Monday, October 27, 2008

My cycling leg

This post is especially for Jason and anyone else that's interesting the the specific set up I have for cycling.

Jason commented on my previous post about his desire to tackle the Alpine challenge. Jason is a below the knee amputee as well.

The Alpine - that's awesome!! No way I could imagine doing that at this stage. I wrote about coaching a rider who did the Alpine a couple of years ago in these two posts.

You go Jason!

So, in summary, have a look at these posts which show my cycling leg set up in a little more detail:

My new leg and socket design

How my cycling leg attachment works

The cycling cleat attachment and adapter plate

The urethane adapter to provide lateral roll for out of saddle efforts

My prosthetics guy made my everyday walking leg socket with quite a shallow rear cut away with cycling in mind. The rear of the socket is such that I am able to pedal with a full length crank.

But remember I have the cleat directly at end of the pylon and so the knee doesn't need to bend quite as much as if the cleat was positioned further forward simulating an "under the ball of foot" position.

The socket also has some funky design at the front.

The other adaptation I haven't shown in pics is some soft foam-like material I place at the front of the stump below the knee, in-between the sock and liner, so that it fills the gap between the stump and top front of the socket when you are pedalling. Bend your knee when sitting and you can put your hand/fingers into the largish gap that forms betwen the stump and socket.

The gap isn't there when standing up of course but with the knee constantly bent on the bike, I found filling that gap really helped with power production and provides a much more secure feeling. I just got some off-cuts from a Clark Rubber store.

As my prosthetics guy says, the aim is to maximise the contact surface area between stump and socket. That will be something we look at when designing a dedicated bike leg socket.

Eventually I intend to have a dedicated socket / cycling leg made, however before that happens I need to further strengthen my hip so that the lateral offset of my "foot" can be brought a little more in line with the hip and knee.

For a permanent cycling leg, I envisage something like what Jody Cundy of Team GB paracycling squad had made. Anyone who can do a 65 second kilo sure has a leg that works!

See this item for more details:

Jody Cundy Interview

In there you'll see his new (the carbon leg) and old leg set ups. I don't expect to have my cleat positioned as far forward as Jody has his - he simply replicated what he was used to with his prior set up when wearing a cycling shoe over a prosthetic foot.

The one thing you have to consider with a direct cleat to pylon arrangement is that you can't walk on it. So logistics becomes a factor when planning on going for a ride.

Another thing I've noticed, since I have more than one bike, is that I am now much more sensitive to the different Q-factors of the cranks on my bikes - to the extent that I need to alter the angle of the prosthetic cleat attachment in order to ride a bike with different cranks. My two road bikes have 175 mm Campagnolo cranks however one is a Record crankset and the other a Chorus model and they have different Q-factors.

I never realised until now how much the ankles do the job for us, managing all the lateral roll when out of the saddle and coping with the small differences in positional set up.

What did Joni Mitchell say to us in that Big Yellow Taxi song?
Don't it always seem to go
That you dont know what you've got
Till its gone....

No parking lots here though!

If you want to drop me a line, just use:
alex A T cyclecoach D O T com

Anyway Jason, good luck with it!


Jason said...

Hey Alex, thanks for all this great information. It will take me some time to digest and understand all the technical jargon surrounding the actual training that you do. However, I fully understand about the design of the prosthesis that you currently use and also the fitting issues that you experience. My experience (and everyone is different) is that the volume of the stump is not stable for at least 3 years. This makes concentrating on high-level performance very difficult as stopping to add socks to make up volume during an event or training is difficult. However, cycling is so much easier than running in this respect. My main issue with cycling is coping with the sweat that builds up in the liner and has nowhere to go. It causes 2 problems. First, the stump can be sitting in a pool of water and the skin becomes more susceptible to wear and tear. Second, slippage starts to occur between the liner and the stump and it is harder to transfer power to the pedal. Over time my stump has learned not to sweat so much but it can still be a problem. I use a really strong antiperspirant available over the counter at the chemist 'Driclaw'. It is an aluminium hexachloride based cream. Also, you can get a 'sock' that actually goes under the silicon liner next to the skin. The one I use is manufactured by 'X-static' in the USA. It relieves skin shear irritations and helps with grip (particularly on warm days). It also seems to help with transport of heat and moisture. I am not sure how much they cost (is anything cheap when it comes to prosthetic limbs?). Fortunately the TAC covers my legs and accessories.
So the main challenge for me at the Alpine Classic will be keeping the skin on the stump in good shape. I can cope with the 6.20AM start but 200km and some pretty sustained climbs is a lot to ask of a stump. I have lots of grafted skin/muscle on the stump so I often don’t feel the problems until I have made a fair mess of my skin. Also, I take delivery of my dedicated cycling leg on Nov 7th. It won’t have a foot so walking will be problematic and hopping when your fatigued is always a bit dodgy.

I read your entry on Sunday, September 21, where your discussed the polyurethane spacer that you a little bit of sideways flexion. In one of my running legs I have a 50mm (approx) block of really dense polyurethane(?) incorporated in the post immediately above the foot. It is designed for suspension but rather to mimic some of the inversion/eversion that is required when over uneven surfaces. I am not sure what the name of this component is but it is certainly the most comfortable running leg I have worn. (but 21km is about the limit due to skin deterioration).

Anyway, this blog is about you not me so thanks for all you info and I’ll leave it at that



jongee said...

Hi Alex what a great story well done on your achevements.I also a below left knee amputee and i go to the manchester velodrome next week for a go on the track.I am 56yrs old but i need to do as many things as i can. I ran my first 100mts last week in 18.28 not bad for an old man with one leg.
john uk

Greg said...

I have a question. I am new to biking as an above knee amputee. I have 1 socket and Genium leg. I'm trying tio get back into cycling for endurance exercise. As I pedal the upper/rear portion of my socket comes into contact with the seat with every stroke. It's caused some skin abrasions so I need to be careful, but worst of all is the constant interference with each stroke that the socket/seat collision causes. Has anyone dealt with this issue?

Alex Simmons said...

Hi Greg

I'm afraid I'm not all that well versed in solutions for above knee amputees. I'd love to point you towards someone that is, but I'm not sure who.

I know that I had to work out some solutions and improvise along the way as there was not a lot of information about. There are guides for non-competitive cycling, but things get a little more complicated when you are trying to race or at least ride in a semi-competitive manner.

Good luck with it