Abstract
The aim of this study was to explore the underlying age-related differences in dynamic motor control during different step ascent conditions using muscle synergy analysis. Eleven older women (67.0 y ± 2.5) and ten young women (22.5 y ± 1.6) performed stepping in forward and lateral directions at step heights of 10, 20 and 30 cm. Surface electromyography was obtained from 10 lower limb and torso muscles. Non-negative matrix factorization was used to identify sets of (n) synergies across age groups and stepping conditions. In addition, variance accounted for (VAF) by the detected number of synergies was compared to assess complexity of motor control. Finally, correlation coefficients of muscle weightings and between-subject variability of the temporal activation patterns were calculated and compared between age groups and stepping conditions. Four synergies accounted for >85% VAF across age groups and stepping conditions. Age and step height showed a significant negative correlation with VAF during forward stepping but not lateral stepping, with lower VAF indicating higher synergy complexity. Muscle weightings showed higher similarity across step heights in older compared to young women. Neuromuscular control of young and community-dwelling older women could not be differentiated based on the number of synergies extracted. Additional analyses of synergy structure and complexity revealed subtle age- and step-height-related differences, indicating that older women rely on more complex neuromuscular control strategies.
Highlights
Aging is associated with gradual changes in neuromuscular control [1,2]
For the group-averaged variance accounted for (VAF), four muscle synergies were required to achieve a threshold level of 85% VAF for reconstructed signals across both age groups, step directions and step heights (Figure 2). This indicates that age, step direction and step height did not affect the number of synergies needed to reconstruct the EMG data
Our results show that complexity of motor control is quite robust across step heights and age groups for stepping in forward and lateral directions
Summary
Aging is associated with gradual changes in neuromuscular control [1,2]. These changes can have a major impact on fall risk, mobility and independence in older adults [3,4,5], which may be exacerbated in post-menopausal women due to accelerated muscle wasting [5]. One major challenge with assessing changes in neuromuscular control in healthy community-dwelling older adults is that, due to the gradual nature of age-related neuromuscular deterioration, pre-clinical changes in neuromuscular control of everyday tasks may go undetected [6]. Sci. 2020, 10, 1987 neuromuscular control can be revealed by increasing task challenge. By increasing gait speed, cadence, step length, and step height [7,8,9]
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