First of all, before anyone puts a hit out on me, let me make it clear that I think yoga is great in a lot of ways, and I commend anyone who gets out and tries different physical activities. A big part of my job is just trying to help people find active hobbies that they don’t hate and will be likely to stick to, because doing something is obviously better than doing nothing. There’s a lot to enjoy about yoga, like the atmosphere, community, the aesthetics of the movement, development of a skill, possible stress relief etc.

However there are a lot of misconceptions about yoga that should be cleared up in order to avoid wasting time and effort on something that isn’t doing what you think it does. So, for starters:

1. Hot Yoga does not burn more calories than regular yoga. The bro-science goes something like “because I’m sweating, my body has to work harder to cool itself down.” This is not the case.
It should be understood that the process of burning calories is an inherently heat-creating process. So if your body is wanting to cool down, you’re probably going to work less hard in order to avoid creating excess heat by burning calories.

The number of calories you burn is determined by the amount of work you do, not by how hard the work felt.

So, heat will probably make you do less work in the same amount of time, due to a higher rate of perceived exertion.

Example: if you have 90 minutes to run as far as you can, you’re probably going to run farther on a cool day than on a very hot day, because the rate of perceived exertion will be lower. More distance covered = more calories burned. Less distance covered = less calories burned.

Additionally, research has shown that even if you do the same amount of work in different temperatures, you will still burn less calories in the heat.

One study compared two non-exercising groups in different rooms with different temperatures and found that despite no intentional differences in activity levels, the group in the warmer room burned less calories.

Other studies have also showed that people tend to burn substantially more calories in the cold than in the heat, due to brown fat activity. (See my article on brown-fat and cold exposure).

2. Yoga isn’t very good exercise. One study measuring caloric expenditure in hot yoga sessions showed that most people burned about 285 calories in a 90 minute session.
Another study concluded: “Metabolic costs of yoga averaged across the entire session represent low levels of physical activity, are similar to walking on a treadmill at 3.2 kph (~2mph) and do not meet recommendations for levels of physical activity for improving or maintaining health or cardiovascular fitness.”

Obviously there are different kinds of yoga, some more challenging than others, but these studies focused on what a typical person is likely to experience.

3. What about flexibility!? Yes. A lot of people could stand to be a little more flexible, but there’s no benefit to being more flexible than your sport or normal movement requires. Some research even suggests that increased flexibility can have a negative effect on certain kinds of performance, due to the decreased elasticity of muscles.

4. Yoga isn’t great for “toning”. Tone = more muscle and less fat in a given area. As we’ve discussed, yoga is suboptimal for weight loss, so we’re already missing that part of the equation. As for muscle, yoga can help you build a small amount of muscle (again: better than nothing), but for people who don’t like waiting longer than they have to to get what they want, resistance training and diet is gonna be your best bet on that front.

Conclusion: The fitness related benefits of yoga are probably overstated in general. Having said that though, I don’t want to deter anyone from trying it. Yoga is great if you just want to get good at yoga, you enjoy the culture and atmosphere, you find it helps relieve your stress or it has any other subjective benefit to you.

As always, sources are cited below!

Impact of stretching on the performance and injury risk of long-distance runners

https://www.tandfonline.com/doi/full/10.1080/15438627.2016.1258640

“…the literature does suggest that an increased running economy has a high association with inflexibility in endurance runners”

The Physiological Responses to Bikram Yoga in Novice and Experienced Practitioners:

https://search.proquest.com/openview/c583828cbbc25481bd8b2d185f46fcb4/1?pq-origsite=gscholar&cbl=32528

Most people burned about 285 calories in a 90 minute hot yoga session (179 = lowest 478 = highest).

Does practicing hatha yoga satisfy recommendations for intensity of physical activity which improves and maintains health and cardiovascular fitness?

“Metabolic costs of yoga averaged across the entire session represent low levels of physical activity, are similar to walking on a treadmill at 3.2 kph (~2mph) and do not meet recommendations for levels of physical activity for improving or maintaining health or cardiovascular fitness.”

https://bmccomplementalternmed.biomedcentral.com/articles/10.1186/1472-6882-7-40

Muscle blood flow and muscle metabolism during exercise and heat stress

“There was no increase in release of lactate and no reduction in glucose and free net fatty acid uptake in the exercising leg in the heat. Furthermore, the rate of glycogen utilization in the gastrocnemius muscle was not elevated in the hot environment. “

Individual variation in the relation between body temperature and energy expenditure in response to elevated ambient temperature

https://www.sciencedirect.com/science/article/abs/pii/S0031938401004772

“Exposure to 27°C (as opposed to 22 C) caused a significant increase in body temperature (both skin and core), a decrease in temperature gradients, and a decrease in energy expenditure. “