(6) PREDICTORS OF REACTIVE LEG DROP PERFORMANCE IN YOUNG AND OLDER ADULTS

Purpose: The reactive leg drop (RLD) assessment is a quick, easy-to-use test that assesses fall risk by mimicking the sudden loss of balance that occurs during a trip, triggering sensorimotor integration. Rapid integration of these systems is required to regain balance, however, age-related declines in integration speed place older adults at increased fall risk. The purpose of this study was to explore age-specific differences in RLD performance and investigate potential sensory and motor mechanisms that contribute to RLD performance. Methods: Forty-one participants were categorized into two groups: young (n=28, 21.19±0.83 years) and old (n=13, 71.17±2.52 years). Participants completed one testing visit four hours fasted. Body composition was assessed using a whole-body dual-energy x-ray absorptiometry scan. Participants performed four RLD assessment trials (two eyes open (EO) and two eyes closed (EC)) in a random order using a twin-axis electrogoniometer placed on the shank and thigh segments to measure sagittal plane knee motion. In the seated position, participants’ dominant limb was passively extended to its maximal range of motion and held for a random interval before being released into free fall. Participants were instructed to kick their leg back to the starting position as quickly as possible when they felt it begin to fall. Drop angle (°) and total duration (ms) were determined from the electrogoniometer signal from the starting position to where the limb was stopped from free fall. The time to detection of passive movement (TTDPM) was identified as the minimum angular displacement (°) participants could perceive when their dominant limb was passively moved into extension or flexion at a rate of 0.25°/s. Participants then completed three submaximal isokinetic leg extension contractions at 180˚/s, followed by three isokinetic maximal voluntary contractions (MVCs) at an unloaded velocity with 30-seconds rest to determine maximal velocity. Next, participants completed three leg extension isometric MVCs with two-minute rest intervals. Leg extensor rapid force (50, 100, 150, and 200 ms) was determined and surface electromyography (EMG) was placed on three superficial quadriceps muscles to determine the electromechanical delay (time period between onset of EMG and force production; EMD). Independent t-tests compared RLD drop angle and total duration between groups. Bivariate correlations examined the relationship between RLD performance and rapid force, EMD, maximal velocity, and TTDPM. An alpha level of ≤0.05 was set to determine statistical significance. Results: Young adults demonstrated a significantly smaller drop angle (p=0.024) and shorter total duration (p=0.006) than older adults in the EO condition. There were no significant differences between groups for the EC condition (p=0.061-0.225). No significant associations were observed between RLD performance and rapid force, EMD, maximal velocity, or TTDPM (p=0.094-0.991, r=-0.007-0.271). Conclusions: There were significant age-related differences in RLD performance during the EO condition, but not when the visual input was removed. Future studies may investigate the impact of eccentric muscle strength on RLD performance. Practical Applications: The RLD test may serve as a novel, easy-to-use assessment of age-related sensorimotor integration changes. More complex neuromuscular function measures beyond basic strength and power may better reflect an individual’s functional capacity in older populations. Acknowledgements: None