a shot in the arm

n.

1. The encouraging letter was like a shot in the arm.
这封鼓舞人心的信,宛如一服兴奋剂。

来自《现代汉英综合大词典》

2. The new player was a shot in the arm for the team,which played noticeably better.
新来的运动员给这个队以鼓舞的力量,这个队明显地有了起色。

来自《简明英汉词典》