Dynamically similar locomotion in horses.

This study delves into the idea that different sized animals can exhibit similar movements or locomotion, with focus on the domestic horse. The research outlines how different biomechanical factors can balance or compensate for size differences, allowing these animals, despite their varied sizes, to move in very similar patterns.

Research Goals

The primary goal of this research was to determine whether horses of varying sizes move in “dynamically similar” ways. This is a concept that suggests animals of different sizes can move in similar patterns if certain biomechanical factors compensate for their size differences. Predictions were made that without anything to balance for size differences, noticeable deviations (from dynamically similar locomotion) would be observed in adult horses of different sizes.

Data Collection

• Data was gathered from 21 trotting horses ranging in body mass from 86 kg to 714 kg.
• Relative stride length (RSL) and duty factor (DF) were measured from these horses.
• The data were then analyzed to predict RSL and DF at equivalent speeds, referred to as Froude numbers in biomechanics (values set at 0.5, 0.75, 1.0).

Findings

• The research found that RSL and DF at the same Froude number did not show a significant relationship with body mass. This finding led to the conclusion that different sized horses can move in dynamically similar ways at equal Froude numbers.
• Researchers also discovered that the nonlinear stress-strain relationship of tendon could help to minimize deviations from dynamic similarity, thus ‘buffering’ the impacts of variation in body mass. However, it was also concluded that this influence alone is unlikely to fully explain the research results.
• The results suggested that a ‘compensatory distortion’ might occur in horses, which would counteract the impacts of size differences. This means that other biomechanical factors could be at play, helping to balance out the effects of the size differences in these animals.

Applications of the Research

The methodology and findings of this study might be further utilized to understand the impacts of size changes within an individual during growth, and could be applied to other species as well. The research provides a better perspective on how animals move, which could be valuable in areas like veterinary science, animal sports, or even in the development of better robotic systems that mimic animal movement.