This picture shows our custom-made enclosed treadmill for measuring energy consumption during exercise in small rodents. The clear plastic working section is on top of the 'stack'; tubes provide the air supply (in at the top, out at the ends) and the latched lid allows quick access to the animal. The closed spaces in front and back of the working section are baffles to mix the air flow and keep the animal away from the rear of the belt. Clearances between the belt and the housing are carefully designed to prevent any chance of injury.
Underneath the working section is the power section, containing a variable speed motor and a set of gears and pulleys for driving the belt at a range of speeds. The coiled cable is the output from a small generator that produces a voltage proportional to belt speed.
At the bottom is the control and display unit (here showing a rotation speed of about 43 RPM, or 1.3 km/h). This unit is attached to the power section by a 1.5 meter cable, which lets us put the working and power sections into an environmental cabinet to measure locomotor costs at different temperatures while the control unit stays outside. At left are the gas analyzers, flow meters, computers, etc. that comprise the rest of the respirometry system.
The animal in the treadmill is a deer mouse. It's running at a moderate pace here; 1.3 km/h is about 1/3 of the species' maximal aerobic speed of roughly 4 km/h, and much less than the highest speed these mice can attain in emergency sprints: about 13 km/h.