This is a super set for the triceps. You will need 3 different weights and a step box.
Lay on your step box with the various weights next to you. (I actually balance mine on my belly so I can reach them quicker). Remind them to keep their lower back pressed to the box.
Starting with your lightest weight, bend your elbow so your elbow points to the ceiling and the free weight barely touches the shoulder of the opposite arm. Do 7 elbow extentions.
Quickly grab your medium weight and do 7 more elbow extensions.
Quickly grab your heaviest weight and do 7 more elbow extensions.
Go back to your lightest weight and do 21 more elbow extensions.
Switch arms and repeat on opposite side.
In order to feel this, their heavy weight should be a weight that they normally would not choose for several reps. And a quick switch is important, don't give their triceps a chance to rest while switching weights! They can rest when they're done with the entire set!