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Something to chew upon... I was perusing t'internet and I still see lots of peeps using kinematic analysis and trying to correct postions and motion, not just of the foot and lower limb, but of the body in general. So my question is this, to what extent do kinematics influence sporting performance? I'm not just thinking about running here, but other sports like cycling etc. If we see someone who's knees adduct during cycling, does this influence power output?

 

If the 'forces' are low, then theoretically the kinematics do not matter as the force to produce movement is low, therefore you can produce more movement economically.
I say 'theoretically' as there is no evidence.
Plenty of anecdotes of what many consider as "bad" kinematics in elite runners runner well.

 

My theory on knee movement in cycling is that the center of pressure on the top of the tibia is not directly above the center of pressure under the foot. When the gluteals and hamstrings contract to extend the hip to press the femur on the top of the tibia a frontal plane moment is created. This will cause frontal plane motion of the tibia that the muscles have to resist to keep the femur directly over the pedal. So, theoretically there will be increased hip abductor or adductor activity when you see increased frontal plane knee movement in cycling. So, bad kinematics could be indicative of increased energy expenditure that could lead to less than optimal atheletic performance. It may not influence power output, but it would influence total energy consumption.

Eric

 

Simon:

I don't think that kinematics absolutely predicts performance but certainly since kinetics determines kinematics, kinematics can help us determine whether abnormal kinetics is occurring during the athletic activity. In the example of cycling, one could make the theoretical case that any knee adduction during the power phase of cycling wastes metabolic energy since, lower extremity cycling motions, in theory, should be pure sagittal plane motion, with as little transverse and frontal plane motions as possible.

In a study I coauthored in the Journal of Biomechanics 24 years ago with a Maury Hull, PhD and others from the UC Davis Mechanical Engineering Department, we found that certain measurement parameters (i.e. total limb varus and subtalar joint axis location) correlated to knee loads during cycling. http://www.sciencedirect.com/science/article/pii/002192909290075C
Certainly one could make the argument from our study that the same kinetics that caused abnormal knee loads during cycling also led to abnormal knee kinematics and that much of that was determined by the forces generated on the plantar forefoot from the bicycle pedal during cycling.

 

Agreed Eric in Cycling Kinematics matter a great deal.

There is much anecdotal evidence that Frontal plane position of the knee does effect power output, not sure if anyone has done a study on it, but is gets discussed from the pro and thus every weekend hack.

Chris Horner broke his ankle years ago left from memory and has this weird pedal stroke, Trek Racing did a biomechancial analysis and through wedging got his knee over the pedal - his power dropped the guys at the team had never seen it, they usually see an increase in power once the knee is over the pedal in the downward stroke

 

Trying to improve cycling performance by just trying to get "the knee over the pedal" is kind of like trying to improve walking biomechanics by only trying to get "the subtalar joint to function in neutral position". There is no evidence for this approach and this is too simplistic of an approach for the complex three-dimensional sport of cycling. Hopefully they did more than just getting his "knee over the pedal".

 

I sure they did Kevin but I believe that in cycling the more the pedal stroke is similar to how the wheels of an old steam engine were driven the greater the mechanical advantage and therefore greater power produced.

With cranks arm length, Saddle height and position of the pedal/cleat interface there is in my Opinion (IMO) dependent on the length of the tibia and femur an ideal pedal stroke.

So in your example of "the subtalar joint to function in neutral position" If we talk of variables of idea in cycling IMO there is a mechanically perfect pedal stroke, where joint angles can be best defined when looking at the position the pedal is in during the pedal stroke, this is of course dependent on if the person is climbing or riding on the flat, standing or sitting.

There is of course Cadence to look at maybe for another time, I might be wrong but I do believe there is a perfect cycling pedaling action

 

I believe to say that "there is a mechanically perfect pedal stroke" is wrong, given the wide variability in structure and function within the human population. Again, your statement is analogous to Root et al suggesting that the "subtalar joint should function in the neutral position". Both statements have no scientific research evidence to back them up and they both seem highly unlikely given what we know about the variability of structure and biomechanics from one individual to another.

Rather, it is better to say that "there are pedal stroke kinematics that produce optimal mechanical efficiency for each individual, given that individual's structural and functional characteristics". Regarding the Root el al suggestion about subtalar joint (STJ) neutral position, a more accurate statement would be "there are STJ kinematics that produce optimal mechanical efficiency for each individual, given that individual's structural and functional characteristics".

I have been doing bicycle analysis now for over three decades and I understand what you are getting at, Mike. However, I also believe that we must be very careful when making claims about ideals or "perfection" when discussing the biomechanics of the human foot and lower extremity.

When I do bicycle analysis and treatment, I aim to get the knee functioning during the power and recovery strokes as much in a straight up and down vertical motion pattern as I can, but, in some patients, this is simply not achievable due to their structural variability or muscle weakness. However, I do understand that in cycling biomechanics and bike fitting we are aiming for "optimal biomechanics", but definitely not "perfect biomechanics"....there is a difference...and it is an important distinction between the two.

About a quarter century ago, while lecturing on bicycle biomechanics, I made the statement that the ideal human biker would be an individual that had no subtalar joint, no midtarsal joints and no midfoot joints since these joints contribute greatly to the mechanical inefficiency seen in many cyclists by creating abnormal knee motions during the bicycle pedal stroke. I still believe that to be true.