This article published in Medical News Today describes a study showing how yoga could be an effective therapy for chronic low back pain. Electromyography was used to show muscular bioelectric activity in the lower back (which is associated with back pain) also improved.

Specifically, scientists looked at the flexion-relaxation phenomenon, which is a clinical tool to assess back pain. When someone bends forward, as if to touch their toes, this movement is known as trunk flexion. During flexion, the muscles of the lower back are engaged. However, at a certain point in the flexion, the muscles actually begin to relax again. How much the muscles are engaged or relaxed during this process can be measured through electromyography. Higher readings indicate more muscle tension which is associated with the risk of low back pain.