How does age affect leg muscle activity/coactivity during uphill and downhill walking?

Highlights ► Old adults exhibited smaller increases in medial gastrocnemius activity with steeper uphill grade than young adults. ► Old adults uniformly demonstrated greater than twice the relative gluteus maximus activity at all grades compared to young adults. ► Gluteus maximus activity approached the maximum isometric capacity of old adults at steep uphill grades. ► Neither uphill nor downhill walking affected the greater coactivation of antagonist muscles in old vs. young adults. ► Changes in muscle recruitment with age may negatively affect walking ability in old adults, particularly at steeper uphill grades.