Overhead triceps extensions are another great exercise to isolate the back of your upper arm. Only one weight is required and you can use a dumbbell or kettlebell to make this one work.
Start in the standing position with one great gripped between your hands.
Raise the weight overhead, and bending at your elbows lower the weight back behind your head.
Return to starting position.
Continue slow and controlled for 15-20 repetitions.