Optimal Fit System

By Michael Lovegren M.S. Biomechanics

In the last two decades, applied biomechanics has advanced the sport of cycling by changing how athletes train and by improving body position on the bicycle. The sport of cycling has evolved due to bike frame geometry changes and expanded the racing venues from simple roadways to a variety of roads and trails. Scientific knowledge has altered cycling performances with the successful athletes utilizing such information gained by wind tunnel testing, power meters, and the geometry changes in seat tube angles.

Definition of Biomechanics

Biomechanics is the study of motion and the effects of forces relative to the human body; a field that combines discipline of physiology and engineering mechanics, which utilizes tools of physics, mathematics, and engineering to describe the properties of physiology [1].

Cycling Biomechanics

Since we just defined biomechanics we can know learn and understand how biomechanics is applied to cycling to optimize cycling performance. The bicycle is a fixed object where only certain parts can be change like the stem, cranks, and saddle height. When looking for a bike you need to recognize other biomechanical factors that can’t be modified like seat tube angle.

As a cycling coach and a biomechanist the goal is to obtain optimal position for the recreational cyclists or competitive athlete’s that provides comfort and efficiency to improve their performance.

Having the optimal position allows the cyclist to produce optimal force in cycling, which is known as power output. The goal is to position the cyclist where he/she will have the lowest amount of oxygen consumption while maintaining optimal power production which is known as efficiency. As a biomechanist you want the cyclist to be able to apply pedaling forces effectively to obtain optimal performance and avoid injury. This article considers some variables of rider positioning and equipment set up that are important to all cyclists.

Crank Arm Length

Crank arm length has been a controversial topic. Some coaches and cyclists think longer cranks are better. This is the same mentality of the small guy in the big truck. I believe this comes back as an ego thing. As you increase your crank arm length from 0.170m for the average 5’9 cycling the pedaling rate or cadence is affected [4]. A taller cyclist requires greater kinematic joint moments than a person of average height, thus enabling the taller person to move the crank due to increased mass and moments of inertia of his/her lower limb segments. The optimal crank arm length increases as the stature of the rider increases. Once crank arm length increases from the standard 0.170m, the result is a decrease in cadence [4]. A resulting benefit of the longer crank arm length is a lower demand of pedal forces, however, it requires more motion from leg segments resulting in increased kinematic moment. The sensitivity of pedaling rate is due to the change in crank arm length. A big concern is that most bikes come stocked with the wrong size cranks.

Seat Tube Angle

Seat tube angle is defined as “position of the seat relative to the crank” [3]. A tall rider would benefit from shifting their hips backwards relative to the crank axis, while a shorter rider would benefit from shifting his/her hips forward relative to the crank axis. A research article by Gonzalez and Hull concluded that an optimal seat tube angle varied on cadence and leg length. The significance of their study was in finding that while cyclist stature increases from the average rider of 5feet 9inches, the optimal seat tube angle decreased from 78 to 73 degrees [3, 7]. Research has shown with a steeper seat tube angle produced significantly higher aerobic power efficiency and lower mean VO2 [3]. Price and Donne noted that optimal seat height is the height which produces the lowest VO2 at a fixed power output and cadence. These angles are especially important when looking for a mountain bike, which commonly has a seat tube angle that decreases performance.

Human Movement Program

Since we just discussed the position and dynamics of the bike which is a fixed object with some moveable parts it is now time to discuss the human body. When performing a bike fit it is necessary to understand the functional anatomy (adduction, abduction, flexion, extension, pronation, and supination) of the human body to perform a movement assessment. A movement assessment can be as simple as an overhead squat, single leg squat, and or manual muscle test [8, 9]. To learn more on how to correctly perform these types of movement assessments you can contact Kinetic Loop training System and go through our Human Movement Workshop. There are also some good books like “Athletic Body in Balance” by Gray Cook, “Diagnosis and Treatment of Movement Impairment Syndromes” by Shirley Sahrmann, and the “NASM Essentials of Corrective Exercise” by Mike Clark. Movement represents how the body functions as a unit. The unit is called the kinetic chain, which is made up of the Nervous system, Myofascial system, and the Articular system. However, we are just going to focus on the myofascial system, which is all the soft tissue (muscle, ligaments, and tendons, etc). To insure optimal performance you need to make sure each cyclist has established normal length tension relationships. If a muscle is overactive or tight then this muscle can’t produce the optimal force. Likewise, if a muscle is underactive then the muscle is weak and lengthened and it can’t produce optimal force. Actin and myosin are the two contractile properties of muscle cells shown in the diagram below. Here is an example of an over active and underactive muscle on muscle balance.

There are exercises you can do to increase elasticity in the muscle and improve optimal performance of the endurance athlete through static stretching, SMR self myofascial release (foam rolling), and isolated strengthening of weak muscles.

References

1. Enoka, R.M., Neuromechanics of Human Movement. 2001: Human Kinetics.

2. Martin, J.C., et al., Validation of a Mathematical Model for Road Cycling Power. J Applied Biomech, 1998. 14: p. 276-291.

3. Price, D. and B. Donne, Effect of variation in seat tube angle at different seat heights on submaximal cycling performance in man. J Sports Sci, 1997. 15(4): p. 395-402.

4. Gonzalez, H. and M.L. Hull, Multivariable optimization of cycling biomechanics. J Biomech, 1989. 22(11-12): p. 1151-61.

5. Peveler, W., et al., Comparing Methods for Setting Saddle Height in Trained Cyclists. J Exercise Physiology Online, 2005. 8(1): p. 51-55.

6. Peveler, W.W., J.D. Pounders, and P.A. Bishop, Effects of saddle height on anaerobic power production in cycling. J Strength Cond Res, 2007. 21(4): p. 1023-7.

7. Garside, I. and D.A. Doran, Effects of bicycle frame ergonomics on triathlon 10-km running performance. J Sports Sci, 2000. 18(10): p. 825-33.

8. Sahrmann, S., Diagnosis and treatment of movement impairment syndromes. 2002.

9. Clark, M.A., Corrective Exercise Specialist - National Academy of Sports Medicine. 2008.