Hanging Leg Tucks
This exercise is performed in the hanging position, with your legs fully extended. If the bar is not high enough to fully extend your legs, keep your knees bent.
Raise your knees towards your chest, bending the knees as shown in the pictures, contracting the abdominals.
Hold for 2 seconds, then slowly lower your legs to the starting position, stretching the abs.
You might find that it is hard to hold on to the bar for too long at first. As you continue to perform hanging exercises, your grip will strengthen.
Search on FreeTrainers.com