• Your protein intake. Your muscles need adequate protein to repair themselves.
• Your calorie intake. Even if you eat a lot of protein, you won't build muscle if you don't eat enough calories daily.
• Your sleep schedule. You won't be able to optimize muscle growth when you don't give your body a chance to recover.
• Your lifting routine. Two key strength training concepts to pay attention to are frequency (how often you train a muscle group) and volume (the total load you place on a muscle.)
• Your training age. The more you advance, the less muscle growth you'll see. The closer you get to your maximum genetic potential for muscle growth, the harder it gets to build more muscle.
• Your real age. Building muscle gets harder as you age.

Muscle-building starts the moment you challenge your muscles to do something. Real beginners will see improvement within six weeks and advanced lifters within six to eight weeks of switching up their regular strength training workout.

Each muscle is made up of thousands of tiny muscle fibers. When you do body weight exercises, your muscles develop tiny tears in the fibers. When you rest, your body begins repairing your damaged muscle cells by fusing torn muscle fibers back together and laying down new proteins within each musc...