Back pain after swimming is mainly due to two reasons: first, it is possible that during swimming, because the muscles are continuously in a state of fatigue and tension, this will lead to the formation of more inflammatory metabolites in the muscle tissue, which will stimulate the peripheral nerves around the pain, or there may be local trauma or strain on the muscle tissue, which may lead to a significant pain in the waist. The symptoms are not obvious because the blood circulation is relatively fast during the activity, but after resting and swimming, the blood circulation slows down and the inflammation builds up, leading to more obvious pain in the lower back after swimming. Secondly, during and after swimming, the cooler water in the pool, or the evaporation of water after swimming, will lead to a cold situation in the lower back, which will cause the muscle tissue to become more tense, and blood circulation will also decline, and the resulting inflammation will further accumulate, which will aggravate the feeling of lower back pain.