Speed and Variability of Chair Stepping and Morphological and Neural Characteristics in Community-Dwelling Older Adults.

Rapid lower limb coordination is directly related to physical activity skills in older adults and is controlled mainly by the central nervous system. This study aimed to investigate the association between chair stepping skills and neuromuscular properties in older adults. Fifty-eight community-dwelling older adults (72.0 ± 5.0 years) participated. High-density surface electromyography from the vastus lateralis (VL) was recorded and was decomposed into individual motor unit activities. The slope (MU slope) and intercept were calculated from the regression line between the individual motor unit recruitment thresholds and firing rates in each participant. Muscle thickness of the VL and vastus intermedius and echo intensity of the VL were evaluated using ultrasonography. While sitting on a chair, they repeatedly opened and closed their legs to position their feet outside and within 30-cm interval lines rapidly for 20 s. The mean steps were associated with echo intensity (r = 0.388, p < 0.01). Step variability was associated with the MU slope (r = 0.324, p = 0.03). These results suggest that the rapid lower-limb movement skills would be determined by neuromuscular quality, such as echo intensity and motor unit firing patterns, in older adults. The chair stepping test can be employed as a screening tool as an alternative to specific assessments.