Purpose: This study aimed to determine the pattern of neuromuscular fatigability that manifests during repeated-sprint running exercise.
Methods: Twelve male participants (mean ± SD: age, 25 ± 6 yr; stature, 180 ± 7 cm; body mass, 77 ± 7 kg), currently training and competing in intermittent sprint sports, performed a repeated maximal sprint running protocol (12 × 30 m, 30-s rest periods). Pre- and postexercise twitch responses to transcutaneous motor point stimulation and transcranial magnetic stimulation were obtained to assess knee extensor neuromuscular and corticospinal function, respectively. Throughout the protocol, during alternate rest periods, blood lactate samples were taken and a single knee extensor maximal voluntary contraction (MVC) of the knee extensors was performed, with motor point stimulation delivered during and 2 s after, to determine voluntary activation (VA) and peripheral fatigue.
Results: The repeated-sprint protocol induced significant increases in sprint time and blood [lactate] from the third sprint onwards (P < 0.001). Furthermore, knee extensor MVC, resting twitch amplitude, and VA were all significantly reduced after two sprints and reached their nadir after sprint 10 (Δ12%, Δ24%, Δ8%, P < 0.01, respectively). In line with a reduction in motor point-derived VA, there was also a reduction in VA measured with transcranial magnetic stimulation (Δ9%, P < 0.05) immediately after exercise.
Conclusions: These data are the first to demonstrate the development of neuromuscular fatigability of the knee extensors during and immediately after repeated-sprint exercise. Peripheral and central factors contributing to muscle fatigability were evident after two maximal sprints, and over half of the drop in postexercise MVC was due to supraspinal fatigue. Thus, peripheral, central, and supraspinal factors all contribute to the performance decrement and fatigability of the knee extensors after maximal repeated-sprint activity.