[SuckaMC]

You need to lift heavy weight and do low reps. Lots of protein after each workout, with a low-carb diet. If you want to gain weight and muscle, you don't need Muay Thai... have you seen UFC? Almost all fighter regimens include some Muay Thai training, and they may be muscular, but they are also very lean. If you want to bulk up, you need to lift weights. You will not gain weight training in Muay Thai. Rather, you are bound to lose weight and become leaner.