Metabolic cost, mechanical work, and efficiency during walking in young and older men

TLDR

In healthy older men, thigh co‑activation correlates with an elevated metabolic cost of walking that is not explained by increased whole‑body mechanical work. The study investigates whether mechanical work, efficiency, and antagonist muscle co‑activation explain the elevated metabolic cost of walking in older adults. The authors measured metabolic, mechanical, and electromyographic variables in age‑matched young and older men walking at four treadmill speeds, finding a 31 % higher net metabolic cost in older adults. Older adults maintained the pendulum‑like exchange of mechanical energy but did not increase total mechanical work; however, their efficiency was 17 % lower and thigh antagonist co‑activation was 31 % higher, partially explaining the elevated metabolic cost.

Abstract

To investigate mechanical work, efficiency, and antagonist muscle co-activation with a view to better understand the cause of the elevated metabolic cost of walking (C(W)) in older adults.Metabolic, mechanical and electromyographic measurements were made as healthy young (YOU; n = 12, age = 27 +/- 3 years) and older (OLD; n = 20, age = 74 +/- 3 years) men of equivalent body mass and leg length walked on a treadmill at four speeds (ranging from 0.83 to 1.67 m s(-1)].Net (above resting) C(W), determined by indirect calorimetry was 31% higher (average across speeds) in OLD (P < 0.05). The integrity of the passive pendulum like interchange of mechanical energies of the centre of mass (COM(B)), an energy-saving mechanism, was maintained in OLD. Furthermore, total mechanical work, determined from fluctuations in mechanical energy of COM(B) and of body segments relative to COM(B), was not significantly elevated in OLD. This resulted in a lower efficiency in OLD (-17%, P < 0.05). Co-activation, temporally quantified from electromyography recordings, was 31% higher in OLD for antagonist muscles of the thigh (P < 0.05). Thigh co-activation was moderately correlated with C(W) at three speeds (r = 0.38-0.52, P < 0.05).Healthy septuagenarians with no gait impairment have an elevated C(W) which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co-activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated C(W).