Sauna suits cause an increase in body temperature but don’t increase intensity
Humans waste a lot of energy. Most of the energy we create to move our limbs is wasted as heat. We need to remove that heat from our body to maintain our body temperature around 37 C. To do this (as adults) we sweat.
When we sweat, we transfer heat away from our skin and this helps to maintain our temperature. But if the air around our skin is humid and contains a lot of water, evaporation doesn’t work so well.
So when our sweating mechanism is impaired, we start to store heat and our body temperature rises. This exactly what happens when you wear a sauna suit because the sweat you produce has nowhere to go. It stays between your skin and the surface of the sauna suit.
This means you get hotter, and you sweat more.
But just because you get hotter doesn’t mean there’s an increase in intensity. Most likely you’ll be running or skipping if you’re wearing a sauna suit. As you feel hotter you’ll also think the exercise is harder. When you feel the exercise is harder, you’ll naturally slow down and drop your intensity.
It’s a subconcious behavioural mechanism that prevents you from putting too much strain on your body. When this happens energy demand, (reflected by oxygen uptake) decreases along with metabolism.
Even if you can fix the intensity of exercise, you’ll still be exercising at a relative intensity that is less than normal. And to top it off you’ll probably quit exercising because it will get too hard.
Crucially, in all cases you’ve cut metabolic rate.