Muscle mechanical work and elastic energy utilization during walking and running near the preferred gait transition speed.

Mechanical and metabolic energy conservation is considered to be a defining characteristic in many common motor tasks. During human gait, the storage and return of elastic energy in compliant structures is an important energy saving mechanism that may reduce the necessary muscle fiber work and be an important determinant of the preferred gait mode (i.e., walk or run) at a given speed. In the present study, the mechanical work done by individual muscle fibers and series-elastic elements (SEE) was quantified using a musculoskeletal model and forward dynamical simulations that emulated a group of young healthy adults walking and running above and below the preferred walk-run transition speed (PTS), and potential advantages associated with the muscle fiber-SEE interactions during these gait modes at each speed were assessed. The simulations revealed that: (1) running below the PTS required more muscle fiber work than walking, and inversely, walking above the PTS required more muscle fiber work than running, and (2) SEE utilization in running was greater above than below the PTS. These results support previous suggestions that muscle mechanical energy expenditure is an important determinant for the preferred gait mode at a given speed.