Incorrect leg position (or seat height) on bicycle. Note the severe bend in the leg at the bottom of the down stroke. |
Adjusting your bicycle seat so your feet are flat on the ground when sitting is great, but when you are actually pedaling the bike, chances are your legs are at a severely bent angle when your foot reaches the bottom of the pedal stroke. This means that you are not getting the full power out of your leg muscles when pushing the pedal on the down stroke.
Maximize your cycling horse power by adjusting your seat so that when your foot is on the very bottom of the pedal down stroke, your leg is only slightly bent. When sitting on the bike, you may be only be able to touch the ground with your toes, or with only one foot, or have to move forward and straddle the cross bar, but when you are actually pedaling the bike, you are almost fully extending your leg which allows you to put more power in each down stroke. You will be able to ride faster and/or farther than before.