Endorphins are released during sex, just as they are during a strenuous workout.
The first President Roosevelt, the old rough rider, advocated the strenuous life.
strenuous scenes can take a toll on the body over time, thus limiting a career to a certain number of years.
"characterized by great effort," 1590s, from Latin strenuus "active, vigorous, keen." Probably cognate with Greek strenes, strenos "keen, strong," strenos "arrogance, eager desire," Old English stierne "hard, severe, keen" (see stern (adj.)). Mocked by Ben Jonson as a pedantic neologism in "Poetaster" (1601). Sense of "requiring much energy" is first recorded 1670s. Related: Strenuously; strenuousness.