Pre-___ (exercise program in advance of surgery)

HAB

Think of the first three letters in a word meaning to prepare your body for a medical procedure.

This clue refers to "prehabilitation," a program designed to strengthen patients before surgery to improve recovery. The answer is shortened to "HAB" by taking the first three letters of "habilitation," the root word in "prehabilitation." It’s a common crossword trick to abbreviate longer medical or technical terms this way.