I would like to know the Japanese verb for "to flex", but I haven't found much information and the few dictionary options I have found are a bit unclear to my understanding so I think that some people here can clear this up for me.

"To flex" one's muscles as when bodybuilders flex their biceps and compare how big and ripped they look.

Example sentences: He flexes his bicep to show how big it is. Bodybuilders flex their muscles to impress the audience.

Answers very appreciated!

  • I understand you have the basic knowledge about Japanese, but please try to include your research attempt before asking a question like this, or it may get closed.
    – naruto
    Feb 20, 2018 at 6:20

2 Answers 2


You can use:

  • ~に力を入れる
  • ~を収縮させる

For example 上腕二頭筋に力を入れる and 大腿四頭筋を収縮させる.

収縮 sounds relatively technical but it can be safely used in conversations.

  • How contrived are these examples? Can I expect regular people to understand these five kanji compounds? To a learner they sound a lot more advanced than English "muscles" or "biceps".
    – kuchitsu
    Feb 20, 2018 at 17:53
  • @kuchitsu 上腕二頭筋 is a famous muscle name. 大腿四頭筋 is not famous, but everyone can read it and correctly guess it's a muscle around your thigh.
    – naruto
    Feb 20, 2018 at 21:55

There's a character in Undertale who is a muscle maniac and likes flexing. Since it got an official Japanese translation, one of the related example sentences is:

Aaron is ready for your next flex.

So I think you can use 力こぶを作る which consists of:

  • 力こぶ = large biceps; well-developed biceps​ (from jisho)
  • を作る = to make

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