Symptoms of a Torn Arm Muscle
Assess if the arm is in pain. Fatigue is usually not accompanied by pain so if a muscle is painful (whether touched or when used) then your arm probably has a torn muscle.
Examine the arm for swelling. Swelling is caused by fluids such as lymph and blood collecting at the point of injury and is a sure sign that something is wrong with your arm and an important indicator of a torn muscle.
Examine your arm muscle for "knots" near the effected area. Subconsciously, your body is trying to protect your muscle and is asking other muscles to do work they are not designed to do. The result is a hard "knot" in your injured muscle. This coupled with pain and swelling almost certainly indicates a torn arm muscle.