Relationships between muscle strength and multi-channel surface EMG parameters in eighty-eight elderly.

Background: Since age-related muscle strength loss cannot be explained solely by muscle atrophy, other determinants would also contribute to muscle strength in elderly. The present study aimed to clarify contribution of neuromuscular activation pattern to muscle strength in elderly group. From 88 elderlies (age: 61~ 83 years), multi-channel surface electromyography (EMG) of the vastus lateralis muscle was recorded with two-dimensional 64 electrodes during isometric submaximal ramp-up knee extension to assess neuromuscular activation pattern. Correlation analysis and stepwise regression analysis were performed between muscle strength and the parameters for signal amplitude and spatial distribution pattern, i.e., root mean square (RMS), correlation coefficient, and modified entropy of multi-channel surface EMG.

Results: There was a significant correlation between muscle strength and RMS ( r  = 0.361, p  = 0.001) in the elderly. Muscle thickness ( r  = 0.519, p  < 0.001), RMS ( r  = 0.288, p = 0.001), and normalized RMS ( r  = 0.177, p  = 0.047) were selected as major determinants of muscle strength in stepwise regression analysis ( r  = 0.664 in the selected model).

Conclusion: These results suggest that inter-individual difference in muscle strength in elderly can be partly explained by surface EMG amplitude. We concluded that neuromuscular activation pattern is also major determinants of muscle strength on elderly in addition to indicator of muscle volume.