If I sorta lean back a bit and puff out my chest I can usually get a few extra reps in, but is this a bad idea to do? I rationalize my decision based on the fact that I do 3 full-body workouts M-W-F and Overhead Press is my only actual pushing movement that day, so I figure I don't mind if my chest fibers are recruited into the movement a bit if that is what is happening (plus the fact that I'm moving more weight is a good thing isn't it?). But if it's a better idea to stand relatively straight/strict and not be able to lift as much then I will do that.
When you lean back you put stress on your lower back that could cause injury also by leaning back and pushing out your chest the exercise becomes more of a standing incline press recruiting your pecs and not working your entire shoulder as effectively.
Risk VS Reward....
i find myself doing this too towards the end of my sets as i try to get another rep or two i start arching my back.. i guess trying to recruit my chest muscles. I look at this like the people that use their lower backs when doing lat pull downs... the momentum and recruitment of the lower back helps them lower more weight. I dont do this because my shoulder is a weak point (for both lat pull downs and over head shoulder presses) but i see how it can help get you a little extra effort out of a set.
This MIGHT help a little overtime produce more gains but Risk Vs Reward comes into play, theirs more chance for injury. Is an injury that could either take you out of lifting for months OR (even worse) be a small injury you can live with but gets worse over time. Its like a cavity once they start they just get worse and i would do everything i could to avoid little injuries like that... you'll be lifting happy for years if you play it safe.
It's hard to track progress if you "cheat" some reps. If you are doing a strict overhead press, keep them strict. That way you'll know if that extra 5 lbs was from strength progress. Plus, it's safer than leaning back. If you want to "cheat" some reps, use a little bit of leg drive.
Hm... alright, thanks guys.