Bike Fit Case Study: Hip Impingement
Mountain bikers are a special breed of cyclists. Their idea of fun is often different than most people. They spend multiple hours climbing and descending on trails with rocks, roots, and steep exposure. While entering the “pain-cave” is inherently part of the sport, some bikers become too accustomed to chronic pain. Chronic pain is much different than the experience of pedaling for hours and feeling exhausted. This is not something cyclists should deal with as it can cause long-term problems and costly rehabilitation in the future. In this case study, I am going to cover how a common problem, hip impingement, can be alleviated with a proper bike fit.
About the Client
Our case study client, Wallace, has been dealing with hip impingement for a couple of years. He first reported having pain/pinching of the anterior aspect of both his hips after some long days ski touring. This problem progressed to the point of needing Physical Therapy and needing to take time off from his passions. While Physical Therapy helped manage symptoms during ski season, his symptoms returned during mountain bike season.
Bike Fit Process:
Step 1: Mobility screening to identify limitations and range of motion
From our table assessment, we were able to identify the following information:
- Hypermobile hips with external rotation & abduction
- Reproducible pain & “pinching” with hip flexion, internal rotation, and adduction.
With this information, we wanted to approach his fit to reduce the motion in his hips that cause pain. To understand this fit process, it is important to review the general biomechanics of cycling.
Step 2: On the bike video analysis
When analyzing someone’s cycling position, we take videos of them pedaling and take still-shots at various pedaling positions. The first three still shots to analyze are the 3 o’clock (level pedals), 6 o’clock (bottom dead center), and 12 o’clock positions (top dead center).
3 o’clock position notes:
- At 3 o’clock, we line up a leveling laser with his pedal spindle, which is the point of contact with his cleat interface on his shoe.
- By looking at this 3 o’clock position while dynamically cycling, we can identify where his knee is in relation to his contact point. Ideally, we should see the laser in between the front of his knee cap and the white joint marker located on his lateral femoral condyle.
- As you can see from photo 1, his lateral femoral condyle (white joint marker) is in front of the laser line. This means that his knee is too far forward.
- To have an appropriate balance of muscle activation, we positioned his saddle so that his knee was further back in relation to his pedal spindle.
6 o’clock position notes:
- At bottom dead center, we look for knee flexion and ankle flexion angles.
- Mountain bikers are typically at a knee flexion angle of ~35 - 40 degrees, although not everyone fits into this range perfectly.
- At an angle of 50 degrees as bottom dead center, this tells us that he is not extending his leg enough, which leads to a loss of power output and comfort.
- To get more power out his pedal stroke and more comfort in his hips, we increased the saddle height. With this change, this knee angle changed from 50 to 39 degrees, putting him in a more acceptable range of motion.
12 o’clock position notes:
- At top dead center, we see cyclists go into a great degree of hip flexion.
- Based on the position of his pelvis, spine, and femur, we concluded that he was at 70 degrees of hip flexion at top dead center.
- While 70 degrees may work for some cyclists, we know that hip flexion bothers him so our goal would be to reduce the degree of hip flexion at top dead center.
- With some changes to saddle height, fore/aft, and angle, we were able to open his hip at this position from 70 to 75 degrees.
After some successful changes to his fit from the lateral view addressing his sagittal plane of motion, it was time to look more into the front view to address the frontal and transverse plane of motion. To make changes in the frontal and transverse plane, we make micro-adjustments to the cleat/shoe interface. The cleat can be adjusted in multiple ways including:
- Medial/ lateral
- Tilting (with wedging)
Knowing that our client has pain with internal rotation of his hip, it was important to look at bone and joint motion while he was generating power from the 12 oclock to 3 oclock position.
12 o’clock to 3 o’clock motion notes:
Based on our table assessment, it is clear that Wallace prefers to keep his femur and hip joint externally rotated in the transverse plane and abducted in the frontal plane. To align his fit with his body's natural alignment, we needed to make sure his cleat interface allowed him to move naturally.
From this view, we determined:
- His cleat interface on his shoe was driving his foot into internal rotation/adduction (pointing in). As you can see in the before photo, this motion was opposing his femur/hip motion. We concluded that the position of his foot was likely driving relative internal rotation of his femur/hip while he was pushing down on pedal stroke.
- We also identified that his femur/hip could benefit from more abduction (pointing away from midline) at the 12 oclock position of his pedal stroke.
- The goal of the adjustments we made were to address the mismatch between the contact point of his pedal and his natural hip/femur motion. Essentially, we want his femur and foot to be pointed in the same direction as his foot shown from the arrows.
- To make these changes, we positioned his cleat so that his foot was positioned more lateral and externally rotated on his pedal.
- As you can see in the after photo, we accomplished this motion for a more aligned pedal stroke.
After the fit, Wallace was able to ride pain-free on his bike with more power and comfort than before! Suffer better, Wallace!