Now temperatures are starting to increase as we edge into summer, it is important to understand how our bodies will react whilst out running. Many runners try and avoid the heat of the day at all costs, often opting for early morning or late evening runs.
80% of the energy generated by our muscles ends up as heat, and this is why exercise keeps us warm in colder temperatures. But when it is hot, the body needs to get rid of it to avoid overheating. One main method is through sweating, as well as diverting blood flow to the skin. However, when running your muscles need blood too, so it becomes a struggle between heat loss and muscle efficiency. Heat loss will always be priority to your body, so the hotter you are, the less oxygen your muscles receive, thereby reducing efficiency.
The human body is very adaptable, and can become more efficient is as little two weeks of training in warmer temperatures, where blood plasma volume starts expanding, giving you more fluid to sweat away without leading to dehydration. Increased blood plasma also makes it easier for the body to supply blood to the skin without overly reducing flow to the muscles. Once you have acclimatised, you start to sweat earlier on your run in anticipation of an increase in core temperature. You also sweat more, and your body holds on to salts more readily to allow efficient muscle function. Heart rate slows slightly to allow the chambers to fill more between beats, allowing more blood to be pumped to working muscles, and to cool the body.
Running in extremes of heat and humidity pushes your body to the very limits, where extreme sweating results in water and salt loss and in turn, insufficient heat loss. The only option here is to slow down so your muscles produce less heat. Staying hydrated and using electrolyte tablets ensures you stay hydrated, this enhances blood plasma volume and offers greater resistance to dehydration.
Preparation is everything, so when it does heat up, build up your training slowly to allow your body to acclimatise and become more efficient.