title: Linear and non-linear analysis of surface electromyograms in weightlifters.
abstract: The present research was aimed at investigating the peculiarities of surface electromyogram (sEMG) signals in 12 weightlifting athletes (WLA) and 9 control subjects (control group, CG) The sEMG signals were recorded from both vastus lateralis muscles during 20 s isometric contractions made at 30% and 60% of the maximal voluntary contraction (MVC). Ground reaction force (vertical component) was recorded using a force plate. The sEMG was analysed in the frequency domain and the median frequency (MDF) was computed over successive 1 s epochs. A non-linear technique, recurrence quantification analysis was also applied to assess the presence and time course of deterministic structures in sEMG. The percentage of determinism (%DET) was used as a synthetic parameter to quantify the amount of regularly repeating sEMG waves within the signal itself (bursts). In 5 WLA the sEMG displayed a clear burst activity centred at 11 Hz. These bursts were correlated with force output 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 long-term changes in firing probability during sub-maximal isometric exercise. The MDF and %DET data provided indications of a greater involvement of fast twitch muscle fibres in WLA than in CG.
authors.affiliation: Postgraduate School of Specialization in Sport Medicine, Faculty of Medicine, Istituto di Fisiologia Umana, University of Rome La Sapienza, P. le Aldo Moro 5, 00185 Rome, Italy. francesco.felici@uniromal.it
authors.forename: F
authors.initials: F
authors.lastname: Felici
authors.forename: A
authors.initials: A
authors.lastname: Rosponi
authors.forename: P
authors.initials: P
authors.lastname: Sbriccoli
authors.forename: G C
authors.initials: GC
authors.lastname: Filligoi
authors.forename: L
authors.initials: L
authors.lastname: Fattorini
authors.forename: M
authors.initials: M
authors.lastname: Marchetti
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D016014:Linear Models; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D017711:Nonlinear Dynamics; D014891:Weight Lifting / Q000502:physiology*