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Pedaling efficiency, effective torque, and saddle posistion

thomasmorristhomasmorris Posts: 373
Recently I have become interested in muscle recruitment during the pedal stroke. I have tendonitus in my left knee, which my physio thinks is due to a weakness in my left glutes, developed by not recruiting my glutes enough during my pedal stroke, leading to the knee not tracking.

For several reasons I can understand the diagnosis, if fits with my symptoms, and I also have a reduction in power in my left leg (typically 43-57%).

I have been given exercises to develop my muscle recruitment in my glutes and have been focusing on recruiting my glutes whilst cycling... but it's actually quite hard to think and recruit these muscles, and certainly takes some mental training to get the muscles firing at the correct time in the pedal stroke to apply effect force.

It's often argued in here that knowing where in the pedal stroke you're applying power is unimportant, and only total power is needed to train effectively.

However, I'm starting to think this is misleading. Until going to the physio, i thought my left leg weakness was just genetics, and I should focus on my power output... i.e. it doesn't matter where the power comes from as long as it comes.

Reading this (it's looking at why recumbent struggle to produce as much power) is really interesting.
http://members.home.nl/vd.kraats/recumbent/pedal.html

People often talk about the dead spot in a pedal stroke. But it's interesting to think about what a dead spot is. This article describes it as the point at which joint angle stops bending and starts contracting (i.e. when the angular speed is 0, the join isn't bending or stretching, and so the muscles on it can;t produce any power).

There are two major joints involved in the pedal stroke, hip and knee. However, their dead spots don't line up. i.e sometimes the hip is stretching and the knee is bending, and sometime they are both stretching.

How you position your weight over the dead spot must make a significant difference in which muscles you recruit, and therefore how much power you can produce. For my interest it will also effect how much load I put through the patella tendons (if I can use hip extendors like the glutes more than knee extenders like the quads I can reduce strain on the tendon).

I'm due for a bike fit soon, but would like to hear your thoughts on this.

Posts

  • imposter2.0imposter2.0 Posts: 11,202
    How you position your weight over the dead spot must make a significant difference in which muscles you recruit, and therefore how much power you can produce.

    It may make a difference, it may not. That's nothing more than conjecture, unless you have any data to support it? Also, the dynamics of pedalling a recumbent are so different to a 'conventional' bike that I can't see how any of the info in that link will have much relevance.
  • It may make a difference, it may not. That's nothing more than conjecture, unless you have any data to support it? Also, the dynamics of pedaling a recumbent are so different to a 'conventional' bike that I can't see how any of the info in that link will have much relevance.

    Are the dynamics that different? The movement of the legs (the angles the joints pass through and the muscles used to move them) can be identical given the same crank length, cleat placement and hip to axle distance. The only difference is what you're pushing against (gravity or a seat backrest).

    The main difference is he body to hip angle (sea the section on seat angle).

    Edit: to add I agree it is conjecture... however, the hypothesis to test would be that by recruiting more muscles groups sustainable power increases (hopefully it will, assuming they are underdeveloped). However, I understand that by training glutes, quads may suffer and total out put may not rise, or that the glutes are a less metabolically efficient muscle to use etc... and even if I did increase total power it would be hard (impossible) to link that back to the specific muscle group.

    More importantly I hope training the glute will reduce my knee pain.
  • imposter2.0imposter2.0 Posts: 11,202
    It's the difference between pedalling at zero degrees or 90 degrees. I would suggest that makes a huge difference, in as much as the two positions are completely alien to each other in reality.
  • ncrncr Posts: 98
    It may make a difference, it may not. That's nothing more than conjecture, unless you have any data to support it? Also, the dynamics of pedaling a recumbent are so different to a 'conventional' bike that I can't see how any of the info in that link will have much relevance.

    Are the dynamics that different? The movement of the legs (the angles the joints pass through and the muscles used to move them) can be identical given the same crank length, cleat placement and hip to axle distance. The only difference is what you're pushing against (gravity or a seat backrest).

    The main difference is he body to hip angle (sea the section on seat angle).

    Edit: to add I agree it is conjecture... however, the hypothesis to test would be that by recruiting more muscles groups sustainable power increases (hopefully it will, assuming they are underdeveloped). However, I understand that by training glutes, quads may suffer and total out put may not rise, or that the glutes are a less metabolically efficient muscle to use etc... and even if I did increase total power it would be hard (impossible) to link that back to the specific muscle group.

    More importantly I hope training the glute will reduce my knee pain.

    http://adventure.howstuffworks.com/outdoor-activities/triathlons/training/pedal-float.htm
  • It's the difference between pedalling at zero degrees or 90 degrees. I would suggest that makes a huge difference, in as much as the two positions are completely alien to each other in reality.

    Not sure if you're agreeing or not?

    By zero and 90 degree, I guess you're referring to seat angle in relation to gravity? Although, strictly speaking the change in angle is ~0-20 degrees versus ~73 degrees... ie virtual seat tube angle.

    Changing virtual seat tube angle (moving saddle forward and back) recruits different muscles and therefore recruiting different muscles will have an effect on knee loading...?

    But dead spots aren't in relation to gravity... they're determined by joint extension... and more specifically zero angular velocity (the moment at which a join is neither stretching or bending).

    On an upright bike we largely push against gravity, by changing our virtual seat tube angle, you can change which muscles groups you use to push against gravity.

    It's a pretty widely held belief that moving the saddle forward utilizes the quads, and moving it back the hamstrings and glutes, thus taking load off the knee. Hence why moving the saddle back or cleats back is advice often given for knee pain.

  • Thanks... I'm not ruling out anything in terms of my knee pain. And hope to discuss knee tracking at the bike fit. However, knee pain isn't always a result of float.

    If there is a skeletal issue or joint misalignment... basically a structural problem, then I would accept float/shims/wedges as a fix for the cause of the problem. However, if the problem is the recruitment of muscles during the pedal stroke, then shimming the shoe, or increasing floats is just treating a sympton, rather than addressing the route cause.

    Hopefully the bike fit will see if I have any skeletal issue that need to be compensated for, if not maybe they could find a position which changes my muscle recruitment instead.
  • chrisw12chrisw12 Posts: 1,246
    OP,how often are you riding your bike?
  • OP,how often are you riding your bike?

    https://www.strava.com/athletes/458344

    A few easy hours last weekend, plus some saddle testing, but not much currently, just keeping the joint moving.

    Historically, typically between 8-15 hours a week for the last year depending on time of the season.
  • imposter2.0imposter2.0 Posts: 11,202

    OT - Burghfield has a cycling club..?? :shock: Is it a real one or a Strava one?
  • ncrncr Posts: 98
    It may make a difference, it may not. That's nothing more than conjecture, unless you have any data to support it? Also, the dynamics of pedaling a recumbent are so different to a 'conventional' bike that I can't see how any of the info in that link will have much relevance.

    Are the dynamics that different? The movement of the legs (the angles the joints pass through and the muscles used to move them) can be identical given the same crank length, cleat placement and hip to axle distance. The only difference is what you're pushing against (gravity or a seat backrest).

    The main difference is he body to hip angle (sea the section on seat angle).

    Edit: to add I agree it is conjecture... however, the hypothesis to test would be that by recruiting more muscles groups sustainable power increases (hopefully it will, assuming they are underdeveloped). However, I understand that by training glutes, quads may suffer and total out put may not rise, or that the glutes are a less metabolically efficient muscle to use etc... and even if I did increase total power it would be hard (impossible) to link that back to the specific muscle group.

    More importantly I hope training the glute will reduce my knee pain.

    You are on the right track here but have a long way to go. The glutes don't need training, they are already powerful enough. Using the mashing style, the power has to come downward from the knee but on a recumbent the power is coming from the glutes through the knee which can greatly reduce knee stress. It is possible to reproduce that same effect from a rearward saddle position on an upright bicycle by using a very different method of applying force from shoe to pedal and it gives the added bonus of maximal torque through the dead spot. But from experience it's too difficult to explain here.
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