Originally Posted by Trevtassie

You're probably burning more calories than him and pedal then coast burns even more than travelling at a steady speed, assuming you end up with the same average speed! Why? Because the amount of energy needed to achieve a speed is proportional to the cube of your speed because of air resistance. So say you pedal up to 15 miles and hour and coast down to 10 miles an hour, so you end up with an average speed of around 12.5mph. The bit where you exceed 12.5mph uses more energy than the bit where you are below 12.5mph. They don't add up to the same energy compared to a steady speed of 12.5mph they add up to more, because it takes more energy to get to 15mph from 12.5mph.