Eagerly pressing or urgent; zealous; ardent; earnest; bold; valiant; intrepid; as, a strenuous advocate for national rights; a strenuous reformer; a strenuous defender of his country.(adjective)
source: webster1913
adjective satellite (s)
characterized by or performed with much energy or force(adj.all)
Example: Strenuous exercise.
source: wordnet30
taxing to the utmost; testing powers of endurance(adj.all)