what exercise can I do to firm up under my arms?

Answer 1

Any type of triceps exercise, i.e. kickbacks, presses, extensions, dips, close-grip bench presses and pushups, etc.

But always remember to participate in 40 continual minutes 3 - 5 times a week of cardiovascular exercises (running, swimming, step aerobics, kick boxing. etc.) to burn the fat off you entire body so you can actually see the muscle you are building. Good luck : )

Answer 2

Sit on the floor in front of a kitchen chair (brace the chair against a wall), with your back to the chair and legs out in front. Reach behind with your hands and put palms down on the seat. Push yourself up so that your body is straight. Repeat. This works your triceps.