Press you arms out directly to the side - where do you feel it? Why in the side delts and triceps and traps off course
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Its almost like a compound version of the lateral raise
But you need a cable machine or bands for resistance. Not the best for mass gains.
But you can do it lying on your side using gravity. But thats not a stable stance for the shoulder joint with heavy dumbells.
So you do it standing up or sitting sideways on an incline bench, lean slightly to one side, about 70-80 degrees to the side opposite the one your working, and then press the dumbells up. I prefer standing since it works your core as well. You can hold onto something for better balance.
Feel the huge pump in your side delts! Then look at the mirror and see how you've gained 1 cm of pumped up delts one each shoulder!! Freaks me out everytime I do em in the gym
You cna either do em with palms facing forward or palms facing out to the side with your hands rotated out, which makes it almost liek a lateral raise but with more weight, but this may cause cuff problems..
And if you press the dumbells up at an angle instead of directly up you get constant tension on the delts
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There are all kinds of variations you can do.
The best bang for the bucks is making an iso move into a compound hybrid. Other ones that spring to mind are Chins and Bodydrag curls for biceps and California presses for triceps.