I shouldn't even bother with you guys. Nobody but Chris seems to be appreciative around here.

WTF have YOU guys done for ME?

the one that goes around your bicep attaches behind you and as low as possible. This prevents the forwards and upwards motion of the elbow, thereby working the SHOULDER.

The one on the wrist attaches behind you and slightly downward. This prevents the upwards motion of the hand without encumbering the true jab mechanics, thereby working the tris and the shoulder. Alternatively, you can attach the wrist one to your back ankle and the elbow one to your elbow, connect them by a piece of byngee and this works well too, IF you don't have any other anchoring options.

You can do one at a time, or both, as I've shown in the last pic. This is the ultimate jab plyo. I'm contacting Grant Boxing tomorrow to propose a meeting of this little gem.