If your gym has a pullover machine, give it a try. If nothing else it is a good finisher at the end of a pectoral workout.
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I use the Hammer Strength pullover machine. There is zero pectoral involvement, zero. With dumbells I can see why people might think it's pecs as you hold the dumbell over your chest, very minor stabilizing by pecs. Some also do the lowering to the chest thing
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But on the machine it's all back.
I did the dumbell pullovers starting out, 30 reps with the heaviest dumbell, which was 100lbs at my gym, lying cross bench at the end of some back sessions. I really lowered my hips. I think I got a umbilical hernia from it and I knew it was a tricep tear waiting to happen
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