Soreness in the muscles on either side of the navel may be related to lactic acid buildup, muscle strain, muscle strain, and other causes. 1. Lactic acid buildup: If you exercise your abdomen, it can lead to lactic acid buildup within the muscles on either side of your navel, which can lead to a feeling of soreness. 2. Muscle strain: This can lead to soft tissue damage, which may result in symptoms such as soreness and pain on both sides of the navel. 3. Muscle strain: When the human body is engaged in strenuous activities for a long period of time, it can cause the muscles to contract excessively without effective relaxation, thus resulting in strain, which can be manifested as muscle soreness and swelling. It is recommended that those who are sore and swollen on both sides of the navel go to the hospital in time to clarify the cause, and if treatment is needed, standardized treatment should be carried out under the guidance of the doctor to avoid delaying the condition.