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 (Fpeak) and rate of force development (RFD); sEMG yielded integrated EMG for the main lower-limb muscles. Results: Unilateral and bilateral squat jumps/countermovement jumps Fpeak 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 Fpeak 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 Fpeak, 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.
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