How to Say "Muscles" in Japanese

筋肉

kinniku[kʲĩɲ̟ːikɯ̟]

The English phrase "muscles" is translated into Japanese as 筋肉 (kinniku).

The most common and standard term for muscles in Japanese is 筋肉. The loanword マッチョ is used informally to describe someone with well-defined muscles.

How do you pronounce it?

kinniku

The character 筋 (suji) used in 筋肉 is also the same character used to describe the 'plot' or 'line' of a story.
Japanese pop culture has a 'muscle' obsession reflected in the term 筋肉至上主義, which describes a 'muscle-supremacy' mindset where physical strength is the highest value.
The loanword マッチョ does not come from 'muscle' but from the English word 'macho', though it is used in Japanese specifically to describe someone's physical muscularity.

体中筋肉痛だよ。
All my muscles are aching.
This sentence shows how to express that all your muscles are aching using 筋肉.
Tatoeba #11912734 by small_snow, translation #11074070 by sundown
水泳は筋肉を発達させる。
Swimming develops our muscles.
This sentence demonstrates how swimming develops 筋肉.
Tatoeba #143688 by bunbuku, translation #270879 by CK
太股が筋肉痛で歩くのもつらい。
It hurts to even walk with my thigh muscles aching.
This sentence describes the difficulty of walking due to 筋肉 soreness.
Tatoeba #3059312 by tommy_san, translation #3064580 by Tappity
彼の筋肉（きんにく）はとても発達している。
His muscles are very well developed.
彼はたくましい筋肉（すじ）を持っている。
He has strong muscles.
彼はすごくマッチョだね。
He is really muscular.
彼は筋肉質（きんにくしつ）な体型が魅力的だ。
His muscular physique is attractive.
6 more sentences on Tatoeba

Ren and Misaki are talking after a workout at the gym.

蓮 Ren

筋肉がついたかな？
Kinniku ga tsuita kana?
I wonder if I've built some muscle?
美咲 Misaki

いい感じに筋肉が出てるよ。
Ii kanji ni kinniku ga deteru yo.
Your muscles are looking defined.
蓮 Ren

でも、明日は筋肉痛になりそう。
Demo, ashita wa kinnikutsuu ni narisou.
But I think I'll have muscle pain tomorrow.
美咲 Misaki

しっかりストレッチしてね。
Shikkari sutoretchi shite ne.
Make sure you stretch properly.

Sources

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