Anatomical Considerations in Bike Fit
by Alan Couzens, MS (Sports Science)
I was fortunate last week to have the company of John “The Whitster” Whittington and Mat “Matty Stein” Steinmetz to see if we could work together to come up with a solution for John’s ongoing posterior knee pain. John had been fitted numerous times by some very respected names in the bike fit world but continued to have issues with recurrent behind the knee pain during a good share of his rides.
It’s my opinion that John’s issues with the bike, and in fact, most athletes’ issues with discomfort on the bike despite being ‘fit’ come from a fundamental flaw in the bike fit paradigm. The most common methodology is to fit a rider to his bike rather than a bike to the rider. I’m not talking so much about fundamentals such as putting someone on an appropriately sized frame, but rather setting a cyclist into a restrictive position on the bike based on arbitrary numbers – angles of knee flexion, hip flexion etc without first looking at what happens to the cyclist’s body when he assumes such angles!!
It’s long been my stance that we should first look at the restrictions of the rider with respect to joint angles and range of motion and then we should ‘build the bike around the rider’ and his/her restrictions.
The ‘big hitters’, the scores that deviate more than 30 degrees from the norm are highlighted in yellow. John has limited range of motion in his left hamstring (surprise surprise), his left ankle and both quads.
More importantly, typical ankle angles of dorsi flexion when pedaling are +10 degrees. With John’s restriction at the left ankle joint (max flexion of -10 degrees), this could cause some problems!!
The Retul system is quite simply the best motion capture tool on the planet when it comes to bike-fitting. It enables the fitter to see each and every joint angle during real time pedaling – a significant step up from the old method of stopping an athlete mid cycle and attempting to replicate a ‘real life’ position.
Sure enough, the keen eyes of Matty Steinmetz spotted that on the initial capture, John’s ‘knee forward of foot measure’ was only -4mm. Considering that in the Retul system, this measure is taken from the Fibula head rather than the patella, this meant that John’s knee was actually projecting beyond the line of the metatarsal head on the foot, creating a good amount of ankle dorsi-flexion, an amount of dorsi-flexion in fact that our good buddy Mr Whittington didn’t have!
This ‘maxing out’ of ankle dorsi flexion was leaving JW with no choice but to externally rotate the tibia to effectively shorten the foot length and decrease the ankle angle. This was clearly visible to the naked eye and was obvious to JW who commented that he was regularly hitting the chain-stay with the heel of his shoe! This was shown on the Retul chart as a lateral hip-foot average off set of -5mm. The problem with this, of course is that it made the Biceps Femoris muscle the big player in knee flexion and effectively lead to a case of tendonitis.
So, to rectify this we made a couple of changes:
As a result the ‘knee forward of foot measure’ was taken back 14mm (!) enabling JW to have a much more open ankle angle. Additionally, this change brought the hip & knee in line (hip knee lateral offset = 0) and enabled JW to ditch the external rotation that he had been using to compensate for poor ankle flexibility.
It is a great shame that, as triathletes, we tend to go to great pains to analyze and rectify gait issues on the run while writing off the bike as such a simple motion that will ‘figure itself out’. In actuality, a bad position on the bike is much worse than a restricted run gait because, in the case of the bike, both ends of the chain are relatively fixed at the seat and the pedal. In other words, if things don’t line up, something’s gotta give. Usually that ‘something’ is the cyclist’s knee!!
Fortunately, cycling in and of itself is not particularly challenging in terms of flexibility and given the right information, as to the individual’s personal flexibility ‘sweet spot’ adequate work-arounds can usually be established. Hopefully in the future more bike fitters will consider both the cyclist and the bike when coming up with the’ ideal’ bike fit.