Alternating Triceps Trigger
Grab both ends of the towel about shoulder-width apart. Relax the shoulders down and back and extend arms forward at shoulder height, keeping a slight bend in the elbow. Twist the right hand down and up, ending with your palm facing you and the towel wrapped around the back side. Then flip palm toward the center of the towel so palm faces forward.
Repeat on the left side so the towel is taut and hands are side by side. Relax shoulders down and back and keep a slight bend in both elbows. Holding this position, push right hand slightly forward. Then switch, pushing left hand forward. Start slow, then speed up, alternating each side.
To make it more advanced, pull the towel in toward chest, elbows in tight to sides. Extend arms forward to return to starting position.