effortful
energetic
Herculean
active
ardent
arduous
bold
breathless
burdensome
demanding
determined
difficult
dogged
dynamic
eager
earnest
enthusiastic
exhausting
hard
indefatigable
intense
intrepid
laborious
lusty
mean
operose
persistent
pertinacious
red-blooded
resolute
rigorous
sincere
spirited
taxing
tenacious
tireless
tiring
toilsome
tough
uphill
valiant
vigorous
vital
wicked
strenuosity
desperate
fervent
fruitless
patriotic
serious
zealous
disingenuous
ingenuous