Adaptation is the process by which the body responds to repeated stress or exertion by becoming stronger and more efficient.
In exercise physiology, training places a controlled demand on systems such as the muscles, heart, lungs, and nervous system. During recovery, the body repairs and adjusts those systems so that the same workload can be handled with less strain or a greater workload can be tolerated. Strength training can produce muscular and neural adaptations, while endurance training can improve cardiovascular capacity and oxygen delivery.
Adaptation is not the same as immediate performance. A single workout creates a stimulus, but meaningful improvement generally develops through repeated training paired with adequate recovery, nutrition, and sleep. If the stress is excessive or recovery is inadequate, fatigue and injury may occur instead of productive adaptation.
The term is broader than muscle growth alone. It can describe changes in coordination, energy use, cardiovascular function, connective tissue, and heat tolerance. Atrophy means tissue loss, degeneration means deterioration, and aging is a biological process—not synonyms for adaptation.