Exercise is a signal the body answers

Physical activity briefly disturbs ordinary balance: muscles demand energy, heart rate and breathing change, and tissues experience mechanical load. Recovery from repeated, tolerable challenges can produce adaptations in cardiovascular fitness, strength and function. The benefit is not located only in calories spent during the activity; it also lies in what the body rebuilds.

Responses differ by age, disability, health, dose and kind of movement, and more is not endlessly better. Injury and inadequate recovery are real. Public-health evidence supports regular activity at population level, but this mechanism is not an individual programme. It simply explains why a temporary demand can leave durable capacity behind.