Biomechanical mechanisms for modulating stride frequency in walking.

Humans typically choose to walk at a self-selected stride frequency that minimizes their metabolic cost. However, when environmental constraints are present (e.g., icy sidewalk), they will change their stride frequency to accommodate. This study provides a comprehensive understanding of the muscle-tendon dynamics when humans walk with different stride frequencies, offering valuable insights into the biomechanics of walking. The study aimed to quantify the effect of stride frequency on the muscle-tendon forces, powers, and induced accelerations on the center of mass. Data was collected with eight subjects walking at 1.3 m/s at their self-selected stride frequency and + 20 and -20 % of their self-selected stride frequency. We used musculoskeletal modeling to compute the muscle-tendon forces and powers, and the vertical and anterior-posterior induced accelerations for nine muscle groups. When comparing stride frequency conditions using statistical parametric mapping, we found that gluteus medius, gastrocnemius, and tibialis anterior had greater forces, powers, or induced accelerations in the -20 % condition. The hamstrings, rectus femoris, and iliopsoas muscle groups had greater forces, powers, or induced accelerations in the + 20 % condition compared to self-selected frequency. The gastrocnemius played a crucial role in modulating forward acceleration across different stride frequencies, driven by changes in segment kinematics rather than changes in muscle forces. Increases in muscle force production as participants deviated from self-selected stride frequency may indicate that the preferred stride frequency of an individual minimizes the overall demand on lower limb muscles during walking. These results advance our understanding of why humans self-select certain movement patterns during gait.