Speed and incline during thoroughbred horse racing: racehorse speed supports a metabolic power constraint to incline running but not to decline running

Abstract

We used a radio tracking system to examine the speed of 373 racehorses on different gradients on an undulating racecourse during 33 races, each lasting a few minutes. Horses show a speed detriment on inclines (0.68 m · s(-1) · 1% gradient(-1), r(2) = 0.97), the magnitude of which corresponds to trading off the metabolic cost (power) of height gain with the metabolic cost (power) of horizontal galloping. A similar relationship can be derived from published data for human runners. The horses, however, were also slower on the decline (-0.45 m · s(-1) · 1% gradient(-1), r(2) = 0.92). Human athletes run faster on a decline, which can be explained by the energy gained by the center of mass from height loss. This study has shown that horses go slower, which may be attributable to the anatomical simplicity of their front legs limiting weight support and stability when going downhill. These findings provide insight into limits to athletic performance in racehorses, which may be used to inform training regimens, as well as advancing knowledge from both veterinary and basic science perspectives.

Fig. 1.

Contour plot of Goodwood racecourse. Racetrack is overlaid onto a contour plot from GPS survey. Color represents vertical height whereas spacing of the contour lines indicates gradient. Race start positions for races of different lengths (in miles and furlongs) are indicated, with all races finishing at the same point in front of the grandstand. One furlong is approximately equal to 201 m.

Fig. 2.

Racehorse speeds at different gradients during racing on Goodwood racecourse for 33 race starts (373 horses). Color represents percentage of race complete [current time point (s)/total race time(s)]. A decrease in speed on both inclines and declines during racing is shown.

Fig. 3.

Regression lines derived from Fig. 1, showing average top racehorse speeds at different gradients during racing. Lines are fitted to the mean of the top 10% of speeds, with horses being represented equally. Error bars represent the SEM.

Fig. 4.

Regression line for incline data from Fig. 3 shown with regression line derived from data by Eaton et al. (4). Comparison shown between speed data from this study and metabolic data from a previous study in relation to incline gradients. Similarity of the gradients of these 2 lines supports the theory of constant metabolic effort.