Exploring mechanisms of reactive balance control in fall-prone older people with neuromuscular and biomechanical analyses

Abstract

Falls and fall-related injuries adversely affect the community-dwelling older people. Even the multifactorial fall-prevention programs could have insufficient effectiveness in reducing falls among the older people with history of falls (i.e., older fallers). Previous studies mainly used postural sways, gait analyses, or age-related neuromuscular analyses to evaluate balance and gait disorders. The neuromuscular and biomechanical mechanisms underlying reactive balance control were less focused. Identifying these intrinsic deficits of reactive balance control among the fall-prone people is essential to guide a more targeted design of fall-prevention exercises for them. This PhD project aims to comprehensively investigate the biomechanical and neuromuscular alterations in reactive balance control that can indicate the fall histories/risks among older adults by using synchronized motion capture, electromyographic (EMG), and mechanomyographic (MMG) technologies. Four observational studies have been conducted, including: a. Exploring response speed and sequence of multiple lower-limb muscles/joints following unexpected translational moving-platform (Study 1) or waist-pull balance perturbations (Study 3) in healthy young adults. b. Comparing neuromuscular and kinematic responses following unexpected translational moving-platform perturbations (Study 2) or waist-pull balance perturbations (Study 4) in older fallers vs. older non-fallers. c. Examining what responses can predict older adults' prospective falls over 1 year (Study 4). Via a step-by-step approach, all the studies are linked together by the theme of probing the more intrinsic mechanisms of reactive balance control in fall-prone people. Pilot studies in healthy young adults (Study 1&3) have shown that ankle muscles had the largest activation rate among the examined leg muscles following either anteroposterior or mediolateral sudden balance loss. Two studies in older adults (Study 2&4) have both revealed that older fallers had insufficient activation of proximal hip muscles for reactive balance control. Study 2 has preliminarily found that fallers had to use the suspensory strategy (e.g., bending knees) to compensate for their slower reaction of ankle/hip strategies following unexpected translational moving-platform perturbations as compared to non-fallers. In Study 4, the reactive balance control induced by unexpected waist-pull perturbations was assessed in 36 fallers vs. 36 non-fallers, and these older adults' prospective falls were tracked. Older fallers were observed with a quicker neuromuscular response following anterior perturbations but slower neuromuscular responses following posterior/medial/lateral perturbations than non-fallers. Additionally, the older adults' prospective falls were predicted by (1) slowed/reduced activation of hip abductor (among the eight investigated leg muscles), (2) altered responses mostly in hip/knee joint (than ankle joint), and (3) alterations mostly in response to the mediolateral perturbations (than anteroposterior perturbations). In conclusion, the findings of this PhD project support the assessment of hip abductor's activity during reactive balance tasks to complement the current fall-risk assessment, providing insights for a more targeted fall-prevention management for older people. Future work is merited to examine the effectiveness of training that targets the identified fall-related factors on preventing falls among the fall-prone older adults.