na-adjective
Describes a person, action, or effort that is full of energy and drive. Often used for sustained, purposeful activity.
彼は精力的に仕事に取り組んでいる。
He tackles his work energetically.
精力的な活動
Known for vigorous activity.
エネルギッシュ is a more casual, loanword equivalent, often implying a dynamic, forceful personality.
From 精力 (せいりょく, 'energy, vigor') + 的 (てき, '-like, -ic').