## TL;DR
Exercise physiology explains how cardiovascular, respiratory, muscular, and endocrine systems adapt to training stress. These adaptations are the biological basis for improved athletic performance and health.

## Core Explanation
The FITT principle (Frequency, Intensity, Time, Type) guides training prescription. Overload triggers the General Adaptation Syndrome: alarm→resistance→exhaustion. Specificity means training adaptations match the demands imposed.

## Detailed Analysis
Energy systems continuum: ATP-PCr (0-10s), glycolytic (10-120s), oxidative (>2min). Lactate is now understood as a valuable fuel source (lactate shuttle theory). Heart rate variability (HRV) monitoring guides training load management.

## Further Reading
- ACSM Position Stands
- Journal of Strength and Conditioning Research
- Sports Medicine (Springer)