A system for a treadmill, the treadmill including a tread that rotates around a front axle and a rear axle and side rails on opposing sides of the tread, the system comprising: a brake configured to slow rotation of at least one of the front axle or the rear axle; a controller; the system characterised by a locking mechanism associated with one or both of the front axle and the rear axle and having a locked configuration and an unlocked configuration, wherein, in the locked configuration, the locking mechanism prevents rotation of the one or both of the front axle or the rear axle and, in the unlocked configuration, allow rotation of the one or both of the front axle and the rear axle; a first presence sensor in communication with the controller and positioned on the treadmill, the first presence sensor configured to detect a user above the tread; and a second presence sensor in communication with the controller, the second presence sensor positioned on a side rail and configured to detect the user on the side rail, wherein the brake is not engaged and the locking mechanism is in the unlocked configuration during operation of the treadmill when the first presence sensor detects the user above the tread and the second presence sensor does not detect the user on the side rail, the controller configured to: in response to the second presence sensor detecting the user on the side rail while the first presence sensor continues to detect the user above the tread, engage the brake; in response to the first presence sensor subsequently detecting that the user is not above the tread and the second presence sensor detecting that the user is not on the side rail, move the locking mechanism to the locked configuration; and in response to the second presence sensor subsequently detecting the user is not on the side rail while the first presence sensor continues to detect the user above the tread, disengage the brake. a brake configured to slow rotation of at least one of the front axle or the rear axle; a controller; the system characterised by a locking mechanism associated with one or both of the front axle and the rear axle and having a locked configuration and an unlocked configuration, wherein, in the locked configuration, the locking mechanism prevents rotation of the one or both of the front axle or the rear axle and, in the unlocked configuration, allow rotation of the one or both of the front axle and the rear axle; a first presence sensor in communication with the controller and positioned on the treadmill, the first presence sensor configured to detect a user above the tread; and a second presence sensor in communication with the controller, the second presence sensor positioned on a side rail and configured to detect the user on the side rail, wherein the brake is not engaged and the locking mechanism is in the unlocked configuration during operation of the treadmill when the first presence sensor detects the user above the tread and the second presence sensor does not detect the user on the side rail, the controller configured to: in response to the second presence sensor detecting the user on the side rail while the first presence sensor continues to detect the user above the tread, engage the brake; in response to the first presence sensor subsequently detecting that the user is not above the tread and the second presence sensor detecting that the user is not on the side rail, move the locking mechanism to the locked configuration; and in response to the second presence sensor subsequently detecting the user is not on the side rail while the first presence sensor continues to detect the user above the tread, disengage the brake. in response to the second presence sensor detecting the user on the side rail while the first presence sensor continues to detect the user above the tread, engage the brake; in response to the first presence sensor subsequently detecting that the user is not above the tread and the second presence sensor detecting that the user is not on the side rail, move the locking mechanism to the locked configuration; and in response to the second presence sensor subsequently detecting the user is not on the side rail while the first presence sensor continues to detect the user above the tread, disengage the brake.