The BicepRoll object represents roll nulls along the length of a bone. When used as deformers on an envelope they evenly distribute twist along the length of a bone giving a more natural skin deformation.

The start and end rotations are determined differently for a bicep division than a forearm division (see ForeArmRoll). In a bicep roll division, the bicep's local rotation without spin is the start rotation, while its rotation with spin is used for the end rotation. Roll divisions are then interpolated between start and end. In the case of forearm roll, the forearm's rotation minus spin (calculated using the bicep's rotation) is used as the starting rotation, while the end rotation is the next bone's rotation (wrist) including spin.