Daily heart rate measurements should be a fundamental part of the day-to-day management of equine athletes. In this newsletter we will discuss the fitness of the horse, with “fitness” referring to the aerobic fitness of a horse and how fitness can be determined using measurements of heart rate at the trot. Aerobic fitness refers to the capacity of a horse to transport oxygen from the air, through the lungs and then be pumped by the heart through the blood to provide the muscle cells with the oxygen to support metabolism of fuels such as glucose and fat. Aerobic fitness is relevant to every equine competition, except perhaps Quarter Horse races, which are all over in less than 20 seconds.
Heart rates at rest
Heart rates (HRs) in a resting horse cannot be used to reliably assess fitness, as they are in human athletes. In human athletes, the resting heart rate, usually recorded first thing in the morning, gradually decreases with improved fitness. However, this technique is not reliable in horses because the resting HR can vary so quickly with the slightest disturbance to a horse’s relaxed state. For example, a very relaxed horse might give a heat rate of 30 beats per minute (bpm), but a few minutes the later the HR can be over 100 bpm, due to fear, sudden noise, excitement, or even anticipation of exercise.
This does not mean that resting HRs should not be recorded. In very relaxed horses, such as some endurance horses, a sudden increase in resting HR at rest can alert the trainer to a potential problem, such as a fever, pain, or other disturbance to the horse’s normal state.
Heart rates during exercise
The best way to simply assess fitness is to use HR measurements during exercise. The key is to measure HR and speed in the horse. This is best done by using a heart rate monitoring system like the Polar RS800G3 for ridden horses that combines HR measurement with speed measurement by global positioning system. I am happy to provide advice concerning the best system for your particular circumstances. Good systems can be purchased for less than $1000.
It is important to measure speed, because not all horses trot at the same speed, and it is possible for the trot speed to differ a little from one day to the next. So the first fundamental measurement is speed, and then to assess the HR at a steady speed. Steady speed means a speed that is constant, not varying more than 1-2 kph, for at least 30 seconds.
Luckily, with the heart rate monitoring systems now available it is possible for riders and trainers to measure heart rate and speed during exercise in ridden (or driven) horses whenever they desire. The Polar RS800G3 for ridden horses measures HR and speed frequently, and the results can be easily downloaded to a computer for closer inspection.
When to measure heart rates
HRs at the start of trotting should be ignored for a few minutes because there is usually unstable HRs, due to excitement and the sudden disturbance to the cardiovascular system. In these first few minutes, HRs are usually higher than their true steady state HR. After a few minutes, the HR settles down. For example, HR might vary from 140-160 bpm in the first few minutes, and then settle down to a steady value in the range of 125-128 bpm, even though the horse has been trotting at 16 kph all the time.
If the HR does not settle down to a steady value, it probably means that the horse is excited. HRs on a day after the horse has not been exercised are often a little higher and more variable, due to excitement. These emotional disturbances are what make fitness testing of horses so challenging, but it is possible to measure fitness reliably if these factors are accounted for. It is always important to watch the horse carefully during the trotting HR test. Is it jumping around abnormally, or is there a new rider on-board? Anything that might disturb the horse from its normal state needs to be accounted for.
HRs during trotting can also be affected (usually abnormally increased) by different ground conditions, the use of a different saddle, riding hills, and so on. So it is very easy to record a false high value. When I examine heart rate data I look at the speed and HR record and look for the lowest HRs at the steady speed. I also test the horse several times before expressing confidence about the true result for each horse.
Signs of improving fitness
If a horse’s HR relationship to its trotting speed is regularly monitored it will be easy to observe trends over time, or even sudden changes. A gradual decline in HR at the same speed means that the horse is responding to training – it is getting fitter. An alternative might be that the horse is slimming down, and so it does not have to increase its HR so much to provide the oxygen needed for the trotting exercise!
What does it mean if heart rates increase over time?
A gradual increase in heart rate over time in a horse in training would be an unusual finding, but it could be explained by increased fatness of the horse. A gradually worsening respiratory problem could also cause HRs to increase.
A sudden increase in HR from one day to the next when trotting could mean that the horse was overly excited on that day, had developed a problem causing pain (such as a bruised foot), or had new gear that was not comfortable. Monitoring HRs regularly helps a trainer know when the problem occurs, and when it is resolved.
Measuring the trot HRs in the days after racing or competition is also a valuable method of assessing the recovery after a race. They should be the same as before the event or race. Higher HRs compared to before the race or competition could mean that the horse has a problem that needs investigation by a veterinary surgeon.
The technology is now available for all horse riders and trainers to regularly monitor HR during trotting. Each day of trotting offers an opportunity to make sure that the horse is responding to training as expected, has not developed any new problems, or has suitably recovered after competition or racing.
Comprehensive tests of fitness for intensive competitions, such as racing and eventing, should include assessments of the HR responses during trotting, as well as measurements of HR and speed during faster workouts. However, day-to-day assessments during trotting are fundamental to the day-to-day monitoring of all athletic horses.
Written by David Evans PhD BVSc
Dr David Evans graduated BVSc (Hons) in 1975 and spent seven years in veterinary practice prior to completing a PhD in equine exercise physiology at the University of Sydney in 1987. His current consultancy activities include university teaching and research in aspects of equine science. Dr Evans has contributed to 11 book chapters on aspects of equine exercise physiology, and to more than 80 refereed research publications. Many of these reports are concerned with aspects of fitness testing and scientific aspects of training and performance. As well, he continues work in Australia and overseas as a consultant to horse owners and trainers, with a focus on practical applications of the science of equine fitness measurement and training.