I was pedaling away on an exercise bike at the local gym the other day when I realized that the RPM I was doing directly corresponded to the BPM (beats per minute) of the song I was listening to on my iPod. This is very natural. Any aerobics instructor knows this when choosing music for her class.
Make an exercise bicycle with an MP3 player built in and a selection of songs at various BPM rates. You can then select the BPM of the song by the RPM that you want to achieve on the bike. Maybe 80 RPM to start out your workout, and work your way up to 100 RPM for the peak, and then come back down to 70 RPM for the cool down.
We already have technology to slow down and speed up music without distorting the pitch. This technology could possibly be applied in my hypothetical bike to fill in gaps for bit rates where you don't have music.
The bikes should come with built in music, but when you buy the bike, you should have the option of subscribing to a program where the company will send you updates of newly released pop songs that can be uploaded into the bikes.
An of course the bicycle should have an iPod dock to allow the use of your own music. The MP3 files should either have the BPM meta information encoded already, or perhaps the bicycle could do some quick analysis. Obviously the effect will be worse with your own music because there's no guarantee that the songs you bring will have a steady tempo.
There's a program called Tangerine! that will analyze your iTunes library and attach BPM metadata to all your songs, which you can then use to make smart playlists. I've tried it, and it doesn't work very well. It will place a mellow Norah Jones song with a jazzy snare beat with a heavy Metallica song with a crunching, distorted electric guitar strumming to the same approximate BPM. Perhaps this simply indicates that a machine alone is not capable of choosing good workout music. I don't know.
There seem to be a few exercise bikes that allow you to plug in MP3 players, like this one, but they don't seem to do anything besides play the music through speakers.
This certainly seems to me like a winning idea. It could be adapted to rowing machines or treadmills as well. If the concept of a subscription service works, it could mean a lot more money that just the bike sales.