The Physiology of the cold - Bike Magic

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The Physiology of the cold

Apparently, archaeologists believe that we humans originated from Africa 10,000 years ago, giving rise to the intuitively named ‘out of Africa theory’. As a species, our formative years were therefore spent in hot climates, and because of this our bodies were designed to cope with these conditions. Since then we have moved around the globe somewhat, with some of us poor souls ending up in more inclement climates such as Britain.Ten thousand years sounds a long time but in evolutionary terms it is no time at all. Indeed there is very little evolutionary difference between our bodies now and those of our African ancestors. Therefore, being humans, we are not designed to perform optimally in cold conditions. A point worth bearing in mind if you are thinking of racing or riding this winter. Having an understanding of how the cold affects the functioning of your body is important because it enables you to make the necessary alterations to counteract the effects of the cold, and create an environment which will optimise your cycling performance.

Warming up

We all know we should warm-up; it reduces the likelihood of injuries, primes our cardiovascular systems, and mentally prepares us for the forthcoming exercise. There is nothing new there. But in addition, a warm-up provides the optimum temperature for the chemical processes of respiration and metabolism to occur, which has a direct influence on our ability to produce energy. It may sound like an oxymoron, but the problems of exercising in the cold can often be caused by over-heating and dehydration.

The efficiency of an exercising muscle, as with any other machine, is calculated as the percentage of energy input that is converted into mechanical work. At best, our muscles are about 25% efficient at converting the chemical energy from food into the mechanical energy needed for cycling. The remainder is lost as heat. This is not a bad thing as it allows for temperature regulation in cold conditions. The problem arises when we wrap up warm when we are sedentary and then begin exercising. The heat produced as a by-product of the energy conversion cannot escape and we slowly start to overheat.

Sweating yet?

The body’s response to this is to attempt to lose heat through sweating. This presents us with a double edged sword: we are faced with possible debilitating effects of dehydration and also the problems of wearing wet clothes in cold conditions. It is therefore important to maximise the benefits of a layering system, removing and adding a layer as appropriate. To exacerbate the water loss problem even further, an increased amount of water vapour is lost during respiration in a cold environment as opposed to a warmer one. To combat these problems, always err on the side of feeling slightly cold rather than hot when starting a winter ride, and always drink frequently.

If you are out on your bike during the winter and wish to punctuate the ride with rest breaks, you must be aware of the effects it will have on your body. As soon as you terminate the exercise, the heat production from the muscles will drop back to near resting levels. Without this supplementary central heating you will begin to feel cold fairly quickly. The warm-up effects of the ride are transient and only most effective for a couple of minutes afterwards, less if it is a very cold environment. There is a gradual loss of the effects of a warm-up during inactivity and this is known as a warm-up decrement.

Keeping it on the boil

Before you resume your ride, you should warm-up again and prime your body for the rest of the ride. In response to the cold your body will increase heat production by throwing an extra metaphoric log on the fire. It achieves this by increasing your resting metabolism. This increased heat production comes at a price: an increased fuel bill. During winter you will burn more calories during a ride and you will need to bear this in mind when you are packing your mid ride snacks.

All of this extra preparation may seem like a hassle at first, but if it means getting some decent rides in this winter, the investment is more than worth it.

(c) Copyright 1999 John Metcalfe

John Metcalfe is a Mountain Bike physiologist, regular mtb magazine contributor and avid racer. In order to pay the bills he is also a Sports Science Lecturer.


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