Primary: Abs (abdominis transversus)
Secondary: Shoulders (infra-/supraspinatus, teres minor, subscapularis)

The two handed external rotation trains especially the lateral core muscles. These muscles support many movements while playing golf or tennis for example.

Variosling-PT-weite-Außenrotation-beidhändig-1-web Variosling-PT-weite-Außenrotation-beidhändig-2-web
Sling Training Bauchübung

Starting Position
Stand with the feet slightly wider than shoulder width apart and lateral to the suspension. The chest is directed to the anchor point. Both arms grab the handle of the Rotate and are stretched towards the pulley  in front of the chest.
The PT is located diagonally behind the trainee in a step position, facing away from the anchor point. The Rotate is under tension.

The hip turns away from the anchor point completely. Your chest and arms rotate away from the point of suspension. Thereby the arms remain stretched in front of the chest.
The PT gives in the pull of the trainee by either transferring the weight towards the anchor point or stretching the previously flexed arm. Afterwards he pulls his partner back into the initial position.

A slow and controlled movement execution avoids jerky movements especially at the     beginning and end of the exercise.