Affiliations: [a] Human Performance Group, Biosurgery & Surgical
Technology, Imperial College London, Charing Cross Hospital Campus, London, UK
Note: [] Address for correspondence: Alison H. McGregor PhD, Human
Performance Group, Biosurgery & Surgical Technology, Imperial College
London, Charing Cross Hospital Campus, London W6 8RP, UK. Tel.: +44 (0)20 8383
8831; Fax: +44 (0)20 8383 8835; E-mail: [email protected]
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.
