Goats decrease hindlimb stiffness when walking over compliant surfaces

Area of Science:

• Biomechanics
• Animal Locomotion
• Comparative Physiology

Background:

• Leg stiffness is a key parameter in terrestrial locomotion, reflecting how a limb deforms under load.
• Understanding how animals adapt leg stiffness to varied substrates is crucial for characterizing gait mechanics.

Purpose of the Study:

• To investigate how goats modulate hindlimb stiffness in response to surfaces of differing stiffness.
• To identify the specific joints and muscles responsible for these stiffness adjustments in goats.

Main Methods:

• Recorded ground reaction forces and hindlimb marker trajectories of goats walking on rigid, rubber, and foam surfaces.
• Utilized inverse dynamics to estimate net joint moments, power, and work.
• Calculated hindlimb and individual joint stiffness from force-length and moment-angle relationships.

Main Results:

• Goats significantly decreased hindlimb stiffness on more compliant surfaces (P<0.002).
• Hip and ankle joints were identified as primary contributors to stiffness modulation.
• Goat behavior differs from human running, where leg stiffness typically increases on compliant surfaces.

Conclusions:

• Goats actively modulate hindlimb stiffness to adapt to surface compliance during locomotion.
• Hip and ankle musculature play a critical role in this adaptive mechanism.
• This study reveals distinct quadrupedal strategies for navigating variable terrain compared to human bipedal locomotion.