Resting your elbow on the edge of a table with the palm facing downwards, form a fist.
Place the opposite hand on top of the fist.
Press the fist upwards towards the hand but use the hand to resist any movement.
Press at a comfortable resistance (~20% resistance to start). Make sure your hand does not move. This is what is referred to as an isometric contraction.
Keep your neck and shoulders relaxed throughout.
Hold for 10-20 seconds.
Release and repeat 2-4 times.