Association between muscle activation and metabolic cost of walking in young and old adults.

BACKGROUND The net metabolic cost of walking (C(w)) as well as the level of neural activation of agonist and antagonist leg muscles are higher in healthy old compared with young adults. This study examined the association between C(w) and agonist muscle activity and antagonist coactivity in young and old adults. METHODS Young and old adults walked at 0.98 m/s on a treadmill set at 6% decline, level, and 6% incline, while C(w) and neural activation of leg muscles were measured. RESULTS C(w) was 7.0% (incline), 19.2% (level), and 47.3% (decline) higher in old adults (overall 18.3%). Old (67.1%) versus young (40.1%) adults activated their leg muscles 67.3% more during the gait tasks and had 152.8% higher antagonist muscle coactivation (old: 67.1%, young: 19.9%). Agonist muscle activation was unrelated to C(w) on incline, but it explained up to 42% (level), 48% (decline), and 70% (three tasks combined) of variance in C(w). Antagonist coactivation accounted for up to 41% (incline), 45% (level), 59% (decline), 39% (three tasks combined) of variance in C(w). CONCLUSIONS Age-related adaptations in the recruitment pattern of leg muscles during gait significantly contribute to the high C(w) in old adults. Clinical interventions optimizing the neural control of leg muscles during gait could reduce C(w) consequently the relative effort needed for exercise and activities of daily living in old adults.