I took the leve I tennis coach course this year, and one of the things the instructor told us (and he's a university teacher and does research), is that, statistically, there is no evidence that someone that does not do warm up, has more injuries than someone that does.
It does not mean that you shouldnt do warm up, because it also prepares you for the workout (e.g. performance), but it appears to have no correlation to the number and severity of the injury.
I have no info. about the streatching..
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