Gait Phase Subdivision and Leg Stiffness Estimation During Stair Climbing

Area of Science:

• Biomechanics
• Robotics
• Human Locomotion

Background:

• Leg stiffness is crucial for analyzing locomotion across various gaits like walking, running, and hopping.
• Understanding leg stiffness changes during stair ascent and descent is key to deciphering complex stair-climbing dynamics.

Purpose of the Study:

• To develop and assess a method for estimating leg stiffness during stair climbing.
• To segment the stair-climbing gait cycle based on leg stiffness characteristics.

Main Methods:

• Leg stiffness was calculated as the ratio of changes in support leg force (F_l) to changes in leg length (L_l) during the stance phase.
• Eight subjects climbed and descended an instrumented staircase at varying cadences.
• Gait cycles were subdivided using center-of-mass (CoM) work rate fluctuations and leg stiffness curve properties.

Main Results:

• The leg stiffness curve exhibited distinct linear segments with relatively constant stiffness values.
• These identified phases in the leg stiffness curve corresponded to phases determined by the CoM work rate curve.
• The force-length relationship during stair climbing was characterized by these segmented stiffness curves.

Conclusions:

• The methodology effectively characterizes leg stiffness dynamics during stair climbing.
• The identified gait phases based on leg stiffness correlate with energy expenditure phases (CoM work rate).
• Findings can guide the development of biomimetic control for lower-extremity robotic devices during stair negotiation.