Kinetics of the trunk in association with the attenuation of upper body acceleration during walking

The acceleration amplitude of body segments during walking is reduced from the ankle to the head. The primary function of shock absorption is performed by the legs, with the trunk also contributing. The aim of this study was to investigate the capability of the trunk to absorb shock during walking. Twenty healthy participants walked at their preferred and unnatural walk ratio (WR) (step length/cadence) at a constant speed. The unnatural WRs comprised 6 cadences (±10%, ±15%, and ± 20% of preferred cadence). Shock absorption was evaluated using the root mean square acceleration at the head (RMS_H) and lower trunk (RMS_T), the coefficient of attenuation from RMS_T to RMS_H, as well as the trunk joint torque and power. RMS_H and RMS_T in the anterior-posterior direction (AP) showed a significant increase (p < 0.05) in high WRs (slower cadence) and a significant decrease (p < 0.05) in low WRs (faster cadence) compared to the preferred WR. The attenuation coefficient in the AP was significantly decreased in high WRs than in the preferred WR (p < 0.05). The average negative power of the flexion-extension torque at the trunk joint had a significant negative correlation (p < 0.001) with RMS_T in the AP. These results suggested that trunk flexion-extension torque played a role in the shock absorption, and this negative power increased in response to an increase in RMS_T in the AP. However, given the limitation of the trunk's shock absorption capacity, the RMS_H in the AP was more pronounced at high WR.