It is typically more difficult for older adults than for younger people to keep their core temperature within a normal range, which makes them more susceptible to heat related stress and illness.
A study published in PloSONE by Joanie Larose and colleagues showed that this decline in thermoregulation starts already as you reach 40, and worsens gradually as you get older. This is important if you are a master athlete planning his/her race calendar for 2014: you might want to plan your most important races when the weather is not too warm.
Joanie Larose and her colleagues examined 85 male volunteers between 20 and 70 years old during 15-min bouts of cycling separated by 15 min rest. The total duration of the test was two hours.
To calculate the amount of heat generated, the researchers measured the volume of O2 and CO2 expired, as these volumes correspond to the amount of fat and glycogen burned to obtain energy. As they knew from the cyclometer how much of that energy was used for exercise, they could easily calculate how much had been transformed into heat.
The researchers used direct calorimetry to measure the total heat loss. This means that they examined the air of the cylinder-like room in which the volunteer was cycling, as any change in the temperature and humidity was due to heat loss from the cyclist.
The difference between the heat generated and the heat dissipated is stored in the body, and results in thermal strain. Joanie Larose showed that from 40 years onwards, men gradually become less good at dissipating the excess heat.
This is important, since it could lead to an increased core temperature. As this is dangerous for your health, your unconscious brain will do what it can to keep your core temperature within the normal range. During exercise, it will therefore slow you down by making you feel tired and reducing the amount of muscle fibres you can use.
Consequently, master athletes will find it more difficult to compete at their best in warm conditions. It is thus a good idea to plan your A races during cooler periods of the year.
This study has been performed on men, and we cannot assume that the same happens to women. We just do not know. Most studies show that women tend to sweat less than men, but it is no clear yet how this affects their thermoregulation. We need more research.
Jay O, Kenny GP. The determination of changes in body heat content during exercise using calorimetry and thermometry. J Hum Environ Syst. 2006; 10: 19–29. doi: 10.1618/jhes.10.19.
Larose J, Boulay P, Sigal RJ, Wright HE, Kenny GP. Age-Related Decrements in Heat Dissipation during Physical Activity Occur as Early as the Age of 40. PLoS ONE. 2013; 8(12): e83148. doi:10.1371/journal.pone.0083148.