The left back pain below the scapula is common for the following reasons: first, strain on the latissimus dorsi muscle, latissimus dorsi muscle is located in the lower back and the posterior lateral side of the chest, is the largest flat muscle in the body, with the tendon membrane stopping at the lower thoracic vertebrae and all lumbar spine, the muscle bundle travels upward to the posterior, stopping at the humeral tuberosity, its role is to make the shoulder joint inward, internal rotation, posterior extension, etc., the upper limb is fixed to lift the trunk, overstrain usually occurs in fitness Overexertion usually occurs due to excessive fitness or upper limb activity, muscle congestion and edema, spastic nodules often form in the muscle, limiting normal muscle activity and aggravating painful symptoms by pressure. Second, myofasciitis, mainly due to acute muscle injury, can also be the accumulation of repeated minor injuries, manifested as local pain, pain symptoms increased in the morning, and symptoms reduced after activity.