"If you don't exercise or use parts of your body for a long time, they will stop working properly."
"If you don't use it, you'll lose it."
- "If you don't exercise or use parts of your body for a long time, they will stop working properly."
"if you don't exercise or use ~" 「〜を使わないと」
"parts of your body" 「体の器官」
"for a long time" 「長く」
"they will stop working properly" 「機能が働かなくなる」"they will lose their function" も使えます。
- "If you don't use it, you'll lose it." 「使わないとなくなる」
ネイティブな表現です。上と同じ意味です。
オーストラリア 
