Carrying children, groceries, and water across varying terrain: Changes in gait and comfortable walking speed.

Background: Carrying items of substantial weight and value in one's arms while traversing challenging terrain is a common task that requires considerable care. Carrying valuable (e.g., child) or variable (e.g., water) items, compared to stable ones (e.g., groceries) demands increased coordination, and is likely to lead to slower comfortable walking speed (CWS) and altered gait mechanics, especially on difficult terrain.

Research Question: How are gait parameters altered by carrying items of substantial weight and varying value and dynamics across more and less demanding terrain?

Methods: In two experiments, participants carried their child, an equally weighted sack of groceries, or an open bucket of water in the same manner across level floor and across uneven stairs of varying heights with gaps between them. Kinematics were assessed for both terrains; kinetics were measured for one step up and one step down on stairs.

Results: Mixed models ANOVAs with repeated measures revealed that CWS on uneven stairs was approximately 65 % of CWS for level floor, regardless of the item carried. Step-to-step coefficients of variation for step length and CWS were also greater. Water was carried most slowly, with shorter steps on level floor and reduced accelerations on uneven stairs. CWS with children and groceries did not differ.

Significance: Carrying items of weight and worth with varying dynamics across more and less challenging terrain illustrates the ecological complexity of walking. Terrain requiring greater flexibility, strength, and coordination reduced CWS substantially, a complexity-speed tradeoff. More variable, difficult to control items altered CWS and other gait patterns regardless of terrain difficulty, suggesting terrain and item dynamics contributed independently to gait adjustments. More valuable items were not carried more slowly than less valuable ones. Carrying tasks deserve greater attention in research and clinical assessment.