This is a great exercise that focuses on a variety of muscles. Raising your feet off of the ground helps engage the core while trying to stabilize yourself during the tricep extension. This is a good exercise for those who may have limited time to workout due to focusing on more than 1 muscle group.
1) Lay flat on the floor with a barbell directly behind you (you can add weight to it if it is too light).
2) Place hands on the barbell shoulder width apart and lift over your head directly above you with arms fully extended (you can move your hands closer together to make the exercise more challenging).
3) Raise your feet about 6 inches off of the floor. If this is too challenging, you can lift them a little higher. Do not arch your back.
4) Slowly lower the bar behind you while bending at the elbow (do not let the bar touch the ground).
5) Keep your elbows close to your ears and raise the bar back to starting point.