During the past several years, yoga has become very popular in the US. According to the Sporting Goods Manufacturers Association, more than 11 million Americans currently practice yoga. An article in the March 2006 issue of Runner's World magazine puts the figure at 16.5 million.

Yoga enthusiasts participate in this type of exercise in hopes of reaping benefits like improved muscle tone and strength, better balance and greater flexibility. However, according to the Runner's World article, yoga is a great addition to the training program for runners, too.

HISTORY OF YOGA

The origins of yoga can be traced all the way back to 2250 BC when the Harrapan civilization in Northern India began to develop postures and breath-control techniques that they hoped would enable them to enter an altered consciousness and access the spirit world.

TYPES OF YOGA

There are many types of yoga. Two of the more popular styles are Hatha yoga and Ashtanga yoga, more commonly known as "Power" yoga. Regardless of the type, all forms consist of a series of sustained poses known as "asanas".

Hatha yoga: Hatha yoga is an eclectic blend of many yoga styles. This type of yoga is frequently recommended for beginners, or for people who are concerned about over-stressing their shoulders, knees, or lower back. Hatha yoga seeks to achieve a balance of mind, body, and spirit through specific poses (asanas) and breathing.

Ananda yoga: This type of yoga is more gentle. It is an inward-focused style that is not as athletic or aerobic as other styles.

Ashtanga yoga: "Power" yoga generally refers to a yoga style that is intense and vigorous. Originally intended to describe an Ashtanga yoga class, this term is now used more loosely. Any yoga class that is a modification of Ashtanga yoga or includes demanding poses and an intermittent flow of movement might be identified as a “power yoga” class. These classes are designed to create a balance of strength, flexibility, and stamina.

Power yoga includes many postures that develop strength in the legs, back, and abdominals, as well as weight-bearing poses that build upper-body strength. When Sun Salutations are included they are usually repeated several times as a warm-up, then repeated throughout the class. Various poses are held for several breaths in between these repetitions.

Bikram yoga: The concept here is that the body is more flexible in a hot environment. So, Bikram yoga involves a series of 26 asanas performed in a room that may be as hot as 100 degrees.  This is to warm up your whole body, and allows you to work deep into your muscles, tendons, and ligaments.  Bikram Choudbury founded the Yoga College of India in Beverly Hills in 1974.  He is one of the pre-eminent Hatha Yoga Masters living today.  His physical fitness Guru was Bishnu Charan Ghosh, brother of Yogananda, founder of The Self-Realization Fellowship.  Bikram is an India National Yoga Champion and has been named most knowledgeable Hatha Yoga teacher in the world.

Iyengar yoga: This style of yoga focuses on precise alignments of each pose, and uses props such as belts and blocks to achieve ideal alignment.

Kundalini yoga: Kundalini yoga is a complete science that combines breathing (pranayama), chanting (mantra), exercises (Kriyas), and meditation.

Vinyasa yoga: Vinyasa yoga is also considered a "power" yoga style. It is recommended for intermediate and advanced students.

RESEARCH ON YOGA TO IMPROVE FITNESS

Potential benefits of yoga include increased strength and endurance, improved balance, and better flexibility. However, despite yoga's long history and the large number of faithful participants, very little research has been conducted regarding its physical benefits.

A small study from the University of California at Davis (Tran MD, et al. 2001) showed that 2 Hatha yoga sessions per week for 8 weeks improved a variety of fitness parameters. Each session consisted of 10 minutes of pranayamas (breath-control exercises), 15 minutes of dynamic warm-up exercise, 50 minutes of asanas (yoga postures), and 10 minutes of relaxation in savasana (corpse pose).

After 8 weeks, the following improvements were seen:

Muscular Strength:

• triceps (elbow extension) strength increased by 31%
• biceps (elbow flexion) strength increased by 19%
• quadriceps (knee extension) strength increased by 28%

Muscular Endurance:

• muscular endurance (measured by knee flexion) increased by 57%

Flexibility:

• ankle flexibility increased by 13%
• shoulder elevation increased by 155%
• trunk extension (leaning backwards) increased by 188%
• trunk flexion (bending forward at the waist) increased by 14%

Another study of Hatha yoga comes from the University of Wisconsin. Researchers Dawn Boehde, a certified yoga instructor, and John Porcari, PhD, from the University's Human Performance Laboratory recruited 34 healthy women (average age: 33) for the study. All of the subjects were sedentary and could not have been involved in a regular exercise program or yoga training for six months prior to the study.

The test subjects were divided into a yoga group and a non-yoga control group. The yoga group participated in 55-minute Hatha yoga classes, three days a week. During the eight-week study period each participant completed an average of about 21 classes.

All of the yoga classes were taught by Boehde. Each started with five minutes of relaxation and yoga breathing (pranayama), followed by 10 minutes of warmup exercises including sun salutations, 35 minutes of yoga postures (asanas), and, finally, five minutes of relaxation and yoga breathing in the corpse pose (savasana). The non-yoga group was prohibited from participating in any form of exercise.

Testing Protocol

Subjects were tested prior to and following the eight week study period using this standard battery of tests:

• Flexibility: Back Scratch, Functional Reach Test, Trunk Rotation, Trunk Flexion and Extension, Trunk Lift, Shoulder Elevation, Ankle Plantar Flexion and Dorsiflexion, Modified Sit-and-Reach
• Balance: One-Legged Stand
• Muscular Endurance: ACSM Modified Push-up Test and Curl-up Test
• Aerobic Capacity: Maximal heart rate and VO2 max
• Pulmonary Function Tests: Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1)

Results

Researchers found that the regular practice of Hatha yoga significantly improved the subjects' flexibility, muscular strength and endurance, and balance:

•Flexibility: After eight weeks, the average flexibility of the yoga group improved by 13-35% and the gains were significantly greater than the non-yoga group, especially in shoulder and trunk flexibility, and ankle range of motion. “We saw very nice changes in flexibility of the entire body, the shoulder girdle, twisting, bending, reaching, good low-back flexibility,” says Porcari.

•Muscular strength and endurance: Similarly, muscular strength and endurance also improved in the yoga group. In particular, chest and abdominal strength and endurance was increased significantly, enabling the yoga group to perform an average of six more push-ups and 14 more curl-ups following the study period.

•Balance: The yoga group experienced a 17-second increase in their one-legged stand time and a modest boost in their functional reach scores. Besides the obvious improvements yielded by simply practicing the variety of one-legged moves that are common in Hatha yoga, researchers point to increased proprioception and strengthening of the muscle in the ankles and legs as part of the reason for the better balance scores.

“For the average person who doesn't have a fitness program, this study shows what would happen if you did eight weeks of Hatha yoga,” explains Boehde.

YOGA IS NOT AN AEROBIC EXERCISE

However, with regards to aerobic fitness, the UC Davis study found that VO2max increased by only 6-7% and there was no significant change in VO2max or maximal heart rate in the U. Wisconsin study. "You get changes in strength and muscular endurance, flexibility, balance -- all those types of things -- but in order to improve aerobic capacity you really have to be working in the aerobic training zone," says Porcari. "Based on what we found, the intensity just wasn't there."

As a companion to the Hatha yoga study summarized above, Porcari and Stefanie Spilde analyzed the exercise intensity and caloric expenditure of two types of yoga. For this study, researchers recruited 15 participants, with at least an intermediate level of yoga experience, and monitored their exercise intensity as they participated in two 50-minute yoga sessions (one Hatha yoga, one Power yoga) following a videotaped routine for consistency.

Researchers found that a 50-minute session of Hatha yoga burns 144 calories, equivalent to a slow walk, and provides no substantial aerobic benefit. Power yoga burns about 237 calories in 50 minutes and boosts heart rates to 62 percent of heart rate max (HRmax), providing just a mild aerobic workout.

Another study showed that 30 minutes of Hatha yoga produced an average heart rate of only 105 beats per minute in middle-aged women. The energy costs of this yoga session were about half that of walking on a treadmill at 3.5 mph and only about 10% greater than sitting in a chair. The authors concluded that "Hatha yoga may have little, if any, cardiovascular benefit" (Clay CC, et al. 2005).

"Yoga is a great muscular workout and you certainly sweat, but it's not an aerobic workout," says John Porcari, PhD.

YOGA FOR BACK PAIN

A study from the University of Washington in Seattle showed that one 75-minute viniyoga class per week for 12 weeks led to more improvement than conventional therapeutic exercise in patients with chronic back pain. Each class included an initial and final breathing exercise, 5 to 12 postures, and guided deep relaxation. Most postures were not held but were repeated 3 or 6 times (Sherman KJ, et al. 2005).

RISKS

Although yoga is a low-impact exercise, it is not without risks.

Musculoskeletal Injuries

Poses such as the plank, half moon, boat, camel and revolved triangle improve strength because they require one to support his or her upper body. However, some of these postures have the potential for straining the shoulder, knee, or lower back. For example, a frequently performed upper-body pose in a power yoga class is the yoga-style push up, Chaturanga Dandasana. This movement requires a lot of strength in the upper arms, shoulders, and lower back.

Stuart M. McGill, PhD, a professor at the University of Waterloo in Ontario, Canada, is a recognized expert in spine injuries and rehabilitation. He has published extensively on spine management. According to McGill, research shows that sustained contraction of the torso muscles causes them to lose oxygen rapidly (McGill SM, et al. 2000). He recommends that postures that require a sustained contraction of the torso muscles should not be held for longer than 5-6 seconds. Instead, to build up the muscular strength and endurance of your back muscles, it is better to do more reps, NOT attempt to hold each position as long as you can. (This concept is explained in greater detail in the related story "Exercise and Back Pain". See Articles.)

Cardiovascular Risks

Power yoga classes present a higher cardiovascular risk than other forms of yoga. Therefore, participants who have existing cardiovascular disease, hypertension, type 2 diabetes, or who are significantly overweight should probably avoid these classes, at least, when first starting out. Participants should be physically fit before participating in power yoga.

YOGA vs. OTHER FORMS OF EXERCISE

Hatha yoga will improve your strength, but you'll get much stronger, more quickly, by simply lifting weights, Pocari says. As for a cardiovascular workout, yoga isn't the answer for that either.

Researchers warn that efforts to boost the cardio benefits of yoga will only result in reduced flexibility and balance benefits. "It's always a tradeoff," says Porcari. "Yoga was designed for relaxation, primarily. The more aerobic you make yoga, the less improvements you'll see in those other areas."

“People's expected benefits need to be in-line with reality,” suggests Porcari. “People often try to make yoga into this all-encompassing thing. Americans have changed yoga and tried to morph it into programs that will improve every aspect of fitness but it was never designed that way.”

That said, some of these "hybrid" forms of yoga do seem appealing. For example, the local yoga studio in my neighborhood offers classes that combine yoga with Pilates (eg., "Pilates mat class", "Yogilates", etc.). "Iron Yoga" is yet another style that Anthony Carillo promotes in his book and DVD (www.IronYogaBook.com).

Nevertheless, Hatha yoga is still an excellent addition to any fitness routine, particularly because it targets aspects of fitness such as flexibility, balance, and relaxation that are often skipped or overlooked.

SUMMARY

Newcomers will benefit from taking a beginner's yoga course to become familiar with a basic repertoire of asanas before joining a power yoga class. In power yoga, proper alignment and good body mechanics are crucial. A preparatory class in which the poses and sequences are broken down is recommended. People with back problems or joint issues should approach this style cautiously.

• Postures that require a sustained contraction of the torso muscles should not be held for longer than 5-6 seconds. Instead, build up the strength and endurance of these torso muscles by doing more reps, NOT by holding each position as long as you can.

• Power yoga classes present a higher cardiovascular risk than other forms of yoga. Power yoga is not recommended for people with hypertension or heart problems, type 2 diabetes, or who are significantly overweight. Participants should be physically fit before participating in power yoga.

FOR MORE INFORMATION

• General information: A general information site on yoga is Yoga Movement (www.YogaMovement.com).

• Bikram Yoga:  The web site for Bikram Yoga is BikramYogaNYC.com.

• Yoga on your computer: Yoga Today (www.YogaToday.com) offers a streaming video of a yoga class conducted outdoors in Jackson Hole, Wyoming.

• Find an instructor: To find a knowledgeable yoga instructor, go to www.YogaAlliance.com. Yoga Alliance® registers both individual yoga teachers and yoga teacher training programs (schools) who have complied with minimum educational standards established by the organization.

• Yoga for men: Yoga is not just for women. Check out the books Yoga For Regular Guys: The Best Damn Workout on the Planet! by former wrestler Diamond Dallas Page, and Real Men Do Yoga by John Capouya.

• Yoga for tennis players: Yoga Movement (www.YogaMovement.com) summarizes a yoga routine for tennis players originally published in Tennis magazine.

• Yoga for personal trainers: Personal trainers interested in learning how to lead yoga classes should visit www.YogaFit.com. YogaFit was founded by Beth Shaw in 1994 and is the leader in training programs for yoga instructors.

Readers may be interested in the following related stories:

• Balance: An Overlooked Element of Fitness?
• Core Training (coming soon)
• Exercise and Back Pain
• Pilates
  
• Stretching

PERSONALIZED FITNESS COUNSELING

If you'd like some help designing your personal fitness program, or have questions regarding exercise, or simply want some regular motivation, sign-up for our Fitness Counseling Service. It may be the best investment in your health that you'll ever make.

REFERENCES

Axler C, McGill SM. Low back loads over a variety of abdominal exercises: searching for the safest abdominal challenge. Med Sci Sports Exerc 1997;29:804-811. Abstract

Clay CC, Lloyd LK, Walker JL, et al. The metabolic cost of hatha yoga. J Strength Cond Res 2005;19:604-610. Abstract

McGill SM, Hughson RL, Parks K. Lumbar erector spinae oxygenation during prolonged contractions: implications for prolonged work. Ergonomics 2000;43:486-493. Abstract

Sherman KJ, Cherkin DC, Erro J, et al. Comparing yoga, exercise, and a self-care book for chronic low back pain. Ann Intern Med 2005;143:849-856. Abstract

Tran MD, Holly RG, Lashbrook J, et al. Effects of Hatha yoga practice on the health-related aspects of physical fitness. Prev Cardiol 2001;4:165-170. Abstract

ABOUT THE AUTHOR

Stan Reents, PharmD, is a former healthcare professional. He holds Personal Trainer and Lifestyle Counselor certifications from the American Council on Exercise and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics).  He can be reached at: Editor@athleteinme.com.