Effects of ageing on soleus H-reflex modulation during shortening and lengthening muscle actions
Chen, YS & Zhou, S 2010, 'Effects of ageing on soleus H-reflex modulation during shortening and lengthening muscle actions', paper presented to the 9th Annual Conference of the Society of Chinese Scholars on Exercise Physiology and Fitness, Beijing, China.
The purpose of this study was to determine the effect of ankle joint position and muscle contraction intensity on soleus (SOL) H-reflex modulation in young and older adults. Twenty young (25±5 years) and twenty older (74±5 years) volunteers participated in the study. The recruitment curve of H-wave and M-wave was established for each participant. H-reflex was tested when the participants performed plantarflexions at 10, 30, and 50% isometric maximal voluntary contractions (MVC) and at ankle joint positions of neutral (0 degree), plantarflexion (20 degree), and dorsiflexion (-20 degree), respectively in a sitting position. The results showed that the maximum amplitude of SOL H-reflex of the older group was significantly smaller than that of the young group under all testing conditions, for example, it was 57% smaller during the 10%MVC in plantarflexion position, and 77% smaller during rest in dorsiflexion position. During voluntary contractions in the plantarflexion position, the young group demonstrated a fluctuation of the SOL H-reflex modulation, whereas the older group showed a facilitation of the SOL H-reflex at 10% and 30% MVC, and a decrease in the SOL H-reflex at 50% MVC. The latency of H-reflex was not joint angle-dependent in the older group but it was significantly influenced by ankle position in the young group. In addition, the young group demonstrated a shorter duration of the H-reflex than the older group. The significant differences in SOL H-reflex modulation found between young and older adults in relation to the joint position and intensity of muscle contraction might be an indication of the age-related changes in motor control strategies.