Relation between sagittal distribution of the foot pressure in upright stance and relative electromyograph magnitude in some leg and foot muscles
Okada, M.; Fujiwara, K.
Journal of Human Ergology 13(2): 97-106
ISSN/ISBN: 0300-8134 Accession: 006294036
Modification of relative muscle activity (relative EMG magnitude in % of the magnitude attained in maximum voluntary contraction) in relation to the sagittal position of the center of foot pressure (CFP) was determined for lower limb muscles. To assess the consistency of the relation, the CFP was not shifted continuously, but repeatedly set at various positions along the feet closed and placed in parallel with each other. An upright stance was held at each position for 20 sec. Ten male students served as subjects. A weak activity below 5% max was observed in the soleus muscle within the natural balance area. Activity was also present yet variable in the medial gastrocnemius muscle within this area. Mean and standard deviation of the relative activity (% max) attained in the forward limit of balance was 19.5 .+-. 3.1 in the soleus, 22.0 .+-. 4.2 in the medial gastrocnemius, 5.2 .+-. 3.0 in the lateral gastrocnemius, and 52.4 .+-. 14.8 in the abductor hallucis muscle. The tibialis anterior muscle enhanced its activity up to 34.7 .+-. 9.3% max in the backward limit of balance. The CFP-EMG relations showed features comparable with those deduced theoretically. Within-subject and between-subject variability of the CFP-EMG relation was less pronounced in the soleus and tibialis anterior muscle, the former in particular, than in the other muscles. The difference was discussed in terms of the number of joints involved in the functioning of each muscle.