Many inadvertently flex muscles they don't need to use, like an isometric exercise and don't even realize they are doing it. The tension you get in the triceps, when you roll that elbow, is the only tension needed in the entire arm -- most especially in the forearm! When you put muscles and their associated tendons under tension, they are more prone to injury. When they are relaxed, there is flexibility that allows movement or better yet, shock absorption.
In archery, DO NOT flex ANY muscle not required for the shot!! Study yourself and see if there is tension, then if there is, see if you can determine how that tension is contributing to the shot. IF it isn't, RELAX IT!!
I see many shooters tense themselves into marble statue hardness for NO reason. Then they discover over time -- PAIN/INJURY.
Arne
PS. Think about when you are standing up. The muscles in your legs are only working to keep your leg bones aligned to support your weight, you don't have all the muscles in your legs all tensed up.