Lower-Limb Muscle Excitation, Peak Torque and External Load Responses to a 120-Minute Treadmill-Based Soccer-Specific Simulation

Purpose The aim of this study was to investigate thigh musculature excitation and torque generation in response to soccer-specific exercise incorporating an extra-time (ET) period. 
Methods Twelve semi professional soccer players performed 120-min treadmill-based soccer-specific exercise. Surface electromyography (EMG) signals for the rectus femoris (EMGRF) and biceps femoris (EMGBF) were measured as the mean response across a pre-determined 10-second sprint bout during each 15-min block of exercise. Peak eccentric torque of the knee flexors (eccKF) and concentric torque of the knee extensors (conKE) were recorded across angular velocities of 60, 180 and 270 deg∙s immediately pre and post-exercise. Tri-axial PlayerLoad™ (PL-T) was monitored throughout exercise and defined across vertical (PL-V), anterior-posterior (PL-AP) and medial-lateral (PL-ML) planes of motion. 
Results A reduction in normalised EMGRF amplitude was evident at 105‒120 min, versus 0‒15 min (−12.5%; p=0.037), 15‒30 min (−12.5%; p=0.047) and 45‒60 min (−14%; p=0.030). Peak torque of the eccKF was significantly reduced from pre- to post-exercise at 60 (−7.7%; p=0.018), 180 (−10.5%; p=0.042) and 270 deg∙s (−7.5%; p=0.034). A main effect for time was identified for PL-T (p<0.010), PL-V (p=0.033) and PL-AP (p<0.010). 
Conclusions These findings suggest that muscle excitation of the rectus femoris is reduced during ET, accompanied with a deficit in the torque generation of the knee flexors following 120 min of soccer-specific activity. Practitioners should adequately condition players for the additional ET period by incorporating exercises into training schedules that develop fatigue resistant eccentric hamstring strength to minimise injury risk.