Horse or Human: who will win the race?


Place your bets now! Because tomorrow, on 11 June, the 36th annual Horse vs Man Marathon will take place in Llanwrtyd Wells, Wales, where humans will test their mettle against horses on 22 miles of mountainous terrain. Who will win this year?

On flat terrain, it would be a no-brainer: horses clearly have a significant advantage over humans. With their lean and muscular physique, thoroughbreds can reach speeds of up to 55 mph, while the world’s fastest human, Usain Bolt, lags behind with a top speed of only 27 mph. So how do horses reach such impressive speeds? We can find some clues by studying their anatomy and physiology.

The first proper studies began over 200 years ago, after the death of a particularly special racehorse, Eclipse, who was never beaten throughout his racing career from 1769 to 1770. His extraordinary success prompted the founding of the Royal Veterinary College in 1791 and ever since then, veterinary scientists have been making great strides in finding out what it is that allows horses to run so fast. It turns out that several factors play a role, including a big heart and the ability to increase heart rate to a remarkable degree:

 

Horses’ ability to increase the amount of blood pumped by the heart around the body to the muscles makes all the difference in a race, and that is helped by the spleen, which contains a store of oxygen-carrying red blood cells that are released into the bloodstream during exercise. They have other tricks up their sleeve too:  compared to humans, they have a far greater tolerance of increased body temperature and blood acidity, both of which go up fast during intense exercise.

We can find other clues to horses’ speed in their long and light-weight legs, which have very springy tendons that save energy needed to move quickly. So where does the muscular power come from?  The leg muscles aren’t in the lower legs as humans’ are, but tucked up close to the body, connected to the lower legs by very long tendons, which also generate  ‘springiness’. As with all four-legged animals, the muscles in the back, neck and abdomen also contribute to the ability to gallop. The quickest racehorses have lots of fast twitch fibres in these muscles, helping them to generate more energy for movement via both aerobic and anaerobic respiration.

Also unlike humans, the stride in galloping directly controls the timing of breathing: the huge weight of the hindgut acts like a piston on the lungs at the front, sucking in the maximum amount of air possible and then expelling it rapidly, as the torso moves with each step. This neat trick means that horses can move large volumes of air in and out of the lungs very quickly, helping to maintain their performance for longer.

And, of course, no racehorse is complete without its rider – who also plays a key role in the horse’s performance. Have you ever wondered why jockeys ride crouching over the horse, rather than sitting upright? Well, this is known as the ‘monkey crouch’ and was invented by Americans in the 1890s in order to improve horse speeds. This position separates the stride of the horse from the rider i.e. as the horse moves forward, the rider moves back, and vice versa. In this way, the rider takes up some of the effort required to move forward, enabling the horse to save some much needed energy for the race.

But what about humans? How can we possibly measure up to all this? By levelling the playing field, to something less level – which is exactly what the Horse vs Man Marathon has done, by holding the race on mountainous terrain. This gives humans a fighting chance – so while it’s true that horses have dominated the Marathon so far, there have been two occasions when a human has won the race. How come?  On rough hilly ground, the horses’ ability to reach and maintain their peak speed is severely reduced. Humans are much lighter, so the changes in direction needed on rough ground take less energy than for the much larger horses.

If we look at the cases where humans have won the race, one factor immediately jumps out, and that is: hot weather. It’s not immediately clear why that favours humans. Our ability to sweat, which cools us down in hot weather, is shared with horses. But, being smaller, we have relatively more skin to sweat from than do horses, and that may be a greater benefit than horses’ greater tolerance of high body temperature. And humans can take on extra fluid during the race, replacing that lost in sweat, without having to stop – something their equine competitors can’t do.

So, who will win tomorrow? The weather forecast predicts maximum temperatures of 19°C, so the human participants will have to draw on all of their abilities, to be in with a chance of winning.

Who will you place your bet on?

 

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