stren·u·ous  [stren-yoo-uhs]

–adjective
1.characterized by vigorous exertion, as action, efforts, life, etc.: a strenuous afternoon of hunting.
2.demanding or requiring vigorous exertion; laborious: To think deeply is a strenuous task.
3.vigorous, energetic, or zealously active: a strenuous person; a strenuous intellect.