"inject enthusiasm" is correct and usable in written English.
You can use it when you want to describe someone who is enthusiastically engaged in an activity. For example, you could say, "John's infectious enthusiasm injected energy into the team's performance."
In his response to the report, Mr Motsoaledi said: "We need to inject enthusiasm into the condom campaign, and we are about to start rolling out new types of free, coloured condoms which are also flavoured".
International organizations needed a big idea to shake governments out of their ennui, to inject enthusiasm -- and more importantly, money -- back into poverty reduction.
He injected enthusiasm into all of us and lifted the annual awards to a new level.
Diamante is only doing what's necessary, injecting enthusiasm into a crowd that is sometimes too hip, too casual, too detached for its own good.
Whether he is hitting fungoes, throwing batting practice or positioning the outfielders, Shines is injecting enthusiasm and instilling confidence with a vocal, demonstrative style that complements the more measured approach of Manager Jerry Manuel, his friend of nearly 30 years.
Ministers injected enthusiasm and ambition into the talks on Friday, which helped achieve Saturday night's progress.
In doing so, he injected enthusiasm, confusion and yet more chaos into an ever-evolving music business.
Our key informants described Pallium as being a major success: "...[Pallium] came and injected enthusiasm, money and expertise into the whole [HPC] field.
There are few who would inject the enthusiasm and vitality or that possess the authority that would be required to make a success of the post.
Mr Blair himself needs to inject enough enthusiasm into the campaign to prevent Labour supporters from staying home on polling day.
Based at the Aquatics centre during London 2012, the former amateur jockey was constantly called upon to inject some enthusiasm and expert commentary on other sports– from equestrianism to running.
