Knee Pain May be Eliminated By Replacing Crankarms
Over the past 18 months, I have collected crankarm length data from my bike fit clients. During the bike fit interview process, most of my clients volunteer that they have had prior bike fits, and even been to a physical therapist or chiropractor, but that they are still in pain. Most of the issues I have resolved focus on the following (a) wrong cleat placement, (b) wrong saddle position and (c) wrong crankarm length. Both (a) and (b) above can be fixed by an experienced bike fitter, while (c) can be fixed by bicycle and component manufacturers placing shorter cranksets [crankarms] on most bicycles.
Proof is in the Pudding
But first, a background story. Two and a half years ago, three best friends, all in their seventies, started cycling after retirement. They have known each other for decades and did everything together. Not long ago, they acquired some shiny new bikes followed by what they thought was a good bike fit. But after riding for several months, they all developed severe knee pain. Initially, they attributed this pain to not having as much ride experience, but when their pain got worse, they went back to their local shops for another bike fit. Fast forward another month and the pain in their knees continued to get worse. They were thinking of giving up on cycling when they decided to try one more bike fitting. Several of the San Diego teams that I do bike fitting for referred these three gentlemen to me.
When they got to me, there were two major problems I needed to immediately address: (a) their cleat placement was way off and (b) each of their crankarms were way too long for them. After fixing their cleats, I placed each of them on my Serotta Size Cycle using the 140 mm to 185 mm Vari-cranks. On client #1 I switched him from a 175 mm crank to a 170 mm crank, on client #2 I switched him from a 172.5 mm crank to a 165 mm crank. Lastly I took client #3 from a 170 mm crank to a 160 mm crank.
Thirty days later I contacted them to follow up on the changes I made after their fit. They all said that their pain was gone and that they are enjoying cycling with friends, and have even gone on several group rides.
Six months passed since the bike fit, and the crankarm replacement was such a success for client #1 that he called asking if he could bring his wife by for a bike fit. He told me that 3 years ago he bought her a new bike and that the bike shop had done a fit for her. The next day, they had planned a 10-mile ride. Two miles into the ride, his wife couldn’t pedal anymore – her legs had locked up. The next morning, she was in so much pain that she couldn’t go to work. Her wrists hurt, her trapezius hurt, her shoulders, lower back and knees hurt. He told me that he convinced her that her pain was due to this being her first bike ride in 20 years, so they tried it again the following weekend. This time she made it 1-mile before calling it quits. He said that her bike has hung in the garage for 3 years, so he brought her to me to see what I could do.
After fixing her cleats, I placed her on the Serotta Size Cycle and adjusted the Vari-cranks to 145 mm from her 165 mm crankarm before. I saw a huge smile! She was suddenly spinning and cycling pain free. He called me the following Monday and told me that after the bike fit, they drove to Dana Point Harbor and rode 20 miles. He said he had trouble keeping up with her. She was spinning easily at 100 rpm, and that was on her first ride. The next morning, she woke up with no pain. The following Sunday they started in La Jolla and did a 25-mile ride including the famous Torrey Pines grade. Both are now enjoying cycling together pain free.
Knee pain is a common problem. The other problem is that most cyclists believe is that the pain is part of cycling. I partially fault the component manufacturers that aren’t making crankarms short enough and, I fault the bicycle manufacturers for putting on too long of crankarms.
So, exactly what crank arm should I use?
Any given frame size (56cm in this case) can come in many different frame sizes. For example, although my preferred frame size is 56cm, I could ride several ‘larger’ 55cm frames. I could also fit on a 57, 58 and even 59cm. But, looking at my general recommendations on crank arm lengths, should I choose a 165, 170, or 172.5 crankset?
The only way to really tell is via a comprehensive bike fit. Most bike fitters will adjust the saddle to correctly determine and set the max extension of the knee. Then, they move on to the saddle fore-aft followed by cockpit controls. But, what I have experienced fitting clients is that the max flexion of the knee is as (or more) important as max knee extension, and this is adjusted by crank arm length.I have metrics on over 100 cyclists that I have helped by replacing their long crankarms with shorter ones. In every case, knee pain went away.
Andy Pruitt is one of the most respected bike fitters in the world and helped to develop the Specialized BG Fit system. Andy also states that cranks that are too long can cause injuries. This is because “the compressive and shear forces in the knee joints ‘go up exponentially’ due to the sharper knee bend. Cranks that are too short are not dangerous, however.” In his book Bicycle Design, Mike Burrows warned against using cranks that are too long to avoid knee problems and Sheldon Brown has written about crank length and how riding with cranks that were too long for him has caused him knee pain.
Cycling is a culmination of micro-injuries and my paradigm errs on the side of caution. Think of your knees during a typical 2-hour ride and spinning at 85rpm. You have pedaled 10,200 circles. Four rides a week and you have pedaled 2,121,600 circles in a year. If anything is out of adjustment, some part of your body is going to absorb it, and that part is usually the knees. You might feel fine at 25 years old, at 35, even 45, but, eventually, this will all catch up to you.
Coach Rick Schultz specializes in coaching cyclists so that they can achieve their best. He is also a certified bike fitter and author of “Bike Fit 101: Your Toolset for a Great Bike Fit.” He has created his own bike fitting educational processes and teaches skills and handling through his workshops. Rick also owns and operates biketestreviews.com and bikefitnesscoaching.com.
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