'over exert' is correct and usable in written English.
You can use it when you want to talk about exerting too much effort or energy and it results in negative consequences. For example: "The marathon runner was warned not to over exert himself, but he kept pushing himself to the limit."
No need for Djokovic to over exert when he knows he'll have the chance to serve for the match soon enough.
The winter before, the writer was very sick with rheumatic fever & had to take special care not to over exert himself.
It's been an impact on my family because I - I don't over exert myself and I've always been the type of person that I - I won't ask anyone to do something because I'd rather do it myself.
If you don't over exert yourself you should start seeing results in about two weeks.
"He doesn't over exert himself, he's balanced".
You may feel the urge to eat more and heavier, but unless you are moving around a lot, lighten up! Rest! Don't over exert yourself and try and have a better night's sleep.
It takes a lot of self-discipline not to over-exert myself.
The tongue is a muscle, but in kissing it doesn't need to over-exert itself.
James Milner also came on for the second half, with Hodgson keen not to over-exert Wilshere, and that meant Drinkwater could take the role where he excelled last season for Leicester City.
While I am "lucky" enough to have relatively mild ME - I work part-time in the sociology department of Goldsmiths, University of London, I have a wife and two children, I have travelled and experienced many of the things that people of my age have - I always have to be careful not to over-exert myself, to balance my need for exercise and stimulation with my need never to exceed my boundaries.
They screamed when he fell on his bottom after over-exerting himself with a kick.
