Weakness and lack of energy in the limbs may be related to a variety of factors such as strenuous exercise, viral infections, myasthenia gravis and so on. 1. Strenuous exercise: After a lot of strenuous exercise, lactic acid will accumulate in the muscles, resulting in muscle weakness, soreness and pain. Physiotherapy methods, such as massage and hot compresses, can be chosen to promote blood circulation. 2. Viral infection: when virus invades the human body, it may invade the muscles of the whole body, resulting in weakness, soreness and pain in the limbs. Antiviral drugs, such as acyclovir, and non-steroidal drugs, such as celecoxib and diclofenac sodium, can be used under the guidance of doctors. 3. Myasthenia gravis: at the early stage of the disease, you tend to feel soreness and discomfort in the eyes or limbs, or blurred vision, easy to fatigue, with the development of the disease, the skeletal muscles are obviously fatigue and weakness, the salient feature is that myasthenia gravis is aggravated by exertion in the afternoon or evening, and is alleviated in the morning after waking up or resting. Therefore, the weakness of the limbs may appear. The symptoms of prolonged weakness of the limbs should go to the hospital in a timely manner, cooperate with the doctor’s examination, identify the cause of the disease, and then treat the cause and symptoms. Drugs should be used under the guidance of a doctor. In daily life, you can strengthen exercise to enhance muscle power and strength.