"Fry Fat With Intervals: 
Intervals Aren't Just for Racers and People Who Care About Getting Faster"
by Selene Yeager

"Riders often tell me they're backing off on speed to stay in the "fat-burning zone." Riding a bike burns calories--thousands of them--even when you're not working terribly hard. And, yes, that type of easy riding does rely primarily on your fat stores for energy. But steadfastly riding at slower speeds isn't the best way to whittle your waistline. If you want to lose weight, your main goal should be to use as many calories as you can, which is what high-intensity riding does.   Even if you can ride fast only for short bursts, you can still dramatically increase your calorie cost. Additionally, intervals increase your lactate threshold (the point at which your legs start to sting and you slow down), so you become a faster rider overall, which means a bigger total calorie expenditure. Finally, intervals also help you torch more calories after you've racked your bike. Exercise researchers have found that your metabolism stays higher for as long as 12 hours after a vigorous workout, which adds up to about 15 bonus calories for every 100 you burned during exercise. All you have to do is follow this simple plan.  

The Speed Factor
This chart shows how many calories a 150-pound rider would expend every hour for various kinds of riding, according to the Compendium of Physical Activities Tracking Guide, a standardized set of calorie-burn measurements. To figure out how many calories you'll use, first take your weight and divide it by 2.2 to express it in kilograms. Then multiply that number by the METS (or metabolic equivalents, a unit of the energy cost of an activity) number in parentheses:" 

1 HOUR RIDING AT                                BURNS
Less than 10 mph, very leisurely                272 calories (4 METS )
10-12 mph, easy                                     408 calories (6 METS )
12-14 mph, moderate                              544 calories (8 METS )
14-16 mph, vigorous                                680 calories (10 METS )
16-19 mph, very fast                               816 calories (12 METS )
More than 20 mph, racing (no drafting)      1,088 calories (16 METS )