Neural and muscular adjustments following repeated running sprints

This study aimed to reveal the neural and muscular adjustments following a repeated-sprint (RS) running exercise. Sixteen subjects performed a series of neuromuscular tests before, immediately after and 30 min (passive recovery) post-RS exercise (12 × 40 m sprints interspaced by 30 s of passive recovery). Sprint times significantly lengthened over repetitions (+17% from the first to the last sprint; P<0.05). After RS running exercise, maximal voluntary contraction torque of the plantar flexors (-11 ± 7.3%), muscle activation (twitch interpolation) (-2.7 ± 3.4%) and soleus maximal M-wave amplitude (-20 ± 17%) were significantly (P<0.05) reduced but returned close to baseline after 30 min. Both soleus EMG activity and maximal Hoffmann reflex normalized with respect to M-wave amplitude did not change during the whole experiment. From pre- to post-RS exercise, evoked twitch response was characterized by lower peak torque and maximal rate of torque development (-13 and -11%, respectively, P<0.05), but was not different from baseline after recovery. Peak tetanus at 20 and 80 Hz were 17 and 8% lower (P<0.05) in the fatigued state, respectively. Acute muscle fatigue induced by RS running exercise is mainly peripheral as the short-term (30 min) recovery pattern of plantar flexors contractile properties follows that of the voluntary force-generating capacity.