well........... you have to lower the bar in a controlled mannor even while doing push pressing, otherwise you will break a clavical. so here is an illustration.
say i can strict press 150lbs overhead for 5 reps. and say i switch to push presses with 200lbs for 5 reps. 1st im lifting more explosive, which means more growth hormone release. 2nd im lifting 50 more lbs......... yes im using leg drive so he concentric phase.......... but you dont use leg drive on the negative phase. so you have to use your shoulder muscles to lower it under control. if your goal is bodybuilding and physique only, then think of it as doing negatives. you have someone else help you raise the weight (but now your using your legs instead of a spotter) and then a negative down. now if your goal is strength, you can just let the weight fall and catch it. but you will still see strength and size results eitherway becuase of the fact: your using more weight.
i hope that made sense.
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