Sample

Eighteen advanced climbers were assigned to an experimental group (n=9) that undertook a plyometric training programme at a frequency of two sessions per week for 10 weeks, and a control group (n=9), which maintained their usual training without the systematic incorporation of additional plyometric stimuli. Random allocation was performed using a simple randomization procedure with a computer-generated random number generator. The athletes had a minimum bouldering level of ≥ V5, at least two years of continuous experience in sport climbing, and a regular training frequency of three or more sessions per week. No priori sample size calculation was performed. The sample size was determined by the availability of advanced climbers who met the predefined inclusion criteria during the recruitment period. Given the difficulty of accessing a homogeneous sample of trained Boulder climbers with similar performance levels and training backgrounds, the present study should be interpreted as a controlled exploration trial.

Inclusion Criteria

Male climbers aged between 20 and 40 years were considered eligible if they had a minimum bouldering performance level of ≥ V5, at least two years of continuous sport climbing experience, and a regular training frequency of three or more sessions per week over the previous six months.

Exclusion Criteria

The absence of active musculoskeletal injuries at the time of the initial assessment was required, with the aim of ensuring comparable baseline conditions and reducing the risk of adverse events during the plyometric programme. Participants with medical conditions or ailments contraindicating reactive or ballistic training were excluded, as were those who sustained injuries during the intervention period that prevented continuation of the protocol. In addition, subjects with an adherence rate of less than 80% of the scheduled sessions were excluded.

Baseline characteristics included age, body mass, and body composition. Body composition was assessed by electrical bioimpedance using an InBody 270S® multi-frequency analyzer (InBody Co., Seoul, Korea). Measurements were taken under standardized conditions, including prior fasting, abstention from vigorous exercise in the preceding 24 hours, and control of hydration (Table 1)

Instruments

Finger Strength on a 20 mm Hold:

A Tindeq Progressor® load cell attached to a standard 20 mm hold was used to assess maximum finger strength and RFD. This device has demonstrated adequate validity and reliability for isometric strength measurements in climbing [24]. The protocol consisted of maximum isometric contractions with a standardized posture, recording the complete force-time curve for subsequent analysis. Signals were acquired at 80 Hz and filtered using a fourth-order Butterworth filter (low-pass, 10 Hz). The onset of contraction was defined as the point at which the force exceeded 5% of the maximum force above the baseline level. From the processed signal, Fmax, RFD0-200 ms, and RFD 20-80% were calculated, including their normalization relative to Fmax and body mass.

Maximum Pull Force (Pull-Up)

Maximum pull force (isometric pull-up) was assessed using the Tindeq Progressor® system. The force-time curve was recorded in a standardised position, following methodological recommendations for the analysis of force-time variables [25]. Signal processing, definition of the onset, and calculation of variables (Fmax, RFD 0–200 ms, and RFD 20–80%) followed the same criteria described for the assessment of finger strength, including the normalisation of values.

Lower-Body Power

Lower limb power was assessed using the Countermovement Jump (CMJ) test on a Chronojump® contact platform (Boscosystem, Barcelona, Spain). Jump height (cm) was recorded based on flight time, and estimated power (W) was calculated. Participants performed the test with their hands on their hips to minimize the contribution of arm swing

Specific Power of the Upper Limbs

Upper limb power was assessed using the plyometric push-up test performed on a Chronojump® contact platform (Boscosystem, Barcelona, Spain), recording flight time to estimate variables such as height (cm) and power (W), as suggested by previous studies [20,21]. In the starting position, each athlete was asked to place both hands on the contact platform in a prone plank position, shoulder-width apart, with elbows extended, the trunk aligned, and feet flat on the ground. From the starting position, the athlete performs a controlled elbow flexion (90°). They immediately perform an explosive arm extension, lifting their hands off the platform. During the aerial phase, the athlete must keep their body aligned (avoiding hip flexion). Flight time is recorded from the moment contact with the platform is lost until it is regained. Three attempts were made, with 1-2 minutes of recovery between each. The best value was recorded for analysis. An attempt was considered valid when there was a clear lift-off of both hands and no compensatory movements (hip flexion or arm asynchrony).

Upper-body specific power was assessed using the Powerslap test on a campus board, recording the distance achieved in centimeters, a procedure described previously [1,26]. The athletes started from a static hanging position on a standardized bar, with both hands in a prone grip, shoulder-width apart, elbows extended, and without support from the lower limbs. From this position, they were asked to perform a maximum explosive pull, reaching as high as possible with one hand, without allowing any prior momentum or body sway. The recorded variable was the distance reached (cm) between the starting bar and the highest point touched. Two to three attempts were made on the dominant arm only, with 3-5 minutes between each, and the best valid attempt was recorded. Only attempts performed from a static position and with clear contact on the target bar were considered valid.

Procedures

The study was conducted in three stages. In the first stage, the initial assessment (pre-test) was carried out, which included standardized measurements of body composition, maximum grip strength, maximum strength, RFD of the fingers on a 20 mm hold, isometric pull strength, and power of the upper and lower limbs. Three attempts were made per test, with the best value recorded for analysis. For the Power Slap test, attempts were performed on the dominant arm only. Pre- and post-intervention assessments were carried out at a climbing centre at the same time of day (±1 hour), under similar environmental conditions and using the same equipment and standardized protocols. To minimize external variability, participants were instructed to refrain from intense training during the 48 hours before each assessment, to maintain their usual sleep pattern (minimum 7 hours the night before), and not to alter their regular diet during the week before the measurements. No specific dietary intervention was implemented; however, participants were asked to maintain consistent nutritional habits during the assessment period to reduce potential confounding effects.

To control training volume, the plyometric load was quantified by the number of reactive contacts per session, considering both lower limb (LL) and upper limb (UL) explosive actions. Reactive contact was defined as any landing or explosive support in lower limb (LL) plyometric exercises, as well as any brief, reactive contact in upper limb (UL) explosive pulls exercises (campus board, plyometric pull-ups, and plyometric TRX). The volume per session was expressed as a range of contacts, as the effective load could vary slightly depending on the level of technical execution, individual selection of progressions, and the neuromuscular tolerance of each participant.

The second stage corresponded to the 10-week intervention (Table 2). During the adaptation phase (weeks 1–4), the volume ranged from 90 to 288 reactive contacts per session, at low to moderate intensities, prioritizing landing control, technical quality, and the progressive preparation of the musculotendinous structures. This initial progression was based on recommendations for the safe implementation of plyometric training in trained populations, where a prior adaptation phase is suggested before increasing intensity to optimize neuromuscular adaptations and reduce the risk of injury [16,17]. In the bouldering-specific plyometric phase (weeks 5–6 and 8–10), the volume progressed to approximately 168–384 reactive contacts per session, at moderate to very high intensities, incorporating greater heights, increased eccentric demand, reduced contact time, and exercises highly transferable to bouldering technique. The seventh week was a deload week, aimed at reducing both volume and intensity, promoting neuromuscular recovery and consolidating previous adaptations [18,27], preserving the quality of the stimulus and reducing the risk of musculotendinous overload [16]. In the third stage, the final assessment (post-test) was conducted, replicating the initial protocols to ensure methodological consistency and control of experimental variability.

Ethical Considerations

The study was conducted in accordance with the regulations governing research involving human subjects and was reviewed and approved by the Scientific Ethics Committee of the University of Viña del Mar ( CEC-UVM 32-25; date of approval: 24 June 2025). Furthermore, the ethical principles established in the Declaration of Helsinki for medical research involving human subjects [28] were observed. All participants signed an informed consent form detailing the procedures, potential risks and benefits, ensuring the confidentiality of the information and the right to withdraw voluntarily at any stage without consequences for their training programme.

Statistical Analysis

Data processing and statistical analysis were performed using Jamovi software (version 2.4.11). In the first stage, we verified that the variables met the assumptions of normality using the Shapiro-Wilk test, given its adequate sensitivity for small samples in applied research contexts. Likewise, the homogeneity of variances was assessed using Levene’s test to confirm the equality of variances across groups, a particularly important consideration in small samples, where the presence of outliers can influence the results. Once the parametric nature of the data and the equality of variances were confirmed, a 2×2 mixed-design analysis of variance (group × time) was applied to examine the main effect of time, the main effect of group, and the group × time interaction, which allowed for the identification of differential changes attributable to the plyometric intervention. Since the time factor had only two levels (pre and post), it was not necessary to assess the assumption of sphericity. To estimate the practical magnitude of the observed changes, effect sizes were calculated using the partial eta-squared statistic (η²p). Effect sizes estimated using η²p were interpreted according to Cohen’s [26] guidelines: small (η²p = 0.01), moderate (η²p = 0.06), and large (η²p = 0.14). (Δ%) was calculated as [Post − Pre) / Pre] × 100 as a descriptive indicator of performance development. To complement the inferential analysis and facilitate practical interpretation, mean changes (Δ = Post − Pre) were calculated for each variable, and between-group differences in change (Δ Difference = IG − GC) were compared using independent-samples Student's t-tests with 95% confidence intervals (95% CI). A 95% CI for Δ Difference that did not include zero was interpreted as evidence of a statistically significant between-group difference. The level of statistical significance was set at p < 0.05 for all analyses.

3. Results

Table 3 shows that the intervention group demonstrated consistent improvements in most variables related to upper-body performance and force production. Increases were observed in pull-up performance (+6.93%), CMJ height (+9.17%), push-up power (+8.93%), and power-slap (+7.50%). Likewise, finger strength variables showed moderate increases, including maximum grip strength (+7.20%) and maximum strength of the right-hand fingers (+4.40%). The highest relative changes in the intervention group were observed in rate of force development (RFD) variables, particularly in isometric push-ups with increases of +477.9% (RFD 200 ms) and +233.7% (RFD 20–80), suggesting significant improvements in the ability to generate force rapidly. In contrast, the control group showed changes of lesser magnitude and variability.

Table 4 shows significant interactions in pull-up performance (F=526; p=0.036; η²p=0.248), with a moderate effect size. In the power-slap test (F=477; p=0.44; η²p=0.23) with a moderate effect, and in the RFD (200 ms) isometric pull-up (F=8.10; p=0.012; η²p=0.336), with a large effect, and in the RFD 20-80% of isometric pull-up (F=5.41; p=0.034; η²p=0.253)with a moderate-to-large effect demonstrating a specific effect of the plyometric training program on rapid force production capacity and upper limb pulling performance.

Table 5 shows that the intervention group demonstrated consistent improvements in specific upper-body variables, notably push-up performance (Δ=+6.00; 95% CI: 2.52, -9.48), power slap in the dominant arm (Δ=+6.11; 95% CI: 0.08, -12.14), and push-up power (Δ=+81.62; 95% CI: -38.00, -201.24). Likewise, significant increases in pull-up RFD were observed at both 200 ms (Δ=+116.60; 95% CI: 30.95, -202.26) and 2080 ms (Δ=+250.63; 95% CI: 44.24, -457.03). Furthermore, regarding CMJ height, the intervention group showed a moderate increase (Δ=+3.61; 95% CI: 1.73, -5.48), while the control group exhibited a smaller change with greater variability.

Table 6 shows significant differences between groups in pull-up performance (Δ Difference = +3.89; 95% CI: 0.30, -7.48; p = 0.036; η²p = 0.248) and push-up power (Δ Difference = +174.25 W; 95% CI: 5.05, -343.46; p = 0.044; η²p = 0.128), and in isometric pull-up RFD at 200 ms (Δ Difference = +107.85 kg/s; 95% CI: 27.54, -188.16; p= 0.012; η²p=0.336), and in the 20–80% range (Δ Difference = +261.78 kg/s; 95% CI: (23.09, -500.47; p= 0.034; η²p=0.253). In contrast, no significant differences were observed between groups in Power Slap (Δ Difference = +2.72 cm; 95% CI: -4.08, 9.52; p= 0.409), nor in CMJ height (Δ Difference = +2.14 cm; 95% CI:-0.64,-4.92; p= 0.122), indicating that changes in these variables were similar across groups. Taken together, these results confirm that the effects of plyometric training were evident in specific upper-limb variables related to rapid force production, whereas more general or coordinative variables did not show consistent differences between groups.

4. Discussion

The main findings indicate that the intervention produced greater improvements than the control group in pull-up performance, plyometric push-up power, and isometric pull-up RFD, both in the early phase (0-200 ms) and in the 20-80% range of maximal force. In contrast, no significant differences were observed between groups in the Power Slap or CMJ height, suggesting a highly specific adaptation to the applied stimulus. The improvements observed in pull-ups and upper limb power are consistent with the literature, which indicates that specific strength and power in the upper extremities are key determinants of climbing performance. Faggian et al. [4], in a recent systematic review, concluded that specific neuromuscular capabilities likely reflect neuromuscular adaptations that optimize force production in pulling actions, which are fundamental in bouldering.

The significant improvement in isometric pull-up RFD, both in the early phase (0-200 ms; Δ difference = +107.85 Kg/ms; p=0.012; η²p = 0.336) and in the 20–80% range (Δ difference = +261.78 Kg/ms; p=0.034; η²p = 0.253), supports the hypothesis that plyometric training improves the ability to generate force within short time intervals as it requires the application of maximum force over a brief period, pre-dominantly targeting fast-twitch muscle fibers [22], which is a determining factor in bouldering performance. Both effect sizes were moderate-to-large, reinforcing the practical relevance of the adaptations of bouldering performance. From a physiological perspective, Maffiuletti et al. [25] note that RFD depends primarily on early neural activation (50–75 ms), in particular on the firing rate of motor units and neuromuscular synchronization. Furthermore, research on climbing has shown that RFD, especially in intervals of <200 ms, is associated with performance in dynamic movements [30], and the literature has established that RFD can be improved through explosive and ballistic stimuli, supporting the use of plyometrics as an effective strategy for optimizing this quality, particularly in upper-body strength and conditioning [22,31]. The significant increase in RFD intervals is consistent with studies showing that explosive and plyometric training improves the enhancement of force production in the early phases of muscle contraction [19,25]. However, unlike studies reporting generalized improvements in RFD across multiple muscle groups following explosive strength training, in this study, the improvements were limited to the pull-up pattern, with no changes in finger RFD. This suggests that, in advanced climbers, the transfer of RFD is highly specific to the trained motor pattern, which is consistent with evidence indicating that adaptations in RFD depend on the type of contraction and the applied force vector [27]. The pull-up, specifically in the context of bouldering, is a closed-chain, multi-joint upper-body strength exercise that, whilst requiring dynamic concentric strength from the arm and shoulder muscles to perform the elbow flexion and shoulder extension necessary for climbing walls [32,33], in the context of bouldering, represents a closed-chain, multi-joint pulling pattern involving the upper body and a complex interplay of factors.

In contrast, no significant differences were observed between groups in the Power Slap, based on the independent-sample t-test comparing the Δ value (p=0.409). However, this important to note that the repeated measures ANOVA did detect a significant group x time interaction for this variable (F=4.77; p=0.044; η²p = 0.230). This discrepancy may reflect differences in statistical sensitivity between the two approaches and underscores the importance of treating the ANOVA interaction as the primary inferential criterion, as pre-specified in the statistical analysis plan. Regardless of the analytic approach, the between-group difference in Power Slap was modest (+2.72 cm) and may lack practical relevance in the context of the bouldering performance. This result partially contrasts with studies that have used explosive upper body strength tests as indicators of climbing performance, including batteries such as the IRCRA [26]. However, our results suggest that the Power Slap may capture only a partial dimension of performance, primarily explosiveness, without adequately integrating technical, coordinative, and centre-of-mass control components, which are decisive in bouldering [4]. This is consistent with evidence indicating that climbing performance is better explained by highly specific tests than by general or less specific assessments [4].

A notable finding is the absence of significant changes in maximum finger strength and RFD. This contrasts with studies that have reported improvements in grip strength following specific interventions in climbers [34]. The absence of significant changes may be explained by the interaction between the nature of the applied stimulus and the climbers’ level of specialization. In this regard, Vigouroux et al. [33] demonstrated that smaller climbing holds impair strength and power, as well as the number of pull-ups to failure among elite climbers. The absence of significant changes in maximum finger strength and RFD can be explained, firstly, by the fact that the programmer implemented was based on plyometric exercises focused on whole-body pull-ups, which differ from the specific isometric stimuli typically used to develop strength on small holds [23,30].

In this regard, the literature has shown that adaptations in the finger flexor muscles are highly dependent on the specificity of the stimulus [35,36], requiring direct and sustained loads on small grips to induce significant improvements [3,15]. Furthermore, advanced climbers exhibit a high level of structural and neural adaptation in these muscles, which limits the scope for improvement in response to non-specific stimuli [37]. In this regard, Francinni et al. [1] previously demonstrated that boulder climbers were able to develop finger flexor strength at a higher rate than lead climbers and that the maximum RFD of the finger flexors was a crucial factor in distinguishing between the two disciplines. Furthermore, the programmer’s focus on dynamic pulling actions may have favored adaptations in the proximal segments (shoulder-elbow) without generating sufficient overload at the distal level [38,39]. Arm training studies conducted to date have incorporated exercises that also involve the fingers [23,40], making it difficult to distinguish between the impact on the fingers and the arms [39]. Taken together, these factors suggest that the absence of changes in finger strength should not be interpreted as a limitation of the programmer, but rather as a manifestation of the principle of specificity, which is well documented in climbing, where neuromuscular adaptations are highly dependent on the type of grip, the mode of contraction, and the distribution of mechanical load [39].

Practical Implications

From an applied perspective, the results suggest that incorporating pull-oriented plyometric training is an effective strategy for improving upper-body explosive capacity and isometric pull-up RFD in advanced boulder climbers. However, the development of finger flexor muscles requires specific stimuli, such as fingerboard or hangboard training. Likewise, if the aim is to improve lower-body explosive power, exercises with greater mechanical similarity to vertical jump should be included, as the present program did not produce significant CMJ improvements relative to controls. Climbing training planning should therefore integrate specific stimuli for each performance component, avoiding assumption of generalized transfers across different neuromuscular domains. From an applied perspective, the results also allow us to suggest that plyometrics is an effective tool for optimizing the time dimension of strength in advanced climbers, but it does not replace specific maximum strength training, nor does it guarantee universal improvements across all assessed performance measures. The strategic combination of maximum strength phases and reactive power interventions appears conceptually sound, provided that dosage and load progression are carefully controlled.

Limitations

Firstly, the small sample size may limit the statistical power and generalizability of the findings. Secondly, the exclusive inclusion of male athletes restricts the extrapolation to female populations. Furthermore, the control group’s external training was not strictly controlled, which may have influenced the results. Baseline differences in isometric pull-up RFD between groups, despite random allocation, represent a potential source of confounding. In addition, it should also be noted that the Power Slap test was performed on the dominant arm only, which limits the assessment of the bilateral explosive capacity and potential asymmetries between the limbs. Finally, specific performance in an ecological context (track or competition) was not assessed, which limits the direct interpretation of the functional transfer of the observed adaptations.

Future Directions

Regarding recommendations for future studies, it is suggested to explore the strategic combination of maximum strength phases and power phases, progressively integrating higher volumes of specific reactive work on the campus board, always in accordance with the criteria of progression and individualized control. Likewise, it would be pertinent to incorporate specific maximum grip load protocols to analyze possible synergistic effects between maximum finger strength and rapid force development in pulling. Another relevant line of development involves evaluating the direct transfer of improvements in RFD to indicators of competitive performance, such as block resolution within a time limit, number of attempts, or execution efficiency in dynamic problems.

From a methodological perspective, future research could increase sample sizes and consider longer intervention periods, with the aim of analyzing structural adaptations of greater magnitude. It would also be advisable to explore differences by gender, competitive level, or age, as well as to integrate biomechanical and electromyographic variables that allow for a deeper understanding of the neural mechanisms underlying the observed improvements. The incorporation of multicenter designs across different regional contexts would strengthen the evidence base in Latin America, helping to bridge the existing gap between international research and local practice.

5. Conclusions

Plyometric training carried out twice a week for 10 weeks produced specificity neuromuscular adaptations in advanced boulder climbers. Significant differences between groups were observed in pull-up performance, plyometric push-up power, and isometric pull-up rate of force development (RFD), both in the early contractions phase (0-200 ms) and in the 20-80% range of maximal force. These adaptations reflect improvements in the capacity to produce force rapidly in pulling specific movement patterns, which are directly relevant to the demands of bouldering.