Abstract
Background: Fatigue is thought to impact performance and may be a factor in injury mechanism. However, the full impact of a potentially fatiguing task on performance is unclear.
Objective: To explore changes in maximum voluntary torque and electromyographic (EMG) activity following a sixty second isometric maximum voluntary contraction (MVC) of the quadriceps muscles and to follow the time course of any changes observed.
Method: 21 subjects (14 males and 7 females) were recruited. Torque during brief maximum voluntary isometric contractions of the quadriceps muscle group was recorded in right and left legs using a Cybex Norm Isokinetic Dynamometer before, during and at intervals after a 60 second isometric fatigue task. EMG activity of the vastus medialis, rectus femoris and vastus lateralis was also recorded synchronously.
Results: Mean peak torque was significantly (p< 0.05) lower in both legs at the end of the fatigue task. However, 10 minutes following the cessation of the task, it had increased and was significantly higher than the pre-fatigue level. It remained higher until the end of the protocol (30 mins post fatigue). The EMG amplitudes decreased slightly compared to pre-fatigue values during the fatigue task, a few of which were significantly lower than those of the pre-fatigue task. Following the fatigue task, EMG amplitudes increased gradually and were significantly higher than those of the pre-fatigue task in all the muscles at the final time point. Median frequencies decreased significantly during the fatigue task and were similar to pre-fatigue values by 5mins post-fatigue.
Conclusion: This study has revealed that both torque and EMG rise following a sustained isometric 60 second hold to higher levels than pre-hold and that this rise is maintained for up to 30 minutes. This rise however, was not associated with increased muscle firing frequency. The mechanisms behind this rise remain to be elucidated.