One hundred and twenty six participants of both sexes having lower back pain with ages between 20 and 45 years were randomly assigned to yoga and control groups using a computer generated random number table. In the yoga group, there were sixty three participants (32 males and 31 females) of both sexes (group mean ± S.D., 37.03 ± 6.76 years) and in the control group also; there were sixty three participants (33 males and 30 females) of both sexes (group mean ± S.D., 36.40 ± 6.54 years). Participants of both groups were staying close to a residential yoga center located in north India. All of them had lower back pain. Their participation in this study was voluntary. Prior to the study, signed informed consent of all participants was taken separately. The study protocol was approved by the Institutional Ethics Committee (IEC). Health status measurement for low back pain (using Rolland Morris Disability questionnaire - RMDQ), physical examination of leg and back, magnetic resonance imaging (MRI) for lumbosacral spine (using Philips Magnetic Resonance Achieva 1.5T A-Series), heart rate variability (HRV) and abdominal respiration (using a two channel EKG and respiration recording system; MP45 Biopac Student Lab, BIOPAC System Inc, U.S.A.), spinal flexibility (using Sit and Reach flexibility tester, model 01285A, Lafayette Instrument), the level of state anxiety (using Spielbergers State Trait Anxiety - STAI) and the level of back pain and mental stress (using analog scales) were measured. Assessments were done before and after three months of intervention. It was a randomized controlled study. Participants of the yoga group practiced loosening exercises, asanas, pranayamas and relaxation techniques in the morning (08:00 - 09:00 hours) thrice in a week for three months conducted by an experienced yoga teacher who had no other part in the trial. For the rest of the week, they were practicing yoga at home. Some educational classes were provided to the participants of the control group. Repeated measures analysis of variance (ANOVA) will be used to compare data recorded before and after three months with pre data, using PASW Version 18.0. There will be two Within subjects factors [Groups (Yoga, Control) and States (Pre, Post)].