The horse’s cardiovascular system consists of the core and blood vessels. It ensures successful blood circulation and the delivery of a significant oxygen volume, particularly to the muscles. The horse’s heart is a powerful organ, and it may develop throughout its life, especially via training.
How does the horse enhance its physiological characteristics during training by using its cardiovascular system?
The horse’s cardiovascular system in action
The horse’s heart is large, measuring up to 25 to 30 cm long and 20 cm in diameter. In a racing horse, the volume of blood evacuated by the heart at each beat during a cardiac contraction is greater than one liter. It weighs roughly 4 kg and accounts for about 1% of a horse’s weight. Training increases heart mass by around 15%. This increases its cardiac capacity and allows the heart to perform more efficiently by beating more slowly for the same length of time.
In comparison, the human heart is 12 cm long, 9 cm wide, and weighs between 280 and 300 g, accounting for around 0.4% of body weight.
2. Heart rate elasticity
Heart rate elasticity indicates how effectively the cardiovascular system of a horse is operating. The elasticity of the horse’s heart rate will be high if it is in good physical condition.
A horse’s heart rates differ according to its physical activity:
At rest, its heart rate is lower than that of a human, ranging between 25 and 40 beats per minute (bpm) and approximately 100 bpm with stress.
During exercise – It increases with pace throughout exercise and can reach 240 bpm.
A racehorse’s heart rate drops by roughly 55% immediately after activity and by about 50% 15 minutes later.
Heart rate values provide a wealth of vital information about its health, notably regarding breathing, movement, and, of course, the heart (detection of possible cardiac arrhythmias, for example).
➡️ To learn more about cardiac arrhythmias, we advise you to read this article.
The effects of training on the cardiovascular system
A racehorse’s heart capacity improves thanks to training. In fact, the heart mass tends to grow and increase by about 15% with regular training. Because it beats more slowly for the same amount of work, the heart becomes less exhausted.
1. Cardiac output
In the horse, physical activity produces an increase in cardiac output through the joint increase in heart rate and stroke volume.
Stroke volume: the amount of blood ejected by the heart with each beat.
Aerobic training produces an increase in stroke volume, both at rest and during exercise. Ten weeks of trotting at a heart rate of 150 beats per minute is sufficient to induce a significant change in stroke volume in the horse. Thus, cardiac output increases, thanks to an increased stroke volume and heart rate during exercise.
This can be summarized by this formula:
Cardiac output = Systolic ejection volume x heart rate
The horse’s athletic superiority comes from its remarkable cardiovascular capabilities. The cardiovascular system must multiply the mechanical power delivered by 8 during maximal exertion. Endurance exertion requires less power, but this power must be sustained over a longer period of time.
A research (David Marlin, Kathryn J. Nankervis. 2002) found that after 18 weeks of training, the horses’ heart mass grew by 33% on average. This adaptation occurs at an early stage, and it appears that extended training does not enable this hypertrophy to continue: horses trained for 2 months or 19 months show no substantial difference in heart structure.
Hypertrophy: abnormal increase in volume of an organ with or without anatomical alteration.
2. VO2 max
To assess the effect of training on the horse, it may be useful to calculate the rate of oxygen consumption during exercise by the VO2 max. During maximal aerobic activity, this is the highest volume of oxygen used by the horse’s body, including the core. The VO2 max is frequently referred to as “peak aerobic power.”
Horses have a VO2 max of 160 to 200 mL O2/kg/min (Noakes, 1992; Rose et al., 1988).
Oxygen consumption rate is the product of cardiac output (COD) and the difference in oxygen content between arterial (a) and venous (v) blood.
This can be represented by this formula:
VO2 = DB x [(a-v)DO2]
Arterial blood is the blood that travels to the muscles and is thus highly oxygenated. Venous blood is the blood that returns to the core with significantly less oxygen since it has been spent on the muscles.
In the horse, higher volumes lead to faster oxygen transport to the muscles. Indeed, horses who run for an extended amount of time at a high percentage of their VO2 max are thought to be more resistant to exhaustion.
Thus, it is the cardiac output that allows for faster oxygen transit in the blood, as well as an increase in oxygen extraction capacity in the muscles.
How to measure the effects of training on the horse’s cardiovascular system?
Training allows the horse to adapt its cardiovascular system. You can use technology to monitor and quantify the evolution of your horse’s training, in order to improve its performance and preserve its health.
1. Quantify the maximum heart rate
The maximum heart rate (or Max HR) is the highest number of beats per minute that a horse may reach when exercising. It’s unique to each horse.
Measuring your horse’s maximum heart rate allows you to better understand his work and train him in heart rate ranges that are appropriate for him.
The maximal heart rate can be recorded during a training session where the intensity of the activity requires a significant energy input. This might be a maximum speed effort of 70% to 80% over at least 1600m, or on a track with positive elevation gain, or an effort of more than 90% of maximum speed over 600m.
Data from the Equimetre Platform
Velocity at 200 bpm or V200 is the speed achieved by a horse when its heart rate is 200 beats per minute. It is a uniform value that allows horses to be compared to each other, provided it is recorded equally.
When measured numerous times during the year, the V200 allows you to objectively track a horse’s improvement over the season or detect a drop in performance. An increased V200 implies that the horse is in better shape, because a horse that goes faster while maintaining the same heart rate has better cardio.
The graph above shows the progression of a horse’s cardiovascular system throughout a certain training time. The red curves represent the end of the training period, while the blue curves reflect the start. The V200 has a greater speed of 0.5 meters per second (m/s). When this horse hits its FCMax (216 BPM), the speed differential climbs to 0.9 m/s. This demonstrates that the horse is more fit.
3. Heart rate levels during recovery
The recovery phase is also an important stage of training to measure. Indeed, this phase makes it possible to measure the impact of the effort on the horse and thus to check its fitness level after the effort.
By studying the heart rate during recovery, it is possible to detect, for example, whether a horse is over-trained or, on the contrary, under-trained.
To analyze the level of recovery, it may be interesting to look at these parameters:
- Fast recovery: this parameter is measured in beats per minute (BPM). It illustrates the degree of effort intensity felt by the horse. Specifically, it is the first stabilization of the horse’s heart rate that occurs just after the effort has ceased. Generally, a suitable rapid recovery is less than 55% of the FCmax.
- Heart rate at 15 minutes: This parameter is also measured in BPM and tells us about the fitness level of the horse.
- Recovery after 15 min as a percentage of HRmax: this parameter is read as a percentage of the maximum heart rate. It is measured after 15 minutes of recovery following the last high intensity exercise. Generally we consider that a recovery after 15 minutes should be less than 50% of the HRmax.
Data from the Equimetre Platform
- Fast recovery analysis:
If we analyze the fast recovery after the effort, we notice that Mrs. Arionea and Arionea assimilated the effort well, with a heart rate of respectively 126 and 120 BPM. Mrs. Arionea has a very good elasticity because her heart rate was up to 236 BPM. Arionela presents the least good recovery with a heart rate of 141 BPM immediately after the effort.
- 15 minutes recovery analysis:
If we now observe their heart rate after 15 min of recovery, we can confirm the very good recovery of Ms. Arionea, with a heart rate of 99 BPM. Ariona also shows a good level of recovery, with a heart rate of 103 BPM. Indeed, we consider that a good level of fitness after 15 minutes is below 100 BPM on average. Arionela seems to have undergone a little more this training with 124 BPM.
We can see that Mrs. Arionea and Arionea have a very good fitness with a very good heart rate after the effort and after 15 minutes. Arionela, on the other hand, seems to need more training in order to strengthen her cardiovscular system.
The horse is a very adaptable creature, particularly in terms of cardiovascular function. It is necessary to objectively assess the effects of training on the horse in order to assist him in improving his metabolism. The data is therefore an objective and measured support, allowing for a follow-up over time.
Evans, D.L. (2000) Training and Fitness in Athletic Horses. rep. Rural Industries Research and Development Corporation.
Hodgson, D.R., McKeever, K.H. and McGowan, C.M. (2014) The athletic horse principles and practice of Equine Sports Medicine. St. Louis: Saunders/Elsevier.
Nankervis, K.J. and Marlin, D. (2002) in Equine exercise physiology. W B Saunders Company.
Travailler l’appareil Cardio-Respiratoire de Votre Cheval (no date) Audevard. Available at: https://audevard.com/espace-sante-cheval/travailler-lappareil-cardio-respiratoire-de-votre-cheval (Accessed: December 5, 2022).
Keywords : training, cardiovascular system, heart rate, Equimetre