Effects of aging on muscle activation during quiet standing on a slope with different angles

The standing balance undergoes declines with aging that contributes the fall of the elderly. But the age-related balance control during quiet standing upon a slope has not been fully understood. This study aimed to investigate the effects of aging on muscle activation during quiet standing on a slope with different angles. Sixteen healthy young subjects and 16 healthy elderly subjects participated in the experiment. They were asked to stand quietly on a slope at -10°, -5", 0°, 5° and 10° inclination with eyes open(EO) and eyes close(EC). The surface electromyography (sEMG) of tibialis anterior (TA), soleus (SOL), medial gastrocnemius (M_GAS) and lateral gastrocnemius (L_GAS) of the lower-limb were recorded simultaneously. The normalized root mean square (RMS) and median frequency (MDF) of each muscle were calculated. The RMS value of the L_GAS of the right leg in elderly group was higher than that of the young group, only on the 5
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slope with EO (p<;0.05). The RMS value of the TA of the left leg in elderly group was higher than that of the young group, only on the 5° and 10° slopes with EC (p<;0.05). The RMS value of the L_GAS of the right leg in elderly group was higher than that of the young group, only on the 0° and 5° slopes with EC (p<;0.05). Compared with the young subjects, the elderly subjects showed significantly increased MDF values of the TA of their right leg with EO while standing on -5° and 10° slopes, as well as with EC while standing on -10°, -5°and 10° slopes (p<;0.05). The effects of aging on the RMS and MDF of sEMG were more significantly observed when the individuals stood on a more inclined flat, particularly under the condition with EC. This finding could help us understand the mechanism of standing balance control with aging and could be used to assess the risk of fall in elderly population.