Simply put, cadence is a measure of leg speed while pedaling. The higher your cadence, the faster you're turning the pedals. Occasional cyclists ride in relatively high gears at 50 rpm, which feels natural and comfortable to them. But those who train for fitness and racing must learn to pedal almost twice as fast usually 80-1 10 rpm in moderate gears. Maintaining such a cadence is called spinning.

How is cadence measured? It's easy to monitor your cadence while riding. Just count the number of times your right or left leg comes to the top of its pedal stroke in 30 seconds, then multiply by 2. The result is your pedal rpm. Some cyclecomputers have a cadence sensor, which does the counting for you. In time, you'll be able to accurately gauge without checking.

Why is a high cadence best for performance cycling? There are several reasons. First, fast riding requires an extremely high rate of work, and you're simply more efficient at a high cadence.

Second, and perhaps most important to racers, a high cadence facilitates rapid acceleration. The reason lies in the mechanics of pedaling. At low rpm in high gears, when a relatively great amount of force is required to turn the pedals, an increase in speed requires a substantial increase in effort. But at high cadences in moderate gears, when there's not as much force being used to turn the cranks, it takes less time and effort to accelerate. It's like being in second gear in your car--the higher engine rpm lets you increase a given speed quicker than if you were in fourth.

Third, a moderate gear requires less effort for each pedal stroke. The faster you spin, the less force is required to rotate the pedals. Thus, you can ride farther with less leg muscle fatigue.

Finally, a fast cadence is easier on the knees. We've all heard of cyclists who have suffered some debilitating trauma from "pushing too big a gear." Doing so results in a relatively slow, struggling pedal stroke that increases the chance of injury.

What’s the perfect cadence? It depends on your type of riding. For instance, millions of people who use their bicycles for daily transportation pedal merrily along at 40-50 rpm. Studies have proven this to be the most efficient cadence for the speeds they normally travel (approximately 10 mph).

However, for reasons discussed earlier, road racers favor a pedal rate of 90-plus rpm, In fact, some criterium specialists cruise at 100 rpm or more because of the quick changes in speed their event demands. Conversely, big-gear time trialists can sustain a powerful stroke best when in the 80-85 rpm range. Fast recreational or fitness riders generally performs optimally in gears that let them maintain 90 rpm.

Interestingly, the benefits of spinning begin to disappear above 100 rpm. While the reason is not fully understood, it's probable that such swift leg movement requires more energy than it produces.

How can I learn to pedal faster? It's simple: Shift the chain to an easy gear and leave it there on flat terrain. Concentrate on spinning the pedals smoothly. If you find yourself bouncing on the saddle, reduce the weight on each foot as it travels upward. This should eliminate the rough spots in your pedal stroke and improve comfort. Choose gears that also allow you to spin when climbing and descending. This will further attune your legs to fast pedaling.

In the off-season, practice spinning on rollers or a resistance trainer. Such a workout -- without the disruption of traffic and hills -- is perhaps the best way to perfect your spinning technique and become a smooth pedaler. Then, come spring, you can move outdoors and into the world of performance cycling.

Steve Johnson, Ph.D.