A commonly biceps exercise which puts your hand in mid-prone position, just like using a hammer. In terms of which elbow flexor becomes more dominant in this position, that award goes to brachioradialis, as well as higher loads into wrist muscles that will preventing ulna deviation (flexing the wrist to the side in the direction of the little finger).
Zip up your abdominals
Grip the dumbbells firmly
Do not allow elbows to drift forwards
Take the dumbbells past 90 degrees at the elbow
Targeted muscles trained
Key movements trained
Wrist radial deviation (via anti-ulna deviation)
Despite this being an elbow dominant exercise, it is a very good options for strengthening the thumb border of the wrist (radial side). Due to the distance between the weight and the elbow, the lever length creates a lot of work over the wrist where forearm muscle have to work very hard to stop the dumbbell from pulling the wrist downwards towards the floor.
This can be a very useful exercise in preparing the wrist for ground contact in performers that have tricks within their choreography, or catching and throwing props.