"Our belief is something as simple and brief as a short (yoga) program would be very useful" at combating side effects from cancer treatment, said Lorenzo Cohen, a psychologist who led the pilot study.

Yoga incorporates meditation, relaxation, imagery, controlled breathing, stretching and physical movements. Although the study was small and preliminary, it's one of the few to try to rigorously measure the benefits of this form of exercise, Cohen said.

Researchers at the University of Texas M.D. Anderson Cancer Center focused on 61 women who had surgery for breast cancer and now were getting six weeks of radiation treatment. Thirty women were assigned to a test group that took twice-a-week yoga classes. The others did not.

At the end of six weeks, study participants filled out detailed questionnaires grading their ability to lift groceries, walk a mile (1.6 kilometers) and perform other physical activities. They also were asked about feelings of fatigue, their sense of well-being and other aspects of their quality of life.

Their scores were converted to a scale that ranged from 0 to 100. The researchers found the yoga group consistently had higher scores in almost every area. It was most pronounced in physical function, the yoga group had a mean score of about 82, compared with 69 for the other group.

Participants said they were in better general health, were less fatigued and had fewer problems with daytime sleepiness. But the researchers found no differences between the groups in measurements of depression or anxiety.

The researchers drew blood and took saliva samples in an effort to measure the participants' immune system function and stress levels, but those results are not finished yet, said Cohen, who presented the results at a medical conference in Atlanta held by the American Society of Clinical Oncology.

A future study will have one group do stretching and another yoga, to see if there is a difference in the result, Cohen said.

Traditionally, such scientific approaches have been lacking in the assessment of yoga's medical benefits, said Alan Kristal, an epidemiology professor at the University of Washington School of Public Health and Community Medicine.

Due in part to increased federal funding for research into alternative therapies, more rigorous studies have emerged in the last three or four years that attempt to provide harder proof, Kristal said.

Recent studies have demonstrated the benefits of yoga for cancer patients and people with carpal tunnel syndrome. Kristal co-authored a study last year that found middle-aged people who regularly did yoga lost weight over 10 years while a non-yoga group gained, on average, more than 13 pounds (5.9 kilograms).

The National Cancer Institute recently awarded Cohen and his team $2.4 million (euro1.87 million) to study the effects of Tibetan yoga on women with breast cancer undergoing chemotherapy. It was the largest ever federal grant for the study of Tibetan yoga in cancer patients.

Teresita Ladrillo, 52, a Houston breast cancer patient currently taking yoga classes at M.D. Anderson, said the stretching helped her regain flexibility in her right arm, which was limited by scarring from surgeries and other treatments.

Learning to control her breathing through yoga has helped her to calm and sleep, she said.

"Whenever you do yoga, the first thing they tell you is forget everything else and just focus on your breathing," she said. "There's something to be said for being still."