Changes in force production, blood lactate and EMG activity in the 400‐m sprint

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Abstract
The neural activation (iEMG) and selected stride characteristics of six male sprinters were studied for 100‐, 200‐, 300‐ and 400‐m experimental sprints, which were run according to the velocity in the 400 m. Blood lactate (BLa) was analysed and drop jumps were performed with EMG registration at rest and after each sprint. Running velocity (PPPP< 0.001). The height of rise of the centre of mass in the drop jumps was smaller immediately after the 300 m (PPr=–0.77, P<0.001). The EMG and EMG:running velocity ratio increased with running distance. It was concluded that force generation of the leg muscles had already begun to decrease during the first quarter of the 400‐m sprint. The deteriorating force production was compensated for until about 200–300 m. Thereafter, it was impossible to compensate for fatigue and the speed of running dropped. According to this study, fatigue in the 400‐m sprint among trained athletes is mainly due to processes within skeletal muscle rather than the central nervous system.