Footwear and illumination modulate muscle cocontraction strategies and joint work redistribution during stair-to-ground transition.

Footwear had a more pronounced effect on lower limb biomechanics than illumination during the stair-to-ground transition.

• Twenty-four healthy adults performed stair-to-level transitions under four conditions: bright vs. dim illumination and shoed vs. barefoot.
• Analysis used two-way repeated-measures ANOVA and one-dimensional statistical parametric mapping (SPM).
• Footwear significantly affected joint moments across multiple degrees of freedom at the hip, knee, and ankle.
• Footwear effects on lower limb joint moments, negative work, and muscle activation were more pronounced compared to illumination effects.

The shoed condition increased ground reaction force loading rates and joint moments at multiple joints.

• Shoed condition increased ground reaction force loading rates during the stair-to-ground transition stance phase.
• Shoed condition increased joint moments across multiple degrees of freedom at the hip, knee, and ankle.
• The shoed condition significantly elevated knee flexion-extension and hip rotational positive work.

The barefoot condition was associated with higher midstance ground reaction forces, greater ankle plantarflexion moments, and increased muscle coactivation.

• Barefoot condition showed higher midstance ground reaction forces compared to shoed condition.
• Barefoot condition showed greater ankle plantarflexion moments during the transition step.
• Barefoot condition resulted in higher knee and ankle muscle coactivation indices.
• Barefoot condition also showed increased hip rotational negative work.

Illumination primarily affected hip flexion-extension work and knee abduction moments during the stair-to-ground transition.

• Bright illumination conditions were associated with increased hip flexion-extension negative work.
• Dim illumination conditions decreased knee abduction moments compared to bright conditions.
• Dim conditions also decreased adduction-abduction negative work at the knee.
• Illumination effects were less pronounced than footwear effects on overall lower limb biomechanics.

The study characterized biomechanics during the stance phase of the transition step from stair descent to level ground in healthy adults.

• Twenty-four healthy adults participated in the study.
• Kinematic trajectories, ground reaction forces, and electromyographic signals were recorded for the dominant side.
• Measurements were taken during the transition step's stance phase across all four experimental conditions.
• The dominant side was analyzed during the stair-to-level transition step.

Footwear cushioning fundamentally redistributes joint moments and negative work during the high-risk stair-to-ground locomotor transition.

• Shoed conditions redistributed joint loading patterns compared to barefoot conditions.
• Barefoot conditions triggered compensatory strategies including higher muscle coactivation to manage impact.
• The findings highlight how footwear-ground interaction properties affect lower limb motor control strategies.
• These results offer insights for improving footwear design for stair descent safety.