Leading limb biomechanical response following compelled forward and descending body shift in old versus young adults.

BACKGROUND: Falls pose a significant health risk in older adults, with stair descent falls carrying particularly severe consequences. Reduced balance control and limb support due to aging-related physiological and neuromuscular decline are critical components in increased falling risk in older adults. Understanding the age-associated abnormalities in balance control and limb support strategies during sudden forward and downward body shift could reveal potential biomechanical deficits responsible for increased falling risks in older adults. This study investigates balance regulatory responses following first-time exposure to compelled forward and downward body shift in young and older adults. METHODS: Thirteen healthy old and thirteen healthy young adults participated in this study. Participants stood on two adjacent perturbation platforms in modified tandem stance. The leading limb support surface dropped 3 in. vertically at an unknown time. The anterior margin of stability and center of mass velocity, peak vertical ground reaction forces, and leading limb ankle and knee joint angular displacement, torque, and power during the initial response phase were compared between age groups. FINDINGS: Compared to young adults, older adults showed higher center of mass velocity, lower margin of stability, peak vertical ground reaction force, peak ankle and knee joint power, and peak knee joint torque during the initial response phase. INTERPRETATIONS: The abnormalities potentially identified in our study, particularly in dynamic stability regulation, limb support force generation, and shock absorption may affect the ability to arrest the body's forward and downward motion. These deficits may contribute to an increased risk of forward falls in aging.

Biomechanical and neuromuscular control characteristics of sit-to-stand transfer in young and older adults: A systematic review with implications for balance regulation mechanisms.

BACKGROUND: Falls are major health concerns in older adults. Sit-to-stand transfer is an important functional movement that can predict falling risk in older adults. Aging-associated declines in neuromechanical control of movement may negatively impact sit-to-stand performance. This systematic review aims to summarize differences in neuromechanical characteristics of younger vs. older adults that likely affect balance regulation during sit-to-stand. METHODS: Five databases (Academic search complete, MEDLINE, APA PsycInfo, Pubmed, and SPORTDiscus) were systematically searched from January 1985 through March 2023. Three reviewers assessed the quality of methodology, study design, results, and risk of bias using the Appraisal tool for Cross-Sectional Studies. Studies reported neuromuscular and biomechanical characteristics during sit-to-stand in young versus older adults were included. FINDINGS: Seventeen studies (343 older and 225 younger adults) were included. Compared to younger adults, older adults showed slower sit-to-stand time, higher trunk flexion, postural sway, agonist-antagonist muscle co-activation of the ankle and knee muscles, and lower ankle dorsiflexion torque. Lower magnitude and rate of vertical ground reaction force development and lower vertical momentum during rising were observed with aging during fast-speed sit-to-stand. There was heterogeneity among studies on sit-to-stand speed, foot position, use of arms, and seat height adjustability. INTERPRETATIONS: Higher trunk angular displacement and velocity accompanied by higher anterior momentum, likely to compensate for knee extensor muscle weaknesses, may lead to higher postural sway upon standing and therefore require higher knee and ankle muscle co-activation to maintain balance stability. Thus, additional attention to trunk control strategies is needed during clinical evaluations.