Inter-limb asymmetry characteristics and their impact on bilateral jump performance in elite gymnasts: a comparison across varying mechanical loads

Abstract

This study investigated task-specific biomechanical regulation and the impact of inter-limb asymmetry on athletic performance in fourteen elite gymnasts. Participants (sex: 7 males, 7 females; age: 20.14 ± 1.23 years) performed bilateral and unilateral drop jump (DJ) and hopping tasks while kinetic data were collected via force plates to calculate vertical stiffness (Kvert), center of mass (COM) displacement, vertical ground reaction force (vGRF), and inter-limb asymmetry. Compared with hopping, the drop jump task exhibited lower Kvert and vGRF but greater COM displacement (all p < 0.001). COM asymmetry was significantly greater during DJ than during hopping (p < 0.05) and was positively associated only with bilateral hopping reactive strength index (RSI) in the pooled sample (p < 0.05). In contrast, vGRF asymmetry during hopping was negatively associated with RSI in both bilateral hopping and bilateral DJ tasks (p < 0.05). These correlation analyses were exploratory and were not adjusted for multiple comparisons. These findings suggest that different forms of asymmetry may carry distinct functional implications under varying mechanical loading conditions. Furthermore, the self-selected frequency hopping task may represent a candidate approach for assessing inter-limb functional balance in elite gymnasts.

Introduction

Gymnastics is an elite sporting discipline characterized by extremely rigorous demands for motor control. Its core competitive performance relies heavily on inter-limb coordination and landing stability during high-speed dynamic tasks [1]. In all-around and individual apparatus events, such as vault, floor exercise, and dismounts, bilateral landings and symmetrical take-offs represent the most frequent movement structures [2]. From a biomechanical perspective, balanced bilateral mechanical regulation is considered important for achieving stable and symmetrical movement outcomes, while also contributing to the effective dissipation of impact forces that may reach several multiples of body weight during landing [3]. However, gymnasts frequently encounter immense mechanical load challenges during training and competition. Any minute imbalance in inter-limb mechanical distribution, such as instantaneous deviations in vertical ground reaction force (vGRF) or lateral shifts in center of mass (COM) displacement, may disrupt kinetic chain transmission. Such disruptions significantly elevate the probability of athletic injuries, including anterior cruciate ligament (ACL) ruptures or ankle sprains [4, 5].

Despite the paramount importance of symmetry in gymnastic performance [6], previous research on lower-limb asymmetry has largely been confined to isolated jumping tasks, often overlooking the dynamic nature of inter-limb asymmetry as it is modulated by specific movement demands. Maloney et al. (2016) noted that stiffness regulation follows distinct neural control logics in cyclic versus non-cyclic tasks [7]. In hopping tasks, the body primarily relies on pre-activation and spinal stretch reflexes to maintain stable elastic output [8]. Conversely, during high-impact drop jump tasks, the lower-limb spring system faces greater instantaneous mechanical stress, requiring superior levels of eccentric control and rapid transition to concentric power [7]. These disparate mechanical environments across tasks may lead to asymmetry manifesting differently across various biomechanical indices.

Furthermore, significant controversy remains regarding how asymmetry interferes with explosive power performance in elite athletes [9]. While some previous studies have used asymmetry exceeding 10% as a reference threshold for potential injury risk and performance impairment [10, 11], the universal applicability of this threshold remains uncertain. Mohammadian et al. (2022) found that the relationship between vertical stiffness and jumping performance is not a simple linear correlation [12]. Under certain strategies, high levels of stiffness may actually exert a negative impact on jump height. This finding suggests that stiffness regulation and COM control play complex roles across different mechanical load tasks. In the context of gymnastics, it remains unclear whether asymmetry exceeding such reference thresholds impairs mechanical efficiency or serves as a “functional compensation” to maintain overall performance.

Therefore, the present study aimed to investigate the characteristics of inter-limb asymmetry under different mechanical loading conditions and to examine the relationships between asymmetry indices and bilateral jump performance in elite gymnasts. Based on the task-specific mechanical demands of drop jump and hopping exercises, it was hypothesized that inter-limb asymmetries would differ between tasks, and that asymmetry under different loading conditions would demonstrate distinct associations with bilateral jump performance.

Methods

Participants

An a priori sample size estimation was performed using G*Power 3.1.9.7 for an F-test repeated-measures ANOVA (within factors). Based on an effect size of f = 0.30, α = 0.05, and a statistical power of 0.80 [7], the required sample size was estimated to be 14 participants. Fourteen elite gymnasts (7 males, 7 females; age: 20.14 ± 1.23; height: 1.65 ± 0.07 m; mass: 58.85 ± 11.29 kg; training experience: 10.86 ± 3.35 years) participated in this study. Both male and female gymnasts were included because the study aimed to characterize inter-limb asymmetry in elite gymnasts as a whole rather than to investigate sex differences. According to the McKay et al. (2022) participant classification framework, these athletes were categorized as Tier 4 (Elite) [13]. The inclusion criteria were as follows: (1) active competition at the provincial level or higher; (2) at least 6 months free from any lower-limb musculoskeletal injuries; and (3) engagement in consistent, high-intensity professional training (at least 3 sessions per week) for the preceding 3 months. All participants provided written informed consent prior to the study. All procedures were conducted in accordance with the Declaration of Helsinki and were approved by the Ethics Committee of Shanghai University of Sport (Approval ID: 102772025RT256).

Experimental design

This study utilized a two-visit, cross-sectional design. To minimize potential learning effects, a familiarization session was conducted 7 days prior to the formal experimental trial. During this session, participants were familiarized with all testing procedures and practiced the jumping tasks. During the experimental visit, participants completed a standardized warm-up followed by bilateral and unilateral drop jump and hopping tasks in a randomized order. All sessions were conducted at the same time of day (13:00–18:00) for each participant to alleviate the effects of circadian rhythms, with the laboratory temperature maintained at 24 °C.

Testing session

The formal testing session was structured into four standardized phases to ensure data reliability and physiological consistency: Preparation phase: Upon arrival, participants underwent a 10-minute seated rest, followed by a detailed briefing and the signing of informed consent. Warm-up phase: The protocol included cycling, dynamic stretching, and neuromuscular activation, with 30-second rest intervals strictly enforced between stages. Baseline Assessment phase: Following a 1-minute rest, participants performed maximal-effort countermovement jumps (CMJ) and multi-height Drop jumps (20, 30, and 40 cm) to determine individualized drop heights. Experimental Trials Phase: Bilateral and unilateral drop jump and hopping tasks were executed in a randomized order. To ensure technical consistency, all trials were monitored and supervised by an NSCA-accredited Strength and Conditioning Coach. All experimental jumps were recorded using a force plate (9260AA, Kistler Instruments, Winterthur, Switzerland; 1000 Hz).

Warm-up

All participants completed the same warm-up protocol: General Aerobic Phase: 5 min of cycling at a moderate intensity. Dynamic Stretching Phase: Included one set of single-leg knee-to-chest (1 × 5 per leg), standing quad stretch (1 × 5 per leg), dynamic hamstring stretch (1 × 5 per leg), and the World’s Greatest Stretch (1 × 4 per leg). Specific Activation Phase: Consisted of submaximal countermovement jumps (1 × 4 per leg) and drop jumps (1 × 4 per leg) to prime the stretch-shortening cycle for subsequent maximal efforts. Transition: A 30-second recovery period was provided between each phase of the warm-up. Finally, a 1-minute seated rest was provided following the warm-up before entering baseline testing.

Hopping testing

Participants performed 3 sets of bilateral hopping and 6 sets of unilateral hopping (3 per leg). Each set consisted of 10 consecutive jumps, with a 1-minute interval between sets (Fig. 1). A self-selected frequency was utilized; however, participants were encouraged to minimize ground contact time while maximizing jump height [14]. Self-selected hopping frequency was calculated as the inverse of the time interval between consecutive ground contacts and averaged across all jumps within each 10-jump set. The self-selected hopping frequency was 1.66 ± 0.15 Hz (range: 1.31–1.89 Hz) for bilateral hopping, 1.91 ± 0.18 Hz (range: 1.50–2.23 Hz) for left single-leg hopping, and 1.87 ± 0.17 Hz (range: 1.42–2.07 Hz) for right single-leg hopping. Data analysis was based on the average of the five jumps with the highest RSI within each 10-jump set [15]. All jumps were performed with hands on hips.

Fig. 1.

Movement sequences for bilateral and unilateral drop jump (DJ) and hopping tasks. Note: The highlighted limb (orange) represents the tested limb. The highlighted limb (blue) represents the preferred limb

Drop jump testing

Participants executed three bilateral drop jumps and six unilateral drop jumps (Fig. 1). For bilateral trials, participants dropped from the box height that yielded their optimal RSI. For unilateral trials, the drop height was individualized to 40% of the participant’s maximal CMJ height [16]. These height-selection criteria were based on established protocols for bilateral and unilateral drop-jump testing, respectively, to provide an individualized drop height appropriate for each task. For bilateral trials, the preferred limb was used to initiate the step-off; for unilateral trials, the specific test limb was used. The preferred limb was defined as the limb that gymnasts typically bring forward to initiate technical jumps during performance [17] and was identified during the familiarization session by the researchers observing which limb each gymnast habitually brought forward when initiating a technical jump. Consistent with the hopping task, participants were encouraged to achieve the shortest possible ground contact time and maximal jump height. A 30-second rest was provided between individual trials. All jumps were performed with hands on hips in a randomized order.

Data analysis

Kinetic data were processed offline using MATLAB (R2021b, MathWorks, Natick, USA). For bilateral trials, vGRF represented the summed vertical ground reaction force from both limbs, whereas for unilateral trials, vGRF represented the force produced by the tested limb. vGRF was smoothed using a fourth-order, zero-phase Butterworth low-pass filter (cutoff frequency: 50 Hz) [18]. Take-off and landing phases were identified using a 30 N threshold [19]. Jump height (h) was determined based on flight time (t). RSI was calculated as jump height divided by ground contact time (RSI = h/t contact). Center of mass (COM) acceleration, velocity, and vertical displacement was calculated via double integration of the vGRF-time trace using inverse dynamics [20]. Kvert was defined as the ratio of peak vGRF to the maximum downward displacement of the COM during the contact phase [8]. To account for individual differences in body mass, stiffness data were normalized by weight [21] and expressed in N/m/kg. In the present study, using a fixed reference limb to calculate inter-limb asymmetry may be inappropriate, as the preferred limb is not necessarily the stronger or better-performing limb in gymnasts. Therefore, the percentage difference method proposed by Bishop et al. (2018) was used [22]. This approach is recommended for unilateral testing and calculates asymmetry based on the relative difference between the maximum and minimum values obtained from the preferred and non-preferred limbs, thereby providing a more objective representation of inter-limb asymmetry. Inter-limb asymmetry (%) = [(maximum value - minimum value) / maximum value] × 100.

Statistical analysis

Statistical analyses were performed using SPSS 26.0 (IBM Corp., Armonk, NY). Descriptive statistics are presented as Mean ± SD. Data normality was assessed using the Shapiro–Wilk test. A 2 × 3 repeated-measures ANOVA was employed to compare differences in vGRF, COM displacement, and Kvert, with Task (Drop Jump and Hopping) and Limb Condition (bilateral, preferred, and non-preferred) treated as within-subject factors. When the assumption of sphericity was violated, Greenhouse–Geisse r corrections were applied. Bonferroni post-hoc tests were conducted for pairwise comparisons where significant differences were found. Effect sizes for the repeated-measures ANOVA were reported as partial eta squared (ηp²). Paired-samples t-tests were used to compare three asymmetry variables (vGRF, COM displacement, and Kvert) between drop jump and hopping tasks. Effect sizes (d) were categorized as small (0.20–0.49), medium (0.50–0.79), or large (> 0.80) [23]. As several variables did not meet the assumption of normality, Spearman’s rank correlation coefficient was used to examine the relationships between asymmetry indices and bilateral jump performance. Exploratory sex-stratified Spearman correlations were additionally performed for associations that reached statistical significance in the pooled sample, separately in male and female gymnasts (n = 7 each), with two-sided exact permutation p values calculated. Given the small subgroup sizes, no adjustment for multiple comparisons, and the absence of formal between-sex comparisons of correlation coefficients, these analyses were considered exploratory. Correlation coefficients (r) were interpreted as: small (0.10–0.29), moderate (0.30–0.49), large (0.50–0.79), very large (0.80–0.89), or perfect (> 0.9) (Hopkins, 2000). The significance level was set at α = 0.05.

Results

A two-way repeated-measures ANOVA revealed significant main effects of limb condition (F (1.40, 18.18) = 8.957, p = 0.004, ηp² = 0.408) and task (F (1, 13) = 32.881, p < 0.001, ηp² = 0.717) on COM displacement. However, no significant Task × Limb Condition interaction was observed (F (1.14, 14.82) = 0.902, p = 0.371, ηp² = 0.065). Averaged across limb conditions, COM displacement was significantly lower during hopping than during the drop jump task (p < 0.001). Bonferroni-adjusted post hoc comparisons indicated that COM displacement was significantly lower during hopping than during the drop jump task (p < 0.001). In addition, the preferred-limb condition exhibited significantly greater COM displacement than the bilateral condition (p = 0.002). For Kvert, significant main effects of limb condition (F (1.082, 14.065) = 49.087, p < 0.001, ηp² = 0.791) and task (F (1, 13) = 31.287, p < 0.001, ηp² = 0.706) were observed, whereas the Task × Limb Condition interaction was not significant (F (1.41, 18.31) = 0.295, p = 0.671, ηp² = 0.022). Averaged across limb conditions, Kvert was significantly lower during the drop jump task than during hopping (p < 0.001). Bonferroni-adjusted post hoc comparisons showed that Kvert was significantly lower during the drop jump task than during hopping (p < 0.001). Furthermore, bilateral conditions exhibited significantly greater Kvert values than both preferred- and non-preferred-limb conditions (both p < 0.001). For vGRF, significant main effects of limb condition (F (1.05, 13.64) = 126.288, p < 0.001, ηp² = 0.907) and task (F (1, 13) = 20.572, p < 0.001, ηp² = 0.613) were identified. However, the Task × Limb Condition interaction was not significant (F (1.09, 14.20) = 0.497, p = 0.508, ηp² = 0.037). Averaged across limb conditions, vGRF was significantly greater during hopping than during the drop jump task (p < 0.001). Bonferroni-adjusted post hoc comparisons revealed that bilateral conditions produced significantly greater vGRF values than both preferred- and non-preferred-limb conditions (both p < 0.001) (Table 1).

Table 1.

Comparison of athletic performance and kinetic parameters across different jumping tasks (Mean ± SD)

Variable	Bilateral		Unilateral
	Drop Jump	Hopping	Drop Jump		Hopping
Height(cm)	27.82 ± 7.28	24.5 ± 4.11	Non- preferred	Preferred	Non- preferred	Preferred
RSI	1.42 ± 0.26	1.48 ± 0.34	-	-	-	-
vGRF (N)	3528 ± 920	3860 ± 954	1832 ± 457	1877 ± 467	2354 ± 479	2336 ± 517
COM (m)	0.14 ± 0.03	0.10 ± 0.03	0.17 ± 0.05	0.17 ± 0.04	0.12 ± 0.03	0.12 ± 0.02
Kvert (N/m/kg)	507 ± 222	677 ± 214	277 ± 59	206 ± 59	392 ± 89	404 ± 113

vGRF vertical ground reaction force, COM centre of mass displacement, Kvert vertical stiffness

Paired-samples t-tests (Table 2) showed no significant differences in inter-limb asymmetry for vGRF (t (13) = − 0.865, p = 0.403, d = 0.231) or Kvert (t (13) = 1.163, p = 0.266, d = 0.311) between tasks. However, COM asymmetry exhibited significant task-dependent variation (t (13) = 2.294, p = 0.039, d = 0.613). Notably, COM and Kvert asymmetry in the drop jump task, as well as Kvert asymmetry in the hopping task, exceeded the 10% threshold.

Table 2.

Comparison of kinetic parameter asymmetry between different jumping tasks

Tasks	vGRF (%)	COM (%)	Kvert (%)
Drop jump	4.71 ± 2.49	13.40 ± 8.56	16.60 ± 10.56
Hopping	5.74 ± 4.73	6.81 ± 5.57*	12.34 ± 12.38

vGRF vertical ground reaction force, COM centre of mass displacement, Kvert vertical stiffness

* Significant difference compared to the drop jump task (p < 0.05)

Spearman rank correlation analysis (Table 3) revealed specific significant associations between inter-limb asymmetry and bilateral athletic performance. COM asymmetry in the drop jump task was significantly positively correlated with RSI in the bilateral hopping task (r = 0.563, p = 0.036). vGRF asymmetry in the hopping task was significantly negatively correlated with RSI in both bilateral drop jump (r = -0.675, p = 0.008) and bilateral hopping (r = -0.554, p = 0.04). Given that this pooled correlation analyses were exploratory and were not adjusted for multiple comparisons, these associations should be interpreted as hypothesis-generating findings.

Table 3.

Correlation between inter-limb asymmetries and bilateral jumping performance

Variable	Drop jump		Hopping
	Height	RSI	Height	RSI
DJ vGRF	r = 0.068	r=-0.403	r=-0.007	r=-0.207
	p = 0.817	p = 0.153	p = 0.982	p = 0.478
DJ COM	r=-0.108	r = 0.330	r = 0.209	r = 0.563
	p = 0.714	p = 0.249	p = 0.474	p = 0.036*
DJ Kvert	r = 0.187	r = 0.290	r=-0.095	r = 0.143
	p = 0.523	p = 0.314	p = 0.748	p = 0.626
Hopping vGRF	r=-0.134	r=-0.675	r=-0.244	r=-0.554
	p = 0.648	p = 0.008*	p = 0.401	p = 0.040*
Hopping COM	r = 0.042	r=-0.035	r=-0.002	r=-0.185
	p = 0.887	p = 0.905	p = 0.994	p = 0.527
Hopping Kvert	r=-0.319	r=-0.216	r=-0.099	r = 0.123
	p = 0.267	p = 0.459	p = 0.737	p = 0.675

vGRF vertical ground reaction force, COM centre of mass displacement, Kvert vertical stiffness

* Significant correlation (p < 0.05)

Exploratory sex-stratified Spearman analyses showed a positive association between DJ COM asymmetry and bilateral hopping RSI in males (r = 0.786, p = 0.04), whereas the estimate in females was close to zero (r = 0.108, p = 0.82). Hopping vGRF asymmetry was negatively associated with bilateral DJ RSI in both females (r = -0.464, p = 0.30) and males (r = -0.595, p = 0.17), although neither subgroup association reached statistical significance. Hopping vGRF asymmetry was negatively associated with bilateral hopping RSI in males (r = -0.893, p = 0.01), whereas the estimate in females was close to zero (r = 0.090, p = 0.85). Each subgroup comprised seven athletes (Fig. 2).

Fig. 2.

Correlation analysis between inter-limb asymmetry and jump performance across jumping tasks; DJ: drop jump; COM: center of mass; vGRF: Vertical ground reaction force

Discussion

The purpose of this study was to investigate the characteristics of inter-limb asymmetry under different mechanical loading conditions and to examine the relationships between asymmetry indices and bilateral jump performance in elite gymnasts. The primary findings were that COM displacement was greater and Kvert was lower during the drop jump task compared with hopping, while specific asymmetry measures were associated with bilateral jump performance. These findings suggest that elite gymnasts exhibit task-specific mechanical regulation when responding to different mechanical loading conditions. The lower Kvert and greater COM displacement observed during the drop jump task support the perspective of Maloney et al. (2016) [7], suggesting that the regulation of lower-limb stiffness depends on the mechanical demands of the specific task. In a non-cyclic and high-intensity task like the drop jump, gymnasts tend to adopt a “soft landing” strategy by increasing lower-limb displacement to prolong the buffering time, thereby effectively absorbing high impact forces and protecting tissue safety [3]. Conversely, hopping, a cyclic task pursuing efficiency, relies more on high stiffness to maintain the transition efficiency of the Stretch-Shortening Cycle. As hopping was performed at a self-selected frequency, inter-individual variability in hopping frequency may also have influenced Kvert and RSI and should therefore be considered when interpreting these outcomes. From a mechanical standpoint, Kvert is the functional ratio of vGRF to the negative displacement of the COM [20]. This implies that the difference in stiffness recruitment is essentially the result of the synergistic regulation of force and displacement. Because these parameters must be precisely coordinated within an extremely short ground contact time, effective neuromuscular regulation is required to optimize force absorption and subsequent force production during different jumping tasks [24, 25]. However, interpretation of the kinetic differences between bilateral and unilateral DJ conditions should also account for the different drop-height selection criteria, as differences in absolute drop height may have contributed to the observed variations in vGRF, COM displacement, and Kvert.

Interestingly, COM asymmetry was significantly greater during the drop jump task than during hopping, whereas no task-related differences were observed for vGRF or Kvert asymmetry. This finding suggests that different asymmetry measures may reflect distinct aspects of inter-limb regulation under varying mechanical loading conditions. Compared with hopping, the drop jump task requires athletes to tolerate substantially greater impact forces and control a larger downward displacement of the body during the braking phase. Consequently, COM displacement may be more sensitive to subtle variations in movement coordination, joint compliance, and landing strategy, which may partially explain the greater COM asymmetry observed under high-impact loading conditions [2, 5, 26]. Notably, COM asymmetry during the drop jump task and Kvert asymmetry in both tasks exceeded the commonly adopted 10% threshold. However, the interpretation of asymmetry based solely on threshold values remains contentious [9, 11]. Although Kvert asymmetry exceeded the commonly adopted 10% threshold in both tasks, no significant task-related differences were observed. This finding suggests that asymmetry thresholds should be interpreted alongside statistical outcomes rather than in isolation. The elevated Kvert asymmetry may reflect individualized stiffness regulation strategies developed through long-term gymnastics-specific training rather than a consistent group-level characteristic [5].

A particularly noteworthy finding of the present study was that COM asymmetry during the drop jump task was positively associated with bilateral hopping RSI in the pooled sample. This finding is not entirely consistent with previous research, which has generally linked greater asymmetry to impaired performance and increased injury risk [27]. Previous studies have suggested that the functional significance of asymmetry may depend on sport- and task-specific demands [28, 29]. Further examination of this pooled association through exploratory sex-stratified analyses showed a positive association between DJ COM asymmetry and bilateral hopping RSI in male gymnasts, whereas the corresponding estimate was close to zero in female gymnasts. However, a significant association in one subgroup and a nonsignificant association in another do not, by themselves, establish a sex difference. Therefore, although COM asymmetry may reflect task-specific regulation of inter-limb mechanics under the high-impact demands of drop jumping [30, 31], the present cross-sectional findings do not indicate that greater COM asymmetry enhances performance. Rather, the observed pooled association should be considered a hypothesis-generating finding that warrants further investigation in larger sex-specific samples.

In contrast to the positive association observed for COM asymmetry, vGRF asymmetry during the hopping task was negatively associated with RSI in both bilateral hopping and bilateral drop jump tasks in the pooled sample. Sex-stratified analyses further qualified these associations: the negative association with bilateral hopping RSI was evident in males but close to zero in females, whereas both sex-specific estimates for bilateral DJ RSI were negative but nonsignificant. Although these findings do not establish sex differences, they indicate that the pooled associations should not be assumed to apply equally to both sexes. Nevertheless, the pooled findings suggest that asymmetries in force production may have different functional implications from asymmetries in movement control [32]. As vGRF directly reflects the balance of force generation and transmission between the lower limbs, greater asymmetry may indicate reduced mechanical efficiency, thereby compromising reactive strength performance. This interpretation is consistent with the findings of Zhao et al. (2025) [6], who reported that greater inter-limb force asymmetry was associated with reduced sport-specific performance. Similarly, Čuk & Marinšek, (2013) highlighted the importance of bilateral symmetry for movement quality in gymnastics, further emphasizing the contribution of balanced lower-limb function to athletic performance [2]. Given the relatively high safety and low fatigue demands of the self-selected frequency hopping task, this test may represent a practical candidate approach for assessing inter-limb functional balance in elite gymnasts. However, its utility for longitudinal monitoring requires further validation.

Several limitations should be acknowledged. First, the study included only 14 elite adult gymnasts, which limits the generalizability of the findings and may reduce the stability of the correlation estimates. The small sex-specific subgroup sizes further limited the reliable assessment of potential sex differences. In addition, the exploratory correlation analyses involved multiple comparisons without adjustment, which may have increased the risk of Type I error; therefore, these associations should be considered hypothesis-generating. Future research with larger and more diverse samples is needed to verify these findings. Second, the findings may reflect adaptations associated with long-term high-level gymnastics training and may not be directly generalizable to athletes from other sports or training backgrounds. Third, several task-design factors should be considered when interpreting the bilateral–unilateral comparisons. Different height-selection criteria were used for bilateral and unilateral drop jumps, which may have resulted in different absolute drop heights and influenced the observed kinetic differences. Moreover, bilateral vGRF represented the summed force from both limbs, whereas unilateral vGRF represented single-limb force; therefore, the limb-condition effect for vGRF may partly reflect the different number of supporting limbs.

Conclusion

This study demonstrated that inter-limb asymmetry characteristics in elite gymnasts are task-dependent and vary under different mechanical loading conditions. Compared with hopping, the drop jump task was characterized by greater COM displacement, lower vertical stiffness, and greater COM asymmetry. In the pooled sample, DJ COM asymmetry was positively associated with bilateral hopping RSI, whereas hopping vGRF asymmetry was negatively associated with RSI in both bilateral hopping and bilateral DJ. However, these asymmetry–performance associations remain exploratory, as sex-stratified estimates were not uniform and the pooled findings should not be assumed to apply equally to male and female gymnasts. These findings highlight the importance of considering both asymmetry type and task demands when evaluating inter-limb asymmetry in elite gymnasts. Furthermore, the self-selected frequency hopping test may represent a practical candidate approach for assessing inter-limb functional balance in elite gymnasts, although its utility for longitudinal monitoring requires further validation.

Authors’ contributions

YM: Methodology, Data curation, Statistical analysis, Writing, and Editing.RJ, KX: Data Curation and Formal Analysis.CC, DX, MJF: Review and EditingCD: Review and SupervisionAll authors have read and agreed to the published version of the manuscript.

Funding

Supported by Shanghai Key Lab of Human Performance(Shanghai University of sport)(NO. 11DZ2261100༉.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Shanghai University of Sport (Approval ID: 102772025RT256) and conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants prior to their participation in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.