Muscle force responses during initial-contact gait perturbations and recovery steps

Responses to gait perturbations are critical for maintaining dynamic stability and preventing falls, yet muscle-level mechanisms underlying these responses remain insufficiently understood, particularly during the initial contact (IC) phase.

How do individual lower-limb muscle forces adapt during perturbations at IC and in the subsequent recovery step?

Twenty-one healthy young women walked on a dual-belt treadmill while perturbations were induced via sudden belt deceleration at IC. Motion capture and ground reaction force data were processed in OpenSim to estimate muscle forces using static optimization. Peak muscle forces (PMF) during perturbed and recovery steps were compared with normal gait using Wilcoxon tests and subsequent FDR correction.

During the perturbed step, PMFs increased significantly in 8 of 30 muscles. Following FDR correction, significant differences remained for five muscles, primarily involving proximal and biarticular muscles (e.g., biceps femoris, gastrocnemius, gluteus medius, piriformis, and adductor magnus), indicating a multi-joint stabilization strategy. During the recovery step, several muscles demonstrated increased PMFs, however none remained significant after FDR correction.

Gait perturbations at IC elicit increased involvement of a limited set of key stabilizing muscles, particularly across the hip, knee, and ankle joints. While recovery-step adaptations were observed, they should be considered exploratory due to the lack of statistical significance following correction for multiple comparisons. These findings provide novel insight into muscle-level mechanisms of balance recovery and may inform rehabilitation strategies targeting fall prevention.