An auto lock system for a manual treadmill, the auto lock system having a locking mechanism comprising a movable arm having a distal end facing one of the front axle or the rear axle, a locking device at the distal end of the movable arm configured to engage the one of the front axle or the rear axle to inhibit rotation of respective front wheels or rear wheels, and an actuator configured to move the movable arm. A controller is in communication with a sensor configured to detect a user on the tread. The controller is configured to, in response to the sensor detecting no user on the manual treadmill, actuate the actuator to move the movable arm such that the locking device engages the one of the front axle or the rear axle.