Fall history does not affect predictive control of dynamic balance during unilateral load carriage in older adults

We investigated the effects of progressive unilateral hand load carriage on the predictive control of dynamic balance during walking in older adults with and without a recent history of falls. Thirty-one community-dwelling older adults (15 fallers, 16 non-fallers) walked at their preferred speed under six randomized conditions: no load and carrying unilateral dumbbell loads corresponding to 2-10% of body mass. Whole-body kinematics and bilateral gluteus medius electromyography were recorded. Mediolateral margin of stability (MoS) was computed using the extrapolated center of mass, both with and without inclusion of the carried load in the center of mass (COM) calculation, to probe predictive control mechanisms. When the carried load was excluded from the calculation, MoS gradually increased on the ipsilateral side and decreased on the contralateral side as the load increased. In contrast, when the load was included, MoS remained stable across all conditions. This stability was maintained through systematic, load-dependent postural adjustments, including contralateral tilt of the head and thorax and increased abduction of the contralateral shoulder. At higher load levels, these changes were accompanied by increased activation of the contralateral gluteus medius. Load carriage did not affect spatiotemporal walking parameters but reduced the shoulder range of motion differently between fallers and non-fallers. Overall, these findings indicate that predictive control of dynamic balance was preserved despite increasing unilateral loads and was unaffected by fall history. MoS maintenance was accompanied by systematic adjustments in upper-body orientation rather than by changes in lower-limb gait characteristics.