Linear and non-linear analysis of surface electromyograms in weightlifters

The present research was aimed at investigating the peculiarities of surfac e electromyogram (sEMG) signals in 12 weightlifting athletes (WLA) and 9 co ntrol subjects (control group, CG) The sEMG signals were recorded from both vastus lateralis muscles during 20 s isometric contractions made at 30% an d 60% of the maximal, voluntary contraction (MVC). Ground reaction force (v ertical component) was recorded using a force plate. The sEMG was analysed in the frequency domain and the median frequency (MDF) was computed over su ccessive 1 s epochs. A non-linear technique, recurrence quantification anal ysis was also applied to assess the presence and time course of determinist ic structures in sEMG. The percentage of determinism (%DET) was used as a s ynthetic parameter to quantify the amount of regularly repeating sEMG waves within the signal itself (bursts). In 5 WLA the sEMG displayed a clear bur st activity centred at Il Hz. These bursts were correlated with force outpu t oscillations and were evident both at 30% and 60%MVC. The MDF decay with time was more evident in WLA than in CG subjects. The %DET increased in WLA , this increase being more evident during 60%MVC contractions. Our results seemed to suggest a special disposition among WLA for the development of lo ng-term changes in firing probability during sub-maximal isometric exercise . The MDF and %DET data provided indications of a greater involvement of fa st twitch muscle fibres in WLA than in CG.