Intramuscular recordings of motor unit (MU) firing pattern during dynamic contractions represent a specific challenge to decomposing programs. MU recognition during length changing contractions and at higher force levels are especially challenging. Further, while a description of MU properties may be extracted from MU recognitions scattered over the contraction, information on firing rate must rely on a reliable tracing of all MUs in a certain activity period. The Daisy decomposition program was developed to offer spike recognition based on multi channel shape recognition, template updating, decomposition of overlapping potentials, manual editing with quantitative as well as graphical guidance and it has been used for identification of double discharges during ballistic finger movements (Olsen 2001, Sjøgaard 2001). The ability to detect subtle changes in firing patterns may be specifically relevant for studying age related changes in motor control. The largest changes are found in fast muscle fibres and this may specifically hamper the ability to react on unexpected disturbances that demand a fast force increase. In addition to these peripheral changes, also central factors may be involved, as for instance the ability to produce doublets for providing fast force changes. It seems that the ageing effect on MU firing rate is most distinct in distal extensor muscles (Kamen et al 1995). Earlier studies on dynamic constant load contractions have shown a larger firing rate in concentric compared to eccentric contractions (Sogaard 1995, Kossev et Christova 1998). However, it is not known how ageing influences firing rate behaviour in dynamic contractions. This may be particularly relevant for the leg extensors that are crucial for locomotion and balance abilities. This presentation will cover some preliminary data from a recent study on 8 YOUNG (25.4±3.1 yr.) and 8 OLD (68.8±5.3 yr.) physically active healthy males. The subjects performed plantar flexions while seated in an ankle dynamometer. The tasks included 1) isometric maximum voluntary contraction, 2) isometric ramp and 3) isotonic contractions, and 4) concentric and 5) eccentric contractions. The preliminary results indicate that in all situations firing rates were lower in the old group. In addition some cases of a burst like firing pattern in the eccentric phase will be presented and discussed. In conclusion, detailed information of firing pattern in dynamic contractions can be obtained by interactive manual decomposition software, revealing subtle changes that may be useful in understanding age related changes in motor control.
© Copyright 2007 12th Annual Congress of the European College of Sport Science, Jyväskylä, Finland - July 11-14th 2007. Veröffentlicht von University of Jyväskylä. Alle Rechte vorbehalten.