Hamstring fatigue and muscle activation changes during six sets of Nordic hamstring exercise in amateur soccer players

The Nordic hamstring exercise (NHE) is a bodyweight movement commonly prescribed to increase eccentric hamstring strength and reduce the incidence of strain injury in sport. This study examined hamstring fatigue and muscle activation responses throughout six sets of five repetitions of the NHE. Ten amateur level soccer players performed a single session of six sets of five-repetitions of NHE. Maximal eccentric and concentric torque output (Nm) was measured after every set. Hamstrings electromyograms (EMG) were measured during all maximal contractions and exercise repetitions. Hamstring maximal eccentric torque was reduced throughout the range of motion after only a single set of NHE between 7.9 to 17.1% (p<0.05), with further reductions in subsequent sets. Similarly, maximal concentric torque reductions between 7.8 to 17.2% were observed throughout the range of motion after one set of NHE (p<0.05). During the descent phase of the NHE repetitions, hamstring muscle activity progressively increased as the number of sets performed increased. These increases were observed in the first-half of the range of motion. During the ascent phase biceps femoris muscle activity but not medial hamstrings was reduced from the start of exercise during latter sets of repetitions. These data provide unique insight into the extent of fatigue induced from a bodyweight only exercise after a single set of five repetitions. Strength and conditioning coaches need to be aware of the speed and extent of fatigue induced from NHE, particularly in practical settings where this exercise is now prescribed prior to sport-specific training sessions (i.e. the FIFA-11 before soccer training).