Thursday, October 8, 2009

Bike Fit

My friend Paul put this article together:

If you buy a suit don’t you have it tailored? When you buy new tires for your car you have them balanced, right? When you get glasses you have a doctor examine your eyes to get the correct prescription. The last time you bought a new bike did you have a proper bike fit performed?

This article will explain all the specific measurements that should be taken in a bike fit and how to best make changes to your bike that correspond to those measurements. It will also explain why most people will need treatment to resolve muscular imbalances and flexibility issues.

Too often many people set up their bike by the way it feels to them only. If you have a bike fit completed not only will you be more comfortable on your bike but you will also perform better and reduce your chances of injury. When having a bike fit performed there are specific measurements that should be taken. The measurement that is most important for power production in the angle of knee bend when you are at the bottom of your peddle stroke. Besides this you also should know your hip angle when holding your handle bars in the position your most often ride in which should be on the brake hoods. The fore-aft position of your knee in relation to the pedal and the amount of sway of your knee during your pedal stroke are all important to power production and comfort on your bike. Cleat placement is also important. Other smaller changes that can affect your optimal position on a bike are saddle size, handle bar size and fore-aft position of the saddle. One aspect to an average bike fit that I think is missing is testing a person’s flexibility and strength. Most bike fitters don’t have the knowledge of how to accurately test someone’s flexibility. Even if the fitter does know how to, no fitter is able to treat those issues.

As I stated earlier the single most important measurement that will be taken during a bike fit is the angle of your knee at the bottom of the pedal stroke. Research has shown that the knee should flex optimally to 35 degrees to produce the greatest amount of force. This can be easily measured using a goniometer. A goniometer is basically a protractor that can be centered at the knee joint with each arm running along the shafts of both the femur (thigh bone) and fibula (shin bone). By lifting your saddle up as little as 2-5mm you can decrease the angle of knee flexion. What if you have an inability to straighten your knee to that degree because of extremely tight hamstrings? No alteration of your bike settings will allow you to have an optimum pedal stroke. This is why you need to check flexibility and then have treatment performed on your hamstring. Soft tissue techniques like Active Release Technique and Graston Technique are perfectly suited for a situation like this. These techniques are what we often use for treatment at Capital Sports Injury Center.

The angle of your hips will be the second most important measurement taken during a bike fit. The smaller the angle of your hips are the more aerodynamic you can become on your bike. With less of an angle you can get your upper body closer to parallel to the ground causing less wind resistance. This angle again can be measured with a goniometer using your femur and the midline of your abdomen centered about the hip joint. The correct angle to use depends on the rider. Are you more interested in comfort or aerodynamics? An aggressive rider would want something around 25 degrees while someone looking for more comfort would do fine closer to 30 degrees. The measurement of this angle is even more dependent on flexibility. A person may have tight erector muscles in their low back or tight hamstrings that don’t allow them to rock their pelvis forward. Even if a rider wants to be aerodynamic they would never be able to sit in that much of a tucked position.

The fore-aft position of your knee can affect the amount of knee flexion you can accomplish at the bottom of a pedal stroke. If your knee is too far forward the amount of flexion will be increased at the bottom of the pedal stroke and vice versa if your knee is too far back. Riders may also be shifting forward on their saddle either for comfort or extra power. This will change all the measurements. It is important to have the rider sit on their saddle correctly.
That brings me to a problem that I had previous to my bike fit. I was sitting on a saddle that was too narrow. This meant that I was not sitting on my ischial tuberosities (sit bones) but was rocking forward onto my pubic bone. As you can guess this was not very comfortable. The average size saddle is 130 mm wide at its widest point. If you are a larger rider chances are this will not be large enough for you. No amount of change in the different parameters of a fit will help if you can’t sit on the saddle correctly.

Cleat position is closely tied to knee sway most of the time. If your cleats are set up so that you have no movement at all or you will clip out your knees will have to sway more if there is a hip problem. Having said that you can make up for hip issues or increased knee sway if you increase the amount of internal rotation of your cleats. By doing this you can increase the internal rotation of your foot and allowed your knee to track straighter up and down.
Although not often an issue the size of your handlebars can be problematic with shoulder injuries. If you have had an injury where you have lost the ability to extend your arms or internally rotate them you may need a larger handlebar. With any shoulder injury some form of treatment and exercise should be performed to help recover the lost movement. A great internal rotation exercise can be performed with tubing. Start with the tube attached to something on one end and grasp the other end with your thumb up and arm abducted (away from your body). Facing perpendicular to the tube internally rotate your arm so that your thumb is down and reach behind your back to the opposite shoulder blade.

The final aspect to a bike fit may involve changing the fore-aft position of your saddle. When this is done it move your entire body either forward or backward. This is usually done when a rider’s knee fore-aft position or knee flexion at the bottom of a pedal stroke can’t be fixed with any of the other bike fit components.

One aspect to a bike fit that is typically missing is testing a person’s flexibility, caused by imbalance, and strength. This is called a functional movement screen (FMS). Since most bike fitters do not have this expertise, Drs. Horwitz and Glodzik add the FMS to help the bike fitter make the best decisions on equipment and placement. These imbalances cause compensatory changes in multiple areas of the body resulting in "energy leakage" and increase the potential for injury. As in the example above, if your hamstrings are tight, this may be due to weak gluteal and core muscles as well as due to adhesions in the muscle itself. A corrective exercise program and a program of care to resolve these issues must be undertaken. This will certainly change the bike fit! Even with all the different changes that can be made to make your bike more comfortable riders still need to fix the problems that are necessitating the changes. A rider should have their injuries treated and still perform other training off the bike to make it easier to be on the bike.

For any questions feel free to contact chiropractors Drs. Horwitz and Glodzik at If you are interested in a bite fit or are experiencing any other problem and would like to make an appointment in our Silver Spring, Cleveland Park, or Georgetown offices, please call us at 301-622-9000.

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