The incline dumbbell curl is an isolation exercise for targeting the biceps. Lying on an incline bench prevents assisting muscle groups from aiding the lift, therefore placing maximum demand on the biceps.
Curling the dumbbell with a supinated grip during the incline dumbbell curl results in the biceps being the primarily worker, with the other arm flexor muscles (the brachialis and brachioradialis) less involved.
Although there is no tangle difference between the two, the athlete can choose to either curl both dumbbells simultaneously or opt to curl one arm at a time.
The incline dumbbell curl isolates the biceps during the flexion of the elbow. This may help some athletes who require strong arm flexor muscles (such as those involved in contact sports), but is unlikely going to be an effective primary choice due to the limited stimulus provided.