Soreness and weakness of the lower legs below the knee may be caused by overexertion. If heavy physical labor or strenuous sports are performed for a long time, causing muscle strain in the lower extremities, the symptoms of weakness in the lower legs may occur. In addition, weakness of the calves may be caused by hypokalemic periodic paralysis. Patients who suffer from hypokalemic periodic paralysis may experience weakness of the muscles of the limbs. Many patients have weakness of both lower extremities as the first symptom when they sleep at night or wake up in the early morning, and in severe cases, it may cause breathing disorders. In addition, patients with Grimballi syndrome, myasthenia gravis, or hypothyroidism may experience weakness in the lower legs. In this case, it is important to rest and avoid exertion. If there are other symptoms, further examination at the hospital is needed to clarify the diagnosis and provide targeted treatment according to the cause.