Is a Tri Bike Harder on the Knees?

author : AMSSM

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Triathlete's doctor recommends road bike over tri bike

BeginnerTriathlete user question:

"I got my bike properly fitted this spring (can't believe I waited to get that done) and while talking with the guy I mentioned that have some issues with my knees. Before the fitting, my knees almost always hurt after a ride but now I am going farther and faster and have no pain or discomfort. What the guy told me was to stick to a road bike and avoid a tri bike because the tri bike can be hard on the knees, is this an accurate statement? Are there any other areas of the body that a tri bike can be hard on?"

Answer from Kathleen Roberts, M.D. and Wade Rankin, D.O., CAQSM
Members AMSSM

I am glad to hear your knee pain has improved! Having your equipment “fitted” by a professional whether it is your bicycle, shoes, etc. is an important first step in injury prevention. Now to get to your question, there are a few structural differences in road bikes and triathlon bikes. After searching through the medical literature there are studies that discuss how these changes can affect the angles of your body on the bike, which muscles are working to propel the bike forward, and the effort needed to maintain certain speeds, however, not many on how the changes effect injuries. With the majority of musculoskeletal injuries from cycling being from overuse or poor technique, the subtle differences in bike geometry could possibly be another precipitating factor.

The most important difference between road and triathlon bikes is the seat tube angle which is defined as the position of the seat relative to the crank axis (center of where pedal arms connect into) of the bicycle. This angle is usually less than 75 degrees in a road bikes and up to 80 degrees in a triathlon bike. 

With a road bike the lower the seat tube angle leads to you having the hips behind the feet, which is a position similar to sitting in a chair. In this position the rider’s back is in a vertical/upright position which is typically more comfortable as well. With a triathlon bike, the higher seat tube angle leads to you having the hips over top the feet, which is a position more similar to running. In this position the rider’s back is in a horizontal or parallel to the ground position.

Along with the seat tube angle, triathlon bikes can also be equipped with “aero bars” which allow the rider to sit in a more aerodynamic position on the bike reducing wind resistance. By decreasing wind resistance the result would be that the rider would not have to work as hard to maintain a certain speed which would allow for an easier transition to the running portion of the race.

Studies have shown that higher seat tube angle and using aero bars results in decreased fatigue and improved times on the run portion after transitioning, although to see this effect the rider must be able to maintain the aerodynamic position which can be difficult.

With all of that information it is important to remember that musculoskeletal cycling injuries are due to overuse and poor technique as discussed earlier. The most frequently seen injuries are knee, iliotibial band, low back, neck, Achilles tendon, wrist, and elbow pain. Overuse injuries typically come from not allowing enough rest between rides or from increasing time or miles too quickly. With technique, it is important to remember to practice using a high cadence and lower gears which will decrease the work of the quadriceps muscles and be gentler on the knees. Therefore if the geometry of a triathlon bike causes you to have poor technique, it is possible you would be more likely to pick up an injury on one!

References:
Deakon, R.T. Chronic musculoskeletal conditions associated with the cycling segment of the triathlon; prevention and treatment with an emphasis on proper bicycle fitting. Sports Medicine and Arthroscopy Review. Dec. 2012, 20(4) 200-205. 11/11/16.

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date: December 1, 2016