力气strength

• 手劲很大

  strong grip

• 用一把劲

  use one's strength

• 再加一把劲

  put one's back into it

• 全身没劲

  one's whole body feels weak

• 感到浑身是劲

  feel invigorated all over

参见：劲头

神情manner

• 一股高兴劲儿

  cheerful manner

兴趣fun

• 下棋有什么劲！

  What's so fun about chess!