It's probably just fatigued
Stretch it gently and hold the position, repeat as often as needed.
There is not a single muscle that rotates the upper arm. The name of the muscle that contributes in rotation of the upper arm is deltoid muscle.
The brachialis is a muscle in the upper arm that flexes the elbow joint.
What are the tendon in your arm?
no
The muscle that raises and rotates the arm is the deltoid muscle. It is a large, triangular muscle located in the shoulder that is responsible for various movements of the arm, including abduction (raising the arm) and rotation.
The posterior deltoid is one extensor of the upper arm.
where you bored when you posted this question or have you pop you muscle in you left arm
Deltoid
Biceps or triceps
which shoulder muscle allows you to adduct your arm
It depends. But, the triceps are 2/3 of your upper arm.