Ankle power biofeedback attenuates the distal-to-proximal redistribution in older adults

Abstract

Background: Compared to young adults, older adults walk slower, with shorter strides, and with a characteristic decrease in ankle power output. Seemingly in response, older adults rely more than young on hip power output, a phenomenon known as a distal-to-proximal redistribution. Nevertheless, older adults can increase ankle power to walk faster or uphill, revealing a translationally important gap in our understanding.

Research question: Our purpose was to implement a novel ankle power biofeedback paradigm to encourage favorable biomechanical adaptations (i.e. reverse the distal-redistribution) during habitual speed walking in older adults.

Methods: 10 healthy older adults walked at their preferred speeds while real-time visual biofeedback provided target increases and decreases of 10 and 20% different from preferred ankle power. We evaluated the effect of changes in ankle power on joint kinetics, kinematics, and propulsive ground reaction forces. Pre and post overground walking speed assessments evaluated the effect of increased ankle power recall on walking speed.

Results: Biofeedback systematically elicited changes in ankle power; increasing and decreasing ankle power by 14% and 17% when targeting ±20% different from preferred, respectively. We observed a significant negative correlation between ankle power and hip extensor work. Older adults relied more heavily on changes in ankle angular velocity than ankle moment to modulate ankle power. Lastly, older adults walked almost 11% faster when recalling increased ankle power overground.

Significance: Older adults are capable of increasing ankle power through targeted ankle power biofeedback - effects that are accompanied by diminished hip power output and attenuation of the distal-to-proximal redistribution. The associated increase in preferred walking speed during recall suggests a functional benefit to increased ankle power output via transfer to overground walking. Further, our mechanistic insights allude to translational success using ankle angular velocity as a surrogate to modulate ankle power through biofeedback.

Keywords: Elderly; Gait; Hip; Plantarflexor; Push-off.

Figure 1.

Real-time inverse dynamics and ankle power biofeedback paradigm. A surrogate inverse dynamic model of the shank and foot estimated, in real-time, the instantaneous ankle moment and angular velocity, which we then used to estimate step-by-step peak ankle power (P_A). Representative raw data from a single stance phase shown. Grey dots represent group mean (±SD; n=10) of the real-time estimate of P_A versus the post-processed full inverse dynamic estimate of P_A alongside their respective % changes. These data demonstrate the efficacy of the biofeedback paradigm in eliciting predictable changes in P_A.

Figure 2.

A) Group mean (n=10) hip and ankle joint powers plotted against % stride during normal walking (black lines) and when modulating peak ankle power in response to P_A biofeedback. Shaded areas represent positive work used for linear regressions. Main Effect p-value and ${\eta }_P^2$ displayed for reference. Light and dark blue lines correspond to 10% and 20% target increases in ankle power, respectively. Light and dark red lines correspond to 10% and 20% target decreases in ankle power, respectively. Dashed grey lines represent reference data from young adults walking normally. B) Linear regression comparing individual subject changes in peak ankle power (P_A) and changes in hip or ankle positive extensor work. Grey dots represent individual subject average change in positive work, calculated as the positive area under the joint power curve during joint extension, compared to individual subject average change in P_A for each biofeedback trial relative to values from preferred.

Figure 3.

A) Group mean (n=10) ankle moment and angular velocity (ω) plotted against % stride during normal walking (black lines) and when modulating peak ankle power in response to P_A biofeedback. Main Effect p-value and ${\eta }_P^2$ displayed for reference. Light and dark blue lines correspond to 10% and 20% target increases in ankle power, respectively. Light and dark red lines correspond to 10% and 20% target decreases in ankle power, respectively. Dashed grey lines represent reference data from young adults walking normally. B) Linear regression comparing individual subject changes in peak ankle power (P_A) and changes in peak ankle moment and angular velocity. Grey dots represent individual subject average change in peak ankle moment and angular velocity, compared to individual subject average change in P_A for each biofeedback trial relative to values from preferred.

Figure 4.

A) Group mean (n=10) propulsive ground reaction force plotted against % stride during normal walking and when modulating peak ankle power in response to P_A biofeedback. Shaded areas represent propulsive impulse used in linear regression. Main Effect p-value and ${\eta }_P^2$ displayed for reference. Light and dark blue lines correspond to 10% and 20% target increases in ankle power, respectively. Light and dark red lines correspond to 10% and 20% target decreases in ankle power, respectively. Dashed grey lines represent reference data from young adults walking normally. B) Linear regression comparing individual subject changes in peak ankle power (P_A) and changes in peak propulsive force and propulsive impulse. Grey dots represent individual subject average change in peak propulsive force and propulsive impulse, calculated as the positive area under the anterior GRF curve during stance, compared to individual subject average change in P_A for each biofeedback trial relative to values from preferred.

Figure 5.

Group mean (n=10) hip and ankle angle plotted against % stride during normal walking and when modulating peak ankle power in response to P_A biofeedback. Light and dark blue lines correspond to 10% and 20% target increases in ankle power, respectively. Light and dark red lines correspond to 10% and 20% target decreases in ankle power, respectively. Dashed grey lines represent reference data from young adults walking normally. Main Effect p-value and ${\eta }_P^2$ displayed for reference.