Energy, vigor, or vitality — the physical or mental drive to be active. Depending on context, it can also refer to sexual vigor.
彼はいつも精力的に仕事に取り組んでいる。
He always tackles his work energetically.
規則正しい生活で精力を回復した。
I regained my energy through a regular routine.
年を取ると精力が落ちることがある。
As people age, their vitality can decline.