No doubt you've heard the gospel on mind-body physical disciplines like yoga and tai chi: They sharpen the mind, build confidence, produce relaxation and offer other benefits usually associated more with psychology than fitness.

Research on the psychological effects of mind-body disciplines is scarce but growing. A study published in 1994 in the Annals of Behavioral Medicine showed that yoga decreased perceived stress and negative mood in participants, compared with a control group that attended a biology lecture.

And research published in 2004 in the Journal of Attentive Disorders showed that boys with attention deficit hyperactivity disorder who took yoga classes showed more improvement in symptoms than boys who did not do yoga; the groups were equally medicated.

"Some of [yoga's] stress-reduction potential may come from elicitation of the 'relaxation response,' " said Timothy McCall, a physician and medical editor of Yoga Journal, a consumer magazine. "You are ratcheting down the sympathetic nervous system -- essentially your fight-or-flight response -- and ratcheting up the parasympathetic system, [which induces] rest and relaxation."

"The breathing is key," said John Schumacher, director of Unity Woods Yoga Center in Bethesda. "Health, especially in Eastern philosophies, revolves around the whole concept of energy, and energy is attention: Through yoga, we learn to work with our own health on a much smarter level than worrying about what your heart rate is for 20 minutes three times a week or how many carbs you're eating."

To wit, McCall cited a 1993 study published in the British Journal of the Royal Society of Medicine in which people practicing pranayama (yogic breathing) had significantly increased perceptions of mental and physical energy and feelings of alertness and enthusiasm over those who simply tried to relax.

Studies of psychological benefits of yoga and other forms of exercise rarely rise to the level of gold-standard science. It can be difficult to ensure consistent quality of the exercise experience for extended periods and to "blind" participants and researchers so neither knows who is receiving treatment and who is in the control or placebo groups. Assessments of psychological benefits are also notoriously difficult to conduct. And mind-body exercise is rarely compared with conventional exercise, which is known to produce psychological benefits as well.

Tai chi, an ancient Chinese practice of controlled breathing and very slow, fluid movements, has both a calming and an invigorating effect because "every move is stimulating your energy pathways," said Peter Mosher of Washington, an instructor of chi chuan, the parent discipline of tai chi.

"Every movement works with the acupuncture points in your body, and there are so many. I'll stand at the bus stop and do [tai chi] moves with my hands -- little, slow movements -- and nobody even knows I'm practicing."

Like yoga, tai chi mandates intense concentration. So why aren't students mentally exhausted after a workout?

"You are releasing blockages, opening up your energy flows," Mosher said. "I come out the other end as if I'd just taken a nice nap."

Bring it on at the Moving Crew chat today at 11 a.m. at www.washingtonpost.com. Note that this is our first recent online appearance on a Tuesday, when this very section appears in the newspaper. So slip off your shoes, log on and join the fun.

-- John Briley

Do yoga or other "mind-body" regimens provide psychological benefits beyond those of conventional exercise?