Hatha yoga, or, as it is commonly called in the US, simply “yoga,” is an exercise system derived from ancient traditions in India. There are many schools or varieties of hatha yoga, but all of them involve “asanas,” or postures. Many asanas function as gentle stretching exercises, increasing flexibility. Others encourage the development of strength and balance.
The practice of hatha yoga goes beyond exercise, however. Special breathing techniques are almost always part of the process; in fact, some forms of yoga focus primarily on breathing, and therefore overlap with traditional breathing practices generally known as pranayama. Because hatha yoga originated in traditional Hindu spiritual practice, it can involve meditation, chanting, as well as philosophical and religious introspection. However, completely secular versions of hatha yoga are widely available.
Hatha yoga is believed by its practitioners to provide benefits above and beyond simple exercise. For example, certain asanas are said to address specific health problems. However, there is only minimal scientific evidence that the practice of hatha yoga actually provides any well-defined medical benefits.
What Is the Scientific Evidence for Hatha Yoga?
Although there is some evidence that yoga may offer medical benefits, in general, this evidence is not strong. There are several reasons for this (including funding obstacles), but one is fundamental: Even with the best of intentions, it is difficult to properly ascertain the effectiveness of an exercise therapy like yoga.
Only one form of study can truly prove that a treatment is effective: the double-blind, placebo-controlled trial. However, it isn’t possible to fit yoga into a study design of this type. While it might be possible to design a placebo form of yoga, it would be quite difficult to keep participants and researchers in the dark regarding who is practicing real yoga and who is practicing fake yoga.
Some compromise with the highest research standards is, therefore, inevitable. Unfortunately, the compromise used in most studies is less than optimal. In these trials, yoga has been compared to no treatment. The problem with such studies is that a treatment—any treatment—frequently appears to better than no treatment, due to a host of factors. (See Why Does This Database Rely on Double-blind Studies? for more information.) It would be better to compare yoga to generic forms of exercise, such as daily walking, but thus far this method has not seen much use.
Given these caveats, the following is a summary of what science has found out about the possible medical benefits of yoga.
#Possible Benefits of Hatha Yoga
Yoga, like Tai Chi , has been advocated as a means of increasing strength, balance, and physical function in seniors. However, there is as yet little scientific proof that yoga offers such benefits or that it is superior to generic exercises such as walking. There is little doubt that yoga, like any form of stretching, will increase flexibility if it is practiced consistently and over a long period of time. 4 Hatha yoga is also said to relieve tension and stress . In one study of 65 women with depression and/or anxiety, a 2-month yoga program specifically designed to address these emotional conditions significantly reduced anxiety (but not depression) compared to enrolled woman who were waiting for the program to begin . 6 Another study found that participation in a 6-week yoga program was associated with reduced anxiety, depression and stress in women having radiotherapy for breast cancer. 7 Finally, a trial of 122 healthy pregnant women demonstrated that daily yoga practice incorporating deep relaxation significantly reduced self-perceived stress scores compared to standard prenatal exercises. 8 Weak evidence hints that hatha yoga may offer modest benefits for people with chronic obstructive pulmonary disease or asthma . 11 For example, in one controlled study, 59 people with mild asthma were randomly assigned to practice yoga and attend a general class or simply to attend the general class. 12 The results showed slight improvements in asthma in the treated group compared to the untreated group. However, even these modest benefits did not last; assessment two months later showed no difference between the groups. Furthermore, as noted above, studies in which the participants in the control group do not receive placebo treatment are inherently unreliable. A small 2009 study of 29 adults with chronic obstructive pulmonary disease (COPD) suggests that a 12-week yoga program may be associated with slight improvement in timed walking distance and self-reported functional ability in these patients. 14 A special breathing technique called yogic-style Buteyko breathing may reduce medication use and subjective symptoms, though it does not appear to actually improve lung function. 15 In another study, 42 people with carpal tunnel syndrome were randomly assigned to receive either yoga or a wrist splint for a period of 8 weeks. 17 The results indicated that use of yoga was more effective than the wrist splint. However, participants in the control group were simply offered the wrist splint and given the choice of using it or not; it would have been preferable for them to have received a more believable placebo, like other forms of meditative exercise.
In a randomized, controlled trial, 8 weeks of daily supervised yoga was modestly more effective than a similar amount of supervised physical exercise in relieving menopausal symptoms (eg, hot flashes), decreasing psychological stress, and improving cognitive abilities among 120 perimenopausal women.  To date, only weak evidence has been reported regarding the possible usefulness of yoga for
- obsessive-compulsive disorder^
- low back pain ^
- general well-being^
- migraine headaches ^
- osteoarthritis ^
- congestive heart failure^
A small trial involving 54 adolescents with eating disorders found that adding 8 weeks of yoga twice weekly to standard therapy was associated with improved eating disorder-related thoughts and behaviors. ^ Yoga has also been studied for schizophrenia . In one small trial, patients who supplemented their regular treatment with a a yoga program lasting 4 months had improved symptoms, were able to function better, and reported a better quality of life compared to those who did physical therapy. ^ Hatha yoga has also been promoted as a treatment for epilepsy (seizure disorder), but a review of all published scientific trials concluded that there is as yet no meaningful evidence that it is effective. ^ Some evidence suggests that hatha yoga is nothelpful for chemical dependency ^ or high blood pressure. ^
What to Expect From a Hatha Yoga Class
Yoga classes typically last about 1 to 2 hours. Most of that time is spent practicing various asanas; however, other activities such as breathing exercises may take place as well. Hatha yoga is generally a gentle, nonaerobic form of exercise. However, some types of yoga, such as Iyengar yoga, are more physically vigorous.
By the end of a yoga class, many people report feeling relaxed and comfortable, and consider this a meaningful benefit in itself. However, without regular home practice, it is unlikely that performing yoga will provide any long-term benefit. For this reason, instructors generally encourage daily practice, ranging from a few minutes to an hour or more.