Framing exercise as medicine changes how it gets prescribed and understood: not a vague, virtuous lifestyle choice but a specific intervention with a measurable dose, a particular amount and intensity of movement linked to particular, well-documented benefits for a wide range of physical and mental health conditions.
The comparison to medicine is useful because it corrects a common misconception: more is not automatically better, and the right dose depends on the individual and the specific outcome being targeted, much like any other treatment a doctor might carefully calibrate to the person receiving it.
Thought of this way, exercise becomes something a person can be specifically prescribed and monitored on, rather than a generic piece of advice to move more, which for many people makes it considerably easier to actually follow through on consistently, since the instruction has become concrete rather than vague. Framed this way, the advice stops sounding vague and starts sounding like something a person can actually follow, track, and adjust as circumstances change.