Mechanics of overground accelerated running vs. running on an accelerated treadmill

Unsteady state gait involving net accelerations has been studied overground and on a treadmill. Yet it has never been tested if and to what extent both set-ups are mechanically equal. This study documents the differences in ground reaction forces for accelerated running on an instrumented runway and running on an accelerating treadmill by building a theoretical framework which is experimentally put to the test. It is demonstrated that, in contrast to overground, no mean fore-after force impulse should be generated to follow an accelerating treadmill due to the absence of linear whole body acceleration. Accordingly, the adaptations in the braking phase (less braking) and propulsive phase (more propulsion) to accelerate overground are not present to follow an accelerating treadmill. It can be concluded that running on an accelerating treadmill is mechanically different from accelerated running overground.