The under grip chin up is considered a compound movement for the biceps.
The primary muscle group is the biceps and secondary muscle groups include the
front deltoids (shoulders), forearms, and back.
This exercise can easily be mistaken for close grip chin ups and rightly so,
they are very, very close. However, the only difference is how you pull your
body upwards. Instead of concentrating on using your back to pull your body
up, your going to be focusing on your biceps. This makes this exercise
especially difficult.
If your new to this exercise, you might want to try this on a lat machine
first. This is one tough exercise to do, however, it is one of the best biceps
buildes out there.
Concentrate on squeezing at the top and come down nice and slow.
Position for the under grip close hand chin up
1. Grasp an overhead horizontal bar with and under grip so that your little
fingers are 6 to 12 inches apart.
Execution of the flat bench dumbbell curl
1. Starting from a dead hang, position with arms entirely straight, pull
upward until your chin is above the level of the bar.
2. Lower under control, and repeat.