Impaired mediolateral postural control at the ankle in healthy, middle-aged adults.

Elderly adults sway more than young adults. Based on the literature, the authors expected the mediolateral ankle postural control mechanism to be affected before age 60 years. Twelve healthy young adults (24.21 ± 2.50 years) and 12 middle-aged adults (51.13 ± 6.09 years) participated in the study. To challenge mediolateral stance, the conditions modified the mediolateral distance among the feet (narrow and standard distances), mandibular position (rest position, left and right laterality occlusion positions), and the occlusion with clenching (intercuspal occlusion, left and right maximal voluntary clenches). As we expected, middle-aged adults exhibited significantly reduced contribution of the ankle mechanism. It was so both in narrow and standard stances. A second objective was to show a greater contribution of the 2 mechanisms in narrow than in standard stances. The results confirmed our hypothesis. As we expected, mandibular conditions only had a significant effect on center of pressure sway. Unexpectedly, middle-aged adults did not increase their range of center of pressure sway in narrow stance. They may have overconstrained their center of pressure sway because of their ankle impairments. On the practical level, our results suggest that older adults should increase their stance width to relieve their hip and ankle control mechanisms and to stabilize their mediolateral posture.