There are three main reasons for swelling and pain in the left back area: first, due to excessive fatigue and strain in the left back position muscles, such as the scapular raphe, rhomboid muscle, such as low head for too long, lack of support for the elbow joint, so that the muscle tissue continues to be under tension, the formation of strain will stimulate the peripheral nerves around it, there will be a feeling of swelling and pain. Second, the left back position muscle strains, such as when lifting and lifting heavy objects, may lead to excessive muscle force, muscle fiber tissue damage, but also in the local formation of bruising swelling and inflammatory edema, resulting in obvious swelling and pain. Thirdly, the symptoms will be further aggravated by cold, especially in the case of strain and minor strains, which will cause the muscle tissues to become more tense after the cold, and the blood circulation will drop, and the venous return will be reduced, leading to further accumulation of local metabolites, thus leading to a more pronounced swelling and pain.