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Scientific and Equine Consultant

Man versus Horse: What does science have to say about who should win?

Man versus Horse: What does science have to say about who should win?    

Dr David Marlin

 

The 35th running of the Man v Horse race takes place on the 14th June 2014 in Llanwrtyd Wells in the County of Powys, in the middle of Wales and to date man has triumphed over horse on only 2 occasions! Over a short distance on the flat, the recorded speeds of Quarter Horses close to 50 mph tell us that the horse would be the winner even if the human representative was Usain Bolt. Bolts world record time set in Berlin in 2009 of 9.58 seconds for 100m equates to an average speed of 10.44 metres/second or 23.4 mph (37.7 kmh). Over the marathon distance (26 miles 385 yards or 42.195km) Wilson Kipsang’s current men’s world record of 2 hours 3 minutes and 23 seconds equates to an average speed of 12.7 mph (20.5 kmh).  As a comparison, the Arab Marathon on Salisbury plane is usually won at a speed of around 17 mph (27 kmh).  But add in a 24 mile course (or 22 miles until 2013) over hilly terrain and variable ground conditions and things get more interesting. Those who have regularly followed the Man versus Horse Marathon or rather Man versus Horse plus Man Marathon will be aware that it wasn’t until the 25th running that a human (Huw Lobb) finally triumphed over a horse with a winning time of 2 hours 5 minutes and 19 seconds. But if we consider the human physiology compared with the physiology of the horse, what would science predict the outcome to be?

 

Ability to use oxygen

One thing that has a major impact on how athletically gifted a species or an individual within a single species is, is the ability to use oxygen. This is something that can be measured and is often expressed as maximal oxygen uptake – the highest rate at which oxygen can be used. This varies with factors such as age (decreases as you get older) and training (increases by 10-15% with aerobic training). A typical maximal oxygen uptake (VO2max) for a young, moderately athletic person who is not a distance athlete would be around 40 ml oxygen/kg/minute. Elite distance runners and cyclists may be in the 80-100 ml oxygen/kg/minute. If we start with an average pony we are already looking at values of around 100 ml oxygen/kg/minute. So the best human athletes are only just equivalent to average ponies. If we look at average Thoroughbred and Arab racehorses the values rise to around 150 ml oxygen/kg/min and by the time we reach elite racehorses, the best have values for VO2max over 200 ml oxygen/kg/min. The ability to run at speed over distances from 2-100 miles is related to the ability to use oxygen, both in people and horses.

 

Heat production & Temperature control

During exercise heat is produced due to the inefficiency of the metabolic processes involved in muscle contraction. For every unit of energy that goes directly to making the muscles contract, 4 times as much is released as heat. Initially the heat production is beneficial as chemical reactions in the muscles work faster and better at slightly raised temperature. But after an increase of a few °C it’s important to try and control the temperature as much as possible as if it gets too high this can lead to fatigue and muscle damage. The body controls its temperature and that of the muscles though the process of blood flowing through the muscles picking up heat. The warm blood then flows through small blood vessels in the skin and heat is lost to the environment either by convection (the process where heat moves from warm skin to cooler air) or by evaporation. The factors that determine how fast heat is lost (removed) are the primarily the amount of surface area (skin area) and capacity for sweating. An 80kg person would have around 2 square metres of skin surface and a 500kg horse would typically have 5 square metres. So although the horse is over 6 times heavier it only has 2.5 times more surface area. The horse has to try to get rid of more heat through a relatively smaller amount of surface area. Large animals lose heat more slowly which is an advantage in cold climates whilst smaller animals lose heat more rapidly which is an advantage in warm climates. The horse has a greater capacity to sweat compared with the human runners. The same area of horse skin can sweat three times faster than the same area of human skin, but there is a cost in terms of energy, water and electrolytes lost. The horse therefore has more of a problem with getting rid of heat and the human runner has more of a problem keeping warm. If it’s a cold day then the horse may have an advantage. If it’s a warm day the horse can still cope but at a price. Interestingly, in 2004 when Huw Lobb became the first runner to beat a horse (by 2 minutes), the weather is recorded as having been “hot”.

 

 

Hydration

Many human runners will be aware of the negative effects of dehydration on running performance. The common rule of thumb is 1% dehydration (reduction in bodyweight through fluid loss) equals a 10% drop in performance. Here the horse has an advantage as it can tolerate a loss of 3-5% bodyweight before any negative effects on performance are observed. The reason for this is that the horse is a herbivore with a large intestine comprising about 12% of bodyweight compared with about 6% in humans. The relatively larger large intestine of the horse holds a large amount of water. As sweat is lost, the horse can draw water from the large intestine to maintain the circulating blood volume. As dehydration develops, the blood volume of a human runner will fall and as a result the heart rate will increase. Because the horse is able to use the reservoir in the large intestines it is able to go for longer before dehydration starts to limit performance. Human runners can counteract this by voluntarily drinking small amounts during the race. However, the horses are not likely to want to drink in the early stages of the race as their thirst will not have been stimulated until they have lost relatively more fluid. Hence the phrase “you can lead a horse to water but you can’t make him drink”.

 

Nutrition and Glycogen Loading (carbohydrate loading, carb-loading, etc)

Many runners will use a technique known as glycogen loading in their race preparation. Glycogen is the way in which glucose is stored within muscles (the equivalent of starch in plant cells). From an energy perspective, Glycogen is also the limiting factor in endurance type events. When you have depleted your muscle glycogen you “hit the wall” and you are then restricted to running on blood glucose and fat! Glycogen loading is a technique to boost muscle glycogen stores prior to a race whereby about a week before the race the human athlete trains hard but consumes a low-carbohydrate diet. But in the last 3-4 days before the race the human athlete then switches to a high-carbohydrate diet, at the same time reducing the training intensity. This technique maximises the muscle glycogen levels. Whilst tapering (reducing the amount but not the intensity of training going into a race) can be used with horses, it is not possible to manipulate the horses diet in order to glycogen load them.

 

Biomechanics

When it comes to biomechanics, there are some obvious differences but who does this favour? The horse has 4 legs compared with the human standard 2 legs! The horse also has long and slender legs with the muscle mass close to the trunk of the body and very large tendons. These adaptations minimise the energetic cost of moving the limbs and the overall energetic cost of locomotion. In fact, in biomechanics the horse is often considered to be like two bipeds (animals with two legs such as ourselves) joined together. Thus, to move 1 kg of horse 1 metre requires considerably less energy than to move 1 kg of human 1 metre. Humans also only have essentially two gaits: walking and running. In humans running is actually less efficient than walking. Horses however have 4 gaits: walk, trot, canter and gallop. Walking is the least efficient, followed by trot. The canter is the most efficient gait and a medium speed canter of 7-9 m/s (25-32 kmh or 15.6-20mph) would typically be the most efficient speed within this gait. Thus, if the horse was able to maintain a steady canter this would offer the horse an advantage in minimising energy expenditure. One final aspect is that whilst the runners can choose to entrain their breathing and stride, that is they get into a pattern of breathing in time with their stride (cyclists do the same) they are not under any biomechanical obligation to do so. The horse however, can entrain breathing and stride at trot but at canter and gallop the horse moves to coupled breathing and locomotion such that each breath cycle is perfectly in time with the stride. This is referred to as respiratory-locomotory coupling and is a technique to reduce the energy expended in moving air into and out of the lungs. The reason the horse has to do this is that the chest is large and stiff so we are back to the problem of inertia. To help overcome the potential limitations of having a large stiff chest the horse uses limb movements to help drive air into and out of the lungs, reducing the energy required. When going up and downhill the weight shifts such that on downhill the front legs take proportionately more load whilst going uphill it’s the hindlegs. So over terrain that varies between uphill, flat and downhill this could give the horse an advantage as it gets to reduce the effort from one pair of legs. However, fell runners have a technique that allows them to run downhill at fast speeds, possibly as to some degree as a result of a lack of self-preservation. In contrast, horses often appear to be more “careful”, perhaps through an appropriate sense of self-preservation.

 

The Course

The nature of the course can have an impact on who has the advantage. A flat, straight course with slightly soft ground would favour the horse as they would be maintain a steady canter pace of around 15-20mph. Road surfaces would tend to be a disadvantage to horses, especially if they are wearing shoes as cantering on such a surface increases the risk of slipping and falling whilst human runners would perform well and be able to run at a fast pace on such a surface. The more turns and the tighter the turns, the greater the horse is disadvantaged. The reason for this relates to inertia and size (mass). Think of large ships. They take ages to get going, a long time to stop and can’t make quick turns. Then think of a small remote control boat – the complete opposite: rapid accelerations and sharp, rapid turns. Small rodents are able to accelerate and stop rapidly as well as being able to make rapid changes in direction. The horse takes longer to accelerate, longer to stop and make turns and uses more energy in the process than a human a runner. So on a hilly course, with varying ground conditions and turns, the human runner would have the advantage.

 

Weight of rider

Perhaps one of the biggest and most obvious differences, but one that is rarely addressed, is the fact that the horse is competing carrying a rider. If a horse of 500kg is carrying a 70kg rider with 10kg of tack (saddle, pad, boots, bridle, etc) then this equates to the horse carrying an extra 16% of its bodymass. Any additional weight carried increases energy that must be expended. It also slightly cuts down the surface area available for heat dissipation. The amount of muscle the horse has to move the total mass is unchanged, so any weight in the form of a rider and tack is a disadvantage. To even things up, an 80kg runner would have to carry nearly 13kg; a considerable load. Think of running with 6 x 2 litre bottles in a backpack! So in this respect the human runner has a clear advantage.

 

Incentive to win

The human runners taking part may well be highly incentivised to win. They may also use sports psychology techniques to help them control race strategy and push through the pain barrier. However, irrespective of whether the race is being run this year or 1000 years ago, it is likely the horse is running with the same incentive so in this respect the advantage might be considered to go to the runner.

 

Conclusion

Both the human runner and the horse have areas where they are advantaged or disadvantaged although clearly the nature of this race currently appears to favour the horse over the runner. The fastest speed achieved by a horse was 16.5mph in 1984 and the fastest speed achieved by a runner was 11.3mph in 1987. The horse dominance is also reflected in the average winning speeds over the 34 running’s of the race. The average winning speed of the 34 horse winners is 11.7 mph, 18% faster than the average winning speed of the human runners (9.9 mph).

 

Copyright Dr David Marlin 2014

Date: October 21, 2015