The Arnold shoulder press is named after the great bodybuilding legend Arnold Schwarzenegger, who performed the dumbbell shoulder press with a rotation element to the exercise which he said was highly effective at targeting the various heads of the shoulder muscle.
The exercise begins with the dumbbells level with the shoulders, with the palms facing towards the body.
The dumbbells are pressed above the head, whilst the wrist rotates throughout the lift so the palms are facing away from the body at the top of the exercise.
The movement is mirrored on the descend to finish in the same position.
The internal rotation of the shoulder during the exercise does add another element to the exercise in comparison to the traditional dumbbell over-head press, with some trainers preferring the Arnold press.
It would be wise to experiment with the various over head pressing exercises to gauge preferences, as well as ensuring a change in stimulus to the target muscles.
The rotational aspect of the exercise may not be ideal for those with injurious shoulders.
The exercise targets the front and side heads of the shoulder muscle (known as the "deltoids"), as well as the triceps (large muscle to the rear of the upper arm).
Some argue the rotation during the Arnold pressing exercise results in greater stimulus to the rear deltoid head, therefore making it a greater overall shoulder exercise.
The truth is the exercise will stimulate the rear deltoid head in a similar fashion to the traditional dumbbell press, which is minimal.
Over-head pressing should not be relied upon to target the rear aspect of the shoulder.
Many back exercises, such as rows and pull ups, recruit the rear deltoid head greatly, as well as isolation exercises such as face pulls and bent over lateral raises.
The Arnold press would likely be used by those focused on increasing muscle mass; therefore a moderate repetition range would be best followed to induce muscle hypertrophy.