Biomechanics and Bike Fitting: Getting Low (Flexibility)

Biomechanics and Bike Fitting: Getting Low

Contents:

The Flexibility Problem

The Internal Problem

The Hidden Problem

The Solution

Other Positional Changes That Might Help

Further Information

The Flexibility Problem

A cyclist will often feel unable to get into a low position on the bike comfortably. This will mean that the lowest hand position available (in the ‘drops’) will feel uncomfortable and only able to be used for short periods, if at all. The result of this is that the rider will be sitting upright more than necessary and creating more drag, meaning they have to put out more power to attain any given speed. In a sport where “aero is everything”, even non racers will benefit from reducing wind resistance. Bike fit can help to enable a rider to get lower but if the rider has intrinsic flexibility issues preventing them from comfortably using the lower positions for extended periods of time they are missing out on these benefits.

The Internal Problem

The issue that will stop most people from getting low on a bike is that it feels uncomfortable to get to, or stay in, the position. People will say that they feel their hamstrings, lower back or some other area is too tight to be able to comfortably drop down to a low position on the bike. To fix this, various stretches of hamstrings, hips, back etc. are often used to try to get more flexiblity in order to ride in a lower position for longer.

A common test of hamstring flexibility is called the Straight Leg Raise (SLR) test. This test is very simple – lie on your back and lift your leg (keeping it straight) and see how many degrees of movement you can achieve. As a guideline for cyclists, I like to see at least 70 degrees and would prefer closer to 90 degrees.

Wiggins great flexibility and biomechanics on a bike

Wiggo getting low!

As you can see from the picture of Wiggo above, in the low position he is pictured at the bottom of the pedal stroke his leg will be close to straight with a leg angle of close to 90 degrees from his torso. Therefore the goal should be to increase the range of motion in the SLR test, which would seem to be helped by stretching the muscles in the back of the leg and hip, right?

The Hidden Problem

However, often the problem is not what it seems! People who say they have tight hamstrings often have another issue that is causing it, which doesn’t get much attention in traditional approaches. As Biomechanics Coaches we will check the whole system to see if there are any issues and/or patterns that may be missed by standard muscle length or functional movement testing. The particular common issue that can affect a forward bending position such as the one we are discussing here is a tightness or tethering or the sciatic nerve. This nerve runs from the head all the way down the back of the body and if it is shortened or tethered (compressed or trapped somehow) it will cause a reflexive tension of the muscles when trying to stretch into a flexed position (such as touching the toes)

Here is a simple exercise to show that a feeling that is often mistaken for ‘tight hamstrings’ is actually a stretch in the sciatic nerve: Sit in a chair, then tuck the chin to the chest and collapse the chest, rounding the upper back. From here, straighten one leg until you feel the start of a stretch sensation in the back of the leg. Holding the leg at this point of a very mild stretch, now look up and lift the chest. You should find that the stretch in the leg either lessens or goes away. This proves that the sensation of stretch you felt when extending the leg was not a tightness in the hamstring, as the position of this muscle has not changed.

The Solution

slump test mobilisation sciatic nerve biomechanics flexibility

There can be a few reasons why the sciatic nerve is short or tethered, and it may not be the only issue that is causing problems – but if the stretch in the test above felt familiar it should help to mobilise the nerve. Often flexibility gains in a SLR (Straight Leg Raise) test of ten or more degrees are seen just by mobilising the sciatic nerve, and without stretching any muscles.

To mobilise the sciatic nerve, we perform the slump mobilisation. This is done by slumping forward as in the test above, moving the leg to the very first point of a stretch sensation and then returning the leg to the start position. Perform 12-15 repetitions on each leg, and repeat the whole thing 3x each side. DO NOT hold the stretch as this can cause irritation and damage to the nerve, potentially causing pain/tingling/numbness that can last for days!

Once the sciatic nerve has been mobilised you should find that the legs can move more freely, feeling less heavy and tight and you may notice comfortable pedalling cadence increases and the legs turn over nicely.

Other Positional Changes That Can Help

Due to the fact that the sciatic nerve goes all the way up the spine, we can help take some of the tension off the leg in the tucked position by arching the back. Think about pushing the chest towards the bars and getting long in the spine. This may require stretching or mobilisation of the ribcage area to be able to do comfortably. It may also require a change in bike geometry.

It also helps to slightly raise the chin, being careful not to hyperextend the neck. As a general guide, even in your low position on the bike you should be able to lift the head a further inch or two from your normal position and not be locked into end range of motion.

If You Need Further Information

As you can probably guess, this article only skims the surface of the long process of getting comfortable being in a low position on a bike. The process should start with the basics such as the mobilisation above, looking at all the joints and muscles in the body and ensuring everything is correctly aligned. The next stage would be to look at your position on the bike and adjust things based on your current physical condition and riding goals.

For a great start to getting optimal function, a Biomechanics Screen will help – with over 25 tests for muscles, joints and nerves throughout the body it gives a unique picture of where you have dysfunction and how to go about correcting it. For more details contact me today and start down the path of riding faster and more comfortably!

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