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Old 2011-09-28, 02:40 PM   #1
Nurse Ben
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Increased leg stress and short cranks?

I have ridden 165-170mm cranks on 26-29" wheels for the past three years, averaging three to four rides per week, typical ride time 1-2 hours during the week, 3-4 hours on the weekend rides, max distance ~20 miles, riding 90% single track/ 10% double track, no road riding. In general, other than sore shoulder, quads, and taint, I have been pain free. I do warm up before rides and stretch when I take breaks from riding.

This past summer I decided to gradually decrease the crank length on my primary muni, KH 29, to improve efficiency. First I went down to a 160's and rode those without much problem, though I did notice I needed to use more brake on downhills and I was out of the seat more for both up and downhills.

About one month ago my left knee started to get "twingy" at the end of long rides. This feeling did go away between rides and wasn't a problem during shorter rides, though at times I did notice some shin pain when walking/hiking. Fast forward another week and I was riding a twenty mile race, when I started having significnat knee pain ~ten miles into the event and it persisted until the end, even after taking ibuprophen.

Intending to further improve pedaling efficiency and thinking that a shorter crank might reduce knee stress, I reduced my crank length to 150's on the 29er. In the meanwhile I let my legs rest for a few days, then gradually increased my mileage to pre-race levels. I didn't notice any knee pain until this past weekend when I rode ~ ten miles (three hours) of tough single track.

I have a fair amount of experience with endurance sports and have dealt with chronic use related injuries such at piriformis syndrome, compartment syndrome, shin splint, ITB issues, etc...but this problem seems to be completely isolated to my left knee, only bothers me during long ride, and seems to be at it's worse on downhills when my knee is unable to straighten; yes, on uphills where my leg is more extended, my knee feels fine.

I have already done ICE, stretching, NSAIDs, etc...so my conundrum is whether by running a shorter crank am I overstressing my knee as a result of having to work harder to control the uni?

Note: I don't want to hear about stretching, physical therapies, meds, or anything that I can do to treat the "injury". I'm asking about experiences and theories relating to
crank length and leg stress.

Last edited by Nurse Ben; 2011-09-28 at 02:42 PM.
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Old 2011-09-28, 03:43 PM   #2
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Another factor to consider is saddle height/position. From what I've read about cycling and incorrect saddle height/position is knee related issues like you describe. I know for MUni that we all tend to ride with the saddle a bit lower than we would for road riding. The assumption is that for road riding we have the saddle height/position dialed in perfectly to avoid knee issues i.e. avoiding either extreme of full leg extension when cranks are at the 6 o'clock position or legs too bent. However, for MUni we're riding with the saddle much lower thus it seems to me we run the risk of having knee related issues, particularly if your riding in the saddle for a prolonged amount of time. Now if your on and off quite a bit I'd expect any issues would not be as pronounced.

I'm going to experiment with riding MUni with more of a "road" saddle adjustment when I come back. Perhaps a bit lower saddle than I have now but nowhere near as low as I had it. When I started exclusively riding roads I ended up adjusted the saddle height up over 1/2" for the same crank size.

As for leg stress with respect to crank size I have no opinion on that, other than feeling faster all around with a bit shorter crank than I was used to riding in years past I can't say I feel any more/less fatigued or pained (outside of my current leg issue which I strongly believe doesn't correlate to changing from 150mm -> 137mm crank sizes, I think I'd have my issue regardless).

Just my two cents...
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Old 2011-09-28, 04:15 PM   #3
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I did some on-line searching for crank length discussions, most of which was in road niking forums, none of which seems to be very "scientific" and all were factoring in gear changing ability. In terms of sizing, the standard seems to be adjusting crank length for rider inseam, so taller riders get longer cranks, etc...

There was a good discussion on an recumbant forum about knee angle and how applying pedal pressure at anything less than 90 degrees of opening will cause increased stress and injury because you are essentially "forcing the knee apart".

In all of this discussion I did not find anything that directly applies to unis as we are not only single speed, but fixed, so we have additional resistance forces to consider, as well as (for muni) needing to out of the saddle to accomodate uneven terrain since we lack suspension and the ability to coast.

I believe a longer crank allows more control over speed on the downhills, which seems to be supported by my increased need to brake, as a result I believe my legs are working harder on downhills (poosibly uphills) to control the uni.
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Old 2011-09-28, 04:29 PM   #4
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Originally Posted by MuniSano View Post
However, for MUni we're riding with the saddle much lower thus it seems to me we run the risk of having knee related issues...
This is true. The general rule is that your seat is going to be lower for any type of rough terrain riding. While an "optimum" seat height works for road riding (unless it's real bumpy), we don't have a choice but to go lower for the rough stuff. Otherwise you eventually end up getting bounced off the seat, losing pedal contact and doing some unintentional coasting. So yes, the lower seat is a necessity. I will often make seat height adjustments on rides that contain long climbs (higher) or long areas of challenging terrain (lower).
Originally Posted by Nurse Ben View Post
I did some on-line searching for crank length discussions, most of which was in road biking forums, none of which seems to be very "scientific" and all were factoring in gear changing ability.
Very little of that information is relevant for us with one speed and one wheel. When you can choose your pedaling speed, it changes the equation.
Originally Posted by Nurse Ben
There was a good discussion on an recumbant forum about knee angle and how applying pedal pressure at anything less than 90 degrees of opening will cause increased stress and injury because you are essentially "forcing the knee apart".
That sounds very relevant to us, at least as a general rule. If your position results in a 90-degree or less angle of knee, it's probably not good for your knees. I will also point out that the recumbent part of that equation plays a role. On a conventional bike, your pedaling force comes from leg power with the addition of gravity. When out of the saddle, you can add a little more force by pulling on the handlebars but that's about it. On a recumbent you have that seat back there, which allows you to put more power into the pedals and can add to potential knee strain. Still, 90-degrees sounds like a good general rule of thumb until some unicycle scientists come up with something better.
Originally Posted by Nurse Ben
I believe a longer crank allows more control over speed on the downhills...
Sounds obvious enough; I have no reason to doubt this. Beyond adding a brake, unicyclists don't have much in terms of options. You can't ride Downieville with a high seat, for example. That's 4000' vertical, much of it on technical terrain. Naturally it will help to increase your braking skills (a weak area for me as I have no MUnis with brakes). This will allow you to take on more difficult downhills without having to wrestle the pedals as much. The other thing you can do, which seems to work for me in places like Downieville, is to ride faster. That may sound stupid, but I think it makes sense. You're spending less time per rotation resisting those back pedals, and less total time doing the whole process. Combining this with good fitness to handle the ride at hand, and it seems to reduce the strain on the knees.
John Foss

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Last edited by johnfoss; 2011-09-28 at 04:34 PM.
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Old 2011-09-28, 04:35 PM   #5
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I would say that you definitely have more stress on your legs with shorter cranks, especially if trying to keep your speed in check without using a brake.

I know you don't want to talk about your "injury" but it sounds an awful lot like what happened to my knees when I was training for RTL. I was developing some pretty bad muscle imbalances and it was pulling my kneecap out of alignment once the stabilizing muscles would get sufficiently fatigued.
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Old 2011-09-28, 04:41 PM   #6
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I don't know if my story would interest you, but I'll go ahead and tell you anyway.

I sprained my ankle 2 months ago while learning to ride, but have since recovered from that.
However, a month ago I changed the 150mm cranks on my 25" to 125mm ones. I've been riding mtb and road regularly since last year, and I must say that the back pressure on the 125mm cranks was initially shocking (compared to 150mm).

I just discovered I've developed Achilles Tendonitis on the right ankle and started a thread. I'm not sure what exactly caused it, but I suspect it must be some residual damage from the sprain, combined with short cranks, and my beginner rider status (lots of wasted energy and corrections). I'm going to stop riding for a month.

The pain in your knee sounds familiar, I started to have the same problem in my left knee when I was in the army. Now I avoid all impact sports like tennis, badminton, basically anything with running. I sometimes get a slight 'twingy' feeling if I'm on my mtb for too long.

In the 2 wheel world, a great deal is made about KNOPS (knee over pedal spindle). But this is hard to achieve with unicycles.
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Old 2011-09-28, 05:16 PM   #7
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After sustaining a knee injury brought about from a stent of excessive training on my single speed mtnbike I, on the advice of my doctor, had a "Bike-Fit" performed. The results revealed that my seat was too far forward creating stess on my knees during the power portion of my pedal stroke. I installed a new seat post and have not had a problem since.

Due to the whole balance thing we unfortunately cannot adjust our seats back in relation to the cranks, however it would seem to me that shortening the cranks places the knees farther forward over the pedals creating the same problem as my seat position on my mtnbike.

Only my experience and observation for what ever it is worth.
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Old 2011-09-28, 05:20 PM   #8
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It might be worth reading up on meniscus tears, you might have a minor one. I (re)tore mine last January. In the beginning I could barely walk, after about two months I had healed to the point where I had symptoms similar to what you describe, but while walking. Walking uphill didn't hurt at all, I experienced sharp pains when walking downhill. For me the pain was located on top, almost as if it were above the knee, centered and felt like it was an inch or so down.

My first bout with this injury was when I was a kid, I had a severe tear and couldn't bend my knee at all for about a week. The re-tear this past January occurred about 25 years after that initial tear. It happened when I fell asleep on the sofa with my leg sideways and my knee bent - forming a triangle. The cat thought the nook my leg formed was the perfect napping location. The sideways pressure against my knee with my knee bent did it, I woke up a few hours later and that's all she wrote.

Anyway, that re-injury healed slowly 1-2 months of sharp pain just about all the time, 3-4 months of the downhill walking pain, and only went away to the point where I was no longer bothered by it after 6 months. I can still feel a twinge now and then. It's a slow healer since there's not much blood flow to that area.

You're usually pretty safe from this sort of thing while cycling, as I understand it usually occurs when lateral force is applied to one of the sides of a bent knee. Usually there are no external forces pressing on the side of the knee when pedaling, but I could see a fall or some hardcore muni-ing creating a bit of a strain.


So if this only happens with shorter cranks but goes away with longer ones the meniscus probably isn't your problem. If it were then after than initial pain you'd likely continue to experience the pain on the longer cranks. Sorry for the epic time waste.

Last edited by jbtilley; 2011-09-28 at 05:26 PM.
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Old 2011-09-28, 06:39 PM   #9
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No knee injuries ever, no high impact sports, no inflammation to speak of, no unusual clicking or hanging up. The knee doesn't bother me except toward the end of a long ride. The shin pain may be unrelated since I have suffered from shin splints since I was a teen.

Of course there is always a possibility of muscle imbalance, but I'm pretty fit and I cross train, always allowing for recovery, know when to sit out and rest, and this is a new problem since going to short cranks; ie my knees have never been a problem as long as I can remember and I have been an avid rider/runner/skiier for 30+ years.

I suppose I answered my own question, though I am curious if anyone has gone to short cranks, then went back to long for similar reasons.

The real "sucky" part of this is that I actually enjoy riding my 29er with shorter cranks, so I'm reluctant to go back, but at the same time if that's the problem I really have no choice because it has limited how far I can ride

Note: Raising the seat did help "a little", but I can only raise the seat so much before I start getting "kicked off" on rough terrain.

Last edited by Nurse Ben; 2011-09-28 at 06:43 PM.
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Old 2011-09-28, 06:45 PM   #10
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Yes, I think there is a relationship between crank length and leg stress. But I think the difference comes mostly from the leverage change, being a function of the ratio of crank length to wheel size.

I was attempting to train for long distance riding early this year. I started out on my Coker with 152mm cranks. Then I bought a Schlumpf hub and put it in my KH29, with 150mm cranks. Just a few days of riding around the neighborhood in high gear resulted in pain in my left achilles tendon area. This was a re-injury, and exacerbation, from over doing it while road recumbent riding a few years ago. I ended up in a couple months of physical therapy, didn't ride hard this summer, and it still bothers me a bit 6 months later. Official diagnosis was calf strain, but I think I have some tendonitis as well.

Prior to swtiching to the Schlumpf, I'd never had any discomfort in my achilles from unicycling. Prior crank lengths had been 150, 125, and 165 on the 29er (in order of amount used), and mostly 152 but a little 125 on my 36er.

From my experience, it appears to me to be the amount of leverage, taking into account both crank length and wheel size, that dictates leg stress. (Although length alone could also be a factor, particularly for riders with longer legs.) I think your switch to shorter cranks probably increased the strain on your legs in a manner similar to how adding the high gear did for me.

Edit/additional thought: Shorter cranks don't really make a significant difference in speed. The only way to significantly affect speed on a unicycle is to change the wheel size or add a geared hub. So best bet is to just ride the cranks that are most comfortable for your body. This helps avoid injury, and keeps it fun. To the extent crank length does affect speed, I think comfort is just as much a factor, so that higher comfort on longer cranks probably cancels out any speed advantage of shorter cranks anyhow.
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Old 2011-09-29, 12:11 AM   #11
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Originally Posted by Nurse Ben View Post
no high impact sports
Originally Posted by Nurse Ben View Post
I have been an avid rider/runner/skiier for 30+ years.
Running is definitely a high impact sport. Unicycling can be high impact, as muni UPDs on rough terrain will add up for longer rides. I have hip problems and get referred pain to the knees sometimes, but have never experienced problems relating to short cranks. Its always the impact of UPDs that make my hips unhappy.

I started at 150mm on my kh29 and moved to 125mm after a few months. I'm generally happy at 125, but could use more crank to maintain control on steeper descents. I plan to try 137mm moments and see if they are a better fit for me.
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Old 2011-09-29, 01:11 AM   #12
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I'm also trying to standardize on 125mm for both 36" and 29" (mainly road), and when I used to get tweaked knees, I'm convinced it was because the Venture cranks had zero q-factor. When I bit the bullet and bought KH cranks because of the wider q, the tweaking in my knees went away. For me, I need to have my legs wider apart when I ride.
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Old 2011-09-29, 07:16 AM   #13
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my own exeriences:
- On Coker switched from 150 to 125 then back to 140
- on 24" Muni with brakes from 170 to 140
- on 29" (without brakes) from 125 to 110 then back to 150
to avoid knee pain it appears that my comfort zone is around 140/150 (150 on 29" being for control when going down).
So yes: for me crank length has some effect on knee pain.
I spin very slowly but decided on a trade-off: better keep my knees and go slowly. I am wondering if a geared uni is an option suited for me .....
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Old 2011-09-29, 07:37 AM   #14
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Haven't been riding too long and use 137/165 moments on my 26". I have found that my knees tend to have more problems when on 165 than on 137. I am quite tall and suspect that the problem lies with the amount of knee bend on the longer setting. There is more control on longer setting, but the comfort on my knees and legs is much better on 137. Another thing that I noticed makes a big difference is that I have to adjust my seat higher when on the shorter crank length, there is a relationship there.

I know that this sounds contrary to your experience Ben, but for me it just goes to show how individual these kind of things are. It's really difficult to find a "rule of thumb".
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Old 2011-10-03, 12:09 PM   #15
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Well I bumped back to long cranks, downhills area easier and less stressful, but my knee remains sore and now my right knee is feeling tweaky. So I sat down to ponder the problem and I may have figured out the change that led to my knee pain: Lower Q factor.

When I went from 170 to 165-160, then 150, I went from a high Q to a low/zero Q. The difference in width from the QuAX 170 to Venture II 150 is a solid inch, a half inch per side, which would force my feet inboard and change the pressure on my knees.

I had noticed how my feet wanted to be on the outside edge of the pedal and now I know why: it's too dang narrow!

So, back to Moments, gonna stick with 150's, long term I'm looking at transitioning to a 125mm disc hub and low Q cranks.

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