Although cycling can provide impressive exercise benefits, a lack of proper bike fit can lead to adverse biomechanical effects for the lower extremity. Accordingly, this author provides an overview of bike fit adjustments, discusses keys to correct footwear choice and positioning, and summarizes the benefits of working with a bike fitter.
The triathlon is one of the fastest growing sports in the United States with many races selling out months prior to the event. Some popular events such as Ironman Florida and Ironman Lake Placid fill the available number of registration slots on the day the race registration opens, one year ahead of the actual race. Many runners are moving to the sport as a progression from road races and see it as a natural extension of the spinning or cycling that they were already doing as cross-training for the running races.
The addition of a bike to an exercise program can provide great cross-training effects, improvements in strength and flexibility, and a way to supplement cardiovascular fitness without the impact and pounding of running. A bike can also be a means of relative rest in a running program.
Even though the bike can be beneficial for improving performance and overall fitness, it does come with potential pitfalls. It is important for the athlete to have at least a basic bike fitting. Local bike shops often perform this service as part of the purchase of a bike.
More extensive fittings may include careful measurements of joint kinematics, segment lengths and sometimes even videotaped imaging while one is riding on a stationary trainer. This is to evaluate motion of the hip, knee and ankle in multiple planes while locked into the bike pedals. The assessment also includes an off-the-bike prior medical history of any injury or limitations in motion. On the bike, the bike fitter would measure, evaluate and adjust positioning of the foot, ankle, knee and hip as necessary.
There are many different bike fitting systems that are often proprietary to a particular bike company or to people who have been specially trained in that system. They vary somewhat in their measurements or philosophy of fitting. Some companies will take a number of anatomical measurements and then recommend a particular bike brand that possesses the geometry to match the anatomical measurements. Other bike fitting systems fit the existing bike to the rider. Even though there are many different ideologies of bike fitting, there are a few basic tenets that the fitting systems have in common.
The bike fit can occur with any type of bike. One can use road bikes, triathlon or time trial bikes, mountain bikes and hybrid exercise bikes for the basic fitting process.
The fit for road bikes and triathlon/time trial bikes often occurs in the same manner, but they vary in their geometry and setup. The major difference is that with triathlon bikes, the seat tube tends to be more vertical to allow the rider to lean forward onto the handlebar at a very aggressive aerodynamic angle to reduce drag. This reduction in drag can shave seconds or minutes off the race time depending upon the course distance.
When fitting a bike, it is important to remember that there are only five contact points with the bike: both feet, both hands and the seat. The seat or saddle comes in many different shapes, styles and cushioning levels. The choice of a saddle is mostly based on personal preference and is usually the result of some trial and error. In terms of bike saddles, bigger and more cushioned does not always mean more comfortable. A narrow, firm saddle that fits appropriately may be much more comfortable than a larger, softer one.
Most bike fits will start with the seat (saddle) height. The general rule is that the leg should be almost fully extended when the foot is at the bottom of the pedal stroke so the tibia is in about 30 degrees of flexion in comparison to the femur. The pelvis should be level and the foot should be in a neutral position for this in order to avoid excessive plantarflexion. One local bike fitter describes imagining mud on the bottom of your shoe and wiping your foot in a posterior direction to remove the mud. This is the appropriate position of the foot at the bottom of the pedal stroke.
The saddle height and 30 degrees of tibial flexion are somewhat variable among riders of different sizes and also different riding styles. However, this height provides a good starting point that one can adjust in the future.
Adjusting the bike saddle height may be the most important aspect of the bike fit and may play the biggest role in injury prevention. Having the seat too low will place a significant amount of pressure on the knees and place them in an inefficient position to help apply pressure to the pedals. This is why many people with a seat that is too low are struggling up hills or moving slowly on flat ground.
After setting the saddle height, one would proceed to address the fore/aft or front to rear positioning of the saddle. Most fitting systems will use some variation of looking at the position of the front of the knee to the metatarsals or to the spindle that attaches the pedals to the crank arms. Historically, bike fitters used plumb lines to measure the position of the front of the knee relative to the foot. Now bike fitters may use lasers to do this measurement.
Then one would move the seat forward or backward to place the knee in the appropriate position over the foot. Sometimes, due to short femurs, the bike seat cannot move far enough forward to place the knee forward enough over the foot. When this occurs, one may exchange the seat post for a seat post with a forward bend to push the seat farther forward or exchange the saddle for one with longer rails.
The reverse also holds true for long femurs that may put the knee in a position that is too far forward.
The next part of the bike fit involves finding the appropriate size handlebars, which are usually around shoulder width. The height of the handlebars will vary greatly and is usually tied to riding style. Faster, more aggressive riders or racers will tend to have the handlebars lower, often below the level of the seat. Less experienced and less aggressive riders, or those riding long distance bike tours, will often set the handlebars higher to achieve a more upright riding position.
The setup of the handlebars may slightly alter the saddle height and fore/aft positioning as there should only be slight pressure on the hands when fit appropriately. Excessive pressure on the hands quickly leads to pain during a ride lasting a couple of hours.
To complicate things further, handlebar height may vary during a given season. Early season rides may have a more upright posture but as the season progresses and flexibility and strength improve, the handlebars may drop to a lower position for more aggressive riding by the end of the season. In addition, too much of a forward lean may also place excessive strain on the lower back.
Pain in the knees and feet are two of the more commonly reported complaints in cycling. One can relieve anterior knee pain by moving the saddle slightly higher and in a more posterior direction. Posterior knee pain may respond to dropping the saddle lower and in a more anterior direction. Medial and lateral knee pain are often a result of foot position, and can be affected by the pedal to bike shoe interface.
Subtle offsets here can make huge impacts at 50 or 60 miles, and thousands of leg rotations into a bike ride. This is where shoe positioning on the pedal and cleat placement become very important.
In general, the rider should place the bike shoe on the pedal in such a way that a vertical line dropped from the tibial tuberosity would intersect the foot at the level of the pedal spindle. This should be around the first metatarsophalangeal joint for most people and is a good starting point.
Sprinters may move their foot position back so the pedals are farther forward toward the toes. Touring, long-distance cyclists may slide the pedal slightly farther back. Achilles tendon pain may be the result of the cyclist placing the pedal too far forward on the shoe and moving the pedal to a slightly more posterior position may relieve this pain.
Some cleats allow for medial and lateral shift of the cleat on the bike shoe while others only allow fore/aft displacement. Typically, the cleat should be relatively centered under the bike shoe. One may address lateral knee pain that occurs during riding by moving the cleat medially and address medial knee pain by moving the cleat laterally. The knee should track directly over the foot. If the knee is tracking outside the midline, then one should move the cleat laterally. The reverse is true if the knee tracks inside the midline.
Rotation also plays a role in appropriate bike fit. This is referred to as float. The alignment of the cleat on the shoe plays a role in the amount of pressure that the knee experiences. A good fit will keep the knee tracking straight. This can be somewhat tricky to identify with a short ride on an indoor trainer during the setup process. What feels fine for a few minutes on the trainer may not feel well over a couple of hours and 40 or 50 miles. To accommodate for this, there is some amount of internal and external rotation (float) that is available within the pedal.
Some cleats such as Look (Look Cycle USA) come in fixed floats of 0, 4.5 and 9 degrees. Speedplay (Speedplay, Inc.) cleats allow up to 15 degrees of float with some models allowing the rider to customize the amount of float to his or her comfort level.
In addition to internal and external rotation, varus and valgus tilt can also cause problems on the bike. This can manifest itself in either knee pain or foot pain. If there is a significant genu valgum, the knee fixed onto a bike cleat may cause the knee to track inappropriately. Adding a varus wedge between the cleat and the shoe may realign the knee.
If the genu valgum and tracking problem are the result of a pronated foot, a posted orthotic may alleviate the problem. Similar shims are also available for riders to place between the cleat and the shoe to accommodate a limb length discrepancy.
Anyone who has ridden extended distances or even century rides (100 miles) will tell you things that feel fine at the 30-minute mark may not feel so fine at the three-hour mark. This is most true in the feet. Subtle problems in shoe fit or mechanics will show up over time.
In addition to setting the rotation and position of the cleat on the shoe, one must consider the shoe fit itself.
Cycling shoes usually have a stiff plastic or carbon sole that has very little flex. Flex becomes wasted energy and prevents full transmission of power to the pedals. The shoe should fit snugly and is secured by a variety of methods, but more commonly two or three straps across the midfoot. The heel should be locked into the shoe and not rise out of the shoe with the pedal stroke. Many of the shoes run slightly narrow but some shoe lines such as those made by Bont and Sidi America (with their Mega versions) offer some wider fitting shoes.
This is important as narrow shoes over time during a ride may produce neuroma-type symptoms that the person may not normally possess. The majority of shoes come with only a very thin felt liner. There have been significant changes over the past few years with the emergence of customizable insoles or heat moldable shoes to allow more of a custom fit.
Custom fit of the shoes may include simple modification of the stock liner with a metatarsal pad, the addition of an over-the-counter orthotic or the insertion of custom-molded orthotics into the shoes. If you choose to add a custom orthotic to a cycling shoe, remember that less is more. There is already a snug fit to the shoe and even with removal of the stock liner, there is very little room in the shoe for an orthotic.
Your typical running shoe orthotic usually will not fit in the cycling shoe or if it does, the patient’s foot will not. The cycling orthotics are usually made from an intrinsically posted graphite plate.
The addition of extrinsic rearfoot posts may push the heel up and cause heel slippage while riding. The graphite keeps the orthotic thin and does not take up too much room. Graphite is also in use because high-level cyclists tend to discuss weight in terms of grams, not pounds. Many of the cyclists find that this type of orthotic works well in the cycling shoe and serves a dual purpose of fitting very well in ski boots.
When evaluating potential injuries related to bike fit, it can be very beneficial to work with an experienced bike fitter at the local bike shop. The combination of the bike fitter’s knowledge of bikes and the fitting process, and your medical knowledge can be a real asset to the cyclist patient.
One should follow up the initial bike fit in a few hundred miles of riding for re-evaluation and fine-tuning of the fit. Subtle changes may occur at that point to really dial in the fit to the needs of the rider, whether it be more comfort, protection of an injured body part or for more speed in a racer.
Local bike shops are also a potential untapped sports medicine referral source for those who understand the basics of bike fit. You do not need to be an expert bike fitter. Just being able to understand the basics of bike fitting and converse accordingly can be beneficial for bike riding patients and possibly increase referral of those patients to your practice.
Dr. Corwin is an Associate of the American College of Foot and Ankle Surgeons. He is board certified in foot surgery and rearfoot/ankle reconstructive surgery by the American Board of Podiatric Surgery, and is in private practice in Media and Phoenixville, Pa.
For further reading, see “Bike Fit Evaluation: Can It Help Diagnose And Prevent Cycling Injuries?” in the December 2006 issue of Podiatry Today, “Secrets To Treating Bicycling Injuries” in the August 2005 issue, “Essential Keys To Treating Triathletes” in the June 2009 issue or “Treatment Tips For Common Triathlon Injuries” in the October 2002 issue.