Aerobic exercise is a popular form of exercise that improves one's cardiovascular health by reducing blood pressure and providing other benefits to the human body.  Aerobic exercise generally involves low intensity physical exertion over a long duration of time.  Typically, the human body can adequately supply enough oxygen to meet the body's demands at the intensity levels involved with aerobic exercise.  Popular forms of aerobic exercise include running, jogging, swimming, and cycling among others activities.  In contrast, anaerobic exercise typically involves high intensity exercises over a short duration of time.  Popular forms of anaerobic exercise include strength training and short distance running. 
Many choose to perform aerobic exercises indoors, such as in a gym or their home.  Often, a user will use an aerobic exercise machine to have an aerobic workout indoors.  One type of aerobic exercise machine is a treadmill, which is a machine that has a running deck attached to a support frame.  The running deck can support the weight of a person using the machine.  The running deck incorporates a conveyor belt that is driven by a motor.  A user can run or walk in place on the conveyor belt by running or walking at the conveyor belt's speed.  The speed and other operations of the treadmill are generally controlled through a control module that is also attached to the support frame and within a convenient reach of the user.  The control module can include a display, buttons for increasing or decreasing a speed of the conveyor belt, controls for adjusting a tilt angle of the running deck, or other controls.  Other popular exercise machines that allow a user to perform aerobic exercises indoors include elliptical trainers, rowing machines, stepper machines, and stationary bikes to name a few. 
One type of treadmill is disclosed in U.S. Pat.  No.  9,216,316 issued to Douglas G. Bayerlein.  In this reference, the invention relates to a manually operated treadmill adapted to generate electrical power comprising a treadmill frame, a running belt supported upon the treadmill frame and adapted for manual rotation, and an electrical power generator mechanically interconnected to the running belt and adapted to convert the manual rotational motion of the running belt into electrical power.  One benefit of the manual treadmill according to the innovations described herein is positive environmental impact.  A manual treadmill such as that disclosed herein does not utilize electrical power to operate the treadmill or generate the rotational force on the running belt.  Therefore, such a treadmill can be utilized in areas distant from an electrical power source, conserve electrical power for other uses or applications, or otherwise reduce the “carbon footprint” associated with the operation of the treadmill.