Acute or chronic physiological processes

Chose one of the following topics from below and define the acute or chronic physiological processes (what is happening on a microscopic level in the body) behind it along with what other systems of the body are heavily involved:   - An Athletic movement to improve (Increase of strength, cardiovascular system, flexibility, Specific recovery techniques etc) - An interesting topic (Loss of breath in a cold shower, deep sea divers, REM cycle during sleep) - A common experience (Leg burn in a workout, Heat acclimation, recovery from an injury, DOMS) - Special population (Training with Diabetes, after heart surgery, high blood pressure, arthritis, etc)