Why? The more I exercise, the thinner I get.

Fitness needs a good plan, not blind practice. Besides, keep up with nutrition, protein. Carbohydrates must be supplemented. Rest should be sufficient, the large muscle group should be more than 48 hours, and the small muscle group should be more than 24 hours, depending on your recovery. If the recovery is not good, you need to increase the time. Get enough sleep for 8 hours every day, quit smoking and drinking, stay up late, and sleep before 10 at night. If you are thin, don't do aerobics, you will only be thinner. In addition, if you want to gain muscle and get quick results, you should buy some supplements, such as muscle gain powder and protein powder.