To increase lean muscle mass, a combination of resistance training and proper nutrition is key. Resistance training, such as weightlifting or bodyweight exercises, can help stimulate muscle growth by creating small tears in the muscle fibers, which then repair and grow stronger during the recovery period. It's important to progressively increase the intensity and volume of your workouts over time to continue challenging your muscles and promoting growth.
In addition to resistance training, proper nutrition is essential for building lean muscle mass. Consuming enough protein is crucial since it provides the building blocks (amino acids) for muscle growth and repair. Aim to consume around 1.6-2.2 grams of protein per kilogram of body weight per day. You should also make sure you're consuming enough calories overall to support muscle growth, but not so many that you're gaining excess body fat.
Finally, make sure you're getting enough rest and recovery time between workouts to allow your muscles to repair and grow. Aim for 7-9 hours of sleep per night and consider taking rest days or incorporating active recovery activities such as stretching or yoga into your routine.