The Physics Of Spinning

If you've ever wondered how many calories you burn in an hour of activity, go find a piece of exercise equipment with a power meter. Most Stairmaster and Lifecycles have power meters, or are calibrated to estimate power, and they're probably fairly accurate. Then get on it, warm up, and set it to a manual mode, and watch the power meter to see how much you can output for your workout. I found I can do about 300 Watts for an hour, or 300 Watt*Hours, or 0.3 kWH of energy.

Now, to figure out how many calories your workout burns, you need to convert the kWH energy into kCal (food calories), taking into account the metabolic efficiency of the human body.

So, lets say in spinning I average 300 Watts for an hour, so I burn a 0.3 kWH. (This is equivalent to powering a 100W light bulb for 3 hours, given a 100% generator efficiency.) We'll use the unit conversion factor of 860 kCal/kWH, which you can find on the web. But, since the body isn't 100% efficient in coverting calories to work, we have to apply a metabolic efficiency factor. For an well-trained athelete using the proper equipment, the efficiency factor is about 22-26%. That means for every 1 calorie delivered, he requires 4 calories of food.

So, finally:

calories required = 0.3 kWH * 860 kCal/kWH * (4 food calories / 1 delivered cycling calorie) = 1032

That's why I end up eating 4 turkey burgers, 1 Dryer's Lite ice cream bar, and 14 oz (400g) of Reece's Peanut Butter Easter Eggs.