What A Week! A Tandem Bike Fit And Prosthetics

Flexibility & Stretching For Cyclists
November 2, 2015

What A Week! A Tandem Bike Fit And Prosthetics

As a young bike fitter (I turn 30 next week, this may be that last chance for me to call myself 'young'), I am always learning. Every client that comes through the door I view as a challenge, and an opportunity to improve my skills. No two cyclists are the same, and no two cyclists react in the same way to positional changes or challenges, and for that reason there is rarely a one size fits all, easy fix for a rider (part of the reason I am not a fan of bike fit 'systems'). Sometimes I wish there was a book or manual that simply said 'change this, and the rider will be increasingly comfortable/faster/aero' but alas, this is not the case.

This week however was a week of 'firsts' for me, and has been particularly challenging. As the title of this post suggests, two riders (from my team, Jewson) and a tandem arrived at the studio looking to improve their position and aerodynamics ready for the season, and particularly the 'Duo Normand' TT in France (which they have previously won, no pressure then...).

There were a few individual niggles to deal with initially, including some knee pain from one of the riders, which I believed to be down to a combination of cleat rotation(see a basic cleat set up guide here), forefoot varus, and a saddle height a touch on the high side. Once I had addressed some of these issues and got the saddles set in a reasonable starting position, the fun stuff could begin. The picture below shows the riders in the position that they started in, with no adjustments made as yet.

Looking at the pilot first of all, the TT position doesn't look too bad, however due to the slack seat tube angle of 72 degrees, the whole position was too far back on the bike. You can see that the aerobars sit under the forearms, rather than under the elbows, and that the stoker has to then adopt a very upright position due to the setback of the saddle infront. To address this, we are looking at an inline seat post (for both riders) to allow a more forward position. This will also get the backside of the pilot out of the way, allowing the stoker to move forward and down into a more traditional TT position, and get his head out of the wind.

To allow the stoker to adopt a different position, the bars will need to be changed. The picture below shows (roughly) the position that we are aiming for, but as yet, no components have been changed. I am thinking that a flat mountain bike bar, trimmed down to a width slightly wider than the pilot's hips/legs, with some clip on aero bars attached to that, will achieve a decent looking TT position for the stoker.

So that is how we left things for that session. With a few components on order, we will be finishing off the set up next Thursday, and I'll get some pictures up to show the final result (provided it all goes to plan!)

The next challenge of the week, was my first bike fit involving a rider with a prosthetic leg. The client was a lovely guy, and great to work with (nice bike too!!)

The prosthetic included a foot which was the same size as the other, and this meant that the affected side was attached to the pedal using a traditional shoe/cleat/pedal interface. This made my job a lot easier than if the prosthetic was attached directly to the pedal. I had anticipated this actually being a bit more difficult than it was, but due to the rider being functionally pretty strong there were only a few considerations and adaptations that we needed to make to the bike fit.

The first and most obvious issue, was that on the side of the prosthetic, there was a notable movement of the knee in towards the frame during the power phase of the pedal stroke. It appeared that this was being caused by a lack of strength in the glutes and hips so a few exercises were prescribed to strengthen this area. As well as this, a couple of wedges were inserted under the cleats which much improved the tracking of the knee. There was still a bit of movement, but this was much reduced.

The second consideration was the zero flexibility in the ankle on the side of the prosthetic. This meant that with a little bit of heel drop on the opposite side during pedalling under reasonable load, there was some imbalance created at the pelvis, almost like having one leg longer than the other. A small shim under the foot of the heel dropping side sorted this out, and the result was an almost perfect 50/50 power split over a 2 minute effort on the CompuTrainer. There was a slight difference still in ATA (average torque angle) but under the circumstances I was not too concerned with this.

With a few more tweaks to the position, a longer stem, and some work on the pedal stroke we were all done! A few lessons learnt, and massive kudos to the rider in question for getting out there and putting in the miles!

Roll on next week I say!

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