Keeping weight in check

There is a temptation to believe that riding a bike is some sort of guarantee of weight loss or control. This is really only the case if you are consistent in your riding and have a little discipline in the eating habits.
On the plus side, riding the bike  is really an excellent mechanism for keeping intensity at that level where fat oxidization takes place. This is the physiological aspect where the body will use fats/lipids to fuel the exercise and a major source of this comes from the body's adipose layer. Less of that means less of you!
For better performance it is best to combine intervals at a higher intensity and then to revert quickly to the lower intensity.
The main downside is the time expenditure. 
The upside is even 30 minutes of moderate work uses fat oxidization as a major source of the energy required.
 














This is fine for weight control.
If you want to race however you may have to put a little extra effort in.

Note the lengthy recovery phases. If you work at the correct levels you will find that you need them. During this time you are re-adapting your body to use plasma free fatty acids.
That feeling of your legs running out of energy is of course completely natural.
Muscle glycogen contains enough fuel for between 800 and 1500 kcals of work.
Once it is gone it is gone by the way..  be careful of burning those matches!