• 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.

Most people won't build much muscle from traditional cardio such as walking or jogging.

But cardio that involves high-intensity exercises like plyometrics or high-volume weight training can help you build muscle to an extend. Beginners can build some muscle with hiking, skiing, and other outdoor cardio.