Did you ever do a stress test on an exercycle at the doctor's office or type in your body weight on the cycle at the gym to get an estimate of the calories you burned in your exercise session?
If so, you have probably benefited from some of the mathematical equations that relate the work done on a bicycle to the metabolic effects, such as the amount of oxygen your lungs are taking in to keep your legs pumping (which correlates with the amount of energy you are burning in the task).
The most commonly used estimate, recommended by the American College of Sports Medicine (ACSM), links the work rate and body mass to the oxygen uptake or calories burned. This equation does not consider how fast the pedals are spinning, a rate known as 'cadence'.
Convincing data from a new study suggests that we should think twice about how fast we are turning the pedals to get the most out of our bike rides. It turns out that spinning fast may be efficient for professionals touring France, but not so great if you want to get the most efficiency out of your ride when you do not have thighs like oak trees.
A team of scientists at Oxford approached the question from two sides. First, the put cyclists in special face masks that measure the actual amount of oxygen they use. They plugged this data into some equations to come up with a modification of the ACSM equation. The new math better predicts the real data when spinning speed is factored into the equation.
Second, they used infrared and video-based motion analysis to see where and how energy is expended at different pedaling rates. The bottom line is this: it takes a lot of energy just to move your legs faster. If you are putting a lot of strength into that speed, the energy to move faster is worth it -- you will go much faster so the investment relative to the benefit makes sense. But if you are putting the amount of effort a typical recreational cyclist can maintain behind each pedal stroke, then pedaling faster represents a waste of energy used to move the legs with not much translating into forward motion.
So if you want to get the most out of the energy you bring to your day, set a nice, easy cadence on your ride to work. Of course, if you really want to burn calories, it seems that being less efficient may pay off, so spinning class may be the place to really break a sweat. Either way, you'll feel good for doing it, and better for knowing when to step on it and when to take it easy.
If you want to study the math yourself: Pedaling rate is an important determinant of human oxygen uptake during exercise on the cycle ergometer.