Originally Posted by
CardiacKid
You clearly have the cardio conditioning to easily ride for 30 minutes. That your legs hurt that much is a good indication you are staying in too low of a gear. Switch to a higher gear and get your cadence up. You should be pedaling at about 90 revs a minute. That way you will be using your heart and lungs and saving your legs.
Don't you mean "Switch to a lower gear"? High gear=low cadence unless you are extremely strong. Spinning in a low gear is the way to save the legs.