tighten up vs constrain

tighten up and constrain both are verbs.

Word	Noun	Adjective	Verb	Adverb
tighten up	No	No	Yes	No
constrain	No	No	Yes	No

As verbs, tighten up and constrain are synonyms defined as:

Other synonyms of tighten up include stiffen, tighten.

tighten up (verb)	constrain (verb)
severely restrict in scope or extent	severely restrict in scope or extent
	to close within bounds, or otherwise limit or deprive of free movement
	compel to behave in a certain way