I'm sure the higher-end treadmill models have better interfaces, but this one in particular uses a standard audio jack which uses encoded sounds to control the various speed and incline settings found on the treadmill. For example, playing the sound encoded for speed-3, incline-7 will set the treadmill accordingly. As you can imagine there are quite a few of these sounds. I was able to acquire these sounds after a little prying into the JavaScript for the treadmill application provided by the vendor.
