Cycling and Knee Pain

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Q. I have started cycling because my doctor recommended it as a safe, low-impact form of exercise. It bothers my knees, though. Is there something that I’m doing wrong?

A. Your seat may be too low—a common mistake made by many recreational cyclists who simply hop on a bike without adjusting the seat height to fit their body. Cycling is a safe activity, but if your alignment is off you can still place excess strain on your joints. For knees, it’s crucial to keep your seat high enough.

If your seat is too low, then you end up cycling in a squat-like position, with your knees bent throughout the entire pedaling motion. This can stress the knees because the leg isn’t able to fully extend at the lowest point in the pedal stroke. If your seat is not far enough away from the pedals, you are most likely to feel the excess pressure in your knees when you are seated and “climbing” (or pedaling against harder amounts of resistance).

So how should you adjust your bike-seat height?

When you are sitting on the bike and your foot is at the lowest point in the revolution—closest to the floor on an upright bike or farthest in front of you on a recumbent cycle—your knee should be mostly extended. This gives you more power when you push on the pedals, and also reduces the compression on the knee when you bend it.

On the other hand, the leg should not be completely straight—or locked out—because that forces you to stretch to reach the farthest point in the pedaling motion. But your leg should be more elongated than bent, especially if you already feel strain in your knees.

Indoor cycling, or spinning, classes use several techniques to determine correct seat height. Some people stand next to the bike and roughly align the seat height to the height of their hip bone while standing. This is an imprecise measure.

Another approach is to sit on the bike and straighten the leg so that it’s vertical to the floor, then gauge the knee angle. The problem with this method is that it’s usually done incorrectly—people do this exercise with their legs skewed and the pedal improperly placed, so they do not get an accurate view of what their leg extension looks like as it moves through the pedaling motion.

To get the correct knee angle, the pedal and the bar that connects the pedal to the bike both must be properly aligned. The connecting bar, or pedal crank, should be perpendicular to the floor. The foot needs to be perfectly horizontal with the pedal and parallel to the floor. Once your leg is aligned in this way, draw an imaginary line extending from your thigh to the floor. If your leg was straight, this angle would be 180 degrees. For the right seat height, the angle at your knee between your thigh and your lower leg should be about 145 to 150 degrees. Looking at the other perspective, the angle beween the line of your lower leg and the line extending from your thigh to the floor should be around 25 to 30 degrees. Once you have this set up, you may need to tweak your seat position slightly since different pedals, shoe types, pedalling methods, etc. can also have an effect.*

Perhaps the easiest, most functional way to gauge seat height is to get on the bike and start pedaling. Notice how high your knee rises in relation to your hip. If you can see your profile view in a mirror, also notice the line that your thigh makes as your knee reaches the highest point. The knee should not come all the way up to hip level—it should rise to a point that’s below hip level so that the thigh is always diagonal, nor horizontal, or parallel to the floor, as the leg circles around. Generally, your seat and hips should be higher than your knees as they reach the highest point in the pedaling revolution.

If your seat height is aligned properly but you still feel strain when you cycle, make sure that you are not adding too much resistance. You should not get stuck or struggle when trying to pedal. The motion should be fluid and smooth. As your legs get stronger, you can add more resistance, but you should never add so much that you are straining to push the pedals.

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Correction, Nov. 17, 2008: After conducting further research, Martica Heaner clarified and updated information about bicycle seat heights and leg angles in this column. Return to the correction section.

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Martica is a Manhattan-based exercise physiologist and nutritionist and an award-winning fitness instructor. She has written for a variety of publications including Self , Health , Prevention , The New York Times and others. Martica is the author of seven books, including her latest, - Cross-Training for Dummies . (Read her full bio.)