One reason why you cannot gain muscle
Every time I go to a particular gym (I go to a few different ones) I see this one thin guy swinging weights around, working as hard as he can, but the problem is that if a person has too low of a body fat percentage, he or she just won’t be able to build muscle.
If your goal is to increase muscle size, increase calories slowly. A pound of muscle a month is a reasonable amount to expect if you’re lifting hard at least three times a week.
Photo of Kasey Housmans, Master Fitness Trainer