Let’s deal straight away with the elephant in the room – the heat. Do you wonder why it’s so hot, and what impact the heat has on your body? Love it or hate it, you certainly can’t ignore it. So let’s have a look at some of the available science and apply it to the hot yoga experience and see if a bit more knowledge changes your view of being in that hot torture chamber.
Dealing with the whole topic of how the heat affects us is a subject worthy of filling a whole book, and as this blog is way too short to do it justice, I’ll tackle the subject in bits at a time, and keep coming back to it in future blogs.
I will assume that you are all pretty happy with the fact that any exercise will demand more of your heart and lungs compared to when at rest. Your body needs more oxygen when working, and oxygen is delivered to working muscles by increased blood flow, which in turn is delivered by increased performance from your heart.
At the same time, an increase in temperature such as that found in the hot yoga room will cause blood to be pumped to your skin to cool you down. Your hot blood needs to be close to your skin so the heat can dissipate through the skin and out of the body, a bit like a radiator. (I’ll deal with the cooling effects of sweat in a future blog.)
Instantly, exercise and heat causes conflicting demands of the circulatory system – deliver blood to muscles or deliver blood to skin – which one? So already, the heat has made the yoga class more of a cardio-vascular challenge than if it was done at normal room temperature and increased the work your heart is doing just to keep you in the room. Your body has a limit to what it can do to meet these dual demands, and when that limit has been reached, you’re probably sat on your mat missing out a posture or two.
The body will chose to supply blood to working muscles first, at the expense of the skin1, and your ability to cope with the temperature becomes limited. Ever had one of those classes where you just can’t deal with the heat? Sitting down on the mat for a moment or two and resting the muscles doesn’t seem like such a bad idea, perhaps because the blood flow you have freed up by not working can now be used for temperature regulation instead, and you start to feel a little better.
The good news is that with practice, our bodies get acclimatised to the heat such that we become more able to cope with the demands made on us in all sorts of ways, and you need to sit down less and less.
Perhaps you will be slightly less reluctant to have that rest now?
(c) Dianne Tayles 2013.
 Gonzalez-Alonso J, Crandall CG, Johnson JM (2008) The Cardiovascular challenge of exercising in the heat. J Physiol 586.1 45-53
 Casa DJ. (1999) Exercise in the Heat. I. Fundamentals of Thermal Physiology, Performance Implications, and Dehydration. Journal of Athletic Training 34(3):246-252
 Saat M, Sirisinghe RG, Singh R, Tochihara Y (2005) Effects of Short-term Exercise in the Heat on Thermoregulation, Blood Parameters, Sweat Secretion and Sweat Composition of tropic-dwelling Subjects. J Physiol Anthropol Appl Human Sci 24:541-549