Whenever you exercise, you will be tired. Consider that it may be related to anemia, malnutrition, myasthenia gravis and other causes. 1. Anemia: Lack of vitamin B12, iron and other nutrients in the body may lead to anemia. Blood cells are not able to carry enough oxygen to fulfill the normal functions of body organs, which may lead to tiredness upon exercise. 2. Malnutrition: prolonged inability to obtain sufficient nutrients from the daily diet may lead to malnutrition, excessive weakness, and may also lead to tiredness upon exercise. 3. Myasthenia gravis: Myasthenia gravis is an autoimmune disease. The patient’s neuromuscular junction transmission disorder may lead to muscle contraction weakness, and after the activity will appear tired phenomenon, called muscle fatigue phenomenon, this situation is related to the autoimmune response in the neurotransmitter, because of the lack of this resistance to the autoimmune hormone, the emergence of the situation of exhaustion after exercise. There may also be other clinical causes of exercise fatigue. It is recommended to go to the hospital as soon as possible, and cooperate with the doctor to complete the relevant examinations to determine the cause of the disease and should be treated accordingly.