Bum knee, cadence, and crank arm length ...

Discussion in 'Health Nutrition and Supplements' started by lumpy, Aug 23, 2005.

  1. lumpy

    lumpy New Member

    Joined:
    Oct 22, 2003
    Messages:
    513
    Likes Received:
    1
    To make a long story short, I have a bad knee that limits my cycling - both in power output and duration.

    First question: I'm rethinking my idea of crank arm length. I thought a shorter arm (170) would be easier on my knee as the range of motion is less. Now I'm wondering if a longer arm (175) might be better because of the increased leverage. Any ideas?

    Second question: My road bike has a 170 and my mtn. bike has a 172.5. I have a 30" inseam by the way and there is no noticable difference in which bike my knee prefers. So today I rode my third bike, an old mtn. bike with 175 arms. I increased my cadence and my knee felt great! Obviously I'll be experimenting with that - and I guess it makes sense that spinning fast is easier on the knee than mashing. But as a general rule, does increasing cadence lessen stress on the knee?

    Any feedback would be greatly appreciated!
     
    Tags:


  2. FrankBattle

    FrankBattle New Member

    Joined:
    May 9, 2005
    Messages:
    141
    Likes Received:
    0
    In short, yes. According to my doctor, also strengthening your calves and quads with leg exercisess generally reduce the stress on your knee (think of it as stronger support muscles around the knee joint).

    Anecdotally, I too started off mashing big gears on a road bike .. with some knee pain. Beginning at the tail end of last season, I switched to a higher cadence style. I have not had any knee pain since, but I also did leg exercises in the off season. These days, I only use the big ring when descending the steepest hills. My knees thank me.

    Like anything else, YMMV.
     
  3. jawnn

    jawnn New Member

    Joined:
    Nov 17, 2003
    Messages:
    96
    Likes Received:
    0
    TIPI-TOE MANEUVER

    There is a zone in the crank circle where there is no power; because when your foot reaches the end of the push stroke the opposite foot is a quarter turn from the right place to push. To help your foot reach the right spot the foot at the end of the push must swipe threw and pull back, with recumbent cycles this is mostly just helping gravity. If you don’t wait until the foot is in the right space, you can push up your kneecap up, causing the infamous knee pain.

    There are several mechanisms invented for stand up bikes to help your foot through this dead zone. Clipless pedals (cleats) or straps, and now a very expensive Rotor crank that eliminates the dead zone (rotorcranks.com).

    Pedaling my 400lb sport utility vehicle (RCN #89 USX trike) gave me such pain in my knees that I had to back off from pedaling hard and try short cranks, which gave temporary relief, but soon led me to damaging my knee-caps again. As I was thinking about spending around $200 on clippless pedals and shoes, I reinvented a maneuver that places my foot at about 80 or 90 degrees to the crank arms at the beginning of the push stroke.

    I push my toes forward as much as I can with out pain (it can’t be done with boots on) positioning my bones in such a way that keeps from pushing my kneecaps up. It’s amazing how much harder I can push now with out creating pain

    At the end of the forward push I push down “swiping threw” and pulling back with my foot still on top of the pedal.

    I don’t need clipless pedals with this maneuver but I do use BMX pedals and place the top of my foot arch on the pedal rather than the ball of my foot.

    Short crank arms are not needed but they can help the foot reach the right position. One person told me that using this maneuver on his “stand on the pedals” mountain bike felt like running on his tippi toes.

    Apparently some people can experience toe numbness from “anterior tunnel syndrome”. So don’t force your feet into this position.

    I think the primary cause of knee pain is simply pushing before the right spot is reached. That’s why it is still possible for me to damage my knee with this maneuver.

    I did move the seat closer to the crank to get more power to the pedals, but still there is a limit to how hard I can push with out lifting my kneecaps. And of course if I could lower the gear-inches below 10.5, I wouldn’t need to crank so hard, but it wouldn’t give me more power.

    Then a faster cadence would be possible for most people. I can’t pedal as fast as some because of my large leg muscles. I believe that Power Saver pedal pendulums can help with cadence speed, but no one in America sells them.

    I don’t think that the crank placement affects this maneuver but for comparison my crank is 4” lower than the seat.
     
  4. mdmai

    mdmai New Member

    Joined:
    Jan 7, 2006
    Messages:
    2
    Likes Received:
    0
    I have a bad right knee and my left leg is 9mm shorter than the right. This results in lower back pain. So, as to your crank arm length question: I went from 172.5 to 175 and noticed less knee pain, less back pain (I'm not sure why) and it will increase your leverage. Pay attention to your seat height and position, but don't make radical changes in postioning. Change saddle height and position gradually over several weeks of riding. All of my ideas are based on various articles and books I've read over the years. I'm 53 and still cranking!

    Good luck and let me know how it works out for you.
     
  5. gclark8

    gclark8 New Member

    Joined:
    Apr 13, 2004
    Messages:
    3,522
    Likes Received:
    3
    See: http://www.greenspeed.com.au/NewGSweb/web-content/australia/measure.html

    I feel the table is the max length, it depends on age and flexability too. I sugest trying 165mm cranks.

    I have a 33" inseam and ride 170mm cranks on both road and MTB @ 88-96 cadence. I tried 175 and didn't make 400m. I have a friend, she has 29" inseam and rides 160mm cranks @ 90-94, but recently she tried 152mm and just loves it!! Both of us are well over 50.
     
  6. EoinC

    EoinC New Member

    Joined:
    Feb 9, 2004
    Messages:
    1,615
    Likes Received:
    1
    There are 3 interelated issues at stake here (1) How far the knee movement extends, (2) How much force is being applied and (3) Cadence.
    (1) Longer cranks require greater movement (the angle of the knee at the top of the stroke will be more acute with longer cranks, given that the extension at the bottom of the stroke remains the same). Generally longer is better until you reach a range where it is inefficient, damaging or the pedals are touching down in the corners.
    (2) The amount of pressure applied is up to you. You should not be pushing to the extent that it hurts your knees. The means of using that available pressure to maximum effect is determined by technique (clipless or toeclip pedals and pedalling in a circle can certainly help), leverage from the cranks (determined by length of crank) and, most important, gearing and cadence. If you need greater 'leverage', choosing the correct gear is the best way of achieving it.
    (3) Controlling cadence (rpm) is a good means of attaining efficiency. Each individual has their own ideal cadence, and it is an ideal that can change over time due to training, or decay. Somewhere around 80-90 rpm is a good starting range to aim for. Just choose the appropriate gear to suit.
    My current ride is a fixed-wheel with daft little 165 cranks. They are too small for me to get full use of my available leg movement (feels like riding a circus bike). Being a fixed-wheel riding on the road, ground clearance is an obvious concern as one has to continue pedaling through corners. However, I seem to have more than enough to spare and, having found 2 cracks in my right-hand crank, I intend (when I get back to Aussie) replacing the 165's with 172.5's.
    Find what your limiting parameters are and work within them. As has been advised before, steer clear of mashing big gears if you have any knee problems - that's why the good people invented gearing.
     
  7. ellno#1

    ellno#1 New Member

    Joined:
    Jan 6, 2006
    Messages:
    63
    Likes Received:
    0
     
  8. EoinC

    EoinC New Member

    Joined:
    Feb 9, 2004
    Messages:
    1,615
    Likes Received:
    1
     
  9. ellno#1

    ellno#1 New Member

    Joined:
    Jan 6, 2006
    Messages:
    63
    Likes Received:
    0
    Right on the nail EoinC....?;)
     
Loading...
Loading...