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Sauna suits have been used for years, but we get the feeling they’re being used for the wrong reasons.

Our message for most things regarding training and preparing athletes is this:

There is a time and a place for most things. But do you know the optimal time and place? 

So we’re here to clear up a few misconceptions. What follows are 6 myths about sauna suits – all of which we well and truly knockout. 

Myth Knockout One – Sauna suits do not increase your metabolism

Firstly, let’s take a look at some basics of calorimetry. Metabolism, or rather metabolic rate (watts), is assessed using calorimetry. In our labs we do this by assessing oxygen uptake and carbon dioxide production.  Then we use known energy equivalents of oxygen to calculate metabolic rate. 

If you want to increase metabolism you have to place an energy demand on your body. This demand is assessed as oxygen uptake. If your body requires more oxygen it is exercising at a greater metabolic rate. The images below show how we assess boxers metabolic rate. 

Kell RMR

 

Simply wearing a sauna suit will not increase metabolism, especially at rest! – as usual, it is more complex than this. 

Myth Knockout Two – Sauna suits cause an increase in body temperature but do not 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. 

This is 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 your metabolic rate. 

Myth Knockout Three – Sauna suits don’t cause you to burn more fat

When you get hot – you’ll prefer to use carbohydrate as a fuel. Fat oxidation is likely to decrease because of this; plus you’ll be exercising at a lower intensity. So no, when you wear a sauna suit you won’t burn any more fat than without it- at best.

At worst, you’ll burn less fat!

We’ve known this for at least 15 years.

Muscle glycogen utilisation

The data above was collected by exercise physiologists and published in 1994. They asked 13 cyclists to exercise for 40 min. Once in an environment that was controlled at 20 C and once in 40 C. Then they assessed how quickly muscle glycogen (carbohydrate) was used during exercise. When the cyclist’s muscles were hotter in the 40 C trial, they used more carbohydrate as a fuel source and reduced the amount of fat they used.

So when you wear a sauna suit and get hot because of it, and you won’t be ‘burning’ more fat.

Myth Knockout Four – 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 your heart rate isn’t increasing because of an increase in energy demand (it’s lower Myth’s 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. 

Myth Knockout Five – Wearing a sauna suit does not act as a detox

Let’s get this straight. There’s no such thing as a detox. Yes, there are toxins and these are produced in our body, but we deal with these things pretty well. We certainly do not detox via sweat. 

Sweat is used to control body temperature via evaporative heat loss. It’s comprised of:

Water (99%)

Some electrolytes (sodium, chloride, potassium) 

Urea

Lactate

It’s worth mentioning that sweat is hypotonic compared to blood plasma. Hypotonic means that it’s ‘less concentrated’ than blood. If sweat was used to detox then it would behypertonicsince toxins would be present in sweat. 

There’s also no evidence to suggest that wearing a sauna suit benefits immune function. 

Wearing a sauna suit does not increase injury healing rates

To recap, a sauna suit will increase blood flow to the skin as you get hot. You get hot by exercising.

So if you’re injured you probably can’t exercise.

But if you can exercise then you’ll get hot. So where’s the blood directed towards? You guessed right, the skin, it is not preferentially directed to your injured site.

Even if it was, would it help healing rate? That depends on your injury. 

Summary

Sauna suits do not increase your metabolism

Sauna suits cause an increase in body temperature but don’t increase intensity

Sauna suits don’t cause you to burn more fat

You can’t use a heart rate monitor to assess energy expenditure when wearing a sauna suit

Wearing a sauna suit does not act as a detox

Wearing a sauna suit does not increase injury healing

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