Humans are a tropical species and as such we use behavioural and technological adaptations to not only survive, but thrive in the vast areas of the globe where strolling around in the nude would lead to frost nip in embarrassing places. Our normal core temperature is regulated between about 36 and 37.5°C.
The ‘neutral’ air temperature for the human body is around 28°C, meaning that simply sitting around in the buff at this temperature keeps our core temperature in equilibrium. As the temperature drops further and further below 28°C, the body works increasingly hard to maintain balance by increasing heat production (shivering and other types of physical exertion being most effective). The absolute lowest core temperature compatible with life is up for debate; however, in practical terms, hypothermia is said to have occurred when it drops below 35°C. Below 32°C it is thought almost impossible that a person would be able to remain conscious and responsive.
Exercising in the cold presents numerous physical challenges and anyone looking to maximise their outdoor training will benefit from understanding these. The record low for air temperature in the British Isles was -27.2°C measured on 10 January 1982 in the Grampians. While it’s unlikely that anyone will be out training in those conditions on a regular basis, it does highlight the need to be properly prepared for dealing with sub-zero conditions.
It’s been reported that while exercising above 70% maximum effort in conditions above -10°C, enough heat is produced by the muscles (around 75% of the energy produced in muscular contraction is lost as heat) to offset the temperature difference. This means that performance, when you’re wearing the correct clothing, is relatively unaffected.
Seeing cross-country skiers routinely going flat out in these conditions would seem evidence enough to back up this theory. However, when the temperature dips below -10°C, numerous issues start to compromise the body’s ability to perform at optimum levels. Although we rarely experience such temperatures here in the UK, wind chill and a combination of wet and cold conditions can create a virtual environment equivalent to this kind of still air temperature.
There are a number of ways in which the cold weather can impact your performance in training. The following gives you an idea of some of the pitfalls you could face heading out in winter…
1. Reduced muscle function
As your body gets cold, nerve impulses move more slowly, and below about 12°C manual dexterity starts to deteriorate if hands are not protected by gloves. This can make changing an inner tube in sub-zero conditions an agonising process, and even tying a shoelace can become tricky at just 8°C. Mountaineers and other adventurers have died due to the simple fact that they could not zip up a tent or jacket in extreme weather and so couldn’t protect themselves from worsening elements. Furthermore, maximal force production in muscles is compromised at low temperatures (reduced by as much as 80% at -22°C) so training at high intensity becomes less productive – even impossible.
2. Reduced cognitive function
Some of the symptoms of hypothermia are confusion and disorientation, slurred speech and mood changes as the brain struggles to deal with the drop in temperature. This makes the condition particularly dangerous because the measures required to prevent getting worse require logical thought and purposeful action. It’s not uncommon for those in a particularly bad state of hypothermia to start getting so confused that they actually remove clothing.
3. Frost nip and frostbite
In order to maintain core body temperature (important for the protection of the brain and vital organs), the body responds to the cold by reducing blood flow to the extremities (such as toes, fingers, ear lobes). These areas then cool rapidly and are at risk of frost nip, which, if left untreated, can turn to frostbite as the tissue temperature drops below freezing. When cycling, the toes, nose and fingers are especially vulnerable to the cold, and numbness followed by painful hot aches during re-warming is common during winter training.
In the cold you lose water to the atmosphere through exhalation as you breathe. Coupled with the fact that you tend to pee more in the cold (increased blood flow to the core of the body causes receptors to think there is more blood circulating than normal and water is off-loaded in extra urine), dehydration can occur. It’s often exacerbated because people perceive they need less fluid in the cold or drink less because cool liquids are less palatable.
5. Torn or pulled muscles
Muscles are more pliable in higher temperatures. Less blood flow to the muscles and more heat lost to the environment means lower working temperatures and increased susceptibility to tears and strains, especially if you’re pushing hard. The first few minutes of a workout can be risky, especially if you pick up the pace to get warm and over-extend cold muscles.