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Tuesday, 14 February 2012

Knee Over Pedal: is this the be all and end all?

A staple rule for fitting a road bike over the last number of years has been that the knee should be positioned over the pedal when the crank is horizontally forward. This rule doesn't change, it's the same for every rider no matter what height or body proportion. It's been used as a part of bike fitting long before the advent of sophisticated video or 3d motion tracking system as it's quick and easy to do by anyone with a plumb bob. But should more research be done regarding the use of knee over pedal as a rule for setting the setback of the saddle?

The knee over pedal rule changes however when we're fitting a tri or time trial bike. All of a sudden, knee over pedal doesn't matter and we move the position so the knee is anywhere from 2cm to 10 cm in front of the pedal depending which fitting guidelines you are following. Why is this? To open up the hip angle as you clear top dead centre (also known as hip closed position).

So why is hip closed position important? A lot of people can not activate their glutes from a closed hip (deep squat) position and also have hip muscle imbalances in hip muscles which are caused by poor posture and incorrect motor mechanics. These tight and/or weak muscles pull you out of a perfect straight alignment as your pedal comes over top dead centre and the hip closed angle decreases. This means that some of the energy being generated by the power stroke of the opposite leg is being sapped stretching these tight hip muscles over top dead centre and can not produce maximum pedal force until further round the pedal stroke when the knee is back inline with the foot. For people with imbalances, the tighter the hip closed position, the more the less power is produced.

So how does the knee over pedal fitting technique effect the hip closed angle? Let's use an example of two riders; both riders are the same height, have the same overall body, arm and inside leg length. Position wise, they are set with the same knee angle at the bottom of the pedal stroke, knee over pedal, the same back and shoulder angle. The difference between these riders is that rider A has long thighs and shorter shins and rider B is proportioned the other way round. Positioning the knee over the pedal will mean that rider A will have to be set a lot further back in the saddle compared to rider B due to the length of the thigh which will close the hip angle and create different hip mechanics between the two riders.

If we spend all this time standardising the knee mechanics at the bottom of the pedal stroke, why aren't we spending the same amount of time standardising the hip mechanics over the top of pedal stroke?

With wider spread use of video and motion capture systems, measuring the hip closed position is easier than ever before. Therefore, I believe that more research needs to focus on this area, particularly it's effect on those with hip muscles imbalances.

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