A Thoroughbred’s cardiovascular fitness on the racetrack can be estimated by his heart rate at the trot on a mechanical walker, suggests a recent report.
The study, carried out by private research and consultation firm, Kentucky Equine Research (KER), monitored the heart-rate velocity relationship and fitness of two groups of horses – young and mature – as they exercised on both mechanical walkers and a racetrack for four weeks.
Ryon Springer, the study’s lead author, presented his team’s findings to delegates of the 2021 Equine Science Society Virtual Symposium last spring. He said previous research has correlated cardiovascular fitness with racing performance in Thoroughbreds and has also indicated heart rate is linear, not only with velocity (speed) at multiple ages, but also with Thoroughbreds on treadmills and on racetracks.
In addition, V200, the velocity (V) a horse reaches when his heart rate is 200 beats per minute, is “highly reproducible as well as a reliable cardiovascular measurement of fitness between the exercise protocols on a treadmill as well as on the racetrack,” said Springer. (Essentially, V200 is a useful parameter to compare a horse’s fitness against his development or that of other horses.) V200 is also found to increase with age and the cardiovascular fitness of the horse past studies have shown.
Springer, who was interning at KER when he worked on this project and graduated last May from the animal sciences program at Tarleton State University in Texas, said the study had three objectives.
1. To detect a difference in heart rate at a trot on the walker between mature and young horses. The hypothesis was the latter group’s heart rate would be higher.
2. To detect a difference in the cardiovascular fitness on the racetrack between the groups. The researchers thought the mature group would demonstrate greater fitness.
3. To determine whether – and hold up the hypothesis that – the trotting heart rate (termed HRtrot) on the walker could predict cardiovascular fitness on the racetrack.
Each group consisted of five horses. The young horses were two- to three-year-olds. Four had been prepped for two-year-olds in training sales. The mature horses ranged in age from five to nine and all had been in race training for more than a year. Over the four weeks, the horses were exercised three days a week each on a mechanical walker and on the track. They had one rest day.
The mechanical walker protocol consisted of a:
- Five-minute warmup walk at 1.4 metres per second;
- 15-minute trot at 2.7 metres per second;
- Five-minute cool down walk at 1.4 meters per second.
Horses wore commercial equine heart-rate monitors fitted to a belt worn around the barrel. Researchers used a smartphone fitness app to take the average heart rate during the final 10 minutes of the trot. They chose this period of the workout as it allowed the horses to settle into the trot after transitioning from the walk.
For the racetrack workout protocol, horses wore the heart-rate monitors. The equine fitness app – which was on a smartphone carried by the exercise rider – determined heart-rate-velocity relationship. Fitness was assessed by velocities calculated at the following heart rates – V160 V180 and V200.
After statistical analysis, the researchers’ hypothesis that younger horses would have a higher trotting heart rate on the mechanical walker held up. The younger horses’ beats per minute (bpm) averaged 77.3 ± 3.8 compared to the mature horses at 87.6 bpm ± 4.5 bpm. These results are “similar to studies concerning aerobic cardiovascular fitness in other breeds and disciplines,” notes Springer.
At the track, the researchers first looked at the average distance travelled between the groups, and this was “significantly different,” he says. Mature horses were exercised for 4.1 ± 0.5 kilometres/session versus the young horses at 3.6 ± 0.4 kilometres/session.
They then examined the time at which the heart rate was greater than 160 beats per minute. (What the researchers set as the anaerobic threshold – which is, more or less, the highest exercise intensity that can be sustained before aerobic systems are overwhelmed.) The mature horses tended to be lower in this category at 2.7 ± 1.3 minutes, while the young horses averaged 3.3 ± 0.8 minutes. The maximum speed was the same for both groups at about 11 metres/second. Cardiovascular fitness on the racetrack was higher in the mature horses at V160, V180 and V200. They also found that HRtrot (if you recall, that’s the trot heart rate on the mechanical walker) and V160, V180 and V200 were negatively correlated in both groups.
These results suggest:
- HRtrot may decrease with respect to age or previous training intensity.
- V160, V180 and V200 may increase with respect to age or training intensity.
- HRtrot’s negative correlation to V160, V180 and V200 suggests cardiovascular fitness under saddle may be estimated from heart rate collected at a trot on a mechanical walker. (A negative correlation means that as one variable increases, the other decreases. In this case, as heart rate at a trot on a mechanical walker decreases, V160, V180 and V200 increases and vice versa.)
Advises Springer, “Future investigation should actually look into whether differences in this study were due to the age of the horse or the cardiovascular fitness between the groups and this is due to previous exercise protocols being different for these horses prior to coming into this study.”