Muscle-building supplements can improve physical performance during resistance training and help stimulate muscle growth. Protein and creatine are two popular supplements that can have these effects.Building muscle requires a positive energy balance, which means that you must take in more calories than you burn. In addition, research suggests that consuming lean protein 15 to 20 minutes before, during and within one hour of working out may help improve muscle gain. Building muscle is a slow process that requires consistent resistance training over long periods.Maintaining a healthful lifestyle and adequate protein intake will support this process. Some people may also benefit from supplementing their diet with creatine, caffeine, and supplements aimed at increasing testesterone levels.