Why Some People Can Deal with the Cold

BBC:

A gene mutation that allowed our ancestors to venture north might also give some of us a competitive sporting advantage.

Plunging into ice baths post-workout might be how some professional athletes choose to recover, but anyone trying to keep fit in the winter will know that the cold can be as harsh as it is rejuvenating.

For Matilda Hay, a recreational swimmer, there’s no choice between a heated pool or cold-water wild swimming. While the latter has been lauded for its health benefits, it’s not for everyone. “When I’ve tried wild swimming, I can’t stay in for long – I lasted maybe a few minutes before I came running out,” says Hay. “My sister is able to stay in much longer than me for some reason. I just think we handle the cold differently.”

Evidence for some of the mental health benefits of cold-water swimming cited in the media is a little thin, too. It’s largely based on the case study of one 24-year-old woman. So why has it proven so popular? And is Hay right; are some people just better at handling the cold than others?

The weather takes the cutting edge off our performance levels. In the cold our muscles slow, taking longer to tense and reducing our ability to both burst into action and the total amount of power generated (though this can be mitigated with a good warm-up beforehand).

The reasons for this decrease in performance in cold weather are a little complex, not least because our tolerance of the cold depends on our genetics, subcutaneous fat levels – the fat just beneath our skin – and body size. One suggestion is that when our bodies cool the rate at which we release energy in our muscle cells decreases.

But exercising in the cold has also been linked to better cardiac health, a stronger immune system and converting white fat cells to brown, contributing to more weight loss. So, if done safely, it could bring serious health benefits.

Some of us might have an advantage when it comes to working out in cold weather. One in five people lack the muscle fibre protein α-actinin-3. This mutation reveals a little bit about our evolutionary history and explains why some modern athletes succeed in the cold, while others remain frozen to the start line.

Sometimes called the “gene for speed”, α-actinin-3 gives athletes a competitive advantage when it comes to powerful bursts of energy and muscle recovery, but it might be less useful in other situations.

All of our skeletal muscles are made up of a combination of two types of fibre: slow-twitch muscle fibres and fast-twitch muscle fibres.

“Muscles have fibres of both types, but the percentages of each may differ from muscle to muscle and person to person,” says Courtenay Dunn-Lewis, a physiologist at the University of Pittsburgh.

Slow-twitch muscle fibres are responsible for slower, aerobic actions. These fibres keep us standing upright, they keep our head from falling forward, our jaw from slackening open, and they propel us through gentler forms of exercise like walking and jogging. If you have ever tried yoga or meditation and have been directed to consciously relax all the muscles in your body, you might be familiar with how many muscles are subconsciously engaged in the background. This isn’t muscle “tightness”, it is a normal bodily function called tonus – the slow-twitch muscle fibres’ way of stopping us flopping around.

Fast-twitch muscle fibres, on the other hand, respire anaerobically, can contract in quick bursts, but fatigue more easily. These fibres are only engaged when we need to lift something, jump, sprint or any of the other explosive movements that might be needed in anaerobic exercise. The protein α-actinin-3 is found only in these fast-twitch muscle fibres.

“About 80% of an elite athlete’s muscle fibres are either fast-twitch, if they are a power athlete, or slow-twitch, if they are endurance athletes,” says Dunn-Lewis. “Consider the long, slender physique of a marathon runner, whose predominantly slow-twitch muscle fibres may be small but are resistant to fatigue and provide lasting energy kilometre after kilometre. This person is also burning less energy in a given unit of time. By comparison, an American football player or hockey player has predominantly large fast-twitch muscle fibres, moves with power and speed, but fatigues quite quickly. Athletes with 80% of one fibre type are simply born lucky. For the rest of us, the percentages are closer to 50% fast-twitch and 50% slow twitch, and that percentage is determined at birth. Fibre type is determined strictly by the nervous system, and for that reason cannot be changed with exercise.”

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