Left ventricular size and systolic function in Thoroughbred racehorses and their relationships to race performance.

This research seeks to establish the correlation between the size and functionality of the left ventricle in Thoroughbred horse hearts and their performance in racing. The studies indicate a clear relationship whereby horses with greater left ventricular size performed better in longer races, substantiating the first firm evidence of cardiac size influencing athletic performance in mammalian running athletes.

Study Purpose and Hypothesis

• The research was primarily aimed at analyzing the impacts of cardiac size, particularly the left ventricle, on the racing performance of Thoroughbred horses.
• In light of existing knowledge regarding varying heart morphology depending on sports-specific endurance in human athletes, the hypothesis of the study was that equine heart morphology would vary among trained horses based on the type of race, and that elite performers would exhibit the largest left ventricular sizes.

Methodology

• An extensive sample of 482 race-fit Thoroughbreds that participated in either flat (1,000-2,500 m) or jump racing (3,200-6,400 m) was used in the study.
• Echocardiography was utilized in examining the horses’ hearts, concentrating on the left ventricle’s size and function.
• These measurements were adjusted according to body weight and sex to ensure a fair comparison.

Findings

• Horses involved in jump racing over fixed fences presented larger body weight and sex-adjusted measures of left ventricular size than those running shorter distances on the flat. The variation in size ranged between 8 and 16%.
• This suggests that distinct differences in training and competition lead to suitable cardiac adaptations in relation to the endurance element of the horses’ event.
• The research also revealed a robust association between derived left ventricular mass and quality rating in horses participating in longer jump races, with the statistical significance marked at P < or = 0.001.
• The correlation was less prominent for horses in flat races. On the contrary, left ventricular ejection fraction and left ventricular mass combined were positively associated with race rating in older flat racehorses running across different distances.
• These combined aspects explained between 25-35% of overall variation in performance and were also closely linked to performance in longer jump races, accounting for 23% of the variance.

Conclusion

• This study presents direct evidence that cardiac size, or more precisely, the size of the left ventricle, influences athletic performance amongst mammalian running athletes; in this case, Thoroughbred racehorses.
• The findings confirm that the heart, determining stroke volume and maximum O(2) uptake in mammals, plays a tangible role in influencing the racing capabilities of these horses.
• This has implications for understanding the physical factors contributing to equine performance, with potential impacts on training and breeding practices.