The cardiovascular system is composed of the heart and blood vessels. It allows efficient blood circulation and ensures the transport of a large volume of oxygen, especially to the muscles. The volume of blood that the heart ejects at each beat during cardiac contraction (stroke volume) is more than one litre in the race horse. The weight of the heart represents about 1% of the mass of a horse during training will tend to increase its cardiac mass to the order of +15%. This improves heart capacity and allows the heart to be less tired by beating more slowly for the same amount of work.
For example, measuring the racehorse’s heart rate provides information on the fitness level and fitness training. To supply the muscles required for exercise, the main source of energy intake comes first from the breakdown of glycogen, then from the fats by oxygen if the duration of the effort exceeds several tens of seconds. The volume of oxygen consumed by the body (VO2) is therefore one of the best indicators of the horse’s athletic ability and the intensity of exercise. As the heart rate is correlated with VO2, it is important to evaluate it during exercise.
Heart rate allows quantification of the intensity of the exercise,
the level of performance, the quality of recovery…
RACE HORSE’S HEART RATE AT REST
At rest the horse’s heart rate is very low, from 25 to 40 beats per minute (BPM). However, it can vary to more than 100 BPM under the influence of excitement (approach of food), fear, or at the beginning of exercise. The mere presence of a person in or near the box can significantly increase the resting heart rate.
A low heart rate at rest (without disturbance) would be associated with a good level of fitness, while a high value can be associated with pain, illness, or fatigue related to overtraining.
RACE HORSE’S HEART RATE DURING EXERCISE
The heart rate changes linearly with speed (see figure 1 below). This relationship can be quantified by a standardized test. The test comprises incremental bearings interspersed with recovery period.
From this test, we can construct the progressive curve of heart rate as a function of speed (Figure 1). Three key values can be identified and will be detailed later:
- Maximum heart rate (HR MAX)
- Speed at the maximum heart rate
- Speed at 200 BPM (V200)
Figure 1 : Estimation of the progression of the heart rate as a function of speed from a standardized test.