Hypertrophy

When you train with weights, you create controlled damage to muscle fibers. The body responds by repairing and reinforcing those fibers, making them larger and stronger than before. This adaptation process is hypertrophy. It's triggered through three main mechanisms: mechanical tension (the load you apply to the muscle), metabolic stress (the buildup of metabolites during the set) and muscle damage (microtears in the fibers).

Stimulating hypertrophy requires three pillars. Resistance training, with sufficient volume (generally 10-20 sets per muscle per week) and adequate intensity (close to failure). Nutrition with a caloric surplus and adequate protein intake (1.6-2.2 g/kg of body weight). Recovery, because the muscle grows during rest, not during training.

The rep range traditionally associated with hypertrophy is 6-12 reps, but modern research has shown you can build muscle in a much wider range (5-30 reps), as long as every set is taken close enough to failure. The key factor isn't a magic rep number, it's the effort and the total volume.

An aspect many underestimate: hypertrophy is a slow process. A beginner can gain 8-12 kg of muscle in the first year of serious training, but this rate drops drastically with experience. After 3-4 years of consistent training, even 1-2 kg of muscle per year is an excellent result.