Time-series analysis of multi-muscle coactivation and center of mass kinematics in older adults during gait

The effect of aging on coactivation and CoM kinematics has been assessed in phase-based analyses, but the scalar time-series analysis of these factors and their associations remain unexplored. To identify the effect of aging on multi-muscle coactivation and whole-body CoM kinematics and their associations during gait. Ankle and knee multi-muscle coactivation were calculated using a time-varying multi-muscle coactivation function. CoM speed and acceleration were calculated with three-point finite difference formulae. Statistical parametric mappingt-tests were used to identify differences in coactivation and CoM kinematics between old and young adults. A pointwise regression analysis with false discovery rate correction was used to assess associations between joint coactivation and CoM speed and acceleration. The pointwise regression analysis was performed for the ipsilateral leg during its respective stride due to effects of time-shifting on the results. Older adults had higher right ankle coactivation (Right stride: 14.7%-17.2%, 30.3%-33.65%, Left stride: 65.7%-68.1%, 80%-82.6%) and lower CoM speed (Right stride: 0.01%-9.1%, 44.7%-61.1%, 94.6%-100%, Left stride: 0.01%-10.7%, 45.8%-68.7%, 93.7%-100%) than young adults. Older adults also had lower deceleration (Right stride: 19.2%-21.4%, 68.1%-72.4%, Left stride: 17.7%-22.4%, 68.6%-72.4%) and acceleration (Right stride: 45.1%-49.2%, Left stride: 99%-100%) than younger adults. The pointwise association results revealed associations between knee (Right: 62.7%-63%, 84.7%-92.1% Left: 62.4%-64%, 85.8%-91.3%) and ankle (Right: 0.01%-0.6%, Left: 54.6%-64.1%) coactivation with CoM speed. For CoM acceleration, the pointwise regression revealed associations with knee (Right: 58.2%-58.7%, Left: 79.4%-80.9%) and ankle (Right: 60.5%-64.2%, Left: 93.9%-94.2%) coactivation. Older adults had lower CoM speed, altered CoM acceleration, and greater ankle multi-muscle coactivation than younger adults, potentially due to adoption of cautious gait. Furthermore, the pointwise regression results suggest limb-specific, temporal associations between coactivation and CoM kinematics, possibly reflecting demands at various phases of gait such as ground clearance, propulsion, and stabilization.