Skeletal muscle is the most adaptable tissue in your body. When you do extreme exercise, like weightlifting, your muscle fibers undergo trauma, or what’s called muscle injury. When your muscles are injured this way, satellite cells on the outside of the muscle fibers become activated. They attempt to repair the damage by joining together and, as a result, increasing the muscle fiber. 

Spending your whole day in the gym isn’t necessary to build muscle. Weight training for 20 to 30 minutes, 2 to 3 times a week is enough to see results. You should try to target all your major muscle groups at least twice throughout your weekly workouts.

While you may not see results right away, even a single strength training session can help promote muscle growth. Exercise stimulates what’s called protein synthesis in the 2 to 4 hours after you finish your workout. Your levels may stay elevated for up to a whole day.