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Bicycle fit
The relation between Bicycle fit and pathology in the rider.. A guide to bicycle fit for the Physical Therapist and Athletic Trainer.
Bicycle riding is a popular recreational and sporting activity. The relationship between rider and cycle is underappreciated as a source of pain and injury.
Most bicycles are "Box Bikes"... That is to say that the owner buys a bike from a bike shop that comes from the manufacturer already assembled. Thus, numerous measurements are set at a particular specification or are adjustable within a within a predetermined range by the choice of components made by the manufacturer. Depending upon the shop, the cyclist may or may not have a bike that fits.
Bike fit has numerous components, and some components vary depending upon the purpose of the rider... ( e.g. - Mountain XC versus criterium racing versus meandering down a paved surface at 8 mph)... we'll take each element of fit in turn. Today we'll only consider adults.
Before we talk about fit we have to make sure we're on the same wavelength when we describe bike parts:
Triathlon Bike Position
("aero position")
The keys to a good fit while on aero bars are few, and easy to grasp. There is now a second angle with which to be concerned, and as is the case with the hip angle above, this second angle is not an angle on a bike-but one formed by your body. Remember that line running from your hip to your shoulder? Now imagine a line from your shoulder to your elbow. This "shoulder angle" formed between your torso and upper arm also ought to be 90 degrees. Achieve this angle and you'll be comfortable. As you progress from a tri bike geometry to a road bike geometry, in general the figure above will rotate backwards as the seat angle decreases.
- Bike size: There are at least two measurement systems for bike sizes. Conventional road bikes come in cm sizing, which measurement demotes an approximation of the distance from the top of the seat tube (or top of the top tube ) to the middle of the bottom bracket. Mountain and compact road bike frames come in XS, S, M, L, XL sizes like clothes.
- Components of bike size: There are multiple components of bike size, the details of which are too complex to discuss today, but here are some of the components.
- Frame size - Commonly determined from inseam length. Approx 0.65 X inseam length.
- Seat height - 0.883 X inseam length.
- Most conventional road bikes are "square". that is to say top tube length approx equals seat tube length(=bike size).
- Seat position - position seat so bottom edge of knee cap is over spindle of pedal.
- Cleat position - If using clipless pedals position cleat so pedal spindle is under the ball of the foot.
- Crank length - Generally 170 mm for heights 68-70+, 165 for 64-67, and 175 mm for 71-74, 180 mm for >75 inches in height.
- Total top length(top tube) - highly variable. This variable depends upon torso length, seat position degree of trunk flexibility, riding experience, neck flexibility, AND specifically on the geometry of the bicycle design. just to name a few factors.
Interaction of pathology and anatomy with bike fit
As the human body varies from person to person, interaction with the bike can be come very important as causal elements for discomfort and injury. Poor fit can cause problems in direct proportion to the experience of the rider, the rate of increase in riding time, and in proportion to total riding time. A common denominator is that correcting the misfit and/or addressing the technical pathology in cycling technique and training schedule commonly results in resolution of the problem. Generally speaking, since cycling has no impact forces on the legs, many athletes with foot, knee and hip problems that limit running sports can cycle on a properly adjusted bicycle.
Beginner's (generally less than two-three years experience) problems:
- Neck pain - Generally, due to neck hyper-extension in a new, unaccustomed position. This is most marked in riders on a tri bike, when in "aero position." It is commonly related to a lack of neck and back flexibility/strength and handle bar position set too low compared to the seat height.
- Back pain - The common denominator here is a lack of core trunk strength and flexibility. Also contributing is a preferred bike position with the max hip/trunk angle less than 90°. In shorter riders excessive crank length may contribute to increased pain. Excessive seat height which causes side to side pelvic rocking with each pedal stroke is another common contributor. Unusual causes include leg length discrepancy, intrinsic hip joint pathology to include arthritis or dysplasia, Osgood Schlatter's. SIJ discomfort is another pathologic outcome occurring from the same causes.
- Hip pain - Hip pain is a difficult nut to crack in beginning cyclists. Causes include lack of flexibility at the hip in flexion/extension, psoas impingement from excessive hip flexion, induced forces at the hip from the recent change to clipless pedals. Piriformis syndrome can also result from use of these pedals, especially in patients with tibial torsion and/or genu varus deformity. This occurs as the pedal holds the rider's foot in a fixed position, which is not his anatomically correct position. The piriformis is then "trying" to pull the leg back into the externally rotated position that allows for the torsion or valgus. When the "attempt" is not allowed, pain and dysfunction of the piriformis and other external hip rotators results.
- Knee pain - Knee pain in a cyclist has many causes. In a beginner, the history may give a clue to the etiology. New cycling activity from a starting position on the couch to 100 miles/week may be just an acute overuse syndrome. This can be exacerbated as beginning cyclists commonly use a low cadence with high resistance (pedaling in the big ring) inducing increased compression and shear at the knee. Pre-existing patellar chondromalacia can be exacerbated by the above phenomena. Iliotibial band tightness frequently causes lateral knee pain in cycling. These patients can be easily spotted cycling with their knees flaring in and out during the pedal stroke. As with hip pain, the use of clipless pedals ,and the ensuing artificial restraint of the foot and consequently the knee, can induce knee pain.
- Generally speaking, the slower the rider's preferred cadence, the more likely that poor bike fit will eventually induce a painful condition as the force per pedal stroke, in almost all parts of the lower extremity, is increased.
- Lower leg pain: - You can get shin splints and compartment syndromes just as well in cycling as in running sports. The type and mode of onset of pain is similar. Stress fractures due to cycling alone are rare. Almost all fractures occur from unanticipated contact with the ground.
- Hand pain: - Carpal tunnel syndrome is quite common, caused by excessive hand pressure on the handlebars. Mild cases are very common in neophytes, severe cases are rare. Causes include riding with the elbow locked, inadequate upper extremity strength coupled with a recent significant increase in riding time. Treatment includes re-examining riding position, handlebar padding( Fizik gel pads), and padded gloves. Putting the rider in a night splint may be helpful, in addition to physical therapy.
- Foot pain: - To begin to analyze the cause of foot pain in a cyclist, you must first know the type of shoes they are using in addition to evaluating the rider's foot and leg anatomy. Conventional flat pedals and tennis shoes may be the most common cause of foot pain, due to the lack of support of the shoe and localized pressure from the pedal. The introduction of clipless pedals introduces a whole new potential for pathology.
- Generally speaking, clipless pedals have completely stiff soles, and a more or less fixed attachment to the pedal while cycling. The most common injuries in the beginning cyclist from the use of clipless pedals are road rash and fractured clavicles from failure to "clip-out" when stopping!(Severe damage to the ego is a concomitant injury here.) On the other hand, the use of the clipless pedal will allow many riders to cycle with a fractured metatarsal or with arthritis in the intrinsic joints of the foot completely without pain. Anomalies in the lower extremity, especially foot pronation and supination, tibial torsion, genu valgus/ varus deformity can be a mechanism to induce pain due to fixation of the foot in an unnatural position during the pedal stroke. Plantar fasciitis can be caused or exacerbated by having the cleats too far forward on the shoe. Moving them back toward the heel can have a dramatic effect on that rider's comfort by reducing tension in the plantar aspect of the foot.
As with shoes, the use of insoles, orthotics, wedging devices generally placed between cleat and shoe base, pedal spacers, pedal risers, and even cleat design and crank length can be used to resolve the pathological components of forces created by pedaling to relieve or prevent pain and injury. The approach is the same as that used to diagnose the foot and prescribe orthotics. It is just that you have a few more tools at your disposal.
- Perineal and ischial tube issues: - Sitting on a bicycle seat is an acquired skill. The two problems are pressure and friction. Friction is treated by utilizing appropriately designed garments without raised central seams, a comfortable pad and liberal use of lubricants designed for bikers to reduce friction. There are an abundance of products on the market for this purpose. Extreme contact can lead to actual sores. A rapid increase in riding or "seat time" is a common denominator.
Pressure complaints are also common. Beginners often opt for a relatively upright position, thereby increasing pressure on the perineum and ischial bones. The solution may, in fact, be a narrower seat rather than a wider one if ischial tube discomfort is the problem. Also, many seats are now made with "cut outs" for male and female genitalia. Male riders who spend several hours in the saddle will complain of perineal numbness (in bike speak "numb nuts") which, in addition to being uncomfortable, can interfere with sexual performance. Those riders will need to investigate a more comfortable saddle and frequently stand up to pedal, relieving the pressure. There is no substitute for a gradual increase in "seat time". It is not uncommon for veteran cyclists to have an entire box of saddles that they have tried and discarded.
Problems with intermediate and advanced cyclists:
As cyclists push the envelope of performance, especially in competition, they are more likely to suffer significant injury. Trauma is much more common in road racing and mountain bike racing, although helmets are now required almost universally in competitive events, which has significantly reduced the incidence of intracranial but not facial injury. Road rash with attendant hematomas and contusion of the underlying muscle is the most common injury. Fracture of the clavicle is the most common fracture. Time trial cycling is associated with less trauma and more simple overuse syndromes.
For each of the categories listed above, the experienced cyclist is more liable to have a subtle bike fit problem that only causes problems with a recent increase in cycling activity. Some idea of the scope of the problem can be gained from the knowledge that some training regimes can extend to 500-600+ mi/week, or 25-35 hours or more on the bike per week!
Overuse syndromes then begin to appear in myriad ways and become the dominant manifestation of poor bike fit or subtle problems with technique, especially if the cyclist takes no rest periods. Cyclists may have spent very considerable funds (~$100-$500+) having a "professional fit" from a popular source and may then be correspondingly less willing to change. However, recent changes in bike position and/or equipment may provide the essential clue to new- onset pain.
Overuse injuries are more common with year to year increase in training hours. Beginners may tolerate an increase in the range of 15-20%. An elite athlete may not tolerate more than a 5% increase without a vastly increased risk of injury. Increases in training intensity have corresponding risks.
Cramping and DOMS are common in competitive cyclists, especially in hot weather. Immune suppression from overtraining begins to occur with increasing frequency as training volumes increase. In advanced amateurs and professionals, as a therapist you must remain cognizant of the possibility of performance enhancing drug use as a potential factor in chronic injury.
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