Bulk
Also known as: Bulking phase
A bulk, or bulking phase, is a planned period focused on gaining body mass while resistance training, usually with muscle gain as the primary objective. Most bulks use a calorie surplus, but the two terms are not synonyms: the surplus is an energy state, whereas the bulk is the overall training and nutrition phase.
An effective bulk combines progressive strength training, sufficient protein, enough total energy, and recovery. The calorie surplus supports rising body mass and can make gaining muscle easier, but no surplus directs all added weight into muscle. Some gain will often come from water, glycogen, digestive contents, and body fat. Training status, genetics, starting body composition, program quality, and the rate of gain affect the result.
There is no single surplus or monthly weight-gain rate that is appropriate for everyone. Newer lifters may have more capacity to add muscle than highly trained lifters, while a person returning after a layoff differs from both. A larger surplus can increase body weight faster without producing proportionally more hypertrophy. The ISSN position stand on diets and body composition recommends interpreting targets in light of training status and starting body composition.
To run a bulk, begin with a reasonable estimate of maintenance, select a controlled increase in intake, and evaluate multiple signals over several weeks. Useful signals include average body weight, waist and other circumference measurements, gym performance, recovery, appetite, and digestion. Do not interpret the first few days of faster gain as new muscle: increased carbohydrate and food volume can raise glycogen, water, and digestive contents.
A lean bulk informally describes a more controlled approach intended to limit unnecessary fat gain. A dirty bulk describes a loosely controlled or very aggressive approach. Neither label is a scientific category, and food quality and surplus size are separate issues. The appropriate end point is also individual; a bulk can end when the planned period finishes, the rate or composition of gain no longer fits the goal, or the athlete chooses to maintain or begin a cut.