You can’t use a heart rate monitor to assess energy expenditure when wearing a sauna suit
If you’re one of those people that points to an increased heart rate whilst wearing a sauna suit as evidence for an increase in energy expenditure, stop it.
When body temperature increases, blood is sent to the skin surface to help you cool down. That means it’s more difficult to get the blood back to your heart and pump oxygen rich blood to muscle and brain. So to maintain cardiac output, heart rate increases.
If you don’t already know, your heart rate monitor will use an equation to estimate energy expenditure. That equation obviously depends on heart rate. But you’re heart rate isn’t increasing because of an increase in energy demand (it’s lower see myth bust 1 and 2) so your interpretation is flawed.
Even worse, if you’re using this data to manage your energy intake, then you could be eating more than you actually need to.
For example, your heart rate monitor says you expended 500 Kcals, then you replace that 500 Kcals. But you actually expended 300 Kcals. You’ve just eaten 200 Kcals more than you needed to.
Needless to say, this has implications for making weight.