In ground force plates

Each participant performed overground walking at a self-selected speed for a Baseline condition with no added mass and for six independent added mass conditions with either a Low or High Mass Amount at one of three Mass Locations: Pelvis (+8 or +16 lb), each Thigh (+2 or +4 lb), or each Shank (+2 or +4 lb), as shown in Table 2. The condition order was randomized, and the mass was added by inserting sandbags into commercial resistance training, or weight, belts wrapped around each segment. Retroreflective markers (n = 43) were placed on each participant’s torso, pelvis, thighs, shanks, and feet (see Supplementary Table S2 and Figure S1 for marker and added mass location details). Before data collection for each condition, the participant walked for 2 min overground to acclimate to the added mass. For data collection, the participants walked along a 23 m walkway for 5 trials for each experimental condition, with each trial including 1 right leg gait cycle. During each trial, retroreflective marker trajectories were recorded at 150 Hz by a Vicon motion capture system with 8 cameras surrounding the walkway (Oxford Metrics, Oxford, UK). Two in-ground force plates located in the walkway (1500 Hz, Bertec, Columbus, OH, USA) recorded the ground reaction forces. The marker trajectories and ground reaction forces were converted into files for processing in OpenSim [31 (link),32 (link)].