Aero Position and Overload Injuries

imagesRoad biking demands that cyclists subject their low back to prolonged flexed posture, exagerated thoracic kyphosis, neck hyperextension, and close-packed hip/knee angles.  Aero positions especially, have some risks associated with them.  Two common injuries riders experience are to the hamstring and erector spinae muscle groups, in the form of low back pain.  

When you are riding on your own, different studies suggest that overcoming air resistance uses as little as 65-70% and as much as 80-90% of your energy. Wind resistance, rolling resistance, and gravity are forces acting on a rider. Power is needed to overcome these forces and move a rider at a given speed.  Drag from the air isn’t a big problem at low speeds. the downside is that the force required to overcome air drag rises as the square of the speed. Because power is force times speed, the power requirement rises as the CUBE of the speed.  Up to about 12-15 mph, you are mostly fighting the rolling friction of the tires. After that, air resistance becomes an increasingly important factor.

The aero position reduces your frontal surface area by lowering torso position. This helps maximize your aerodynamic efficiency. Aero positions have some risks associated with them.  Two common discomforts and injuries riders experience are to the hamstring and erector spinae muscle groups (low back pain). These injuries are primarily caused by the muscle groups being put into positions that overstretch them beyond their capabilities for optimal contraction (stretch weakness) and adequate recovery (overtraining).

Lowering the torso into a more aero position, without making other changes simultaneously, will increase the strain on the erector spinae and hamstrings.  When strain on a muscle exceeds its capacity to respond and/or adapt, injury can result. Microtrauma will progress to macrotrauma and pain will result. Addressing this from a cycling position perspective demands some attention.

There are four primary, and individual, items that should be addressed to reduce strain on uncomfortable or injured low back and hamstrings in an aero position:

1. Proper saddle height.

2. Proper saddle fore/aft positioning.

3. Proper arm pad height.

4. Proper bike length.

1) Regardless of the other potential solutions, riding with an appropriate saddle height is crucial to comfort and power. A saddle that is too low can prevent the lower spinae from extending fully and thus effectively cramp the muscles while a saddle that is too high can over extend the muscles and repetitively pull on them. Both can lead to discomfort. Because of the greater pelvic rotation encouraged by a lower torso position, most triathletes should be riding with a saddle height slightly below what they would ride on their road bike. Flexibility and alignment are variables that should be assessed and considered before determining proper saddle height.

2) If you are riding on a more relaxed seat angle road bike (<76˚ seat angle), or with your saddle far back on its rails on your triathlon specific bike, moving the saddle forward can take load off strained hamstrings and lower spinae. As the saddle is moved forward, it relaxes the angle created between the lower back and the leg. This can not only take strain off the lower back, but can also reduce pull where the hamstrings attach to the ischial tuberocities (sitz bones) on the pelvis.  Moving the saddle on the rails should be done with care as it will also effect the length of the bike and the relation of the knee to the foot while riding. Both of these items can directly effect other aspects of comfort and performance while riding.

3) If you are already riding in a forward seat angle and are experiencing hamstring or lower back pain, you will want to look at the height of your aerobar arm pads. Many athletes, in their quest for speed, are riding bikes with very low arm positions. Regardless of forward seat angles, this can still put a lot of load on the musculature of the lower back and hamstrings. Except in very rare circumstances, the solution is to raise the arm pads until the height places the torso angle within the rider’s comfort zone for their flexibility and strength.

4) A bike that is set-up too short from saddle to handlebar can cause the spine to curve and will load up the lumbar and lower thoracic areas causing discomfort. For riders in this situation, the length of the bike needs to be extended. Depending upon the situation, this is best accomplished through a saddle adjustment, longer aerobars or a longer stem.

There is a segment of riders who simply cannot ride comfortably in an aero position. These people may have severe sciatica or other mitigating factors (injury) that limit them.

The most efficient aero positions possible require excellent flexibility and strength to be held comfortably without risk of injury. If you want to ride in such a position, it is important that you consistently focus on stretching and strengthening the associated muscle and tendon groups (erector spinae, hamstring, psoas, iliotibial tract and hip flexor). Most inexperienced riders and riders with lower flexibility should start riding in a more upright and relaxed road based position that places less strain on the lower back musculature and hamstrings until their riding experience, cycling strength and flexibility develop. As they progress, a program to develop into a more aggressive position can be instituted over time.

It’s important to make small changes in your riding position over time versus large adjustments. If a new position is painful or causes an overuse injury, reverse it immediately. If you spend most of your time on the hoods (on top of the brake levers), a good place to start is by switching to a lower hand position (drops) for short periods of time. Start off with as little as five minutes and progressively increase the amount of time you spend in the drops. Eventually, you should spend a majority of your time here unless you’re climbing a steep grade.

Once you’re comfortable in the drops, you can lower your stem height. Lowering your stem height decreases the angle at your torso. Stem height can vary from zero to four inches below the height of the saddle. When you lower your stem height, there’ll be less aerodynamic drag from your upper body, but power and climbing ability will be reduced. Lower the stem in small increments and let your body adjust to the new position.

Remember, the faster you get the more the air around you slows you down. If you can ride consistently at or over 20 mph (on your road bike), an aerodynamically-efficient riding position could become a primary objective. The type of riding you do should also be considered. Generally, the more time you spend in the saddle during your goal events the more of a priority comfort should be.

Regardless of experience and flexibility, if you want to maximize your power, aerodynamics and efficiency while riding, it is crucial that your position is built around what your body is capable of holding comfortably. Your position should address your individual needs and physical capabilities. Your flexibility, core strength, body measurements and alignment, riding experience, and any other mitigating factors (injuries, mileage…) must all be assessed before a position is built. Once these variables are established, a qualified technician can combine the information into a dynamic session on a fit cycle where angles can be polished and your body can be balanced until a position that will keep from straining muscles, while maintaining an efficient and powerful pedal stroke, can be constructed. For strong and experienced athletes, computer based assessments of aerodynamics, power output and efficiency, and oxygen transfer can also be integrated into an advanced fitting session to further perfect the rider’s efficiency.

Riding position is dynamic and will change as you age, gain experience and as your body changes.  It is always a good idea to have it reviewed and adjusted periodically by a well-trained specialist. Until you really know what you are doing, trying to fix it on your own can often create more problems than it solves.

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