Effects of aging on mechanical efficiency and muscle activation during level and uphill walking

Purpose: The metabolic cost of walking is greater in old compared to young adults. This study examines the relation between metabolic cost, muscular efficiency, and leg muscle co-activation during level and uphill walking in young and older adults. Procedures: Metabolic cost and leg muscle activation were measured in young (22.3 ± 3.6 years) and older adults (74.5 ± 2.9 years) walking on a treadmill at six different slopes (0.0-7.5% grade) and a speed of 1.3 m s−1. Across the range of slopes, 'delta mechanical efficiency' of the muscular system and antagonist muscle co-activation were quantified. Main findings: Across all slopes, older adults walked with a 13-17% greater metabolic cost, 12% lower efficiency, and 25% more leg muscle co-activation than young adults. Among older adults, co-activation was weakly correlated to metabolic cost (r = .233) and not correlated to the lower delta efficiency. Conclusion: Lower muscular efficiency and increased leg muscle co-activation contribute to the greater metabolic cost of uphill slope walking among older adults but are unrelated to one another.