When holding the straight bar, the palms are up and parallel. At this time, the forearm external rotation angle is the largest, and the biceps brachii contraction is also the strongest (the biceps brachii contraction will be felt when the wrist is rotated horizontally).
When using the crank, the palms of the grip are not parallel and have a certain angle. Although it is not the best way to contract the biceps brachii, it is more comfortable to hold the racket and will not exert excessive pressure on the wrist.