Synonyms: arduous, straining, strenuous
Definition: taxing to the utmost; testing powers of endurance
Usage: his final, straining burst of speed; a strenuous task; your willingness after these six arduous days to remain here- F.D.Roosevelt
Similar words: effortful
Definition: requiring great physical effort
Synonyms: strenuous
Definition: characterized by or performed with much energy or force
Usage: strenuous exercise
Similar words: energetic
Definition: possessing or exerting or displaying energy
Usage: an energetic fund raiser for the college; an energetic group of hikers; it caused an energetic chemical reaction