Sports scientists have been obsessed with the benefits of heat training, Alex Hutchinson notes:
The extra stress of heat triggers various adaptations that help you handle hot conditions, like more sweating. Some of these adaptations, like increased blood volume, may even give you a boost when competing in cooler conditions. As a result, many top athletes now incorporate elaborate heat protocols into their training.
Dominique Gagnon‘s research suggests that cold training has its own advantages:
Back in 2013, for example, he published data showing that cold-weather exercise relies on a different fuel mix than warmer conditions, burning more fat and less carbohydrate.
[…]
Human metabolism is only about 25 percent efficient — comparable to the internal combustion engine in your car — so three-quarters of the energy in your food is released as heat in the muscles. That means that the temperature inside your muscles can be high even when the rest of you is cool. The advantage of exercising in the cold, then, is that it prevents your muscle cells from overheating and enables them to keep burning more fat for aerobic energy, which relies on the mitochondria in your muscles. In the long run, that should boost mitochondria levels and train your body to become more efficient aerobically.
[…]
In Gagnon’s new study, 34 volunteers trained three times a week for seven weeks, doing interval workouts on an exercise bike. Before and after the training period, they had muscle biopsies, which involve removing a small chunk of muscle from the leg, in order to analyse how much mitochondria was present. Sure enough, the group that trained in 32-degree air [versus 77 degrees Fahrenheit] had a significantly greater increase in several different markers of mitochondrial content.
[…]
Stephen Cheung and his colleagues at Brock University in Canada showed that getting superficially cold, with no drop in core temperature, reduced time to exhaustion in a cycling test by about 30 percent. That involved sitting in a 32-degree room with a light breeze for half an hour before the subjects even started cycling. Staying in the room for longer, so that their core temperature actually dropped by a degree, reduced endurance by another 30 to 40 percent. This is not what Gagnon is aiming for.
Some mad scientist tried tubes from your arteries running through refrigerator coils during heavy exercise. Greatly increased endurance.
A refrigerated glove can cool humans quickly.