The Relationship Between Lower-Limb Asymmetry and Speed-Climbing Time: The Role of Muscle Thickness and Neural Activation.

Purpose: This study investigated lower-limb asymmetry in speed climbers and its relationship with climbing time while exploring the underlying mechanisms through muscle-thickness and activation.

Methods: Nineteen speed climbers completed muscle-thickness measurements, single-leg countermovement-jump tests, and speed-climbing tests. Muscle thickness was assessed using ultrasound, single-leg countermovement-jump tests were performed on a force platform, and climbing tests were conducted on a standardized climbing wall. Data were used to calculate muscle thickness, peak force (Fpeak), rate of force development, and integrated electromyography [EMG] percentage (iEMG %). Correlation analysis assessed the relationship between lower-limb asymmetry and climbing time, while paired t tests and asymmetry indices were used to analyze differences and asymmetry levels.

Results: Results showed significant positive correlations between climbing time and asymmetry indices of Fpeak (r = .57, P = .028) and rate of force development (r = .52, P = .045). No significant differences were observed in Fpeak, rate of force development, muscle thickness, iEMG (%) during jumping, or iEMG (%) of the biceps brachii and medial gastrocnemius during climbing (P > .05). However, significant differences were found in rectus femoris iEMG (%) during climbing (P = .028, d = 0.89). Most asymmetry indices, except for Fpeak, muscle thickness, and iEMG (%) of the biceps brachii and medial gastrocnemius, exceeded 15%, indicating high asymmetry levels.

Conclusions: This study highlights significant lower-limb asymmetry in speed climbers, potentially affecting performance. Findings suggest neural-activation differences, rather than muscle thickness, as the primary contributors. Regular monitoring and targeted interventions are recommended to reduce asymmetry and its impact on performance.