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.