strenuous (
http://definr.com/strenuous)
adj 1: characterized by or performed with much energy or force;
"strenuous exercise"
2: 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 [syn:
arduous,
straining]