The causes of hemiplegia include insufficient muscle strength of bilateral trunk muscles, psychological reasons and poor cardiorespiratory function. 1. Insufficient muscle strength of bilateral trunk muscles: after the nerve function of hemiplegia is impaired, the muscle strength is insufficient, the trunk control is decreased, and the patient cannot effectively dominate his/her own trunk and limbs, which leads to the difficulty of activities and the inability to sit up after hemiplegia. 2. Psychological reasons: If the patient has good sensory and motor function of limbs, meets the condition of sitting up, has good muscle strength and balance, but cannot sit up, psychological factors are considered and psychological treatment and encouragement from family members are needed. 3. Poor cardiorespiratory function: hemiplegic patients have poor cardiorespiratory function due to lack of exercise, which will lead to activity-related shortness of breath, dyspnea, fatigue and other manifestations of decreased endurance, and they will be unable to sit up. After hemiplegia, you should seek medical treatment in time and carry out rehabilitation training under the guidance of doctors and therapists, do not train on your own to avoid injury.