You can answer this question first. First of all, it is relatively difficult to check whether your physiological function is normal, such as people with poor gastrointestinal absorption or people with abnormal metabolism. Secondly, weight gain is different from muscle gain. Weight gain means weight gain, including fat content and muscle increase, and muscle gain requires higher muscle content. Many thin friends have low fat content and can't measure their body fat. Once again, we understand that our energy comes from food, and nothing but carbohydrates, fat, protein, trace elements and water participate in human metabolism. If you want to gain weight, you should consume more than you consume. Eating more foods with high content of protein is beneficial for the extremely thin people to consume a certain amount of fat. Ok, speaking of diet, let's talk about exercise. You can do anaerobic training, that is, strength training. It is divided into self-resistance training and equipment resistance training. You need to know your own strength foundation and physical foundation in order to do your best in sports and have good sports results. Large muscle groups that exercise, such as pectoralis major, latissimus dorsi and quadriceps femoris, especially in the platform period of weight gain, need to do squat strength exercises to break through themselves. The last sentence, as long as you persist hard and use the right method, you can become strong. Come on!