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HEART MONITORS AND LACTATE ANALYSIS
Eight days after winning the longest and most grueling of the Triple Crown races, the Belmont Stakes, Swale died of a heart attack. Was this great champion pushing himself so far to the limit that his heart could not cope?
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QUINE exercise physiology has been subject to major scientific advances over the last three decades. The advent of the equine high-speed treadmill created the opportunity to use more advanced recording techniques and the knowledge obtained from this, combined with that from human athletes, leaves us in a much more informed position as to what exactly goes on inside the racehorse at exercise. With the introduction of new technology such as horse-walkers and synthetic surfaces, training methods have become more advanced than they were 30 years ago. Nevertheless, this article will question whether trainers should be taking a more scientific approach and using tools such as heart monitors and lactic acid analysis to aid in the daily training of the racehorse. The racing fraternity considers great horses to have great hearts. However, there seems to be a lack of conviction behind this view as only a few individuals scan the hearts of young-stock and only a small number monitor cardiac function. The average 1100lb racehorse has nearly 50 liters of blood, which the heart pumps throughout the body. The main function of this cardiovascular system is to release carbon dioxide and pick up oxygen in the lungs and spread it throughout the body where it can be released and used. The heart is the centre of this system with its right side pumping blood with low oxygen from the body to the lungs and the left side pumping highly oxygenated blood from the lungs to the body. It stands to reason that a great racehorse needs a good-sized, efficient heart and it should be easy to monitor how much training is stressing the heart, and therefore the horse, by simply recording the heart rate – yet this is rarely done. The equine heart is a large structure of approximately the same size as a football, which beats quite slowly at rest but which is capable of increasing its resting heart rate by as much as six to ten times when at peak exercise. The horse is the only mammal
capable of such an increase (a human is doing well to achieve an increase of three fold) and this perhaps explains why it is such a talented athlete. The heart is situated in the horse’s chest just behind the elbow, almost completely surrounded by the lungs – only a small part of the heart is left uncovered, which is called the cardiac notch. This is the area where the heart makes contact with the left chest wall and so it is the best place to listen to it and to perform cardiac ultrasound. Ultrasound of the heart (echocardiography) enables veterinarians to visualize what is going on in this most central organ. There are several veterinary surgeons who believe that the best racehorses have the most efficient hearts and travel from sale to sale examining yearlings using ultrasound to advise potential purchasers of the ‘best’ hearts on offer. Unfortunately, as anyone who has followed their advice will know, having a heart that looks great on ultrasound examination does not seem to guarantee that the racehorse in question is a champion. The reader can come to their own conclusions as to why, but surely having the ‘best’ heart is only one part in th e selection of a future champion. Veterinarians routinely listen to horses’ hearts in an attempt to detect abnormalities such as murmurs. However, should trainers be routinely monitoring heart rate in response to exercise? Not only might they find abnormalities like the atrial fibrillation recently found in Britain’s best jump racing horse, 2008 Gold Cup winner Denman, but much more commonly and more importantly, they might get an idea as to whether they have just asked a particular horse to do a little more work than they had intended and so could alter its training regime appropriately. There are several heart monitors available on the market but nearly all trainers make the decision that it is a piece of information that they can do without. Heart Monitors Measuring a horse’s heart rate is straightforward. Simply attach the heart-belt to the horse, turn on the transmitter and monitor the horse’s heart rate on a watch whilst it exercises. The obvious benefit of such a system is that heart rate reflects cardiac output and hence we learn how hard the horse is working. On a daily basis, we watch horses blowing after exercise, we ask the riders how fit they think they are and we weigh horses. Measuring and recording heart rates in response to exercise can provide another useful tool in the training of the racehorse. However, science is rarely so simple and a horse’s heart rate also increases in response to external stress, which is one way that misleading results can occur. For example, a horse may return a higher heart rate during a particular piece of work than truly reflects its fitness if it ‘shied’ at something. In the same way that trainers ISSUE 11 TRAINERMAGAZINE.com 21