EXCLUSIVE ACE-SPONSORED RESEARCHACE STUDY

EXAMINESEFFECTS OF
BIKRAM YOGAON CORE BODY TEMPSBY EMILY QUANDT, M.S.,
JOHN P. PORCARI, PH.D.,
JEFF STEFFEN, PH.D.,
MANNY FELIX, PH.D.,
AND CARL FOSTER, PH.D.,
WITH DANIEL J. GREEN

ACE-sponsored research
examines heart-rate
and core-temperature
responses to Bikram yoga.

A TYPICAL BIKRAM YOGA SESSION IS 90 MINUTES LONG
and consists of 26 poses and two breathing exercises, all performed in aroom heated to 105° F with 40 percent humidity. Practitioners often findthemselves absolutely drenched in perspiration by the end of a session,
their yoga mats puddled with sweat. For many Bikram enthusiasts, having
the mental strength and focus to overcome this type of challenge is a big
part of the draw. It is primarily advocates of this extreme version of “hotyoga” who claim improved mindfulness, flexibility, strength, muscle tone
and general fitness as a direct result of practicing this form of yoga.

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temperature sensor (CorTemp Ingestible Core Body
Temperature Sensor, HQ Inc., Palmetto, Fla.) and wasgiven a heart-rate monitor (Polar HR monitor, HRM
USA Inc., Warminster, Pa.) to wear during the Bikram
yoga class.
Core temperature was recorded prior to the startof class, as well as every 10 minutes throughout thesession. Heart rate was recorded every minute during
the class and session ratings of perceived exertion(RPE) were recorded at the end of class using theBorg 1 to 10 scale.
Research conducted in the past few years has provided
some support for these claims, while also finding
benefits in the form of lower perceived stress levels,improved cardiorespiratory endurance and improved
balance (Hewett et al., 2001), as well as increased
dead lift strength and shoulder flexibility, and modestly
decreased body-fat percentages (Tracy and Hart, 2013).
In addition, Hunter and colleagues (2013) found that
Bikram yoga improved overall glucose tolerance andinsulin resistance in older adults who were at highrisk of developing metabolic disease.
Despite all of these proven benefits, the questionof whether or not it is safe to practice yoga in such a
hot and humid environment has remained. To betterunderstand the body’s response in such a setting,ACE enlisted John P. Porcari, Ph.D., and his teamof researchers at the University of Wisconsin–La
Crosse’s Department of Exercise and Sport Scienceto investigate.

THE STUDY

The research team recruited 20 apparently healthy
volunteers, seven males and 13 females, ranging inage from 28 to 67 years old. All of the participants
were regular practitioners of Bikram yoga, which means
they were familiar with the 26 standard poses andacclimatized to the hot and humid exercise environment.
Participants in the study provided written informed
consent, and approval from the University of WisconsinLa Crosse Institutional Review Board for the Protection of
Human Subjects was obtained prior to the study.
Before participating in the session, which wasconducted at a Bikram yoga studio by a certified
instructor, each participant swallowed a core body

2| May 2015 • ACE PROSOURCETHE RESULTS
While heart rate fluctuated throughout classdepending on the difficulty of the pose being
performed, core temperature steadily increased
throughout the 90-minute class for both men andwomen. It is important to note that heart rate,
maximum heart rate and RPE were consistent
between genders, but when the average heart rateand highest heart rate attained were presented
as a percentage of maximum heart rate, men had
significantly higher values than women. The averageheart rate was about 80 percent of the predictedmaximum heart rate for men and 72 percent for
women. The highest heart rate recorded during theclass among the male participants was 92 percent of
the predicted maximum heart rate, while it was 85
percent for the female subjects.
The average highest core temperature was103.2 ± 0.78° F for men and 102.0 ± 0.92° Ffor women, with men having a significantly higher
core temperature overall. Of the individuals in thisstudy, one male participant had a core temperatureof 104.1° F by the end of the 90-minute class, andseven of the 20 subjects had a core temperature
greater than 103° F. While none of these subjects
exhibted signs or symptoms of heat intolerance, coretemperatures such as these can pose concern forsome participants, as the risk for heat-related illness
increases at 104° F. [Note: The National Athletic
Trainer’s Association (NATA) and the American
College of Sports Medicine (ACSM) both state thatexertion-related heat illness and heat stroke can occur
at a core temperature of 104° F.]

Interpreting the Results
Emily Quandt, M.S., who led the study, says that thefact that the core temperature saw a steady increaseduring the class raised her concern for participants,
especially given that the postures performed in a Bikramclass focus primarily on balance and strength rather
than cardiovascular training. “The dramatic increases
in heart rate and core temperature are alarming when
you consider that there is very little movement, andtherefore little cardiovascular training, going on duringclass,” says Quandt. She goes on to explain that, while
the excessive perspiration that participants experienced
during class is often cited by those who practice thisstyle of yoga as a benefit in terms of the release of
toxins, the results of this study show that this sweating
was insufficient to cool down the body.
Quandt offers three recommendations to improve
the safety of Bikram yoga sessions: Shorten the class,lower the temperature and focus on hydration. Let’slook at each of these suggestions individually.

just one designated water break. However, many teachers
acknowledge that students should hydrate as needed
throughout the 90-minute session. For some Bikram
enthusiasts, minimizing the number of times water
is consumed during class is perceived to add to themindful aspects of the practice, as fewer water breaks
decreases the potential for mental distraction. Of course,
most exercise scientists could not disagree more.
“Nothing is gained from withholding water in anysetting,” argues Dr. Porcari, head of the University’s
Clinical Exercise Physiology program. “Exercise leaders
must actively encourage hydration, particularly whenclasses take place in extreme environments like thoseseen in Bikram yoga classes.”
Bikram yoga teachers should be familiar withessential exercise science principles and concepts,
says Dr. Porcari, as a clear understanding of thephysiology of thermoregulation is important. “Knowing
the risks associated with things like blood pooling andvasodilation, as well as the signs and symptoms ofheat-related illness, is absolutely essential.”

Duration
Quandt points out that the participants startedto experience dangerous core temperatures about
60 minutes into the session (remember, coretemperature was not posture-specific, but instead rosesteadily over the duration of the class). Shortening theclass to 60 minutes or less could help to minimize thepotential for heat intolerance among students.

Temperature
Lowering the temperature of the room might seem
obvious to some, but as a signature aspect of thisstyle of yoga, many believe the high temperatures arewhat help drive the benefits. Like Quandt’s suggestion
regarding the duration of the session, such changeswould significantly alter the very essence of Bikram
yoga, given that the 26 poses, a room temperature of
105° F with 40 percent humidity and 90 minutes induration are the very things that define this particular
style of yoga.
Which brings us to hydration…

Hydration
Hydration lies at the heart of the Bikram yoga
controversy, as in many classes there is commonly

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Cedric X. Bryant, Ph.D., Chief Science Officerat ACE, agrees with Dr. Porcari. “Bikram teachers
should recognize that participants’ thermoregulatory
systems will be challenged in this environment,” says
Dr. Bryant. “It is essential that they are aware of theearly warning signs of heat intolerance.” These signs
include cramps, headache, dizziness and general
weakness. It is important that teachers respond
appropriately and are trained in what to do in theevent of an emergency to keep the participant’s safety
as the top priority (see Table 1).

THE BOTTOM LINE

Although there are potential benefits assiciatedwith practicing Bikram yoga, the potential for heat
intolerance among some students, including those
who may not yet be acclimatized to the heat, should
not be entirely overlooked. Although an extreme
core temperature was not seen in all participants inthe study and no signs of heat-related illness wereobserved, a large number of the participants reacheda core temperature greater than 103° F, with one man
exceeding 104° F.
Exercising in hot and humid environments—
whether inside a studio while practicing Bikram
yoga or outside running during the warm months ofsummer—can place participants at risk for heatrelated illness, especially if those individuals do notadequately hydrate before, during and after exercise.
Instructors of Bikram yoga, fitness professionals wholead outdoor exercise sessions, and physical-activity
participants who simply like breaking a sweat in hotand humid conditions should all be educated on therisks, and recognition and prevention of heat-related
illness. Not only does it take time for the body toacclimate to activity performed in hot and humid
environments, proper hydration is crucial.
“Given the popularity of Bikram yoga and its provenbenefits, it is likely here to stay,” says Dr. Bryant. “Itis our job to make sure it is done safely.”

REFERENCES
Hewett, Z.L. et al. (2011). An examination of the effectiveness ofan 8-week bikram yoga program on mindfulness, perceived stress, &physical fitness. Journal of Exercise Science & Fitness, 9, 2, 87–92.
Hunter, S.D. et al. (2013). Improvements in glucose intolerancewith bikram yoga in older obese adults: a pilot study. Journal ofBodywork & Movement Therapies, 17, 4, 404–407.
Tracy, B.L. and Hart, C.E.F. (2013). Bikram yoga training &physical fitness in healthy young adults. Journal of Strength &Conditioning Research, 27, 3, 822–830__________________________________________________________________
Daniel J. Green is an editorial consultant and freelance writer basedin Asheville, N.C. In addition to his consulting work with organizations
including the American Council on Exercise, International Associationof Fire Fighters and Agriculture Future of America, Daniel has writtenfeature articles for local publications in Western North Carolina (WNC),
including WNC Parent and WNC Magazine.

Heat Exhaustion and Heat StrokeHeatExhaustion

Signs and Symptoms

Treatment

Weak, rapid pulse

Stop exercising

Low blood pressure

Move to a cool, wellventilated area

Fatigue
HeadacheDizziness
General weakness
Paleness
Cold, clammy skin

Lay down and elevate
feet 12–18 inches(30–46 cm)
Give fluids
Monitor temperature

Profuse sweating
Elevated body core temperature (<104° F or 40° C)
Heat Stroke

Hot, dry skin

Stop exercising

Bright red skin color

Remove as much clothing
as feasible

Rapid, strong pulse
Change in mental
status (e.g., irritability,aggressiveness, or anxiety)
Labored breathing
Elevated body core temperature (≥105° F or 41° C)

Try to cool the body
immediately in any way
possible (wet towels, icepacks/baths, fan)Give fluids
Transport to emergency
room immediately

This study was first published in the April 2015 issue of the Gundersen Medical Journal.
Quandt, E., J.P. Porcari, J. Steffen, M. Felix and C. Foster. Heart rate and core temperature
responses to Bikram yoga. Gundersen Medical Journal (in press).

4| May 2015 • ACE PROSOURCEPractical Tips for Teaching a Bikram Yoga Class
Jessica Matthews, M.S., E-RYT 500, senior advisor
for health and fitness education for ACE, offers thefollowing practical tips for certified practitioners
teaching Bikram yoga or any form of hot or heated yoga.
Create a class culture that encourages adequate
hydration. While some yoga teachers and styles of yoga
strongly dissuade students from consuming water at any
point during a class, in a hot and humid environment
in which classes range from 60 to 90 minutes inlength (Bikram classes are typically 90 minutes inlength; hot and heated yoga classes can vary from 60to 90 minutes) ongoing hydration is imperative froman exercise physiology perspective. Increased sweating
results in a greater reduction of water in the body, which
can lead to dehydration. In addition to encouraging
students to adequately hydrate before and after class,
you should also extend to students aninvitation and permission to consume
water as needed throughout the hot
yoga class experience as they deem
appropriate.
Offer students the time and space toacclimate. It is important to remind
students, whether they are newcomers
to yoga or experienced Bikram
practitioners, that it takes time for thebody to acclimate and re-acclimate
to performing physical movements ina heated environment. On average,
it takes approximately 10 to 14 days for most healthy
individuals to acclimate to engaging in physical activity
in a heated environment. It is also important to offer
students options to regress poses throughout the classand to encourage them to perform resting, grounding
postures as needed.
Remain present in your teaching and cognizant of signsof heat-related illness. Mindfulness is such an important
aspect of a yoga practice, and it is imperative thatyou remain present and are able to identify any signsof heat-related illness that may arise during a Bikram
or hot yoga class experience. While heavy sweating is

not unusual in a hot or heated environment, profuse
sweating coupled with other symptoms (as summarizedin Table 1) warrants moving the individual outside of theroom to a cooler location to lie down and apply cool, wet
towels to the body, and having the participant consume
water while you contact emergency personnel.
If a student exhibits signs of heat stroke, which
can come on very suddenly and quickly become life
threatening, emergency medical attention must becontacted immediately. Being fully present and aware
during each class ensures your students’ safety andwell-being.
Embrace the process of sweating and encourage
students to do the same. In Bikram and hot yoga
classes, it is not uncommon to encounter students
who feel embarrassed or ashamed about how muchthey sweat. It is important that youease anxieties about how students
feel they will be perceived byothers by educating them about
the importance of sweating. Whilesweating is important, the processof sweating alone does not cool thebody; rather, it is the evaporation
process that ultimately protects thebody from overheating. Therefore,
you can encourage students not only
to embrace the natural process ofsweating during hot yoga classes,
but also encourage them to avoid
becoming distracted in their practice by constantly
wiping sweat from their skin, which, from a safety
perspective, can lessen the amount of evaporative
cooling that occurs, resulting in retained body heat
and, in turn, an increased risk of dehydration andoverheating.
To promote student safety, you can encourage themto utilize a yoga mat that has absorbent qualities and/or to place a specifically designed yoga mat towel—suchas those made by Gaiam (Gaiam Americas, Inc., WestChester, Ohio) or YogiToes (YogiToes, LLC, El Segundo,
Calif.)—atop their existing yoga mat to help absorb themoisture to reduce the risk of slipping while practicing.

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