Effects of age and speed on the ankle–foot system’s power during walking

Abstract

Structural and functional changes in the foot have been associated with age-related changes in gait mechanics, but walking speed may be a confounding factor in this relationship. The aim of this study was to investigate the effect of aging and speed on the ankle–foot power output during level walking. The effects of speed and aging on features of the mechanical power and work of the ankle and foot were quantified with a gait analysis of 24 young and 16 older individuals walking at different speeds. We observed gait speed having a significant effect on all the investigated features: peak power and positive and negative work of the ankle, foot, and sum of the ankle and foot (average effect size: 0.64 ± 0.22, from 0.26 to 0.87). We observed age having no effect on these same features (average effect size: 0.23 ± 0.12, from 0.03 to 0.39), with the exception of age’s effect when combined with speed on the negative work of the foot. We performed additional analysis to illustrate how the speed can become a confounding factor to the understanding of the age effect on the gait biomechanics. Based on the influence of gait speed on the mechanical power of the ankle–foot system, it is essential that studies control for the effect of gait speed if there is interest in understanding age-related effects, particularly when studying frail older individuals.

Reassessing the Role of Foot Power in Human Gait

“…Although our average falls outside of the first standard deviation, we believe our results are aligned with this study. Previous studies 11,12 and a preliminary analysis on an additional dataset (Supplemental S2) show that net work is closely related to speed. The pediatric sample walked at 1.30 ± 0.16 m/s while our sample walked at 1.58 ± 0.14 m/s.…”

“…The foot's function is important, for example when its mobility is limited the metabolic cost of running increases 1 . The tissues spanning the longitudinal arches absorb power during the first half of stance, as the arches flatten, and generate power during push-off, as the arches recoil [2][3][4][5][6][7][8][9][10][11][12][13][14][15] . The timing of positive power production implies that arch recoil directly propels the body's center of mass during locomotion by lifting the talus forward and upward 1,2,16 ; however, a recent study that focused on the kinematics of the longitudinal arch argued that if the foot remained rigid, the body's centre of mass would be higher and more forward compared to when the arch recoiled (Figure 1a) 17 In what we call the "arch recoil-upright gait hypothesis", arch recoil during propulsion supports ankle function by keeping the talocrural surface level, allowing the tibia (and the body) to remain more upright 17 .…”

Mechanics and Energetics of Human Feet: A Contemporary Perspective for Understanding Mobility Impairments in Older Adults

“…During level-ground walking at a constant speed, young adults typically perform more negative work (i.e., energy absorption) than positive work (i.e., energy return or generation), thereby losing mechanical energy each step. Comparatively, feet in older adults lose even more energy [6,7], due to both a greater negative work and a reduced positive work. Moreover, this energy loss in older adults is exacerbated when walking fast or against impeding forces that challenge the propulsion [6].…”

“…While many studies involving older adults have examined ankle kinetics, kinematics and some aspects of foot mechanics (e.g., kinematics, plantar pressure) [5], until recently, there were relatively few studies investigating mechanical energetics in asymptomatic feet in older adults [6,7]. During level-ground walking at a constant speed, young adults typically perform more negative work (i.e., energy absorption) than positive work (i.e., energy return or generation), thereby losing mechanical energy each step.…”

“…While these studies serve as an important launching point to understand the mechanical behavior of foot structures, the mechanisms of energy loss within the feet of older adults are currently unclear-for example, whether the energy loss is due in part to abnormal muscle activation or strength and/or to alterations in structural properties (e.g., passive tissues or bone morphology). Furthermore, our current understanding of foot function in older adults is limited to mostly level-ground walking [6,7], and much is unknown about how older adults adapt their foot mechanics when tasked with activities that require net energy dissipation (e.g., walking downhill, stair descent, gait termination) or net energy generation (e.g., walking uphill, stair ascent, gait initiation).…”