RESEARCH REVIEW: Yoga to make you sweat

Yoga is a firm fixture in most fitness facilities these days – so what effect does the more vigorous, fitness-based variety have on heart rate and body temperature? Review by Dr Mike Climstein PhD & Joe Walsh

Title: Heart Rate and Thermal Responses to Power Yoga

Authors: Dr’s Schubert and colleagues. (Department of Kinesiology, California State University USA)

Source: Complementary therapies in clinical practice, 32, 195-199

Introduction: I’m originally from the South in the US, so it’s fair to say that I like the heat and humidity, grew up on it, so it really doesn’t bother me. Having also completed most of my training in the western US, where it snows and snows (Park City Utah and other resorts there get 12.5 to 13.7 metres of snow each season), I can confidently say that, having been there done that, it’s way too cold for me.

So when my partner Claire decided it was time we visit Uluru in Australia’s red centre I thought it was a brilliant idea, and off we headed. In February. Mistake number one. After a three-hour direct flight from Sydney we landed. Because it’s a regional airport, there’s no air bridge, so we descended the plane’s steps onto the tarmac and hit a wall of heat. The temperature hit 41°C every day we were there.

The itinerary that I had drawn up had us walking around the base of Uluru. The Traditional Owners, the Anangu people, do not climb Uluru because of its great spiritual significance and have long requested that visitors follow this example, partly due to the path crossing a sacred traditional Dreamtime track, and also due to a sense of responsibility for the safety of visitors (many people have died climbing Uluru, mainly from heart attacks). From 2019 this request will be replaced by an outright ban on climbing the rock.

So, now we were ready for mistake number two. My research told me that it was only a 10.6km walk around the base of Uluru, so I figured that, hydration-wise, our 1.5 litre and 0.75 litre water bottles would suffice. Needless to say, we only made it half way around the rock. Huge disappointment, but the heat stress I was experiencing was unbelievable, like nothing I had ever felt before.

So, given this recent experience, you can appreciate my hesitation when a friend asked me if I wanted to join her at a hot yoga session. I’m keen to improve my flexibility though, so what the heck, nothing ventured, nothing gained. Which leads us into this Research Review.

Yoga is very popular now, with an estimated 2 billion people practicing it worldwide. Here in Australia, it is believed 2 million people ‘grab a mat, take a breath and pose as a cobra, cat, child and downward-facing dog’ (Ray Morgan research, 2016). It’s been the fastest growing sport/physical activity in the country over the past eight years, and is especially popular with younger women (aged 14 to 34) and men (aged 25 to 34). There are many different branches and styles, however the research we are covering here pertains to ‘power yoga’, which is considered to be a vigorous, fitness-based type of yoga. The investigators chose to examine the heart rate, hydration and thermal responses to 45 minutes of power yoga in a neutral environment (23.5°C and moderate humidity of ~ 47%). The yoga session comprised 21 poses (Table 1 in the article has the complete list/order of movements/poses), most of which were held for approximately six breaths, while other poses were conducted ‘breath to movement’, which occurs when participants complete one pose per inhale or exhale (approximately three seconds).

The researchers recruited 27 healthy young men and women, inexperienced in yoga, to complete a 45-minute power yoga class in the neutral environment (23.5°C). The researchers measured heart rate with the use of Polar heart rate monitors (Polar OH1, which is worn on the upper arm) and used an iButton (a small microchip which is a digital thermometer) to record skin temperature.

Results: All of the subjects completed the yoga sessions without any adverse effects. With regard to heart rate, the authors chose to report the results in terms of heart rate zones, where light was < 60% maximum heart rate (HR max), moderate was 60 to 75% HR max, vigorous was 76 to 90% HR max and near maximal was > 90% HR max. From their overall results, they found the mean heart rate rose from approximately 80 beats per minute to a peak of approximately 150 beats per minute. Some participants’ heart rates rose to near 175 beats per minute, while others had a peak heart rate which rose to approximately 130 beats per minute. The majority of the participants’ heart rates were in the moderate to vigorous heart rate zones (36% and 38% respectively).

With regard to skin temperature, the mean starting skin temperature of the group was approximately 30°C and it rose to a peak of just under 32.7°C with participants experiencing a mean weight loss of 0.43% (0.28 kg). This loss of body weight equated to a fluid loss of approximately 280ml.

The authors concluded that cardiovascular demands of power yoga were such that it lay within the heart rate recommendations of the American College of Sports Medicine, i.e. that exercise intensity should lie between 65 and 90% of HR max if the goal is to improve cardiovascular health.

Pros: As the authors constantly measured heart rates and skin temperature over the entire power yoga session, this demonstrates the heart rate fluctuations between the different poses. However in the middle of the session, from roughly 10 minutes to 35 minutes (of the 45-minute session) heart rate remained fairly stable and elevated. With regard to skin temperature, it rose continually from the start of the session.

Cons: There are a number of benefits that can be gained by regular practice of yoga, however there are contraindications that some fitness enthusiasts need to be aware of for inverted poses, which includes individuals with heart conditions, glaucoma, uncontrolled high blood pressure, detached retinas, forward bending in individuals with osteoporosis, back extension in individuals with spinal stenosis or herniated discs and if you (or your clients) are pregnant. It is highly recommended you speak with your GP or specialist if you have any medical issues and are thinking about taking up yoga.

Incidentally, Uluru was an unreal experience which I highly recommend – just not in February!


References
Roy Morgan. (2016, October 13). Strike a pose: Yoga is the fastest growing fitness activity. [Press release]. Retrieved from here


Dr Mike Climstein, PhD FASMF FACSM FAAESS AEP is one of Australia’s leading Accredited Exercise Physiologists. He is a faculty member in Clinical Exercise Physiology, Sport & Exercise Science at Southern Cross University (Gold Coast). michael.climstein@scu.edu.au

Joe Walsh, MSc is a sport and exercise scientist. As well as working for Charles Darwin and Bond Universities, he is a director of Fitness Clinic in Five Dock, Sydney. fitnessclinic.com.au