straining vs strenuous

straining is a noun but strenuous is not a noun.

Word	Noun	Adjective	Verb	Adverb
straining	Yes	Yes	No	No
strenuous	No	Yes	No	No

As adjectives, straining and strenuous are synonyms defined as:

straining and strenuous: taxing to the utmost; testing powers of endurance

Other synonyms of straining include arduous.

straining (noun)	strenuous (noun)
the act of distorting something so it seems to mean something it was not intended to mean
an intense or violent exertion

straining (adjective)	strenuous (adjective)
taxing to the utmost; testing powers of endurance	taxing to the utmost; testing powers of endurance
	characterized by or performed with much energy or force