What principle states that training must be progressively increased to cause adaptation?

What principle states that training must be progressively increased to cause adaptation? The principle is progressive overload.

It holds that the body adapts when training stress is greater than a familiar baseline. Once a workload becomes routine, increasing resistance, repetitions, total volume, duration, frequency, or intensity can provide a new stimulus for improvements in strength, power, endurance, or hypertrophy.

The idea has an ancient association with Milo of Croton, a Greek wrestler whose legendary training reportedly involved carrying a young bull as it grew. Modern progressive overload is more systematic: load and volume are adjusted gradually, with recovery, technique, and the athlete’s training status taken into account.

Progressive overload does not mean making every workout harder or adding weight recklessly. Excessive increases can outpace recovery and raise injury or overtraining risk. It is also different from specificity, which says adaptations reflect the kind of training performed, and reversibility, which describes the loss of adaptations when training stops.