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

RMS acceleration at the head and lower trunk in the anterior-posterior direction increased significantly at high walk ratios (slower cadence) and decreased significantly at low walk ratios (faster cadence) compared to preferred walk ratio.

• Twenty healthy participants walked at preferred and unnatural walk ratios at constant speed
• Unnatural walk ratios comprised 6 cadences: ±10%, ±15%, and ±20% of preferred cadence
• Shock absorption was evaluated using root mean square acceleration at the head (RMSH) and lower trunk (RMST)
• Changes in RMSH and RMST in the AP direction at high WRs were significant at p < 0.05
• Changes in RMSH and RMST in the AP direction at low WRs were significant at p < 0.05

The attenuation coefficient from lower trunk to head in the anterior-posterior direction was significantly decreased at high walk ratios compared to the preferred walk ratio.

• The attenuation coefficient represents the reduction of acceleration amplitude from lower trunk (RMST) to head (RMSH)
• Decrease in attenuation coefficient at high WRs was significant at p < 0.05
• This indicates reduced shock absorption capacity of the trunk at slower cadences with longer step lengths
• No significant decrease in attenuation coefficient was reported for low WRs

Average negative power of flexion-extension torque at the trunk joint had a significant negative correlation with lower trunk RMS acceleration in the anterior-posterior direction.

• The correlation between average negative power of trunk flexion-extension torque and RMST in the AP direction was significant at p < 0.001
• Negative power of trunk flexion-extension torque increased in response to increases in RMST in the AP direction
• This relationship suggested that trunk flexion-extension torque plays a role in shock absorption during walking
• Both trunk joint torque and power were measured as part of the kinetic analysis

The trunk has a limited shock absorption capacity, such that head acceleration in the anterior-posterior direction was more pronounced at high walk ratios despite increased trunk energy absorption.

• At high walk ratios (longer step length, slower cadence), RMSH in the AP was more pronounced
• Although negative power of trunk flexion-extension torque increased with higher RMST, this was insufficient to prevent elevated head acceleration
• The primary function of shock absorption during walking is performed by the legs, with the trunk contributing additionally
• The limitation of the trunk's shock absorption capacity was identified as a key factor in the elevated RMSH at high WRs

The study design involved healthy participants walking at a constant speed while varying only the walk ratio through manipulated cadences.

• Sample size was 20 healthy participants
• Seven walking conditions were tested: preferred WR and six unnatural WRs
• Cadence was varied at ±10%, ±15%, and ±20% of preferred cadence while speed was held constant
• Walk ratio was defined as step length divided by cadence
• Acceleration was measured at both the head and lower trunk segments