Cycling biomechanics: Impact of Inflexible Achilles Tendons?

I have VERY inflexible achilles tendons stemming from two separate achilles tendon ruptures many years ago. Once recovered, I started running a fairly high volume and realized that my inflexibility was good for leg spring stiffness which is a good indicator or running performance.

However, compared to myself as a runner, I’m apparently a pretty mediocre cyclist, so I have a couple of questions about cycling biomechanics and pedalstroke efficiency in an effort to identify how to deal with my - uhmm - “unique” achilles tendons. :slight_smile:

  1. Could my inflexible achilles tendons be making my pedalstroke less efficient? Could this be reducing my power? Would it affect my power differently along the spectrum of NM up to FTP?

  2. How important is achilles tendon flexibility and strength for cycling? I listened to an interesting interview with @Coach.Neal.H on the Fast Talk podcast and there seemed to be an implication that the ankle only contributes around 9% of power output (although this can often be higher in non-pros). Trevor (one of the hosts) described a study that found that low cadence work can simulate a higher hip contribution and @Coach.Neal.H described the triple extension of hip, knee, and ankle in cycling and that the ankle’s job is primarily to stabilize. Does a strong but inflexible achilles tendon help stabilize the transmission of power through the pedals or does it “misdirect” (for lack of a better word) the transmission of power to the pedals?

The podcast section of interest starts is about 2-3 minutes long starting at about 35m12s

PS: For what it’s worth, it just so happens that (1) I love low cadence work and (2) I haven’t seemed to be able to find the same success in cycling as I found in running.

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I’m no coach and my anatomy and physiology knowledge is somewhat out of date now but I’d go down the line of the kinetic chain. If there is a weak (or stiff) link in the chain then that can adversely impact on the performance of the chain as a whole. Inflexible achilies, reduced mobility of calf then hamstring then hip and perhaps affecting cycling gait which then impacts on pedal stroke which impacts power.

I’m just putting ideas out there. The scientists and coaches here will probably debunk my theory with proper and up to date knowledge!

It sounds however like it doesn’t hold you back too much and it’s great you’ve been able to come back strong from ruptures… the sufferlandrian in you is strong!

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Hi JF! Glad you were able to find some value in that podcast. With regard to your prior injuries and resulting tightness in your achilles and likely reduced ankle dorsiflexion there might be some impacts on your pedal stroke and potentially on power production. The limitation in dorsiflexion will likely be most notable at the top of the pedal stroke which would be more noticeable if you have an aggressive position or are riding in aerobars (TT/triathlon position). Using a shorter crank arm can reduce the hip flexion angle if you’re having difficulty getting over the top of the pedal stroke. The increased stiffness of your achilles tendons will likely not drastically impact force production in cycling since we do not get similar stretching forces that occur in running since the cycling pedal stroke is almost exclusively a concentric muscle action where as running involves for eccentric muscle actions. Even with a likely reduction in dorsiflexion, I would guess that your plantar flexion is appropriate for cycling - and that’s where the triple extension is occurring (yes, I know ankle movements described as dorsiflexion and plantar flexion can be confusing - see photo below). As you suggested, there could be an increased impact on your NM peak power as we tend to stand in those kinds of efforts and there is a reduced contribution on glutes to the force production and an increase in kneed (quads) and ankle (calves) contribution when standing for NM sprint efforts.
One of the other major things to consider is that endurance running tends to favor more slow-twitch oriented athletes (high relative FTP, lower NM and AC capacity) whereas most types of cycling efforts require a bigger contribution from MAP, NM, and AC than we see for endurance running (5K/10K/half and full marathon). From that perspective, it might be more related to your physiology/rider type than to your biomechanics. Let me know if that helps and makes sense!
Ankle_flexion

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Thank-you for the thoughtful reply! Your points completely resonate with my experiences so far in cycling.

For example, I tend to have a lot of trouble in a crouched position and hate using the drops … not only because it tends to compromise my power output but also because my inflexibility seems to push my legs up into my ribs at the top of pedalstroke, compressing my diaphragm, making breathing more shallow and difficult.

Shorter cranks to make it easier to get over the top of my pedalstroke is an interesting thing for me to try, and the point you made about the possible negative impact on my NM power from standing is fascinating and another point to help me understand my strengths and weaknesses.

This is also a good point, as I used to run marathons and mountain trail ultramarathons, but it won’t help me save face with my riding buddies! :wink:

Thanks again!

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Interestingly, the whole reason I picked up cycling and am working on giving up running is that I’ve got osteoarthritis in my lower back that became painful in 2017. I imagine this may have been caused by those high-volume running years combined with my poor achilles flexibility.

Thank-you for the kind words @Sir_Paul! :muscle:

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What @Coach.Neal.H said!! :joy::rofl:

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I was a really good runner in my early 20’s and then took up Triathlon around my mid 20’s. I realized quickly that running endurance doesn’t transfer well to cycling. It took me a few years to build up that cycling power in my legs.

Also, I have had a blown Achilles also and I don’t notice any impacts to my cycling. It does still give me some pain with running once I get about 12 to 15 miles in my legs over a few weeks. I would say it has zero impacts and zero pain for cycling at all.

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Hey @aaron.johnson … hopefully I start seeing similar cycling performances to those I used to see in my running soon … maybe it’s just a matter of patience. Thanks!

Regarding your point about your Achilles rupture not affecting your cycling … that’s great for you, but I was referring to Achilles inflexibility, and not the fact that I’d had a rupture. My surgeries led me to have pretty terrible range of motion which is what led me to ask about the possible impacts on cycling.

You can do a self-assessment at home using this protocol. It’s quick and easy.

To put things in perspective, I scored a lowly 3.5 cm on my left and 4 cm on my right.

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Now I’ve done that test for a very long time. And That inflexibikity kills my skiing and MTB’ing. Really pisses me off. I measure in mm’s what others measure in inches :slight_smile:
Centimetres sounds ok !!

One thing … active mobilisation of the ankle joint helped me a bit.

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@jfc my range of motion is really, really bad. I can barely get my foot to just flat standing straight up. The second I bend my knee when I am doing squats, that heel comes up. The only thing that helps when I squat is pushing my toes outward. So, for my cycling shoes when I was set up, my heel comes in a bit and my toes go out a few degrees to help with the range of motion. So, for my experience pushing my toes out and my heels in close to the frame has helped with my range of motion issues. There are limitations however, and your heels start hitting the crank arm.

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