Energy cost of individual lower leg muscles in walking : comparison between young and elderly men at different walking speeds

The cost of transport (COT) in elderly subjects is increased in comparison to young adults, independently of the walking speed. The changes in the neuromuscular activity of the lower extremity muscles could explain this phenomenon. The objective of this thesis was to qualitatively compare the muscle activity pattern of the lower extremities between healthy young and elderly subjects, over a range of walking speeds in order to infer the contributions of individual muscles to changes in COT in both age groups. 26 participants were recruited (13 young aged 18-30; 13 old aged 70-80). Mean oxygen consumption was used to calculate COT and electromyography signals from 10 leg muscles were used to calculate the cumulative muscle activity per distance traveled (CMAPD) for each muscle, over seven walking speeds. At the group level, COT was higher for most speeds in the old group, and qualitative analysis implies the same trend for CMAPD. Young and old had speed-dependent changes in COT occurring in parallel with changes in mean CMAPD of all tested muscles. At muscle level, in both groups most of the muscles exhibited higher CMAPD at speeds faster and slower than the energetically optimal, whereas soleus CMAPD was independent of speed. Proximal muscles such as vastus lateralis presented a higher correlation between CMAPD and COT. These results suggest that soleus CMAPD may be relatively independent of age. The metabolic cost of contraction in proximal leg muscles seems to make a relatively large contribution to changes in COT regardless of age.