The energetics and mechanics of trunk angle during flat and inclined walking in humans

ABSTRACT During flat walking, the trunk typically maintains an upright posture. However, when walking up slopes, humans tend to increase trunk flexion. This behaviour is not easily understood as increasing trunk flexion increases the torque required at the hip joint to stop the trunk from falling forwards. In this study, we investigated how trunk flexion affected metabolic cost and mechanical work during flat and inclined walking. Seven healthy subjects walked on a flat and inclined surface while trunk flexion angle was enforced using visual feedback. We found that healthy individuals tended to walk at the trunk angle that minimizes metabolic cost, and this trunk angle increased with the incline angle of the walking surface. As trunk flexion increased, hip work rate increased whereas knee and ankle work rate decreased. This study suggests that trunk flexion angle is another feature of gait controlled to maintain energetic efficiency by altering joint level mechanics.