Brachioradialis muscle very sore. affects both arms. no history of trauma or overuse. has been a month. some neck pain. what might be the cause?

Get seen: My first concern, especially if it's also week, is that you're coming down with inclusion body myositis. One of several possibilities, but a reason in itself for perhaps specialist consultation.

Muscle pain: Pain in the area of the brachioradialis can be related to radiating neck pain or radiculopathy—which is caused by a pinched nerve by disc herniation or arthritis likely at c5-6. If this seems worse with movement of the neck (down the arm), it could be related. Also, if associated with numbness or tingling into the thumb, likely a neck issue. I suggest all patients >50 yo be seen by a doc.

Could be neck issue: The pain in that region of your arm could be related to a pinched nerve in the neck. See an orthopedic physician/surgeon, or a physiatrist if it doesn't improve.