Watts vs. calories per hour
With regards to the extra credit assignment, many cardio machines have outputs that tell you about your power exertion. the two most common units are Watts and Calories per hour (which is an energy unit per time unit, or power).
Here's the trick: Machines that give an output in watts typically are referring to the actual mechanical output you're exerting, estimated using sensors embedded in the instrument. The Cal/hr measurement refers to how many food calories you need to be burning in your body to produce your rate of output. The human body, as with anything that converts one form of energy to another (chemical potential to Mechanical, in this case), is not perfectly efficient; in fact, you need to burn 4-5 calories of energy for every 1 calorie of actual mechanical work that you do.
This means that if you are using calories per hour to estimate your power, you need to divide this number by about 4 to get your actual mechanical energy output. For instance, for a rate of 800 calories per hour:
800 chem. Cal........1 mech. cal........ 4184J..........1 hr.......1 W
---------------------x- ---------------x---------------- x---------x -------- = 230 W
1 hr.....................4 Chem. cal........1 calorie.....3600s....1 J/s
Without the factor of four, your mechanical output will appear to be artificially high when you convert it to watts.
If you don't get this message in time to make adjustments, don't worry about this. I didn't realize that was what exercise equipment measured until somebody just brought it up. Just don't be too surprised if you used a cal/hr reading and your numbers are wildly high.
jay-