Abstract
BackgroundAgonist and antagonist muscle co-contractions during motor tasks are greater in the elderly than in young adults. During normal walking, muscle co-contraction increases with gait speed in young adults, but not in elderly adults. However, no study has compared the effects of speed on muscle co-contraction of the ankle joint during dynamic postural control in young and elderly adults. We compared muscle co-contractions of the ankle joint between young and elderly subjects during a functional stability boundary test at different speeds.MethodsFifteen young adults and 16 community-dwelling elderly adults participated in this study. The task was functional stability boundary tests at different speeds (preferred and fast). Electromyographic evaluations of the tibialis anterior and soleus were recorded. The muscle co-contraction was evaluated using the co-contraction index (CI).ResultsThere were no statistically significant differences in the postural sway parameters between the two age groups. Elderly subjects showed larger CI in both speed conditions than did the young subjects. CI was higher in the fast speed condition than in the preferred speed condition in the young subjects, but there was no difference in the elderly subjects. Moreover, after dividing the analytical range into phases (acceleration and deceleration phases), the CI was larger in the deceleration phase than in the acceleration phase in both groups, except for the young subjects in the fast speed conditions.ConclusionsOur results showed a greater muscle co-contraction of the ankle joint during dynamic postural control in elderly subjects than in young subjects not only in the preferred speed condition but also in the fast speed condition. In addition, the young subjects showed increased muscle co-contraction in the fast speed condition compared with that in the preferred speed condition; however, the elderly subjects showed no significant difference in muscle co-contraction between the two speed conditions. This indicates that fast movements cause different influences on dynamic postural control in elderly people, particularly from the point of view of muscle activation. These findings highlight the differences in the speed effects on muscle co-contraction of the ankle joint during dynamic postural control between the two age groups.
Highlights
Agonist and antagonist muscle co-contractions during motor tasks are greater in the elderly than in young adults
We applied the Shapiro–Wilk test to test all variables for Results After normality testing, Center of pressure (COP)-Vymax, mean %maximal voluntary contraction (MVC) of tibialis anterior (TA), and contraction index (CI) were defined as non-normally disturbed variables and are presented as medians
On the functional reach test (FRT), data were missing for two young subjects and one elderly subject
Summary
Agonist and antagonist muscle co-contractions during motor tasks are greater in the elderly than in young adults. Examining the relationship between muscle co-contraction and postural sway in elderly people, Nagai et al [4] showed a greater muscle co-contraction of the ankle joint during static standing, the functional reach test (FRT) [12], the functional stability boundary test (shifting body weight toward toes without heels off from quiet standing [13]), and gait in elderly people. We hypothesized that fast movements have different influences on dynamic postural control in elderly people in comparison with young people Poor postural control with muscle co-contraction is likely during fast dynamic postural control tasks in elderly people
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