腕うでが鈍にぶる

expression, godan verb (-ru)

become less capable; lose one's touch; get rusty

Used when a skill or ability declines due to lack of practice. Often implies a former high level of proficiency.

• しばらくピアノを弾ひいていなかったので、腕うでが鈍にぶった。

  I haven't played the piano for a while, so my skills have gotten rusty.

• 毎まい日にち練れん習しゅうしないと腕うでが鈍にぶるよ。

  If you don't practice every day, you'll lose your touch.