Heart Rate During Exercise In The Horse Explained
An article by Dr David Marlin, a scientist with more than 25 years’ experience in equine physiology and biochemistry. His specialist areas include exercise physiology, respiratory and cardiovascular physiology and disease, thermoregulation, physiological measurement, imaging and diagnostic devices.
David welcomes enquiries from Fine Equinity customers to provide supplementary data analysis and interpretation consultancy services and can be contacted as follows:
Email: dm@davidmarlin.co.uk
Telephone: +44 (0)7572 124264
Web: www.davidmarlin.co.uk
Q&A with Dr Lesley Young, Specialist in Veterinary Cardiology
Horses heart rates, recovery and what you should expect to see:
What would you expect to see your horses' heart rate reach in each gait?
- Gallop: 185 – 240 bpm
- Canter: 120 – 185 bpm
- Trot: 70 - 120 bpm
- Walk: 50 - 70 bpm
NB. These values will depend on the gradient that the horse is working up, going conditions and on the weight and ability of the rider. Remember in the slower paces the fright and flight effect comes into play and the horse's heart rate usually reflects its level of anxiety or excitement, rather than the physiological demands of the exercise itself. You will soon establish though what is normal for your horses on your own gallop.
Do all horses have the same maximum heart rate?
Maximal heart rate is not affected by training or ability, rather it is influenced by the horse's breed and, just like in humans, its age. In general a young flat horse can reach up to 240 beats per minute, whilst a veteran jumper may only achieve a maximal rate of 225 beats per minute.
What would you expect to see as your horse gets fitter?
It's heart rate at each speed will be lower and it will fatigue later, or not at all. If you train at the same speed, it will finish its work with a lower heart rate. In general, after the same piece of work the quicker the recovery the fitter/more able the horse is.
How long would you expect it to take for your horse to recover?
The horse may blow for a while, but this is usually more to do with losing heat than recouping oxygen debt. In general heart rate falls very quickly in the first 90 seconds after a horse pulls up in most fit horses. You would expect to see the heart rate to fall to 110 bpm or below at walk after 2-3 minutes following a good bit of fast work (to a heart rate of >220 bpm). However, the rate of heart rate recovery will depend on what the horse does after it stops and how hard it worked, or more specifically the heart rate reached beforehand. If it jogs, or trots back from the gallop the heart rate will be higher than if it walks off quietly to cool down.
If your horse carries out its fast work at a consistently low heart rate (200-210bpm) does this mean it has more ability?
It might, or it might mean it isn't trying very hard, so be sure that you know how hard the rider is working too!
If your horse has a longer heart rate recovery time than usual, what could this mean?
It could be a sign of many problems or anxiety resulting from a virus, orthopedic discomfort, poor performance, chronic fatigue/over-training syndromes. It might also reflect poor fitness or the presence of atrial fibrillation. If it is persistent and can't be explained by a difference in the horse's recovery pattern, ie cantering on the spot all the way home, instead of walking, it should be investigated. Continuing to train horses with most of the above problems, won't make the horse fitter, more likely it will make the problem harder to fix or introduce some new ones!
Atrial Fibrillation and abnormal heart rate readings:
What signs or trends should be looked for to spot Atrial Fibrillation more quickly?
If it develops during work, the cardinal sign is a very rapid increase in heart rate. The horse might suddenly slow, a percentage will whinny, but sometimes the rhythm can develop in early recovery, so poor performance might not be so obvious. The horse's heart rate recovery is always very delayed and you (with your hand) or the rider (with his/her leg) might feel the rapid irregular beat of the heart as it vibrates against the left chest wall, just by the elbow. Occasionally horses can bleed badly when this develops, sometimes they wobble, and very occasionally they can collapse. If the rhythm doesn't self correct, the horse will have a high heart rate every time it works and unless you have a very flat gallop, it will perform badly at home during fast work. The heart rhythm will also feel irregular all of the time.
If a horse is showing signs of Atrial Fibrillation, what should the next step be?
Get your vet to examine it. If the problem is there all of the time, a stethoscope examination might be all that is required to confirm your suspicions. An electrocardiograph (ECG) will ultimately confirm the diagnosis and your vet will explain about the treatment options.
If the rhythm problem comes and goes, the horse's heart rhythm might need to be monitored using an ECG during exercise. This is easily accomplished at home, but the vet or specialist will probably want to see the horse worked hard. If your horse pulls up at the races unexpectedly, always get his heart rhythm checked there and then because, it might have normalised by the time he gets home, so your own vet will be none the wiser.
If it happens at the races, don't panic, take him home, over two thirds of horses will normalize on their own and the problem is a one-off. It is worth getting your vet to check its general health and make sure there aren't any heart valve problems that could be increasing the horse's risks.
If a horse has Atrial Fibrillation, what risks are there?
The horse will be no use on the racecourse and he will rapidly become stale, if you continue to train him, because working with a defective cardiovascular system is no fun at all. Doing so increases the risk of stress related problems like gastric ulcers and behavioral issues. There is also an increased risk of bleeding and exercise-induced collapse and sudden death in some horses with AF.
If the condition is left untreated for a long time >2 months, there is a higher risk that treatment will fail or that the condition will recur. Treatment also carries a higher risk to the horse in chronic cases. The moral of the story is: before putting a disappointing horse in the field for a rest, make sure its heart rhythm is normal.