Stable and Unstable Load Carriage Effects on the Postural Control of Older Adults

The aim of this study was to investigate the effects of backpack load carriage on quiet standing postural control and limits of stability (LOS) of older adults. Fourteen older adults (65 [6] y) performed quiet standing and a forward, right, and left LOS test in 3 conditions, unloaded, stable, and unstable backpack loads while activity of 4 leg muscles was recorded. Stable and unstable loads decreased postural sway (main effect η ² _p = .84, stable P < .001, unstable P < .001), mediolateral (main effect η ² _p = .49, stable P = .002, unstable P = .018) and anterior–posterior (main effect η ² _p = .64, stable P < .001, unstable P = .001) fractal dimension, and LOS distance (main effect η ² _p = .18, stable P = .011, unstable P = .046) compared with unloaded. Rectus femoris (main effect η ² _p = .39, stable P = .001, unstable P = .010) and gastrocnemius (main effect η ² _p = .30, unstable P = .027) activity increased in loaded conditions during LOS and quiet standing. Gastrocnemius–tibialis anterior coactivation was greater in unstable load than stable loaded quiet standing (main effect η ² _p = .24, P = .040). These findings suggest older adults adopt conservative postural control strategies minimizing the need for postural corrections in loaded conditions. Reduced LOS may also increase fall risk when carrying a load. However, there was no difference between unstable and stable loads for postural control variables.