Transverse and dorso-ventral changes in thoracic dimension during equine locomotion.

The research investigates the changes in the shape of a horse’s thorax during different types of movement and under different conditions. It found that the side of the thorax corresponding to the trailing limb changes its dimensions more significantly than the side with the leading limb, and that the speed and slope of the horse’s movement had some measurable influence on these changes.

Objective and Methodology

• The researchers wanted to understand how the shape of the horse’s thorax (chest area) alters during movement, specifically, whether there is a correlation between the changes in transverse (side-to-side) and dorso-ventral (back-to-front) dimensions, and how different factors such as the leading limb, treadmill slope, and speed impact these changes.
• To track these changes, reflective markers were placed on the horse’s thorax. The movement of these markers was then recorded using a motion capture system while the horse was trotting and cantering on a treadmill.
• Researchers manipulated the treadmill’s speed and slope, as well as the horse’s leading limb while cantering, to observe the subsequent effects on the dimensions of the thorax.

Findings

• The study found that there is a negative correlation between the changes in transverse and dorso-ventral dimensions. In simpler terms, when the width of the thorax increases, its depth tends to decrease, and vice versa.
• The strength of this negative correlation was seen to increase with speed on the side of the thorax corresponding to the trailing limb. Conversely, on the side of the leading limb, this correlation was either weakly negative or even positive.
• It was also found that the changes in the dimensions of the thorax were significantly greater on the side of the trailing limb as compared to the leading limb.
• While speed did have minor effects on these changes, inclined exercise specifically led to an increase in the width of the thorax on the trailing limb side.

Implications

• The changes in the shape of the horse’s thorax during movement are not likely to contribute significantly to the process of ventilation, and the researchers propose that the movement in the ribcage is more likely due to the motion of the forelimbs (i.e., advancing and retracting).
• The study suggests that the observed thoracic shape changes could be indicative of asynchronous ventilation of the lung lobes. This means that different parts of the lungs may not be ventilated at the same time, which could partially explain the prevalence of a condition known as exercise-induced pulmonary haemorrhage that commonly affect racehorses.