indefatigable
I remember how indefatigably he mowed the lawn, even on a hot summer's day.
Both news presenters are larger than life and indefatigably self-confident.
He is indefatigably industrious.

SMART Vocabulary: related words and phrases

Energetic and lively
ablaze
alive
astir
barnstorming
be alive and well/kickingidiom
be as fresh as a daisyidiom
be full of beansidiom
boisterous
crackling
freshness
friskily
frisky
frolic
frolicsome
fury
refreshed
refreshingly
rejuvenate
rejuvenation
rumbustious