The Brake Unit is attached to the Power Sled using two screens and a spring loaded cable.
The 2000XR Users Manual says:
Primary Braking System: Pull the hand brake lever to engage the rear brake. IMPORTANT: THIS BRAKE IS NOT EFFECTIVE WHEN GOING DOWN STEEP INCLINES OR LONG, SHALLOW GRADES. USE THE SECONDARY BRAKING SYSTEM INSTEAD.
Secondary Braking System: The secondary braking system on the Motorboard is engaged by placing the heel of your shoe on top of the rear wheel, and applying pressure. By varying the amount of pressure, you can vary the amount of braking power. Make sure that when operating the Motorboard you are wearing appropriate footwear in order to operate this braking system. This technique is especially effective when riding down small hills.
WORK IN PROGRESS