There are two main reasons for soreness and swelling in the left shoulder position: first, it is due to strain and cold in the left shoulder position, such as when lifting and carrying heavy objects, resulting in too much shoulder joint activity and excessive muscle fatigue, which will form a local strain, and the strain will produce more inflammation and metabolites such as lactic acid, which will stimulate the peripheral nerves and cause soreness and swelling. If there is a cold, it will cause the local muscle tissue to become more tense and the blood circulation will be reduced, which will lead to a decrease in venous return and the accumulation and increase of inflammatory metabolites and other related metabolites, thus aggravating the symptoms of soreness and swelling. Secondly, if there is a slight strain on the left shoulder joint, for example, when lifting and carrying heavy objects with too much force, it will lead to damage to the fibers of the muscle tissue and make it easy to feel sore and swollen. This can effectively relieve the symptoms of localized soreness and swelling.