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Editor’s Note: Due to the number of comments about this article, Kit Vogel wrote more on the subject of asymmetry among cyclists.
Asymmetric knee tracking
I am a bike fitter at Silicon Valley Cycling Center. For some reason, more folks seem to have the left knee track further out than the right and I’ve been wondering, “Why?” I’ve been noticing that I have a lot of right 20-mm pedal spacers accumulating. Someone has to have this figured out…
You have an excellent and very relevant question for the cycling world at large. Mechanics of the lumbar spine, pelvis and lower extremities are wonderfully complex. There is more to the story than I can do justice in this shortened forum.
The human body is designed asymmetrically. In a NORMAL human being (male or female), the normal pelvic alignment is also asymmetrical and almost always results with an anterior rotation of the right side of the pelvis (innominate) and a posterior rotation of the left side of the pelvis. (This assumes that the femurs and tibias are the same length and without a structural leg length difference.) This position is exaggerated on the bike because we are sitting on a symmetrical bike seat.
Here is the catch: A posterior rotation of the left side of the pelvis is associated with an out-flare of the same side of the pelvis. In short, this out-flare and posterior rotation of the left side of the pelvis will make the left knee track more laterally than the right because the femur is following the direction that the acetabulum/hip socket is pointed. Additionally, this architecture predisposes the left sacroiliac (SI) joint to jam, which accentuates the lateral position of the left knee.
Therefore, the left knee has more of a tendency to track laterally than the right due to the normal asymmetrical architecture of being human. This is simply addressed with moving the foot laterally and placed under the knee with:
1) Moving the cleat IN to bring the foot OUT.
2) Placement of a 1mm washer or 20mm spacer between the crank and pedal.
3) Using a pedal with a longer pedal spindle (Speedplay Zeros, additional 1/8, ¼ & ½-inch spindle lengths).
I am not surprised that you have extra right 20mm spacers. According to our records at Bike Fit Systems, at least 40 percent of cyclists that we fit need to have the left foot moved laterally beyond the range of most pedal and cleat combinations. In other words, we need to add an additional spacer or longer spindle to place the left foot laterally underneath the left knee. Cyclists who ride like a “V-twin” may also be retroverted (structural lateral twist of the femur bone) or have other hip issues, such as osteoarthritis. However, this leave 50-60 percent that may or may not demonstrate the left lateral knee. Not everyone will demonstrate this specific mechanic.
As always, be careful when working with carbon cranks and know the limits. You need to know if the crank is totally carbon or aluminum wrapped in carbon. (Hint: If you touch it and it feels COLD then it is probably metal inside.) If in doubt, contact the dealer and ask for their specific specs and limitations. To our knowledge, 100 percent carbon cranks are not appropriate for use with 20mm spacers. (Frankly, avoid selling 100 percent carbon fiber cranks to the big dudes that ride like a V-twin. It is a disservice to them.)
So, whenever a person is told, “Your pelvis is rotated,” then it is absolutely correct. We are naturally designed that way with the right side of the pelvis rotated forward/mild in-flare and the left side of the pelvis rotated back/moderate out-flare. Totally normal! The asymmetrical architecture can become a problem if joints of the spine/pelvis become locked or hypermobile. However, one needs then to assess if and when it is a really a problem. Ahhh … thus the necessity for our bike fitting world and our clinical world to work together. We are working on that.
Katrina Z. “Kit” Vogel was described as one of the “rock stars of cycling science” in VeloNews in 2007. She earned her Doctorate in Physical Therapy at USC and MS in Biomechanics/Human Movement & Performance at WWU. She is the Director of Education for Bike Fit Systems, teaches clinically-based bike fitting classes and guest lectures in Biomechanics for the University of Wash PT Department. She is a Cat. 2 track cyclist.
Any information or advice offered by the members of the Coaches’ Panel should not in any way be viewed as personal medical advice. The recommendations made in this column are offered as general information for healthy, physically fit amateur and professional athletes. None of the information provided by members of the Coaches’ Panel should be viewed as a replacement for personalized, professional medical treatment or to replace the advice or services of your physician. While some members of the Coaches’ Panel are Licensed Medical Doctors, Licensed healthcare professionals, and certified coaches, their advice in no way establishes a doctor-patient relationship between the writer and readers of this column. If you are beginning or resuming a vigorous exercise program, it is important to visit your health care provider for a complete physical examination in order to identify and treat any potential risks you might face.