Trunk deformation in the trotting horse

Area of Science:

• Biomechanics
• Equine Locomotion
• Animal Modeling

Background:

• Traditional biomechanical models assume rigid body segments, which may not accurately represent the equine trunk.
• The trunk constitutes a significant portion of a horse's mass, making its deformation critical for locomotion analysis.

Purpose of the Study:

• To quantify errors in center of mass (CM) position due to equine trunk deformability during trotting.
• To determine the temporal patterns of these CM position errors throughout the stride cycle.

Main Methods:

• Forty skin markers were placed on the trunks of six horses, with hoof markers, and tracked using an 8-camera motion system.
• Trunk CM was calculated using both rigid body assumptions and volume-based methods to assess deformation effects.
• Horses were tested at ten different trotting velocities.

Main Results:

• The equine trunk exhibited repeatable shape changes during locomotion, leading to cyclic variations in CM position.
• Trunk deformation caused CM displacements of equal magnitude in transverse and longitudinal directions, and half that amplitude vertically.
• The magnitude of these displacements was highly dependent on the individual horse.

Conclusions:

• Equine trunk segment deformation significantly impacts CM position calculations during locomotion.
• Accounting for trunk shape changes in the horizontal plane is crucial for accurate equine locomotion modeling.
• Horse-specific variations in trunk deformation complicate the development of generalized correction algorithms.