Optimum traction and minimizing energy loss are factors that need to be considered for performance [5]. Matching shoe sole composition (solid rubber, gum rubber, ethyl vinyl acetate (EVA), polyurethane, etc.) and tread pattern [5, 35] (configuration, depth, orientation, etc.) to specific playing surfaces is the goal to prevent excessive sliding and/or foot fixation. Note: Due to many and varied hard court surfaces found in tennis , the shoe companies have had a difficult time adjusting their outsole materials to match these court surfaces (Personal Communication, David Sharnoff, D.P.M.).

From a performance perspective, players are willing to sacrifice injury prevention for increased traction which is a factor that must be considered. In many of the racquet sports (racquetball , squash , and handball) gum rubber has been traditionally used as the outsole material of choice. When used on a finished hardwood floor, translational traction of gum rubber is high due to an increased coefficient of friction which results in problems with “foot fixation.” This increases the potential for ankle sprains and other injuries. The importance of tread patterns is underscored when appreciating specific tread patterns that are used for certain tennis court surfaces such as grass and clay. Grass courts mandate use of a “nub” outsole design (see Fig. 23.3) whereas clay courts require a wide channeled herringbone outsole design (Personal Communication, David Sharnoff, D.P.M.).

E nergy aspects of sports shoes include two issues: how to maximize energy return and minimize energy loss [36]. The influence energy return of sports shoes has on performance is probably minimal with one study finding a 30% loss of energy input with shoe midsole materials and poor timing, frequency, location, and direction of returned energy [36]. Minimizing energy loss appears to be a more realistic focus. This can be achieved by reducing shoe weight (lighter the shoe, less energy expended), using appropriate cushioned materials to minimize soft tissue vibrations (decreases need for muscle dampening), stabilizing the ankle (limits need for internal muscle stabilization), and increasing midsole bending stiffness at the metatarsophalangeal joints (improves running economy and jumping ability [36, 37]. Note: Concerning the issue of lighter shoes, this has been a significant issue especially in tennis as the shoes have become substantially lighter at the expense of stability and support. This has resulted in a higher rate of elite professional tennis players having to use ankle braces and foot orthoses to enhance their shoes stability and support (Personal Communication, David Sharnoff, D.P.M.).

The final functional design feature for sport shoes is comfort. Although this is the most important initial factor to consider when purchasing a shoe, there are few studies available that have addressed this issue [5, 38, 39]. If a sport shoe is not comfortable, it can never truly function the way it was intended. Comfort factors to consider include fit, climate control, and various mechanical variables including skeletal alignment (heel eversion—more discomfort), torsional stiffness (stiffer—more discomfort), and cushioning [5, 37] (less cushion—more discomfort). Comfort is not exclusive, as it can influence the other design features, injury prevention, and performance. An example of this is the positive role of internal heel counters which are used to control excessive rearfoot pronation/supination as well as improve shock absorbency of heel. This feature has been touted to prevent injury and improve performance as well as provide comfort [39].

Appropriate fit is paramount to achieving comfort in a shoe. Four phases of proper shoe fit include evaluation at rest (static), standing (weightbearing), while performing activity (functional), and after activity taking into account foot swelling [40]. Matching the athlete’s foot to the appropriate shoe is based on the external shoe last (form or shape on which the shoe is manufactured) and proper sizing. Court shoe external lasts are usually inflared to a variable degree with straight lasts being less commonly found. Proper sizing is dependent on length, width, and volume of the foot. For court sports, toe box shape, depth, and construction are paramount as well. Proper ventilation is dependent on hosiery used and a variety of breathable upper and insole materials presently available.

The aforementioned discussion has focused on comfort factors that one needs to be aware of. But how does one measure comfort and how does determination of comfort affect injury prevention, performance, and shoewear choices? Michael Kinchington, a podiatrist from Sydney, Australia, submitted his thesis for his doctorate in philosophy on this very topic publishing a series of peer-review articles in the process [41–45]. He developed and studied a Lower Limb Comfort Index (LLCI) applying it to three different groups (“codes”) of footballers (Australian Rules, Rugby League, Rugby Union) [41–43]. The LLCI encompassed five anatomical areas (foot, ankle, calf/Achilles, shin, and knee plus footwear). Each area was ranked by the player on a regular basis (e.g., weekly) on a scale of 0–6 with 0 being extremely uncomfortable and six being no discomfort [41]. Dr. Kinchington concluded that this index is a reliable instrument to record lower extremity comfort in a football environment but could be applied to other sports as well [42]. A coordinated footwear management program based on comfort guidelines proved to be beneficial for injury management [44]. Poor lower extremity comfort was highly correlated to injury and was also utilized as a predictor of injury [43]. This concept has relevance for future use in sports medicine, research, and clinical practice. High comfort scores can be interpreted to be a protective mechanism for lower extremity injury.

There are specific features recommended for racquet sport shoes based on current court shoe design and research (see Table 23.1). In addition to general shoe inspection (make sure heel of shoe is straight (perpendicular to ground) and lined up well while shoe is on a flat supporting surface), there are four simple tests that can be used for evaluation of court shoes : (1) midfoot sagittal plane stability (shank stability)—bend shoe and appreciate stiffness in midfoot. It should be firm; (2) midfoot frontal plane flexibility—twist shoe as if wringing a towel. There should be good flexibility (not too stiff); (3) rearfoot stability—grasp and squeeze heel counter. It should be stiff and firm; (4) upper stability of forefoot—put your hand inside forefoot area of shoe, splay out your hand and move it back and forth in transverse plane. The shoe upper should be firm and not extend over the midsole/outsole. If shoe meets these criteria, it should be an acceptable shoe and likely a reasonable choice.

It is the author’s opinion that many court shoes available today are poorly designed and are generally disappointing in that many of the desirable features are missing. Due to this situation, the role of over-the-counter (OTC) and custom orthoses have been critical in enhancing ability of shoes to prevent injury, enhance comfort, and increase performance potential. One notable example is use of orthoses to address the generalized lack of midfoot or shank stability found in most court shoes . An orthoses can provide this needed shank stability. Another factor to consider is lack of pronation/supination stability as court shoe design is usually generic and not specific to excessive pronators or supinators as many running shoes are. Custom fabricated orthoses can complement a generic court shoe to address excessive pronatory/supinatory problems and impact loading issues. A new paradigm has been introduced to explain the efficacy of orthoses based on muscle tuning and preferred joint movement pathways [46]. These new paradigms challenge the conventional thinking on impact loading and skeletal alignment, respectively [46]. Specific recommendations for court shoe orthoses fabrication can be helpful (see Table 23.2).