A standing side bend primarily stretches the muscles along the sides of the torso, which include: Intercostal Muscles, Obliques, Quadratus Lumborum, Latissimus Dorsi, Erector Spinae, Intertransversarii Muscles.
By stretching these muscles, the standing side bend pose helps to increase flexibility and mobility in the lateral body, improve spinal flexibility, and relieve tension in the sides, back, and shoulders.