Older Fallers and Non-fallers’ Neuromuscular and Kinematic Alterations in Reactive Balance Control: Indicators of Balance Decline or Compensation?

Abstract

Background: Falls and fall consequences in older adults are global health issues. Previous studies have compared postural sways or stepping strategies between older adults with and without fall histories, to identify the associated factors of falls. However, more in-depth neuromuscular/kinematic mechanisms have remained unclear. This study therefore aimed to comprehensively investigate and compare the muscle activities and joint kinematics during reactive balance control in older adults with different fall histories. Methods: This pilot observational study recruited six community-dwelling older fallers (≥1 fall in past one year) and six non-fallers, who received unexpected translational balance perturbations in randomized directions and intensities during natural standing. The whole-body center-of-mass (COM) displacements, eight dominant-leg joint motions and muscle electrical activities were collected, and analyzed using the temporal and amplitude parameters. Four-way ANOVA and post hoc analyses were conducted to examine the effects of fall history, perturbation direction, perturbation intensity, and postural sway/joint/muscle on each parameter. Results: Post hoc analyses revealed that compared to older non-fallers, fallers had significantly: (a) smaller activation rate in ankle dorsiflexor, delayed activation in hip flexor/extensor, larger activation rate in knee flexor, and smaller agonist-antagonist co-contraction in lower-limb muscles; (b) larger knee/hip flexion angles, longer ankle dorsiflexion duration, and delayed timing of recovery in joint motions; and (c) earlier downward COM displacements and larger anteroposterior overshooting COM displacements following unexpected perturbations (p< 0.05). Conclusion and Implication: Compared to older non-fallers, fallers tended to use more suspensory strategies to maintain reactive standing balance. Such strategies could enable older fallers to compensate for their inadequate initiation of ankle/hip strategies, but led to prolonged and overacted balance recovery among them. This study’s comprehensive neuromuscular/kinematic analyses and controlled balance perturbation preliminarily uncovered some specific declines and ineffective strategies in fall-prone older adults during reactive balance control, which can potentially enhance the instrumented assessments for early identification of fall-prone older adults and facilitate the targeted training to prevent their falls. Further longitudinal studies are still needed to examine diagnostic accuracies of these identified neuromuscular/kinematic factors in differentiating fall risks of older people.