strenuous in WordNet English dictionary

1. taxing to the utmost; testing powers of endurance
   "his final, straining burst of speed"; "a strenuous task"; "your willingness after these six arduous days to remain here"- F.D.Roosevelt
   arduous  straining  strenuous 
   
2. characterized by or performed with much energy or force
   "strenuous exercise"
   strenuous