Fitting your bicycle to your body.
Cycling is extremely repetitive: in one hour you may average up to 5,000 pedal revolutions. A small malalignment, then, can result in a big problem over time. Most bicycle shops will evaluate and adjust your bike fit at a reasonable cost. Still, it helps to know what a good fit looks like, especially if you share a bike with another person. There are four basic variables in bicycle adjustment:
Saddle height. The correct saddle (seat) height can be determined a few different ways. The first method is simply to have someone measure your knee flexion angle while you sit on the bike. Drop the pedal to the six o'clock position on the side you will measure. The angle formed by your bent knee should be 150 degrees. In other words, your knee should be bent 30 degrees from a standing position (an angle of zero). In the second method, measure your inseam (in cm) and multiply by 0.883 to obtain the optimal distance from the top of the saddle to the center of the bottom bracket. This is the piece the pedal arms revolve around. If your hips rock back and forth when pedaling, the saddle is too high. Lower it until your pedal strokes are smooth.
Another method for obtaining the right saddle height is as follows: With someone else supporting the bike, place your heels on the pedals at the axle and back pedal. If your pelvis does not rock side to side and your knees come close to fully extended, the saddle position is close to correct. Lower the saddle if your pelvis rocks and raise it if your knees do not fully extend. Make adjustments of no more than 1 cm for every 100K of riding.
Saddle fore/aft. Sit on the bike with one pedal at three o'clock. The front-most portion of your knee should align with the ball of your foot on the pedal.
Cleat fore/aft. The bike's cleats allow you to clip your shoes directly onto the pedals. You can determine proper positioning by ensuring that the ball of your foot sits over the axle of the pedal.
Cleat external/internal rotation. Many bikes offer enough leeway here that this measurement is not as important as it once was. If you have an older bike and wish to check that your foot rotation axis isn't placing undo stress on the knee, you'll need a bike shop "fit kit". These kits have a rotational adjustment device that measures the natural angle of your foot on the pedal and allows you to adjust the cleat to accommodate this angle.
Troubleshooting. You can often tell where a bicycle needs alignment based on where you feel knee pain. If you feel sharp pain on the outside (lateral part) of the knee, you may be irritating your iliotibial band (ITB), the long tendon that runs down the outside of your leg from hip to knee. This generally means the saddle is too high or too far back, and the overextension is causing uncomfortable rubbing of the ITB over the knee. The angle of pedal rotation can be another cause of lateral knee pain. During a pedal revolution, your leg normally rotates internally. If it's rotating too much, you may experience lateral knee pain. If you've tried saddle adjustments to no avail, have a shop look at and optimize your cleat rotation.
Conversely, if your toes are pointing outward as you pedal, the cleats are rotating externally. This can result in inside (medial) knee pain. And if you feel pain at the front (anterior) of the knee, the saddle is most likely too low or too far forward. You don't want to be pedaling in a hyperflexed position; this places unwanted stress on the knees. Note that pain at the back (posterior) of the knee is not as common, but a saddle positioned too high can be responsible for this as well.
(Phys. Sportsmed., 2004, Vol. 32, No. 4, pp. 23-30; Sheldon Brown's Bicycle Glossary, www.sheldonbrown.com/glossary.html)
Did you Know?
Computerized running shoes that automatically adjust their cushioning to different surfaces may be in stores by the end of the year.
(The New York Times, May 13, 2004)