Age-related relative increases in electromyography activity and torque according to the maximal capacity during upright standing

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Abstract
The aim of this study was to assess the relative torque (a percentage of the maximal capacity of torque production) at the ankle joint in young and elderly adults during different postural tasks of increasing difficulty. Seven young (approximately 22 years old) and seven older (approximately 80 years old) men took part in this investigation. Maximal agonist torque was estimated from resultant and antagonist torques in both populations in plantar-flexion (PF) and dorsi-flexion (DF). The sum of PF and DF maximal agonist torques was considered as the maximal capacity of torque production. The centre of pressure (CoP) displacement was analysed during Normal Quiet Stance, Romberg and One Leg Balance. During maximal contractions and postural tasks, the electromyographic (EMG) activity was simultaneously recorded on the triceps surae and tibialis anterior muscles. We observed that the maximal capacity of torque production was negatively correlated with the CoP displacement, whatever the population and the postural tasks. The relative torque during all postural tasks was positively correlated with the CoP displacement in both populations. Moreover, older adults needed more EMG activity than young adults to produce the same torque. From this knowledge, one can assume that increasing strength in the muscles of the ankle joint may improve postural stability in older adults; this might have implications in the prevention of falls in elderly persons and in rehabilitation programs for elderly people who have already fallen.