Acquisition of mechanical energy directly contributing to sideward propulsion in sidestep cutting manoeuvre

Humans seldom perform steady-state forward locomotion and often change locomotive direction through non-forward propulsion. Such manoeuvrability is essential for humans; however, unsteady-locomotion mechanics are understood less than steady-state locomotion because of the difficulty in research on unsteady locomotion with a wide range of variations. Here we show the body sideward propulsion mechanism in a sidestep cutting manoeuvre. We analysed the motion and ground reaction force of 10 males during the stance phase in 90° sidestep cutting with maximal efforts and determined the segmental components to the changes in the mediolateral-kinetic (E_ML), anteroposterior-kinetic (E_AP), and superoinferior-kinetic plus gravitational-potential energies (E_SI). The medial velocity and E_ML increased from the beginning to the end of the stance. The stance-leg shank rotation increased E_ML and decreased E_AP(early stance: 0.54 ± 0.17 and -1.49 ± 0.59 J/kg, late stance: 0.25 ± 0.14 and - 0.40 ± 0.17 J/kg), even while the knee and ankle work outflowed energy from the shank. The shank rotation induced over half the total increase in E_ML during the early stance (58 ± 7%). The stance-leg thigh rotation increased E_ML and decreased E_AP (early stance: 0.28 ± 0.12 and -0.26 ± 0.15 J/kg, late stance: 1.43 ± 0.26 and -0.47 ± 0.13 J/kg). We added the transformation from E_AP to E_ML by the shank and thigh rotations in the transverse plane to the sideward propulsion mechanisms, similar to the transformation from E_AP into E_SI in running single-leg jumps in a previous study. Coupled with previous studies, we prove the commonality in propulsion mechanisms across non-forward locomotion modes with different objective directions, which bridges the knowledge between unsteady locomotion modes.