January 2013

Choosing children’s shoes: Mechanical considerations

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istockphoto.com #9283822

Children’s shoes often are designed to look like adult shoes but lack the same structural components. Perhaps not surprisingly, research has dem­on­strated that running kinematics and kinetics differ significantly between seemingly similar child and adult shoes.

By Janet S. Dufek, PhD, Dana Forrest, MS, and John A. Mercer, PhD

Much of parenting consists of making choices for one’s child. One of the many decisions to be made is what footwear, if any, is right for a child. As children grow and develop, footwear needs change, not only because the foot changes, but also because of the ways in which children’s movement changes.

Current interest in barefoot or minimal-drop footwear for active adults has led to a rethinking of footwear needs for children and adolescents. An understanding of the developmental needs of children, along with locomotor performance characteristics, may help guide in defining salient criteria to assist parents and practitioners in footwear decision-making for children.

For the purpose of this paper, it is important to note that the primary functions of the shoe include protection from the environment (e.g., scrapes and abrasions) and performance features symbiotic with gait and movement patterns during physical activity. The focus is not on leisure, but on activity.

Child foot and locomotor development

The foot of a newborn is developmentally different from the adult foot and is characterized by supination and forefoot adduction.1 During the first few months of development, plantar flexion is more readily achievable and the fat pad on the calcaneus grows thicker. Most experts agree that footwear for infants is optional; in fact, some caution that footwear at this stage may constrain growth and development.1-3 Experts also agree that avoiding shoes during infancy may help to promote tactile sense, improve balance, and mitigate negative influences on the natural development of the foot.4 When an infant approaches walking age at around one year, the need for footwear is driven largely by society as well as by safety, i.e., preventing cuts and abrasions by protecting the foot’s plantar surface.

As children grow and develop and display purposeful movement, including locomotion, footwear needs may vary; however, care should be taken to match footwear to foot structure. During the progression to standing and walking, a child’s foot shape and its loading characteristics change, and, as the child’s foot contact becomes similar to the adult form, mechanical factors vary, due to children’s walking kinematics.

For example, as toddlers begin to walk with a greater portion of the plantar surface of the foot in contact with the walking surface, maximum force and impulse production is different for children than adults.5 Toddlers walk with the hip and knee joints flexed and their legs externally rotated, which results in the center of gravity passing through the knee joint medially. Therefore, in accordance with Wolff’s Law, the differential load to the structure results in faster growth of the medial and femoral condyles than those on the lateral side,1 which helps reduce any bowlegged alignment. Through this developmental stage, the child may display a forefoot-strike walking pattern, which is typically short-lived.

Children can present with a host of foot deformities that would require specific intervention, the most common of which is pes planus.6,7 Wolf et al8 suggested that adults who present with flexible flat feet can trace the condition back to inappropriate footwear during childhood. Ligamentous laxity related to pes planus results in valgus positioning when weight bearing.

The use of training shoes, which address potential heel soreness for children donning shoes, can alleviate this problem.6 Some argue that footwear constrains natural foot motion9 and suggest the arch will develop normally without footwear.10 Most professionals do not recommend intervention for toddlers with pes planus since it is often a condition children outgrow.11

Tudor et al12 investigated the functional significance of pes planus by examining correlations between motor skill performance and arch type in adolescents aged 11 to 15 years. Their results showed a lack of correlation between sport performance and arch type, lending support to the view that arch height need not be of concern for the toddler and does not require intervention.

Child footwear

Infants don their first pair of walking shoes at an average age of 8.1 months.13 Friends and relatives, not medical professionals, typically advise parents on footwear purchases. The typical “first shoe” described in the medical literature has laces, a high top, and a hard outsole.13 Interestingly, 77% of queried pediatricians (n = 127) opined that inexpensive canvas sneakers are an adequate footwear choice, while only 37% of parents (n = 104) shared this belief.13 Experts generally suggest that shoes for infants be flexible and soft to allow for foot development.1,14

For children aged between 2 and 4 years, footwear needs include plantar protection from the environment. A soft flat-soled shoe is generally recommended.1 While 50% of parents selected infant walking shoes with arch supports,13 this feature is not generally recommended as it has potential to create a negative influence on natural foot development. Stability of the rearfoot, in the form of a high soft strap over the Achilles tendon, is advocated.1 Children become more active between the ages of 4 and 6, and footwear should reflect functional needs. The additional suggested componentry to the shoe at this phase is forefoot flexibility.1

Activity patterns for children aged 6 to 10 years continue to change, with movements becoming more like those of adults. This was demonstrated by Brown and Bates15 in a group of children aged 3 to 10 years. Lower extremity joint motion produced lower harmonics in older children than in younger children. The lower harmonics demonstrated by the older children represent the “skilled movement pattern,” whereas higher harmonics represent “noise,” or error in performance. For example, toddlers tended to project their center of gravity upward, more vertically at toe-off when walking (resulting in higher harmonics), as opposed to the more fluid pattern and more horizontal projection angle of the center of gravity seen in the older children at toe-off. In addition to lower harmonics, research has also shown that children in this older age group increase their stride length while shod compared with walking barefoot.16 During this phase, children place greater load on their heels than adults.5 Foot loading patterns tend to be asymmetrical during early locomotor development5,17 and disappear across time.

Plantar pressure patterns are child-specific, yet some children have demonstrated a somewhat mature loading pattern after a year of walking (when they are aged about 2.5 years).5 In addition, around this time, gender differences begin to appear in the foot, with boys having a wider midfoot and girls having a longer narrower foot. Outside of cosmetic differences, there is cause for developing gender-specific footwear at this age to accommodate changing foot morphology. Taking these patterns into consideration in total, footwear for this age group should consist of some degree of rearfoot cushioning and continue to provide rearfoot stability and forefoot flexibility.1 The importance of forefoot flexibility was tested empirically by Wolf et al.8 Their results demonstrated significant differences in tibiotalar range of motion as well as longitudinal axis foot torsion range of motion between barefoot and traditionally shod conditions. These differences were mitigated when a lighter shoe with a slimmer outsole and more flexible upper was worn.

By the time children reach the age of 15 years, the connective tissue has near the same integrity as that found in adults and, typically, the feet have stopped growing.1 Girls’ feet reach maturity when they are aged about 12 years; boys reach this threshold at 14 to 15 years. It is at this point that footwear components of concern become more adult-like, and the focus is generally on motion control and rearfoot cushioning. However, though children’s may be fully grown at these ages, they are not fully mature.18

Biomechanics of child locomotion

Greer et al19 conducted a kinematic and kinetic assessment of 3- and 4-year-old walkers (n = 18) while participants were barefoot. Correlations between various anthropometric measures of the children and temporal-spatial descriptors identified weak relationships, with few exceeding r = .50; this seems to suggest little relationship between body maturation and locomotor descriptors.

It is well established that the growth, development, and gait patterns of children younger than seven years are highly variable.20-24 However, Schepens et al25 observed that, in an older population of children (aged 11-13 years), gait is very similar to that of adults. It is important to remember that, even though children at this stage of development have similar gait patterns to those of adults, they are still growing and should not be considered “miniature adults.”21

Bhanot26 examined the impact characteristics of children aged 9 to 12 years running at different stride lengths. Although maximum vertical force impact peaks in adults have been shown to be influenced by stride length,27,28 children did not exhibit this difference. The authors suggested that children attenuate the force of impact in a unique manner compared with adults.

Child vs adult shoes

Figure 1. Vertical ground reaction force profile for a child running in a youth shoe for two different trials. The top graph depicts a pattern typically observed during rearfoot contact, with an initial impact peak (circled) during the initial contact phase. The bot- tom graph documents the same child running at the same speed in the same shoe. Note the absence of the impact peak during initial foot contact. The bottom profile is that which is typically observed during a midfoot strike.29

Figure 1. Vertical ground reaction force profile for a child running in a youth shoe for two different trials. The top graph depicts a pattern typically observed during rearfoot contact, with an initial impact peak (circled) during the initial contact phase. The bottom graph documents the same child running at the same speed in the same shoe. Note the absence of the impact peak during initial foot contact. The bottom profile is that which is typically observed during a midfoot strike.29

Morphologically, at some point in a child’s development, their feet can “fit” in either child or adult shoes. What are the advantages and disadvantages of selecting either shoe model? Before answering that question, it is important to note that footwear companies face many challenges when developing children’s shoes that mimic adult models. For example, there are practical marketing concerns, including the relationship between base costs of production versus sales volume. It is not unusual for developers to retain shoe molds over time and make only cosmetic changes to the uppers. From a manufacturing and marketing perspective, one needs to be mindful that products are often made available with an eye toward corporate fiscal responsibility.

When a shoe model is available for both children and adults, it is important that consumers be aware of the structural and component differences between shoes. Consumers can only achieve this by consulting footwear professionals and by closely examining comparative products to make an informed decision. For example, because of the marketing-driven constraints, as well as production costs, it is likely that some features of the adult model shoe will not be present in the child model.

Forrest et al29 examined the impact characteristics of girls aged 11 to 13 years running in adult and children’s styles of the same shoe. Although both shoes were considered the same style, they differed in their construction in a number of ways. The adult model had a bit more cushioning, a full lightweight and durable midsole with an additional premolded crash pad, and a solid thermoplastic polyurethane (TPU) shank to control torsional rotation through the midfoot. The children’s model had a one-piece midsole construction with no additional cushioning in the crash pad (it was just painted to appear that way). The TPU shank was also painted on the shoe, but not evident as a functional component. Mechanically, impact test results showed significant differences between shoes.29 Likewise, researchers observed a greater loading rate while children ran in the children’s shoe compared with the adult shoe.30

Forrest et al29 concluded the adult model was the better choice for reducing impact forces that could be associated with overuse injuries. The relationships between the initial vertical ground reaction force peak—and time to its occurrence (loading rate)—have long been associated with lower extremity injury in running,31-33 though this is not definitively “proven.” Bredeweg and Buist34 have challenged this belief. They examined injured versus noninjured novice runners and did not find significant differences between groups in vertical impact force or loading rate, thus concluding there is no causal relationship. Their work has not yet been replicated.

In addition to the impact results reported by Forrest et al,29 an interesting phenomenon was observed for some child runners. Independent of the footwear worn, some children produced different vertical ground reaction profiles within a single shoe condition. Specifically, there were running trials where a “typical” impact peak was produced (Figure 1, top) and other running trials where this impact peak was not apparent (Figure 1, bottom). This observation may suggest that the children were variable enough in their running performance that they changed foot-strike pattern within footwear.30

This observation is significant as manufacturers are developing contemporary footwear to accommodate various foot-strike patterns.35-37 An adult runner wearing the current minimal-drop shoes will typically perform with a mid- or forefoot strike pattern.37,38 This vertical force profile could be similar to that produced by children running barefoot.19,26,39 The observed variability in the children’s running kinetics may mean the subtle differences between child and adult footwear may be less of an issue in selecting appropriate footwear.

Conclusion

This review provides an overview of shoe-related research addressing child foot morphology and development, with an emphasis on identifying salient age-appropriate footwear characteristics. The biomechanics of child gait is complex and variable, and the most appropriate choice of footwear is not always clear. It may be wise, however, to select a shoe that does not interfere with the foot’s natural development and that also provides appropriate protection and sport-related performance characteristics. It should be noted that appropriate fit is an underlying construct that must be embraced during all phases of child development.

Janet S. Dufek, PhD, is an associate professor of kinesiology at the University of Nevada, Las Vegas (UNLV). Dana Forrest, MS, is a footwear developer at Brooks Sports in Bothell, WA. John A. Mercer, PhD, is an associate professor and associate dean of the School of Allied Health Sciences at UNLV.  

REFERENCES

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38. Lohman EB 3rd, Balan Sackiriyas KS, Swen RW. A comparison of the spatiotemporal parameters, kinematics, and biomechanics between shod, unshod, and minimally supported running as compared to walking. Phys Ther Sport 2011;12(4):151-163.

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One Response to Choosing children’s shoes: Mechanical considerations

  1. I love this article it will help me as I develop our new line of children´s shoes! Thank you for sharing this with the reading public!

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