Effects of ageing on motor unit activation patterns and reflex sensitivity in dynamic movements

Kallio, J.; Avela, J.; Moritani, T.; Kanervo, M.; Selänne, H.; Komi, P.; Linnamo, V.

doi:10.1016/j.jelekin.2009.12.005

« Previous Next »Journal of Electromyography and Kinesiology
Volume 20, Issue 4 , Pages 590-598, August 2010

Effects of ageing on motor unit activation patterns and reflex sensitivity in dynamic movements

J. Kallio
- Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Finland
- Corresponding author. Address: Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland. Tel.: +358 (0) 14 260 2084; fax: +358 (0) 14 260 2071.
J. Avela
- Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Finland
T. Moritani
- Graduate School of Human and Environmental Studies, Kyoto University, Japan
M. Kanervo
- CEO, White House Finland Ltd., Finland
H. Selänne
- Chief Physician, LIKES – Foundation for Sport and Health Sciences, Finland
P. Komi
- Professor Emeritus, Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Finland
V. Linnamo
- Professor of Sports Technology, Vuokatti Snowpolis, Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Finland

Received 2 June 2009; received in revised form 22 December 2009; accepted 23 December 2009. published online 01 February 2010.

Abstract

Both contraction type and ageing may cause changes in H-reflex excitability. H reflex is partly affected by presynaptic inhibition that may also be an important factor in the control of MU activation. The purpose of the study was to examine age related changes in H-reflex excitability and motor unit activation patterns in dynamic and in isometric contractions. Ten younger (YOUNG) and 13 elderly (OLD) males performed isometric (ISO), concentric (CON) and eccentric (ECC) plantarflexions with submaximal activation levels (20% and 40% of maximal soleus surface EMG). Intramuscular EMG data was analyzed utilizing an intramuscular spike amplitude frequency histogram method. Average H/M ratio was always lowest in ECC (n.s.). Mean spike amplitude increased with activation level (P<.05), whereas no significant differences were found between contraction types. Both H-reflex excitability, which may be due to an increase in presynaptic inhibition, and mean spike frequency were higher in YOUNG compared to OLD. In OLD the mean spike frequency was significantly smaller in CON compared to ISO. Lack of difference in mean spike amplitude and frequency across contraction types in YOUNG would imply a similar activation strategy, whereas the lower frequency in dynamic contractions in OLD could be related to synergist muscle behavior.