The Relationship Between Lower-Limb Explosive Strength and Climbing Speed in Elite Speed Climbers: A Comprehensive Analysis Based on Muscle Morphology and Electromyography

Purpose: This study evaluated how lower-limb explosive strength relates to 15-m speed-climbing performance by combining jump kinetics, muscle morphology, and surface electromyography (sEMG). Methods: Fifteen Chinese speed climbers (10 men, 5 women) who had placed within the top 3–6 at national-level competitions underwent ultrasound imaging of the rectus femoris (RF) and medial gastrocnemius (GM), and then, in random order, completed unilateral and bilateral squat jumps, countermovement jumps, and a 15-m speed-climbing test. Force plate recorded peak force ( F peak ) and rate of force development (RFD); sEMG yielded integrated EMG for the main lower-limb muscles. Results: Unilateral and bilateral squat jumps/countermovement jumps F peak correlated with climbing speed ( r = .63–.77, P = .004–.029). Both right-leg ( r = .62, P = .033) and bilateral ( r = .62, P = .03) countermovement jumps RFD correlated with speed. Bilateral-jump F peak correlated with right-side RF thickness ( r = .59–.81, P = .001–.043), whereas bilateral RFD with both GM thickness and fascicle length ( r = .58–.63, P = .029–.049). During climbing, speed negatively correlated with left-side RF integrated EMG ( r = –.6, P = .041) and positively with bilateral GM integrated EMG ( r = .59–.64, P = .026–.045; other muscles P > .05). Conclusions: Right-leg RF thickness appears to drive F peak , and thus climbing speed, whereas GM thickness and fascicle length primarily influence RFD. A contrasting activation pattern (lower RF, higher GM engagement) likely underlies these morphology–performance links. Coaches can target maximal-strength and plyometric training to enlarge the right RF and GM and lengthen GM fascicles, potentially improving speed-climbing performance.