Synonyms and related words :
Herculean, active, arduous, breathless, burdensome, demanding, determined, difficult, dogged, dynamic, eager, earnest, effortful, energetic, enthusiastic, exhausting, hard, indefatigable, intense, laborious, lusty, mean, operose, persistent, pertinacious, red-blooded, resolute, sincere, taxing, tenacious, tireless, tiring, toilsome, tough, uphill, vigorous, vital, wicked, zealous