Effects of frailty and walking speed on gait variability in older adults

Background Gait variability is crucial for predicting frailty. This study aims to explore the effects of frailty and speed on endpoint variability and coordination variability (CV) during walking. Methods Forty-seven adults (≥60 years; 18 males, 29 females) participated in this study. Gait kinematics were captured using Xsens MVN inertial sensors at three speeds (preferred, fast, and slow). Endpoint variability was evaluated using standard deviations (SD) of support times (total, single, and double). The coordination of the lower limb during braking phase and propulsive phase was quantified by continuous relative phase (CRP) analysis for interlimb (hip-hip, knee–knee, ankle-ankle) and intralimb (hip-knee, knee-ankle), and then CV was assessed through SD of interlimb CRP and intralimb CRP. Effect sizes were calculated using partial eta squared (η p 2 ). Results The results revealed an interaction between frailty and speed on total support time variability ( p = 0.044, η p 2 = 0.116), knee-ankle CV during braking phase ( p = 0.020, η p 2 = 0.123), and hip-hip CV during propulsive phase ( p = 0.002, η p 2 = 0.170). Compared to the robust group, the frail group ( p = 0.036) and/or pre-frail group ( p = 0.011) exhibited greater total support time variability during fast walking, but lower knee-ankle ( p < 0.018), hip-hip CV during fast walking (both p < 0.001). Compared with other speeds, the total support time variability of fast walking (frail: p = 0.015; pre-frail: p < 0.001) and knee-ankle CV of preferred speed walking (frail: p = 0.016; pre-frail: p = 0.017) were greatest for frail and pre-frail groups. Frailty significantly decreased CV, with frail and pre-frail groups demonstrating lower hip-hip ( p < 0.001, η p 2 = 0.933), ankle-ankle CV ( p = 0.014, η p 2 = 0.175) during braking phase and knee–knee ( p < 0.001, η p 2 = 0.837), ankle-ankle CV during propulsive phase ( p < 0.001, η p 2 = 0.511). Walking speed differentially affected CV without showing a consistent pattern. Specifically, the CV of preferred speed was the greatest for hip-knee during propulsive phase ( p = 0.011) and ankle-ankle during braking phase ( p < 0.012), while the CV of fast walking was the greatest for knee–knee during propulsive phase ( p = 0.006). Conclusion Frail elders exhibited greater endpoint variability but smaller CV, especially interlimb CV. During preferred speed walking, frail and pre-frail elders may demonstrate more flexible distal joint coordination, while rigid distal joint coordination during braking phase may increase instability risks during fast walking. This study used a cross-sectional design with a limited sample; future longitudinal studies are needed for verification, and more gait parameters and population differences should be explored.