There is a phenomenon in horses that many people are unaware of but means their athletic capability is even greater than we may realise. It is known as splenic contraction or to put it another way, natural blood doping.
In human athletic competition it has been known for athletes to store blood and inject it prior to competition to boost the number of oxygen carrying red blood cells in an attempt to provide more oxygen to muscles during hard exercise and enhance performance without using banned substances. However this practise is illegal and extremely dangerous as the human body is not designed to cope with this increase in circulating red blood cells. What actually happens is that the increased number of cells means circulating blood becomes thicker and doesn’t circulate as easily; where blood was circulating like water it becomes like thick gravy and the body has to work harder just to move it around the body. This additional strain isn’t beneficial at any time but during hard exercise can increase the risk of heart attack.
Now, what makes horses so incredible is this phenomenon known as splenic contraction. An average racehorse has approximately 50-55L of circulating blood with approximately 10L being stored in the spleen to be released in to the blood stream whenever the body requires it. The reason they can cope with this is because the volume of red blood cells circulating day to day is lower by comparison than what we have so the capacity to cope with an increase in red blood cells is always available. What makes them amazing is that they can intensively train with this lower amount of available oxygen then at the point more oxygen is required, their spleens contract and make this extra energy available to them. This is why a racehorse’s heart rate can go from a resting rate of between 28 and 40bpm to maximum rates of 235-240bpm. When you compare this to maximum heart rates in human athletes of around 130-135bpm, it just shows what incredible athletes horses have the natural capacity to be.
by Lauren Cooper
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