我对健身比较感兴趣。

Wǒ duì jiànshēn bǐjiào gǎn xìngqù.

I'm rather interested in fitness.

我对这个计划挺感兴趣的。

Wǒ duì zhège jìhuà tǐng gǎn xìngqù de.

I'm quite interested in this plan.

她好像挺喜欢你的，你对她感兴趣吗？

Tā hǎoxiàng tǐng xǐhuān nǐ de, nǐ duì tā gǎn xìngqù ma?

She seems to really like you, do you have any interest in her?