Answer:
Icy storms with decreasing temperatures.
I believe the triceps brachii is acting as an agonist. The triceps is an extensor muscle of the elbow joint and antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the fore arm and hand are used for the fine movements. For example during elbow extension the triceps Brachii acts as the Agonists while the Biceps Brachii acts as the Antagonist.
