I always wonder about this question to to myself.
Q and A
the person at the site says muscles will still grow the same even if performed on same session
another Q and A
read answer 2. in the answer portion. This is what it says...
2. Yes, it is Okay to do cardio a day after doing lower body exercises, because they do not coincide. This is because cardio exercises do not affect a specific muscle group, they just burn fat. It is, in turn, okay to do cardio exercises the same day or the day after working lower body muscle groups.
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so this means it is okay to do cardio on the same day as weightraining, but not the same day as working lower body muscle groups. Cardio is fine being done on the same day as upper body workout.