Fatigue effects on the knee flexors neuromuscular parameters during repeated sprinting

Abstract

Background: To identify at which point fatigue on neuromuscular parameters occurs in the knee flexors during a repeated sprint protocol. Methods: Physical active males without previous hamstring strain injury were recruited. Neuromuscular parameters such as peak torque (PT) and rate of torque development (RTD) were assessed after every two sprints in a 5 × (2 x 30 m) repeated sprint protocol. Results: Twenty physical active males participated in the study. A significant effect of sprint number was found (p < 0.001; η2p = 0.643) with a decreased sprint speed by 6.9% from fastest to slowest sprint. No significant differences were observed in the time between finishing the sprint and performing the first MVIC (46.3 ± 4.7s; p = 0.423), nor in the time between finishing a set and starting the next set (121.2 ± 7.6s; p = 0.503). Regarding neuromuscular parameters, the only significant difference found was in PT between before and after two sprints (117.95 ± 5.61 N⋅m vs. 110.64 ± 5.71 N⋅m; p = 0.048, d = 0.289) and on RTD 0-50ms before and after ten sprints (465.78 ± 223.76 N⋅m/s vs. 382.30 ± 189.56 N⋅m/s; p = 0.008; η2p = 0.149). Conclusions: A recovery time of 46s between sprints and testing neuromuscular parameters (due to experimental design) seems sufficient to restore the neuromuscular system. Therefore, it can be suggested that time recovery is the principal factor in detecting fatigue on neuromuscular parameters.