Thursday, August 13, 2009
The Bike Fitting
I showed up at Mark Payares’ Start2Finish studio at 9 am. He told me it would take about three hours and I thought that was an exaggeration, but it wasn’t.
The first thing he did was measure me. Turns out, after years of claiming to be 6 feet and a half inch, I am actually 6 feet and nine-hundredths of an inch. The years have taken their toll I guess. Or maybe back in high school they didn’t bother with those pesky decimals. I don’t care, as long as I don’t slip below the six foot barrier. Then he measured inseam (34.3”) and torso (27.1”). Then he had me lay on a massage table and checked my leg length. My left leg is slightly longer, but not enough that it should require special adjustments.
Next was an assessment of my flexibility and strength. This assessment involved determining how far he could push a body part until it became uncomfortable and determining how much resistance I could provide when he had me lie on my stomach and try to lift my arms as he held them down. I had average to above-average strength (at least for my age), tight hamstrings, very tight quadriceps and weak gluts.
The flexibility and strength assessment is critical because while it is possible for him to set up my bike for optimal efficiency that set-up might, for example, require a higher saddle position, which will allow the leg at the bottom of the stroke to be more extended, which puts more pressure on the hamstrings. So when he makes his adjustments he has to build in to the calculus the fact that my body might not be ready for the “optimal” set up.
The next step was to custom fit the bike using the Retul™ 3-D motion capture software. Mark had the new Guru™ tri bike set up on his compu-trainer. I got on the bike and he velcroed LED tabs to my body. I was going to describe the process in detail, but I suck at the technical descriptions so I decided to steal the verbiage from Retul’s website. I figured they should know:
Biomechanics are Best Assessed in 3-Dimensional Space
Fit data collected in a traditional 2-dimensional plane (i.e. video based systems) is fairly limited because the fitter can only look at one view at a time and those views stand as independent reference points. In order to make the best fit recommendations, the fitter must realize that the front and side view are actually interdependent reference points. In other words, the front and side view must be viewed simultaneously in 3-D in order to see how all the applicable movements of the body are working together.
Retül uses 3-dimensional views to see just these precise mechanics to be able to see knee extension (from side view) in relation to knee wobble (from front view) in order to make the best decisions on adjustments to the cyclist.
How it Works
Using eight (8) anatomical LED markers strategically placed on the wrist, elbow, shoulder, hip, knee, ankle and ball of the foot, the retül sensor gathers information in real time and transmits it to the PC. In real time.
It generates a ton of data. There were fourteen specific charts and thirty different statistics for such things as knee angle extension, knee lateral travel, hip angle open & closed, hip to wrist distance, elbow angle, knee travel, tilt, forearm angle and much more.
One of the key measures that Mark focused on was the knee angle extension. He could tell that I had been riding with a saddle position that was too low. My knee angle extension on my road bike before he adjusted it was 57 degrees. The guidelines for an elite triathlete is for an angle of under 40 degrees. Mark determined, given my flexibility limitations, that he could not make that large of an adjustment in my ride.
On the first test with the Retul my knee angle extension was 53 degrees. Mark raised the saddle height a little over a centimeter and that brought my knee angle extension down to 46 degrees.
Another interesting chart that Retul™ generates is a front view diagram that tracks the movement of the knee. Ideally the knee stays in the same vertical plane throughout the pedal stroke. If it does, the chart will show a solid horizontal line. My chart showed that my left leg tracked close to that goal, but that my right knee “tomahawked.” My chart was a long narrow oval. Basically my right knee splayed as I pedaled. Because my saddle was too low, I think it is possible I made positioning adjustments (leaned to the right slightly?) so that my stronger left leg could more fully extend. That caused my right leg to be even more cramped, which made the knee splay.
When he was done with all of this adjustments, I felt much more comfortable on the Guru™ than I had on my road bike. When he tested me on the compu-trainer I was able to crank out 180 watts – at a simulated 25 mph with a sustainable aerobic effort.
It took almost three hours, but I was pleased with the investment in time and money. My road bike has been refitted so I know it is optimal for my current situation and as I improve my flexibility Mark will make adjustments. And I have a brand new super-fast tri bike that I am anxious to try out. I am hoping that I can make the adjustment from road bike to tri bike so I can use the tri bike in the Tuscaloosa race in ten days.
That’s not much time to get ready.
Tomorrow: My first ride on the tri bike
Workout: Brick - Bike 5 miles ran 1 mile; repeated three times; 1 hour 36 minutes; leg felt okay; made good transitions, hard to get much bike speed because of the route through residential streets;