Article

The purpose of this study was to examine the relationships between the integrated electromyogram (IEMG) and two methods of counting surface spikes during different levels of isometric tension. Five male and three female subjects performed four, two trial bouts of isometric elbow flexion at 25, 50, 75 and 100 per cent maximum voluntary isometric contraction (MVIC). Frequency of the surface electromyogram was determined by digital and manual spike counting techniques. Discriminator levels of O (zero crossings), 25, 50 and 75 per cent of peak EMG amplitude at MVIC were used for digital counting at each tension level. Manual spikes were determined from an ultra-violet light trace taken during the same sampling period and IEMG data were concurrently summed digitally each milivolt second. Statistical analysis indicated a significant correlation between IEMG and digital spikes at discriminator levels of 25, 50 and 75. No significant correlation was found between IEMG and manual spike counts. A significant quadratic relationship was found between IEMG and tension and a repeated measures analysis of variance indicated significant main effects for tension on IEMG. Subsequent post-hoc analyses revealed significant differences between all levels of tension excluding 75 and 100 per cent MVIC. The results of this study indicate that choosing an inappropriate discriminator may lead to a spike count-IEMG relationship which is inconsistent with that which could be expected from differential motor unit recruitment. It was demonstrated that manual spike counting should not be used as a technique for assessing the relationships between IEMG and frequency discharge. Further, the relationship between IEMG and tension may reveal a changeover in the type of recruitment (phasic versus tonic motor units) at higher levels of tension.

Langue : ANGLAIS

Identifiant basis : 1986000081