Isometric elbow flexion in mid range - forearm in neutral

Stand with your upper arm by your side and your elbow bent to 90 degrees.
Your knuckles should be pointing outwards and your thumb should be on top.
Grasp your wrist from above with your other hand.
Keeping your upper arm by your side try to bend your elbow whilst resisting the movement with your other hand so that no movement occurs.
Hold the tension, and then relax.