Abstract: A motorized exercise apparatus energized by a power source. An electronically commutated motor drives the exercise apparatus. A commutation switch selectively connects the power source to the motor and conducts a switch current when the power supply is connected to the motor. A safety shutdown switch responds to a safety shutdown signal. The safety shutdown switch has a first mode wherein the power source is connected to the motor, and a second mode wherein the power source is disconnected from the motor. A threshold circuit associated with the commutation switch generates a switch current signal representative of switch current. The threshold circuit comprises a threshold detector responsive to the switch current signal for generating the safety shutdown signal and placing and maintaining the safety shutdown switch in the second mode when the switch current signal indicates the switch current is above a threshold.