Brimming with vitality; vigorous and energetic—having strong physical or mental energy (often used descriptively).
彼は年齢を感じさせないほど元気旺盛だ。
He is so vigorous that you wouldn't guess his age.
犬は散歩に行くと元気旺盛に走り回る。
When taken for a walk, the dog runs around full of energy.
仕事に対する好奇心が元気旺盛な人は伸びやすい。
People with a lively curiosity about work tend to grow quickly.