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  • Author: Robert M. Erskine x
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Conall F. Murtagh, Christopher Nulty, Jos Vanrenterghem, Andrew O’Boyle, Ryland Morgans, Barry Drust and Robert M. Erskine

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] cm3; P = .001), and PCSA (227 [42] vs 193 [25] cm2; 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.

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Harry E. Routledge, Jill J. Leckey, Matt J. Lee, Andrew Garnham, Stuart Graham, Darren Burgess, Louise M. Burke, Robert M. Erskine, Graeme L. Close and James P. Morton

Purpose: To better understand the carbohydrate (CHO) requirement of Australian Football (AF) match play by quantifying muscle glycogen utilization during an in-season AF match. Methods: After a 24-h CHO-loading protocol of 8 and 2 g/kg in the prematch meal, 2 elite male forward players had biopsies sampled from m. vastus lateralis before and after participation in a South Australian Football League game. Player A (87.2 kg) consumed water only during match play, whereas player B (87.6 kg) consumed 88 g CHO via CHO gels. External load was quantified using global positioning system technology. Results: Player A completed more minutes on the ground (115 vs 98 min) and covered greater total distance (12.2 vs 11.2 km) than player B, although with similar high-speed running (837 vs 1070 m) and sprinting (135 vs 138 m). Muscle glycogen decreased by 66% in player A (pre: 656 mmol/kg dry weight [dw], post: 223 mmol/kg dw) and 24% in player B (pre: 544 mmol/kg dw, post: 416 mmol/kg dw). Conclusion: Prematch CHO loading elevated muscle glycogen concentrations (ie, >500 mmol/kg dw), the magnitude of which appears sufficient to meet the metabolic demands of elite AF match play. The glycogen cost of AF match play may be greater than in soccer and rugby, and CHO feeding may also spare muscle glycogen use. Further studies using larger sample sizes are now required to quantify the interindividual variability of glycogen cost of match play (including muscle and fiber-type-specific responses), as well examining potential metabolic and ergogenic effects of CHO feeding.