Effects of trunk deformation on trunk center of mass mechanical energy estimates in the moving horse, Equus caballus.

The research focused on measuring the impact of potential distortions in a horse’s torso on the estimated location of the body’s center of mass (CM) and the resulting implications on biomechanical analyses. The primary takeaway is that while for the most part such estimates closely match reality, in certain situations, deviations in assumed body rigidity can lead to significant inaccuracies in CM estimation and associated mechanical energy calculations.

Research Methodology

• The researchers attempted to quantify the shift in the trunk’s center of mass following changes in the external shape of the torso.
• This was done by recording the kinematics of a mesh that had been placed over a horse’s torso.
• During the horse’s walk, the researchers described the variations in the shape of its trunk using a frame of reference that was fixed to the horse’s spine.
• They also examined if walking speed and individual differences played a part in these variations.
• Crucially, they determined the significance of torso deformation by calculating the potential variance in mechanical energy profiles.

Research Findings

• In most cases, any deviations in the estimated position of the horse’s torso center of mass arising from a rigid body assumption were minor along the vertical axis.
• However, noticeable discrepancies potentially affecting accurate measurement could emerge along the transverse (side to side) and longitudinal (head to tail) axes, especially at high walking speeds.
• The impact of such differences is enough to alter mechanical energy expenditure estimates by as much as one quarter (25%).
• This implies that researchers using data from horse cadavers to estimate center of mass location must account for this additional source of potential error, which differs from the measurement error of the cadaver’s center of mass.
• The study also discovered considerable variations between individuals, which adds to the complexity of theoretical correction procedures.

Suggested Further Steps

• The team proposes the use of additional markers on a horse’s torso during a gait analysis to correct the center of mass shifts experimentally.