The Neuromuscular Determinants of Unilateral Jump Performance in Soccer Players Are Direction-Specific

Purpose : To investigate differences in neuromuscular factors between elite and nonelite players and to establish which factors underpin direction-specific unilateral jump performance. Methods : Elite (n = 23; age, 18.1 1.0 y; body mass index, 23.1 1.8 kg·m −2 ) and nonelite (n = 20; age, 22.3 2.7 y; body mass index, 23.8 1.8 kg·m −2 ) soccer players performed 3 unilateral countermovement jumps (CMJs) on a force platform in the vertical, horizontal-forward, and medial directions. Knee extension isometric maximum voluntary contraction torque was assessed using isokinetic dynamometry. Vastus lateralis fascicle length, angle of pennation, quadriceps femoris muscle volume ( M vol ), and physiological cross-sectional area (PCSA) were assessed using ultrasonography. Vastus lateralis activation was assessed using electromyography. Results : Elite soccer players presented greater knee extensor isometric maximum voluntary contraction torque (365.7 66.6 vs 320.1 62.6 N·m; P = .045), M vol (2853 508 vs 2429 232 cm 3 ; P = .001), and PCSA (227 42 vs 193 25 cm 2 ; P = .003) than nonelite. In both cohorts, unilateral vertical and unilateral medial CMJ performance correlated with M vol and PCSA ( r ≥ .310, P ≤ .043). In elite soccer players, unilateral vertical and unilateral medial CMJ performance correlated with upward phase vastus lateralis activation and angle of pennation ( r ≥ .478, P ≤ .028). Unilateral horizontal-forward CMJ peak vertical power did not correlate with any measure of muscle size or activation but correlated inversely with angle of pennation ( r = −.413, P = .037). Conclusions : While larger and stronger quadriceps differentiated elite from nonelite players, relationships between neuromuscular factors and unilateral jump performance were shown to be direction-specific. These findings support a notion that improving direction-specific muscular power in soccer requires improving a distinct neuromuscular profile.