Bike Fit Evaluation: Can It Help Diagnose And Prevent Cycling Injuries?

    The sport of cycling has seen tremendous growth in the past decade. Athletes are utilizing bicycling not only as their primary sport but also as a form of cross training and rehabilitation. As a result of this growth, there has been a corresponding increase in the incidence of non-traumatic (overuse) injuries. Wilber, et. al., found 85 percent of cyclists to be suffering with one or more overuse injuries with the following distribution: neck (48.8 percent), knee (41.7 percent), groin and buttocks (36.1 percent), hand (31.1 percent) and back (30.3 percent).1     While overuse injuries of the foot, ankle and leg are not as common, they can have an impact on the cyclist. Sports medicine podiatrists are commonly called upon to consult on cyclists’ lower extremity injuries, especially those injuries that have defied diagnosis and those that have not responded to initial conservative treatments.     Since overuse injuries in cycling can result from many causes and are often multifactorial, a thorough evaluation of the cyclist is paramount. Comprehensive evaluation of the cyclist includes a patient history, physical exam, an equipment check and cursory evaluation for proper bike fit. Video analysis can be helpful to evaluate cycling technique but it is usually not necessary in the initial evaluation. By systematically evaluating the cyclist, one can determine a definitive diagnosis and the exact cause(s) of the overuse injury.     The patient history can uncover training errors, identify environmental factors and reveal systemic disease. The physical exam localizes the problem and identifies biomechanical faults and muscle imbalances. An equipment check ensures that the bicycle and shoes are appropriate for the patient and in good working order. Evaluation for proper bike fit is often overlooked in the clinical evaluation process but one should consider it, especially in patient/cyclists who have persistent symptoms despite attempts at initial treatment that has been ineffective.     The goal of the sports medicine podiatrist is to ensure that the cyclist has a reasonably good fit to the bicycle as this will enhance comfort and decrease the potential for injury. If there is any concern about bike fit being an issue in the evaluation process, a professional who specializes in bike fitting can always perform a formal bike fit analysis at a later date. Bicycle fitting has become a highly specialized field with special measuring systems and equipment developed to aid in the process.

How To Assess Frame Size

    There are several key factors to consider in doing a cursory bike fit evaluation. By considering each of these factors and making appropriate adjustments as necessary, one can help optimize patient comfort and efficiency on the bike.     Frame size. One should consider this factor, especially if it is obvious during the initial observation that the bike frame is either too large or too small. Two methods of determining proper frame size include crotch clearance and use of the inseam measurement to determine seat-tube height. Crotch clearance applies to most road bikes with a horizontal top tube. (This method will not work for bikes with angled top tubes.)     While patients straddle their bike in bare feet, there should be at least 3/8-inch to 1 inch of clearance between the top tube and the cyclist’s crotch. On most road bikes, one can measure frame size in terms of seat-tube height from the center of bottom bracket to the top of seat tube. This is called center-to-top or c-t sizing. To determine seat-tube height, measure the inseam height. Have the cyclist stand barefoot with his or her back against a wall and his or her feet 6 inches apart. Place a book between the legs and push it firmly up into the crotch area to simulate saddle pressure while riding.     Record the distance from the top edge of the book to the floor in centimeters as the inseam height. When you multiply the inseam height by 0.67, the resulting number is the frame size in terms of the seat tube height (Bike frame size (cm) = inseam height (cm) x 0.67). Accordingly, if the inseam is 86 cm, then the patient will probably fit a 58 cm road bike (86 x 0.67 = 58 cm). For fitting a mountain bike, subtract 10 cm and convert to inches to give an estimate of mountain bike frame size (58 - 10 = 48 cm or 19 inches). If there is any question about appropriate frame size, then obtain more detailed measurements that take specific bike frame geometry into consideration.

What To Consider When Evaluating The Bike Seat

    Seat angle. The seat ideally should be positioned horizontal or slightly nose-up (up to 3 degrees). This promotes a stable base for the cyclist. Confirm this by placing a level on the seat. Nose-up positions can cause pressure points in the crotch area. A common misconception is to point the nose of the seat down to relieve excessive crotch pressure. This downward position transfers too much weight to the handlebars, affecting bicycle handling and increasing upper extremity fatigue and discomfort.     Seat height. This remains a controversial topic of bicycle fit. This is a critical factor because improper seat height can commonly lead to knee problems. People have commonly used various percentages of inseam height in order to determine appropriate seat height but these measurements can be confusing.     We recommend the following simple technique in determining seat height, which establishes a great starting point. After the cyclist assumes the riding position, place the heel of the bike shoe on each pedal and then have the rider pedal backwards. Adjust the seat height so the cyclist’s knees are fully extended at the bottom of pedal stroke (with the pedal crank in line with the seat tube and the heel on the pedals positioned parallel to ground). The cyclist then clips into clipless pedals with the forefoot on the pedal and again positions the foot at the bottom of pedal stroke in an identical manner as mentioned above. In this position, the knee should be flexed about 15 to 20 degrees. Check this position with a goniometer.     When evaluating the cyclist from a rearview while he or she rides on a trainer, the rider’s pelvis should be level. If the pelvis is rocking side to side in the frontal plane when pedaling backwards or forward, the seat is too high and should be adjusted. Once one has established the seat height, mark the seat tube with an indelible marker for easy future repositioning.     Seat fore-aft adjustment. To determine this, have the cyclist in the usual riding position with the crank arm in a 3 o’clock position parallel to the floor. Drop a plumb line (a thread with a nut on the end works fine) from the inferior patella and adjust the seat fore and aft on the seat rails until the plumb line bisects the pedal axle. This is referred to as the KLOPS (knee line over pedal spindle) position. To ensure this position is correct, we recommend the balance technique. From the KLOPS position, one can adjust the seat forward or backward to the point where riders can lift their hands off the handlebar and maintain the torso position without strain.     Cyclists should not feel like they are falling forward when they lift their hands off the handlebar. If they are falling forward, move the seat back until you have reached a balanced point. It is important to know that saddle rails are sloped. As the saddle moves forward, the seat height gets higher and as the seat moves backward, the seat height gets lower. Always recheck saddle height after any fore-aft seat adjustment.

Keys To Optimizing The Shoe/Pedal Interface

    Shoe/pedal interface. Serious road and mountain bike riders should use a dedicated bicycle shoe that offers a rigid sole. Bike shoes should fit well and have adjustment straps to aid in fine-tuning the fitting process. There are two options for maintaining the bike shoe on the pedal in the most appropriate position. These options are older style toe clips and the popular, in-vogue clipless pedal systems.     Toe clips consist of a cage and attachment straps controlling only the fore/aft position of the shoe on the pedal by using various sized cages. Clipless pedal systems involve mounting a cleat onto the bike shoe sole and then clicking the cleat of the shoe into the clipless pedal. Some pedal systems allow for rotation on the pedal and some fix the foot to the pedal in the desired position. The clipless pedal systems allow for fore/aft and side to side adjustments as well as some internal and external rotation.     Make all adjustments with the cyclist in his or her shoes with cleats loosely attached and shoes clipped into the pedals. Generally, the ball of the foot is centered over the pedal axle. Specifically, we recommend adjusting the cleat on the bike shoe so the bunion area, which is easy to identify, is directly over or up to 1 cm proximal to the pedal axle.     If the cyclist walks with a foot position that is in-toed or out-toed (for whatever reason), one can reproduce this position to some degree at the shoe/pedal interface. For an intoed cyclist, position the cleat on the shoe as far medial as possible and then internally rotate the shoe on the cleat, usually up to 10 degrees. For an out-toed cyclist, position the cleat as far lateral on the shoe as possible and rotate the shoe externally up to 10 degrees. Take care that the medial malleolus does not contact the crank arm in this position.     After establishing the desired position, firmly fix the cleat to the shoe. There are commercially available systems to assist with the shoe/pedal setup. The Fit Kit® (New England Cycling Academy) has a rotational adjustment device (RAD) that is useful in determining proper transverse plane positioning on the shoe. One can make additional adjustments to the shoe/cleat/pedal interface that include medial and lateral canting of the forefoot and buildups for limb length discrepancy. One can accomplish these adjustments within the shoe, sometimes between the shoe and cleat and rarely on the pedal itself. Address excessively everted or valgus heel positions with medial (varus) cants or wedges. Address excessively inverted or varus heel positions with lateral (valgus) cants or wedges.     One can add buildups for limb length discrepancies within the shoe up to 1/4-inch to 3/8-inch. Larger discrepancies will require a pedal or shoe sole buildup. It must be noted that accommodating limb length discrepancy for cyclists is a challenging topic and strategies to address the discrepancy depend on the level of discrepancy (e.g., femur (proximal) vs. tibia (distal)). Distal discrepancies usually require in-shoe, shoe sole or pedal buildups for the short side whereas proximal discrepancies may require asymmetric crank arm lengths in addition to shoe or pedal buildups. We have found limb length studies (sequential X-rays of hips, knees and ankles with a grid) to be helpful in determining the exact amount and level of discrepancy before deciding if and how to accommodate it.

What About The Handlebars?

    Handlebar height and handlebar reach. These are subject to comfort and personal preference. Most cyclists place the handlebar height 2 to 4 cm below the saddle height. Recreational cyclists prefer a higher handlebar height whereas racing enthusiasts will tend to lower their bars for a more aerodynamic position. Evaluate handlebar height in relation to seat height by placing a yardstick on the seat and extend it over the handlebars. One can then easily measure the difference in height.     Handlebar reach depends on top tube length and handlebar stem length. While riding with hands positioned on brake hoods, the cyclist should be able to gaze down at the front wheel and the handlebar should obscure the view of the wheel hub (center of wheel). Check all hand positions on the handlebars for comfort with elbows maintained in a slightly flexed position. If the rider constantly has to scoot forward or back on the seat, then check the handlebar reach.

In Summary

    What this article provides is a practical though efficient bicycle fit evaluation protocol that should complement conventional clinical evaluation of the cyclist. Establishing a specific diagnosis and identifying etiologic factors will dictate appropriate treatment.     Poor bicycle fit is often overlooked when it comes to potential etiologic factors that can affect clinical success. One should consider bicycle fit evaluation on all cyclist patients to some degree, especially when it comes to cases in which the diagnosis is not certain and/or initial treatment has been ineffective. Hopefully, this article will stimulate further study and research.     Dr. Bouché is a Staff Podiatrist at the Sports Medicine Clinic in Seattle. He is a Fellow of the American Academy of Podiatric Sports Medicine, a Diplomate of the American Board of Podiatric Surgery and a Fellow of the American College of Foot and Ankle Surgeons.     Dr. Vincent is a Staff Podiatrist at Washington Foot and Ankle Sports Medicine in Kirkland, Wash.     Dr. Sullivan practices in Seattle, Wash.     Dr. Caselli is a staff podiatrist at the VA Hudson Valley Health Care System in Montrose, N.Y. He is also an Adjunct Professor at the New York College of Podiatric Medicine and a Fellow of the American College of Sports Medicine.
 

References:

1. Wilber CA, Holland GJ, Madison RE, Loy SF: An epidemiological analysis of overuse injuries among recreational cyclists. Int J Sports Med 16(3):201-6,1995.
Additional References
2. Francis PR: Injury Prevention for the Cyclist: Biomechanical Approach, in Science of Cycling ed by ER Burke, Human Kinetics Books, Champaign, IL 1986.
3. Burke ER: Two Wheeled Athlete, Physiology for the Cyclist, Velo-news, Brattleboro, VT, 1986.
4. Furman A: Lower Extremity Overuse Injuries in the Cyclist, In Foot and Leg Function, Langer Biomechanics Group, June, 1990.
5. Borysewicz E: Bicycle Road Racing: Complete Program for Training and Competition, Velo-News, Brattleboro, VT, 1985.
6. Kolin MJ: Cycling for Sport, Velosport Press Seattle, WA, 1984.
7. LeMond G: Complete Book of Bicycling. Putnam Publishing, 1987.
8. Sanner WH, O’Halloran WD: The biomechanics, etiology, and treatment of cycling injuries. J Am Pod Med Assoc 90(7):354-376, 2000