Neuromechanical Bases for the Increased Energy Cost of Walking in Aging

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

PROJECT SUMMARY Age-related mobility loss is a major public health concern due to its profound negative effect on health and quality of life. An increased energetic cost to perform activities such as walking has been well-documented in older adults and may be a primary contributor to age-related mobility loss. However, the mechanisms that lead to increased energy cost of walking (CoW) remain unclear. The overall aim of this proposal is to determine how age-related changes in gait strategy combine with contractile and bioenergetic deficits in 3 major locomotory muscle groups to increase CoW. Our working hypothesis is that proximal extensor muscle weakness in older adults requires relatively greater muscle activation and thus greater use of these muscles to produce the joint moments needed for walking. This greater “neuromechanical demand” would increase muscle energy needs, translating to a greater CoW. Robust evidence indicates older muscles are generally smaller and thus weaker than young muscles, but there is also evidence that declines in muscle strength may exceed the loss of muscle size in old age. We will address missing knowledge on relative changes in specific torque (strength/size) of 3 locomotory muscle groups, the consequences on neuromechanical demand and CoW, and the potential effects of biological sex on these outcomes (Aim 1). The gait strategy used by older adults may exacerbate the problem of greater CoW. However, comprehensive studies are lacking about the impact of joint work distribution (e.g., gait strategy) on the neuromechanical demands of proximal muscles, which may experience a larger decrease in specific torque, and the subsequent consequences for CoW (Aim 2). Finally, exacerbation of greater CoW in old may occur due to an intrinsic muscle bioenergetic deficit, quantified as muscle metabolic economy (energy used for a given contraction relative to muscle size). We expect lower metabolic economy in older than younger muscle, and consequently even greater CoW (Aim 3). Data will be collected for 30 young (25-40 y) and 60 older (65-85 y) community-dwelling adults. Groups will be balanced by sex to assess sex as a biological variable and habitual physical activity will be quantified using accelerometry. We will address these mechanistic hypotheses by measuring: neural (electromyography) and mechanical (gait analysis, dynamometry) demand during gait, muscle specific torque (dynamometry, magnetic resonance imaging), and metabolic economy (magnetic resonance spectroscopy, dynamometry) in all 3 major locomotory muscle groups (hip extensor, knee extensor, plantar flexor). We will also quantify the distributions of joint work in walking (gait analysis) and energy CoW (indirect calorimetry). The planned approach builds on our preliminary data, is novel in its assessment of both bioenergetics and biomechanics, and tightly integrates rigorous biomechanical and physiological methods to arrive at a mechanistic understanding of greater CoW in aging. The problem addressed- the role of gait mechanics in the increased CoW in older adults- tackles stated goals of the NIA, as described in this RFA.