knee bend vs leg exercise

knee bend and leg exercise both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee bend	Yes	No	No	No
leg exercise	Yes	No	No	No

As nouns, leg exercise is a hypernym of knee bend; that is, leg exercise is a word with a broader meaning than knee bend:

knee bend: exercising by repeatedly assuming a crouching position with the knees bent; strengthens the leg muscles
leg exercise: exercise designed to strengthen the leg muscles

knee bend (noun)	leg exercise (noun)
exercising by repeatedly assuming a crouching position with the knees bent; strengthens the leg muscles	exercise designed to strengthen the leg muscles