A 47-year-old man awakens with low back pain after a weekend of gardening. He recalls no specific incident of trauma and has never had back pain before. There is no radiation of the pain and no disturbance of normal bowel or bladder function. The ROM of the low back is painful and restricted in all planes, and there is paraspinal tenderness from L2 to L5 on the right. Scoliosis and kyphosis are absent. Findings on straight-leg-raising test are negative, reflexes are active and equal, and the patient can walk on his heels and toes. Findings on x-rays of the lumbar spine are normal. Which is the best treatment?