In 2014, when I arrived in Cambridge to complete my neuroscience internship, my lab was piloting a yoga study and I got involved. Yoga is in a unique position to improve well-being because it engages both the mind and body, two closely intertwined psycho-physiological loops. As a neuroscientist, this made a lot of sense to me. That's how nearly 2 years of data collection started, and, after countless hours of data analysis, we published the research in a peer-reviewed journal (full academic paper here).
Despite its high potential to promote well-being, I was surprised to discover that yoga remains relatively understudied. The burden of mental illnesses leads to an annual 1 trillion USD in lost productivity (World Health Organization, 2017), which motivates public funding to subsidise activities to enhance well-being. Yet, because there are many positive psychology interventions (yoga is only one of them) researchers' attention is divided.
So far in yoga research…
Most studies in the yoga literature have focused on participants with clinical conditions, like anxiety and depression, often with small sample sizes and low-quality study designs. For example, out of the 97 yoga studies reviewed, 90 had sample sizes of less than 200 participants, which may not have been sufficient to detect the main effects, examine underlying mechanisms, or explore individual differences. The number of yoga practitioners in the US surged from 20.4 million to 55.1 million between 2012 and 2020. Yet, research on the benefits of yoga for healthy adults has not matched this rise.
While many practice yoga to relieve mental ill-health, for the majority, it is about seeking overall well-being. That’s why focusing solely on the relief of clinical symptoms does not fully capture what these 55.1 million yogis might be seeking. Well-being is a complex concept, and previous studies have not often measured all the facets of well-being that could be influenced by regular yoga practice and its benefits. Specifically, there is limited research on the effects of hot yoga, which has gained a lot of popularity and attention.
The experiment
Our study examined the impact of hot yoga on different aspects of well-being and aimed to address limitations in previous research designs. We enrolled 290 healthy volunteers with no prior yoga experience to participate in a six-week randomised controlled trial (RCT).
137 participants received 90-minute sessions of Bikram yoga practised in a 105°F room for a maximum of four classes per week. They took part in an average of 17 yoga classes over 6 weeks out of 24 classes, which was equivalent to 2.8 classes per week.
153 participants were placed on a waitlist. They completed the yoga intervention after their waitlist period
To understand the impact of the yoga intervention on participants’ well-being, we collected the following data:
Before and after the intervention all participants (yoga or waitlist), completed a wide range of questionnaires including: general health, life satisfaction, peace of mind, mindfulness, eudaemonic well-being, psychological flourishing and mental health.
Throughout the study, both groups reported their emotional experiences four times per day using a dedicated app designed to assess their emotional well-being.
Results
Hypothesis 1: Hot yoga would have positive effects on a range of well-being indicators, including mindfulness, peace of mind, satisfaction with life, general health, eudaimonic well-being, and flourishing.
The results showed that the hot yoga group experienced improved well-being compared to the wait-list control group, from pre- to post-treatment. These improvements were observed in areas such as life satisfaction, general health, mindfulness, peace of mind, and eudaimonic well-being, but not in flourishing.
Hypothesis 2: Hot yoga would have a positive effect on daily emotions (e.i hedonic well-being) over time.
Using the app, we evaluated participants’ momentary emotions and measured their hedonic well-being in real-time. Our findings indicate that the hot yoga intervention was more effective in enhancing momentary positive emotional experiences compared to the wait-list condition. Only in the yoga group did these momentary positive emotional experiences increase significantly throughout the trial.
Hypothesis 3: The effect of hot yoga on daily emotions would last for a certain time.
We discovered that being at the yoga studio while completing one of the app surveys significantly predicted an increase in positive emotional experiences. Although we suspected that this positive effect might be due to the novelty of discovering yoga, it remained consistent throughout the six-week duration without any noticeable change over time. In other words, there was no habituation to this “positive boost” associated with being at the yoga studio throughout the study.
Hypothesis 4: The long-term benefits of hot yoga on well-being would be related to (and potentially caused by) the increase in daily positive emotions
Increases in positive emotion explained the improvement in post-yoga intervention for: mindfulness, peace of mind, and general health by 21%, 31%, and 11%, respectively. In other words, positive emotional experiences associated with practising hot yoga could be a key mechanism and reason why participants’ well-being increased after the trial. Those results are consistent with the “broaden and build” theory of positive emotions, which states that experiencing more positive than negative emotions broadens one’s awareness and encourages novel and exploratory thoughts and actions, thereby leading to resources for long-term well-being for individuals to flourish.
Hypothesis 5: People with lower levels of baseline well-being (before starting yoga) would benefit more from the increase in daily positive emotions than other
The benefits of hot yoga were more notable in individuals with lower levels of well-being before starting the yoga classes. Meaning, hot yoga participants with lower levels of flourishing, mental well-being, and eudaimonic well-being before starting classes, experienced a stronger boost in positive emotion during the six-week intervention. Our research has added valuable insights suggesting that people with lower levels of well-being, such as those who are depressed and stressed, were getting the most benefits from practising yoga.
Conclusion
Our research is probably the largest evaluation of the impact of yoga in general, and hot yoga in particular, on multifaceted well-being indicators so far. The study demonstrated a broad range of benefits from a six-week hot yoga intervention studied using a randomised controlled trial These benefits included the immediate boost of momentary hedonic well-being following the practice of hot yoga each time. This change could potentially explain the observed increase in post-treatment well-being, especially in people who had the lowest baseline well-being.
Coupled with previous empirical evidence, our findings may provide insights into not only positive psychological interventions but also the allocation of social resources to people most susceptible to mental health issues. While practising yoga, especially hot yoga, can be beneficial for healthy adults, it also holds promise in supporting vulnerable groups, such as individuals with mild psychological disorders or those at risk of developing mental health problems. Mental illnesses result in a global economic loss of at least $1 trillion annually due to decreased productivity, with depression being the primary risk factor. By providing hot yoga interventions to individuals at high risk and enhancing their well-being through this practice, we can alleviate a portion of the global burden at a reasonable cost. While future research should focus on evaluating the cost-benefit ratio of various psychological interventions, our study suggests that hot yoga could be a viable option.
You can find the full academic paper here.
There are some limitations to this study, which should be addressed in future experiments:
There is a lack of an active control group undertaking a different form of exercise. Engaging in hot yoga sessions up to four times per week constitutes a somewhat intensive physical exercise intervention which we were unable to disentangle this from other potential elements and their synergy.
We did not look into whether the benefit of the intervention could be translated into longer-term effects, such as the effects after one month or even half a year.
Although we recruited a community sample, female participants accounted for almost 80% of our sample, which might limit the applicability of our results to the general population.
We looked at only one specific type of yoga and have not addressed other variables, including the variety of yoga types (e.g., Hatha, Ashtanga, etc.), duration of classes (20 to 90 minutes), frequency of classes (daily, weekly), and lengths of yoga intervention (weeks, months).
The sample sizes of both groups could have been more balanced (137 vs 153). This imbalance may have occurred because the random assignment was done before the phone screening process. In future RCTs, conducting pre-screening before random assignment can help ensure a better balance of groups on potential confounding variables.