Bidwell and her co-authors, one of whom is a physician, randomly assigned 20 individuals aged 20 to 65 to practice Hatha yoga two-and-a-half hours a week or to join a (non-yoga) control group, for a total of 10 weeks.
Results were based on a questionnaire that measured frequency and severity of symptoms, activities associated with breathlessness and social and psychological functioning.
'We hold poses up to a minute and focus on deep breathing, which is critical to asthmatics' said Bidwell, who is also a yoga instructor.
Heart rate variability, oxygen consumption and ventilation were also assessed while volunteers performed each of two tasks: handgrip for three minutes and an upright tilt for five minutes.
Overall, scores of individuals participating in the yoga arm of the trial improved an average of almost 43 percent.
There were few or no differences between the groups in heart rate variability, oxygen consumption or ventilation.
'There's not much of a downside to yoga unless you have a major orthopedic problem,' said Bidwell, who does not hesitate to recommend the practice to asthmatics after receiving proper instruction.
'Breathing symptoms are such a big part of asthma in terms of gaining control over them. Yoga enhances awareness of breathing and you may be able to recognize early on when breathing is not at a level it should be, which would promote earlier care,' Field said. 'Also, it's been recognized that deep breathing in athletes -- swimmers or runners -- actually improves asthma. When you have more functional use of lungs, it protects against asthma.'