Fig. 22.1
Clipless pedal and cleat on outsole of shoe for road cycling
Fig. 22.2
Clipless pedal and cleat on outsole of shoe for mountain biking
Pedaling Technique
Competitive cyclists strive for an efficient circular pedal stroke that involves not just exerting a downward force during the first half of the stroke but also sweeping the foot backward at bottom dead center, pulling through the second half of the pedal stroke and then pushing the foot forward through the top dead center. This circular pedaling technique has long been presumed to be the most efficient; however there is not any scientific data that confirms this presumption. In fact, one group of researchers, after testing cyclists with four different pedaling techniques, found that cyclists were most metabolically efficient when pedaling in their preferred pattern [13].
Pedaling technique is almost as varied as running technique. Some cyclists may be “mashers” meaning that they ride in low gears at a low (40–60) rpm and exert force only during the downward portion of the pedal cycle. “Spinning,” a technique using higher gears and higher rpms (80–100+), has been advocated as a more efficient pedaling technique but research does not confirm this. Some cyclists attempt “ankling,” a technique where the ankle is plantarflexed during the power phase and dorsiflexed during the recovery phase. Just as runners and walkers self-select stride length and movement patterns to maximize metabolic economy and comfort [14], it has been suggested that cyclists will make technique, gearing, and cadence adjustments to alter pedal forces and maximize metabolic efficiency [15].
Pedaling Forces
Pedal forces acting on the foot are approximately half of bodyweight with seated pedaling and can approach up to three times bodyweight when standing, sprinting, or climbing [9]. Plantar pressures within the shoe are primarily localized to the forefoot and first ray while heel and arch plantar pressures remain low [16, 17]. Peak plantar pressure occurs between 90° and 110° of the pedal cycle [18–21]. Researchers have shown that stiffer cycling shoes increase peak plantar pressures when compared to less stiff shoes [17, 22]. Pedaling technique must be considered in injured cyclists as researchers have found that medial plantar loading increased with increased power output but decreased with higher rpm [16].
Much of what has been written on adjustments or modifications to address injuries or biomechanical faults has been described as trial-and-error processes. After selecting the proper frame size based on rider’s height, parts of the bike can be adjusted to in accordance with a cyclist’s body segment lengths. It is beyond the scope of this chapter to discuss the theory and practical applications of fitting the rider to the bicycle; however those who regularly treat cyclists and triathletes should become familiar with bike fit.
Cycling Injuries and Risk Factors
Risk factors for overuse cycling injuries include training errors, poor pedaling technique, improper bike fit, anatomical malalignment, biomechanical faults, muscle imbalances, and inadequate cycling equipment. For all injured cyclists it is important to evaluate training distance and intensity, other athletic activities (many cyclists cross train and/or weight train), bike fit, anatomic factors such as muscle imbalances, lower extremity biomechanics, flexibility/ROM, limb length asymmetry, and previous injury history. As with any athlete, activity modification and symptomatic treatment are important in addressing the injured cyclist.
There is a lack of evidence-based biomechanical treatment of cycling injuries. Many experienced cycling sports medicine specialists describe anecdotal and trial-and-error treatment methods. Most authors agree that addressing faulty biomechanics is important to prevent recurrence of injury in many cyclists. Excessive subtalar joint pronation has been linked to patellofemoral pain, iliotibial band syndrome, Achilles tendonitis, plantar fasciitis, metatarsalgia, and forefoot neuritis. Limited subtalar joint pronation and cavus foot type have been linked to sesamoiditis, Achilles tendonitis, extensor tendonitis, metatarsalgia, and forefoot neuritis as well [23].
Most research on bicycling injuries is focused on the area of traumatic injuries [24, 25]. Overuse cycling injuries are just starting to receive more attention from researchers. In a survey of 473 recreational cyclists researchers found that 85% had experienced an overuse injury [26]. The knee was the most commonly injured lower extremity site ranging from 35 to 65% or riders and females reported higher incidence of knee pain than males [26–28]. Foot injuries were reported in 15.6% and ankle/Achilles injuries in 7.3% of cyclists [26]. Many cyclists report chronic discomfort especially to the neck, butt, hands, and feet related to riding which they may not classify as an injury but more as a nuisance or discomfort.
Cycling Footwear
Cycling shoes, like other types of footwear, have become increasingly specialized. Since the shoe is only a part of the foot/shoe/pedal interface, this section also discusses cleats and pedal systems.
The perfect cycling shoe transmits energy efficiently to the pedal yet distributes forces evenly, dampens vibration, does not bind the foot, and allows heat/moisture dissipation while offering resistance to weather conditions. Sport-specific cycling shoes combined with a cleat and pedal system have been shown to increase pedaling efficiency [18]. Unlike many other sports where shoes are selected for fit, comfort, and biomechanical considerations, cyclists must select their footwear based on the type of cycling they participate in (road, touring, mountain), and type and brand of pedal system they will use, and then select the shoe with appropriate fit and comfort for their foot. For cyclists who choose to use a clipless pedal system, once they have purchased shoes they must then purchase cleats and attach the cleats to the shoe’s outsole with bolts.
The unique structural features of cycling shoes are the stiff midsole/outsole and the cleat holes. Efficient energy transfer from the foot to the pedal is optimized with stiff materials [3]. Manufacturers of cycling footwear use rigid materials in the midsole/outsole for its ability to resist longitudinal as well as torsional bending. Less expensive and recreational cycling shoes are often made with plastics. More expensive and racing-oriented cycling shoes are made with carbon fiber composites which are lighter and more rigid. The more rigid materials have also been shown to increase peak plantar pressures in cyclists which have implications for those who experience foot pain [22].
The conflict that some cyclists encounter with cycling footwear is that structural features designed to enhance performance such as snug fit and stiff outsoles have also been linked to decreased comfort and foot pain. Some cyclists who experience significant foot pain or discomfort may benefit from less performance-oriented but more comfortable footwear. Some researchers have found that a lack of comfort negatively affects performance and increases the risk of injury [29, 30].
Cycling Shoe Fit
Much like skiers and skaters, competitive cyclists will fit their shoes to be snug so that there is minimal motion of the foot inside the shoe and maximal energy transfer to the shoe interface. Recreational cyclists are more willing to make performance allowances in favor of comfort and walkability. Ideally, the cycling shoe is snug in the heel and midfoot to minimize wasted motion and provides adequate forefoot length and width to minimize discomfort. Allowances in toe room are common to accommodate foot edema experienced in weight-bearing endurance sports like running but research has shown that cyclists do not increase foot volume due to edema at shorter intervals of cycling activity [31]. As with any footwear there should be minimal side-to-side pressure at the widest part of the foot which usually corresponds to the first metatarsal phalangeal joint and fifth metatarsal phalangeal joints of the foot. The midfoot fit should be snug without creating pressure. Cycling shoes that are too loose in the midfoot will cause the cyclist to compensate by overtightening the closure system which may result in discomfort or dorsal foot injury. Heel fit of cycling shoes should not allow pistoning of the heel inside the shoe.
Some brands of cycling footwear are available in wide sizes and recently custom cycling shoes have become easier to find. Manufacturers are starting to introduce off-the-shelf shoes that can be heated and molded to the heel and arch. In addition, some manufacturers have started to offer shoes made on women-specific lasts.
Cycling Shoe Construction
Cycling shoe construction is discussed below. Three general categories of cycling shoes will be described: road, sport, and mountain biking shoes (Fig. 22.3).
Fig. 22.3
Sport shoe , mountain bike shoe, road shoe
Road Cycling Shoe Construction
Like ski boots, road cycling shoes are not made for walking. The rigid sole and external cleat allow for only minimal walking. They are designed to be light, stiff, snug structures that allow the nonweight-bearing foot to transfer force efficiently to the pedal while minimizing wasted motion of the foot within the shoe.
Last
Road cycling shoes are lasted much like track spikes, on a curved “performance” last with a board-lasted footbed. Performance lasts provide a low-volume, snug fitting upper and are narrower than conventional lasts. The board last combined with the stiff midsole/outsole provides rigidity for maximal energy transfer.
Upper
The road shoe upper is typically made of a fabric mesh, leather, and/or synthetic materials that allow for maximal ventilation. A rigid heel counter is incorporated to minimize rearfoot motion. The shoe’s upper is secured to the foot with laces, ratchet-style buckles, Velcro straps, cable and rotary dials, or a combination thereof. The tongue is padded to distribute pressure of the closure system on the dorsal foot. High-performance racing shoe models will have a shroud or low-profile closure system to minimize wind resistance. Triathlon cycling shoes are road cycling shoes with simpler closure systems (such as a single Velcro strap) to allow for quick entry/exit. They usually have a seamless or fabric liner since some triathletes prefer to cycle without socks.
Footbed/Insole
Most cycling shoes are now made with removable insoles which can vary in quality and features. Many resemble the footbeds found in running shoes and may be made from closed cell foams or ethyl vinyl acetate and have a wicking fabric top cover. More expensive models may incorporate arch support, metatarsal support, or plastic shells.
Midsole/Outsole
In order to minimize weight and maximize stiffness, the midsole also serves as the outsole in road shoes. High-performance road shoes are made with the lightest, stiffest materials such as carbon fiber composites. Recreational road shoes use nylon which is still relatively stiff but heavier and less expensive than carbon fiber. Some cycling shoes incorporate the heel counter into a one-piece midsole construction. This helps lend significant stiffness to the shoe while minimizing weight. One manufacturer has introduced shoes that incorporate a forefoot varus wedge of 1.5° into the outsole [32]. The performance road cycling shoe outsole typically curves in the sagittal plane. This outsole shape slightly dorsiflexes the digits and, when the cleat is engaged with the pedal, facilitates plantar flexion of the ankle (Fig. 22.4). Most road cycling shoes are compatible with external cleats that attach the shoe to a pedal much like a binding attaches a boot to a ski. Road cycling shoes come with predrilled holes in the forefoot for placement of the external cleats. This exposed cleat design raises the foot off of the pedal and makes walking in road shoes difficult (Fig. 22.5).
Fig. 22.4
Road cycling shoe engaged with pedal
Fig. 22.5
Road shoe with external cleat
Outsole
Some road shoes may have small rubber bumpers on the toe and heel for walking traction. In an effort to remove every last gram of unnecessary weight, racers often remove the bumpers.
Sport Cycling Shoe Construction
“Sport,” “trail,” “fitness,” “touring,” and “recreational” are all terms used for cycling shoes that tend to be more comfortable than road shoes yet also allow attachment of recessed cleats. They are designed with less emphasis on performance and more emphasis on comfort and walkability. Unlike road cycling shoes which are too rigid and have an external cleat which makes it almost impossible to walk, this category of cycling shoe is easier to walk in. Sport cycling shoes are usually heavier, less aerodynamic, and more flexible and may have little to no sagittal plane curve when compared to road shoes. This category of cycling shoe is popular with commuters, casual riders, cycle tourists, stationary fitness class participants, and those who simply cannot comfortably wear road shoes. Sport cycling shoes also may accommodate certain types of custom orthoses better than road shoes.
Last
Sport cycling shoes are lasted on semi-curved or semi-straight lasts much like walking and hiking shoes. The conventional last provides more width and volume than that found in road shoes. Most have a board last to provide some stiffness and torsional resistance.
Upper
Uppers are constructed of mesh fabrics, and leather or synthetic materials. Most sport cycling shoes use laces but some have Velcro straps, buckles, or a combination of closure systems. Plastic heel counters are incorporated into the upper along with a padded collar and tongue. The uppers often resemble hiking or walking shoes and in fact are often indistinguishable. The larger volume upper of recreational cycling shoes makes them a better choice for those with exceptionally wide feet, or those who are uncomfortable in the stiff, snug road shoes.
Footbed/Insole
Like road shoes, most sport shoes now come with a removable insole that may incorporate padding, metatarsal, and arch support. Some footbeds offer minimal protection from the cleat bolts in the forefoot.
Midsole
Some sport shoes incorporate a polyurethane midsole to provide additional cushioning and walking comfort and may have a dual-density midsole as well. Some sport shoes will reinforce the midsole with fiberglass to lend more rigidity.
Outsole
Sport cycling shoes are constructed with carbon rubber outsoles and can be used with or without a recessed cleat (Fig. 22.6). The outsole is stiffer than a conventional hiking/walking shoe yet still provides traction and versatility when off the bike and is significantly less stiff than a road cycling shoe. Outsoles may come with predrilled bolt holes for cleats or may have a section under the forefoot that can be removed for placement of recessed cleats. The recessed cleat design protects the cleat from debris and makes walking much easier than road shoes.
Fig. 22.6
Outsole of sport shoe without cleat
Mountain Biking Shoe Construction
Mountain biking (MTB ) shoes are also popular for their comfort but have other unique features since mountain biking often requires cyclists to dismount their bikes to navigate obstacles such as logs, rocks, or streams. For this reason, MTB shoes have a more aggressive outsole traction design, a recessed cleat, and a rubberized sole for traction during walking. Some MTB shoes may be considered a hybrid of road and sport shoes —combining the performance features of the road shoes and for some the comfort features of the sport shoes. Within the category of MTB shoes there are shoes geared more for racing and competitive riders and those for more recreational MTB riders. Racing MTB shoes often resemble road shoes with recessed cleats and rubber outsoles while the recreational MTB shoes are more similar to the sport cycling shoes. The recessed cleat is protected from weight bearing and is less vulnerable to damage or to picking up debris such as mud like the external road cycling cleat would.
Last
Competition MTB shoes are lasted on a performance board last like road shoes but recreational MTB shoes will offer a standard curved or semicurved board last.
Insole/Footbed
Like road and sport shoes, most MTB shoes now come with a removable insole that may incorporate padding, metatarsal, and arch support. Some footbeds offer minimal protection from the cleat bolts.
Midsole
The midsole of an MTB shoe may be made with stiff nylon, fiberglass, or carbon graphite. Some shoes will use a polyurethane midsole reinforced with a plastic or fiberglass plate for stiffness.
Outsole
Rubber sheet or studs: MTB shoes have threaded bolt holes drilled through the outsole for placement of a recessed external cleat (Fig. 22.7). Most MTB shoes have a rubber outsole with a rectangular rubber window that can be removed so that a cleat can be added to the shoe if the cyclist chooses. Toe-and-heel spikes may be found on the outsole of racing MTB shoes. The spikes resemble those found on soccer or football spikes and provide traction in mud. Some models have removable spikes.
Fig. 22.7
MTB outsole with recessed cleat
Selecting the appropriate type and model of shoes is only a part of the decision making process for many cyclists. Many will then purchase a cleat and pedal system as well. The interface of the shoe with the bike is via the cleat and pedal system and we would be remiss in a chapter on cycling footwear to ignore this important component of cycling. In many ways, cleats and pedals have become more technically sophisticated than the footwear.
Cycling Cleats
Cleats attach the shoe to the bike through an engineered pedal system (Fig. 22.8). The cleat/pedal interface is a single point of attachment at the ball of the foot. The cleat is attached to the sole of the shoe with bolts. The pedal is engaged by placing the cleat over the pedal and exerting a downward force until the spring-loaded pedal accepts the cleat. (One popular pedal/cleat system manufactured by Speedplay® places the spring in the cleat instead of the pedal.) Most cleats are released from the pedal by externally rotating the heel. Some cleats can be released in multiple directions. Many pedals have adjustable tension so that the force required to release the shoe can be altered as needed. For example, newer cyclists may prefer a lower tension setting for ease of exit from the pedal while experienced cyclists, like aggressive mountain bikers, may set the tension higher to minimize the risk of early release from the pedal.
