ECSS, Oslo, 2009;

Electromyographic Activity During Whole Body Vibration: Motion Artifacts or Strech Reflex Responses?

Year: 2009

Kramer A, Ritzmann R, Gruber M, Gollhofer A, Taube W
ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG, UNIVERSITÄT POTSDAM

Abstract

Introduction:
The validity of electromyographic (EMG) data recorded during whole body vibration (WBV) is discussed controversially. Some authors have suggested filtering because of vibration-induced motion artifacts (Abercromby et al., 2007; Fratini et al., 2008) while others have interpreted the EMG signals as muscular activity caused at least partly by stretch reflexes (Mesters et al., 2002; Rittweger et al., 2003; Kvorning et al., 2006). The aim of this study was to investigate the origin of the EMG signal during WBV using several independent
approaches.
Methods:
The EMG activity of four leg muscles was determined in ten healthy subjects during WBV. Additionally, to test whether the movement of the cables and electrodes during WBV caused motion artifacts in the EMG signal, special dummy electrodes were developed, thus providing a signal only influenced by motion artifacts, without interference from muscle signals. The three following protocols had the same goal, but used a physiological approach and in addition they were designed to verify whether the characteristics of the
EMG signal were consistent with the characteristics of a stretch reflex response. For that purpose, frequency spectra and latencies of mechanically evoked stretch reflexes and of the EMG signal during WBV were evaluated and compared. Moreover, pressure application via a blood pressure cuff served to reduce the amplitude of the short latency component of the stretch reflex, thus allowing an estimation of the stretch reflex contribution to the EMG signal.
Results:
The dummy electrodes, designed to monitor motion artifacts, showed almost no activity during WBV. The frequency analyses showed no evidence of motion artifacts. The latencies of the stretch reflex responses evoked by the dorsiflexions in an ankle ergometer were almost identical to the supposed stretch reflex responses during vibration (differences of less than one millisecond). Pressure application significantly reduced the amplitude of both the supposed stretch reflexes during vibration (by 61±17 %, p<0.001) and the stretch reflexes in the ankle ergometer (by 56±13 %, p<0.01).
Discussion:
The present results support the hypothesis of WBV-induced stretch reflexes. Contribution of motion artifacts to the overall EMG activity seems – at least with accurate recording conditions – insignificant. Therefore, we recommend not to filter the EMG signal on account of motion artifacts, due to probable distortion of the information content.
References:
Abercromby AF, Amonette WE, Layne CS, McFarlin BK, Hinman MR and Paloski WH. (2007). Med Sci Sports Exerc, 39, 1642-1650.
Fratini A, Cesarelli M, Bifulco P and Romano M. (2008). J Electromyogr Kinesiol.
Kvorning T, Bagger M, Caserotti P and Madsen K. (2006). Eur J Appl Physiol, 96, 615-625.
Mester J, Spitzenpfeil P and Yue Z. (2002). Strength and Power in Sport, 488-501. Blackwell, Oxford.
Rittweger J, Mutschelknauss M and Felsenberg D. (2003). Clin Physiol Funct Imaging, 23, 81-86.

GID: 2038; Last update: 16.11.2009
More information: Original Article