Before a customer purchases a bike from me, I ask her to complete a questionnaire that covers everything from measurements of herself and her current bike, her cycling aspirations and her flexibility. If you’ve followed the evolution of fitting techniques, you’ll know that flexibility is becoming as important as an inseam measurement in setting up a properly fitting bicycle.
Achieving a “neutral” or flat back position can be difficult if the hamstrings are tight. These muscles attach to the pelvis at the ischial tuberosities (sit bones) and behind the knee joint. If they’re tight, they effectively pull down on the pelvis, causing it to rotate back. On the bike, this often leads to a rounded back, which can cause neck pain from rotating the head up to watch the road. The upside is that rotating the pelvis back reduces pressure on the sensitive “bits” that land on the front of the saddle.
It’s easy to see how a rider who is flexible can have an advantage over a rider who is not as flexible, since the former will be able to get into a lower and longer position on the bike. In this position, the rider is more aerodynamic and can generate more power than a rider sitting upright. The pelvis rotates forward, allowing the spine to settle into a neutral position, reducing the possibility of low back pain. The downside is that there is more pressure from the saddle on the rider’s crotch.
Jo McRae, a trainer in the U.K., distinguishes between the “upper” and “lower” hamstrings. She maintains that as a cyclist pedals the upper part of the hamstring, which connects to the pelvis, is stretched more than the lower end of the hamstring at the knee. As a result of this dynamic motion, the upper end of the hamstring tends to be more flexible than the lower end. Specific stretching exercises are needed to address that area.
The correct saddle height can be determined through a variety of formulas.  Hamstring flexibility, or lack of it, affects saddle height. A rider who has tight hamstrings might not feel comfortable with the saddle at the high end of the range, but this can be addressed by stretching to improve hamstring flexibility.
Flexibility has a an important role to play in how the bicycle is set up most effectively for you. In the end, it’s up to you to decide what the proper trade-offs are between comfort and power.
- Lemond method: Set the saddle height at 88.3% of the inseam length. Measure from the center of the bottom bracket to the top of the saddle.
- Hanley method: Set the saddle height at 109% of the inseam. Measure from the center of the pedal spindle to the top of the saddle.
- Place the heel of the foot on the pedal when it’s at the bottom of the pedal stroke. Set the saddle to the height at which the knee is locked. Measure the angle between the lower and upper leg at the knee at the bottom of the pedal stroke. Most experts agree it should be between 145º and 155º.
This blog is also posted on Women’sCycling.ca.