張(は)り切(き)るto be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point

部長(ぶちょう)：「張(は)り切(き)って仕事(しごと)をしましょう！」

Chief: 'Let's work enthusiastically!' {to be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point}

張(は)り切(き)った糸(いと)がバチンと切(き)れてしまいました。

The taut thread snapped with a twang. {to be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point}

監督(かんとく)：「選手(せんしゅ)は次(つぎ)の試合(しあい)にも勝(か)ちたいと張(は)り切(き)っています。」

Coach: 'The player is eager to win the next game as well.' {to be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point}

勉強(べんきょう)好(ず)きの姉(あね)のことだから、今頃(いまごろ)張(は)り切(き)って机(つくえ)に向(む)かっているはずだ。

Since it's about my study-loving sister, she should be eagerly facing her desk by now. {to be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point}

あの張(は)り切(き)った筋肉(きんにく)からして、彼(かれ)は筋(きん)トレが趣味(しゅみ)なのではないだろうか。

Judging from those enthusiastic muscles, he might be into weight training as a hobby. {to be in high spirits, to be full of vigor (vigour), to be enthusiastic, to be eager, to stretch to breaking point}