We are young and vigorous; It is precisely because of our young, so we work harder!

我们年轻，富有朝气；正因为我们年轻，所以我们更加努力！

youdao

Reconstruct cell structure, prolong the life of ageing cells, restore firmness, and keep skin young and vigorous.

重建细胞结构，延长衰老细胞的生命力，增强皮肤的弹性，永葆青春活力肌肤。

youdao

Shrink pores from within, firm and lift skin, obviously remove wrinkles, and make skin young and vigorous day after day.

由内至表收细每个毛孔，收紧并提拉面部肌肤，日复一日，让皱纹看起来明显减少，肌肤焕发年轻活力。

youdao

But rodeo clowning has become such a valued specialty that most clowns are as young and vigorous as the competitors.

VOA: standard.2010.01.25

Voloshin told the interviewer that Yeltsin was not clinging to power for the sake of it, and wanted to hand over to a young, vigorous successor who would continue on the path of reform.

BBC: Presidential aide says Lenin's body to be buried

They might, however, contain it and stop the deaths of many of the young, vigorous people whom poor countries need.

ECONOMIST: Even in Africa, it can be won

For "lean" and "fit" you could easily transpose "young" or "vigorous".

BBC: Analysis