If I understand the description correctly you are doing a reverse-grip curl (aka drag curl or overhand grip curl). The reverse curls, when done properly, have been thought to stimulate brachialis growth. I like to work in this variation about every other week while on a hypertrophy training block or to really get my arms to burn.
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Tips: The late Vince Gironda, the “Iron Guru.” used to force everyone at his old gym in Studio City to try these if larger biceps were a stated goal. To perform drag curls, keep the elbows in back of you rather than pinned at your side. Using an overhand grip, curl the bar up and at the same time keep it in contact with your torso. In effect, you are dragging it up. Be sure not to let the elbows or shoulders rise up or this can turn into a half-ass upright row real fast. You won't need much weight to make your brachialis burn and ache like there are lumps of liquid fire buried within your outer biceps.
Hope this helped
DM
