Bulging Disk and the Aero Position

author : AMSSM

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I am racing in the Florida Ironman. My question is this: which position is going to be better for me to ride in, the aero position or the traditional road position?

Member Question

I have a lower back problem (bulging disk L5 S1). I am racing Ironman Florida. My question is this: which position is going to be better for me to ride in, the aero position or the traditional road position? Which one causes the least amount of stress on the lower back?

Answer by Dr. Deanne Eccles
Member AMSSM 

The lower back is made up of a bony column of vertebral bodies, thick supporting ligaments that connect the bones together, strong paraspinal muscles that attach to the bones via tendons and discs that cushion the vertebral bodies and allow fluid motion such as flexion and extension.  The discs are cushions that have an outer fibrous ring called the annulus and an inner gel material called the nucleus.  The nucleus has more hydration which can be depleted with aging or trauma.  This would be considered a degenerative disc.  In addition, if there is trauma to the discs they can also become displaced - where they extend beyond the edge of the vertebral bone and can either be called a disc bulge or herniation.  The difference between a bulge and herniation usually depends on the amount of displacement.  This can occur when the fibrous outer ring stretches too far or tears.  As the disc bulges or herniates it can irritate nearby exiting nerves and cause sciatic leg pain.

In general, discs are usually stressed while the lumbar spine is in flexion.  The most stress occurs to the disc when there is a combination of forward bending and lifting with or without rotation.  Flexion causes pressure to the anterior aspect of the disc and forces the disc to move posteriorly.  This can stretch the fibrous annular ring which can eventually weaken and either bulge or tear.  In order to minimize stress to the disc it is recommended that the spine be either in a neutral or slightly extended posture.  This helps take stress off the posterior aspect of the disc and can allow a displaced disc to resorb to some degree.  Traditionally, people with disc issues will have more trouble sitting or driving and less trouble with standing or walking.

In triathlon the biking posture can cause stress to the lower back.  Ideally with either the road bike seat angle or the triathlon bike seat angle your spine should be flat/neutral and the angle of the back to the hip will be 90°.  However some people do not have adequate hip flexibility to allow the back to remain flat.  Therefore to accommodate the loss of hip flexibility the spine will flex so that the athlete can ride in the desired bike position.  Therefore I would recommend working with someone who specializes in bike fitting to try to see which seat angle will allow your back to maintain a neutral posture as to not stress the lumbar disc.  You may sacrifice some of your aerodynamic position for this but it will take stress off the lumbar discs and diminish the overall pain.  You may find that with less of an aerodynamic position your overall power output improves because you are having less pain. 

In addition to a proper bike fit I would recommend working with a physical therapist to focus on core strengthening, flexibility and extension-based lumbar stretches.  One good set of exercises is known as the McKenzie program.  If you do feel that you have some flexibility to gain in the hip you can also add stretching for the hip musculature to improve your positioning on the bike.  Good luck with the Ironman and finding a good bike fit!

Sincerely,

Dr. Deanne Eccles

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date: October 10, 2012