a shot in the arm : 腕への注射（元気を回復させるもの）

a shot in the arm

腕への注射　→　元気を回復させるもの、Something that boosts one's spirits.

一般例文

• We all agree that the economy needs a shot in the arm, but we can't agree on exactly what it should be.

英字新聞からの例文

• 引用元 : Financial Times (by Pan Kwan Yuk) - Teva climbs on report it is mulling 10,000 job cuts (2017/12)

  Teva Pharmaceutical's US-listed shares received a shot in the arm on Friday following a report that the struggling Israeli drugmaker could be looking to cut up to 10,000 jobs ...

• 引用元 : New York Times (by KATIE BENNER) - Apple Report Expects New iPhones to Jump-Start Growth (2017/11)

  Strong demand for the devices could give a shot in the arm to Apple, which could become the first publicly traded company to reach a $1 trillion market value but has faced more questions about its growth in recent quarters.