stretching vs physical exertion

stretching and physical exertion both are nouns.

Word	Noun	Adjective	Verb	Adverb
stretching	Yes	No	No	No
physical exertion	Yes	No	No	No

As nouns, physical exertion is a hypernym of stretching; that is, physical exertion is a word with a broader meaning than stretching:

stretching: exercise designed to extend the limbs and muscles to their full extent
physical exertion: the activity of exerting your muscles in various ways to keep fit

Other hypernyms of stretching include exercise, exercising, physical exercise, workout.

stretching (noun)	physical exertion (noun)
exercise designed to extend the limbs and muscles to their full extent	the activity of exerting your muscles in various ways to keep fit
act of expanding by lengthening or widening