Age-associated changes in lower limb weight-bearing strategy during walking.

BACKGROUND: As people age there is a proximal shift of joint moment generation from ankle plantarflexion and knee extension toward hip extension and flexion moments. This age-related redistribution has been documented in the context of propulsive force generation during the push-off phase with less evidence in the context of weight bearing. Additionally, these sagittal plane joint moments have been a primary focus of studies though the hip frontal plane moment also contributes to vertical support but has received less attention. Furthermore, how aging affects the relationships between changes in sagittal and frontal joint moments and changes in vertical support force as a function of walking speed remains unclear RESEARCH QUESTION: How does aging affect the contributions of sagittal and frontal plane joint moments to weight-bearing across different walking speeds? METHODS: Gait analysis was performed on 24 young and 17 healthy older subjects walked on the treadmill at their preferred and 30 % faster speeds. Stepwise linear regression analysis was performed to determine the joint moments that predict the peak amplitudes of the vertical ground reaction force (VGRF) across different walking speeds. RESULTS: Hip abduction and knee extension moments were the primary contributors to leading limb weight-bearing in young, whereas hip extension moment was the primary contributor in older adults. Ankle plantarflexion moment was the main contributor to trailing limb weight-bearing in young and hip flexion moment was the main contributor in older adults. From preferred to faster walking speed changes in knee extension moment were the primary contributor to changes in the trailing limb weight-bearing in young whereas changes in hip extension moment were the primary contributor in olderadults. SIGNIFICANCE: These findings suggested that older and younger adults used different joint moment contributions to produce leading limb and trailing limb vertical support forces across different walking speeds.

Biomechanical mechanism of peak braking force modulation during increased walking speed in healthy young adults.

Walking speed is an important indicator of health and function across a variety of populations. Faster walking requires both larger propulsive and braking forces, thoughof the two, propulsive force generation has been far more extensively investigated. This study seeks to develop and validatea quasi-static biomechanical model of braking forcein healthy individualsacrossself-selected and fast walking speeds. Additionally, the model was used to quantify the relative contribution of knee extension torque versus leading limb angle (LLA) to changes in braking force across walking speeds. Kinetic and kinematic data from 44 young healthy participants walking overground at 2 different speeds were analyzed. The model prediction correlated strongly with actual braking force production at the self-selected speed (r = 0.9; p < 0.01), the fast speed (r = 0.97; p < 0.01) andthe change between speeds (r = 0.95, p < 0.01). On average, increases in knee extension torque and the LLA contributed 132 % and 12 %, respectively, to increases in peak braking force (PBF). Increases in the external lever arm length operated to reduce predicted braking force by 56 %. The results highlight the importance of rapid eccentric contraction of the knee extensors during braking force modulation in healthy gait.