Manual Load Carriage Impairs Compensatory Step Reactions to Recover Balance

Manual materials handling is a common occupational task associated with workplace falls. The aim of this study was to examine whether an anterior manual load impacts balance recovery via compensatory stepping. Step recovery following unpredictable perturbations to standing were compared with and without a manual load in 12 young healthy male and female adults. Recovery from forward perturbations was measured via the margin of stability during and following the step, as well as by step coordination in terms of maintaining lateral stability in shifting support between legs when stepping, along with step timing and placement. While the load did not affect forward destabilization during the step, it did delay the reversal of the falling motion after landing the foot. Moreover, the load disrupted lateral stability control such that a greater fall toward the unsupported step-leg side occurred but with no increase in step-width to compensate. Step-length was also unchanged, but the load did elicit slightly earlier step timing that in turn reduced the prestep interval to enact lateral weight shifts. These results show that a load compromises step recovery by delaying poststep restabilization and disrupting step coordination, identifying step response efficacy as a possible factor in fall risk associated with manual loads.