Recent studies in shoe- and sports-research

How much toe allowance do children’s shoes need? A review by Annette Switala

How much toe allowance do children's shoes need? Do high heels cause musculosceletal changes? How reliable is the comfort assessment of athletes? These are the questions of recent studies summarized in the following reviews.

The correct determination of the toe allowance in children’s shoes is crucial for a healthy development of children’s feet and for the shoes’ functionality. How much toe allowance is needed for a healthy development of children’s feet has only been scientifically examined by few studies – the current implementation is based on practical knowledge.
Often the rule-of-the-parent’s-thumb is used to determine the toe allowance in children’s feet. According to this method the children’s feet should have as much space in front of the toes as the parent’s thumb width. Further methods to determine the correct shoe length were developed in the 1960s and 70s by a German consortium of manufacturers and researchers (Arbeitskreis Kinderschuh). The guideline developed by this consortium managed by Erne Maier, AK64-WMS, recommends at least 12 mm. Maier proposed to determine the toe
allowance from the respective shoe size according to EU standard divided by two, assuming that longer feet require more toe allowance than shorter feet.
Stracker thought that the toe allowance depended on the foot length, the ligaments and the muscle tone. He suggested fixing 5 % of the footlength for the toe allowance (1966). Schmidt (1989) however felt that feet of younger children grew faster and concluded that younger children needed more toe allowance than older ones. So far there has not been a scientific evaluation of all of these recommendations.

The study [1] was supposed to evaluate scientifically how much toe allowance there should be in children’s shoes. Here also the correctness of the previous methods to determine the toe allowance was to be evaluated. Also it should be considered if the toe allowance depends on the children’s gender, footlength or weight.

Patients and methods
The toe allowance was considered in this study to be the sum of the growth rate, foot extension and walking advance (calculated on the base of the anterior point of toes).
2554 children, aged between 6 and 16 years, were examined with a new scanner system, allowing the three­dimensional capture of the change in the footshape when walking. The scanner system captured the static and the dynamic footshape. One foot of each child was randomly defined and measured during standing with half weight-bearing. The load distribution was captured with flexed and subsequently extended knees. Age, gender, body weight and size were documented.
The body mass index was calculated. The average data of three dynamic measurements were used for the calculation of the foot extension and the walking advance. The foot extension was determined at the medial ball length, defined as the distance between the most posterior point of the heel and the most medial spot of the metatarsal-1-head. The growth rate was calculated with the help of a cross-sectional analysis.
With the help of a linear regression analysis the impact of gender, footlength and medial ball length on the toe allowance was calculated.

The foot length of boys did not increase after the age of 15 years, of girls not after the age of 13 years. The highest growth rate of boys and girls was found between 7 and 8 years and also of boys between 10 and 12 years. The increase of the footlength however strongly varied individually. The footlenght of boys aged 6–14 years increased from 2.5 to 5.6 mm. The girls had similar values. The values of the foot extensions also differed considerably individually, whereas the ones of the walking advance were similar.
The mean values for the toe allowance was 5 mm for girls and 6 mm for boys. Yet the present study recommends the 90th percentile as suitable value for the toe allowance (the value below which are 90 percent of the measuring results). This was considered to satisfy more feet than the mean values. The 90th percentile of the toe allowance for girls was 9.8 mm and for boys 11.5 mm.

The mean values of the toe allowance calculated in the study were lower than in all regulations so far on the deter­mination of the allowance. The toe allowance of 9.8 mm in girls and of
11.5 mm in boys is smaller than the width of an adult’s thumb (with a supposed mean thumb width of 25,4 mm). Since the width of a thumb varies strongly – according to a different study between 11 and 24 mm in men and 10 to 24 mm in women – only the most narrow thumbs are indicative of the correct toe allowance.
The 12 mm allowance, proposed by the “Arbeitskreis Kinderschuh” in the guideline AK64-WMS, is closer to the result of the study. However the recommended 12 mm of the WMS exceed the toe allowance found by the present study. The study thus concludes that the 12 mm can be seen as a ­generous recommendation and not as a minimum recommendation for the toe allowance.
The 90th percentiles differ depending on the footlength. Stracker had ­already indeed recommended a toe ­allowance that depends on the foot­length (5 percent of the foot­lenght). But the present study does not confirm that longer feet require more toe allowance than shorter feet – if any at all they need less. Because the walking advance and the foot extension when walking are comparable in all fields of footlength, but the growth of feet considered in the growth rate decreased with bigger feet. The 5-percent-recommendation is thus disproved, also the recommendation to calculate the half of the EU-shoe size in millimeters for the toe allowance.
The study comes to the conclusion that only 15 percent of variance is explained by gender and footlenght. The influence of the footlength is not practically relevant, as opposed to the
assumptions of Maier and Stracker. The authors think that it can be speculated that there are other influencing factors, as done in different studies, e.g. the characteristics of ligaments, muscle tone and foot type.

For the first time this study presents empirical data for the required toe allowances in children’s shoes, based on statistical and dynamic 3D-scans and the 90th percentile of the measuring values. The toe allowance was smaller than in all recommendations and regulations so far. There was no significant influence of the footlength and the gender.
The results are important for the shoe industry. In order to implement them, several points have to be considered:

  • The toe allowance does not increase with increasing footlength. It is identical for all shoe sizes. This is related to the decreasing growth rate and the slightly increasing foot extension in longer feet.
  • Girls do not need different toe allowances than boys – no different grading is required.
  • The toe allowance is smaller than previously assumed. Yet this does not permit a simple shortening of the forefoot or toe box, since many shoes already have a forefoot or toe box area that is too short due to fashion reasons. But this result can help to correctly place the flex line in children’s shoes when constructing the lasts. The consideration of the medial ball length is crucial for the correct toe allowance and the correct positioning of the flex line.
  • The results can only be implemented if the overall fit of shoes will be reconsidered. A shorter toe allowance is only recommendable for shoes with appropriate lacing to ensure that the foot within the shoe will not slide forward.
  • The toe allowance always needs to have sufficient height so that the toes are not impaired. 

The findings give parents the assurance that one thumb width is enough toe allowance when buying children’s shoes. However it has to be considered that the amount of toe allowance depends on the overall shoe fit. Additionally, parent’s thumb widths vary and do not provide information on overall shoe fit. This study offers that basis for standardizing toe allowances in children’s shoes.

A scientifically excellently secured study – even if it would have been
still more informative to study the growth rate in a longitudinal survey. For the first time it is evaluated – with highly developed measuring technology – how big the toe allowance for children’s shoes should be. It has also been considered that the toe allowance in a shoe can only have the desired effect if the overall fit of shoes is correct. A valuable contribution for the health of developing feet.

1. Barisch-Fritz B., Plank C., Grau S.: Evaluation oft he rule-of-thumb: calculation of the toe allowance for developing feet. Footwear Science 2016, Vol. 8, No.3, 119-127.
2. Maier, E., & Killmann, M. (2003): Fußgerechte Kinderschuhe. Kinderfuß und Kinderschuh. Entwicklung der kindlcihen Beine und Füße und die Anforderung an den Fußgerechten Schuh. München: Verlag Neuer Merkur.
3. Stracker, O. A. (1966): Kinderfuß und ­Kinderschuh. Archiv für orthopädische und Unfallchirurgie, 59, 286-294.
4. Schmidt, C. (1989): Die optimale Längen­zugabe in Sport- und Freizeitschuhen bei Kindern. Dissertation. Universität Erlangen-Nürnberg.
Is retail footwear fit for purpose for the feet of adults who are obese?
A review by Annette Switala

Obesity has become an epidemic. Obese individuals often report that it is difficult for them to find appropriate footwear. This fact might have even more harmful consequences given that the feet of obese individuals exhibit lower sensitivity; a condition that can be exacerbated by the late sequelae of diabetes.
Studies cited by the authors suggest that the feet of obese individuals can deviate in form, morphology, soft tissue proportions and performance from the feet of normal-weight persons. This increases the probability that ready-to-wear, normal-width shoes are not suitable to meet the needs of obese wearers. It is not yet clear how shoes should be designed for obese individuals.

The study aimed to determine whether the feet of the obese participants in overly-wide shoes provided a comparable amount of space as for the feet of normal-weight persons in standard shoes. The objective was to find out whether the wide-fit shoes actually matched the needs of their target group. Measurements were taken to document which regions of the foot require different shoe dimensions than in the original design .

Subjects were selected for the study who self-reported wearing shoe size 43. The right foot of each subject was measured in the two-legged stance
using a three-dimensional (3D) scanner. The mean dimensions of the right feet of 13 male obese subjects were defined as the measure of the obese foot. The mean measures of the right feet of 12 healthy-weight persons defined the measure of the healthy-weight foot.
Three comparably priced, leather lace-up retail shoes in width “H” (Marks & Spencer Airflex, Clars Line Day, Padders Taxi) were tested by the obese wearers; a standard-fit shoe (Ecco Transporter) by the healthy-weight subjects. The shoes were cast in plaster; the plaster molds (regarded as approximations of the lasts) were measured using the 3D scanner.
Firstly, standard measures usually used for last design were taken of the feet and lasts. Secondly, cross-sections were measured along the longitudinal axis of foot and lasts for height, width and circumference at intervals of one centimeter.
The relationship between last and foot in normal-weight subjects (last/foot difference) was used as benchmark for a good foot/last relationship. The foot/last relationship in the obese subjects was measured against this benchmark. The difference between normal-weight last and shoe was subtracted from the difference between obese last and shoe. The results were viewed as indicative of the extent of deviations in the foot/last relationship in mm across different regions of the foot in obese individuals.

The obese subjects had less space than the healthy-weight subjects in their shoes overall. All overly wide shoes provided the obese foot with significantly less space in the heel region (in terms of heel width and heel circumference) than the standard shoe provided for the healthy-weight foot. The ball width of one of the three wide-fit shoes was even lower than in the standard shoe and had measures that were lower than the ball circumference of all obese feet in this study. The inner length of the wide-fit shoes was 4 to 10 mm shorter than in the standard shoe.
Over the entire foot length, the cross-sectional measures revealed that the obese feet in wide-fit shoes had less space than the feet of healthy-weight subjects in standard shoes. One exception was in the toe region where the wider-fitting shoes had more girth than the standard shoes.
Overall, the extent of the shoe/foot difference of obese wearers was smaller than in the standard shoes (-26.2 mm plus/minus 17.3 mm in one of the wide-fit shoes).

Based on their findings, the authors concluded that wide-fit retail footwear currently do not meet the needs of obese wearers in terms of width, height and circumference and therefore is currently not fulfilling its intended purpose. Especially in the rearfoot region, but also around the ball section, these shoes should be constructed with a wider girth. This conclusion is consistent with the literature which states that obese individuals have a more difficult time finding suitable shoes.
The overly wide footwear provided the feet with almost exactly as much space in length as the standard footwear, although the overly-wide shoes were shorter than the standard ones. From this, the authors conclude that the obese subjects self-selected larger shoe sizes than they actually needed in order to compensate for the lack of shoe width. This might also explain the study's finding that the foot-shoe-relationship provided significantly more space in the toe region in the obese compared to the healthy-weight persons. The authors warn that excess room in the forefoot region can lead to adverse frictional forces and blisters.

It is commendable that a study has dealt with the issue of how well shoes actually on the market fit the feet for which they are intended. Given the increasing growing proportion of the population with obesity, it is important to focus attention in the footwear provided to treat this target group.
That said, the results of this study should be viewed with caution.
More conclusive results would have been obtained if the study had compared individuals with equivalent foot lengths (who therefore would have required size 43) and not individuals who self-reported wearing shoe size 43. As the authors of the present study themselves noted, many subjects with obese feet wore shoes that were too large; presumably to compensate for the too narrow girth provided by their actual shoe size. Even the "German Foot Report" (Richter 2009) established that self-selected shoe sizes are usually wrong. It can be assumed that the feet of obese subjects would have had even less space in the shoe, if the subjects were compared to individuals who required size 43 for their in foot length.
In our opinion, the fact that the relationship between foot and shoe of healthy-weight persons was used as a benchmark for a good fit raises some concerns. This is predicated on the majority of healthy-weight individuals possessing comparable foot morphologies. However, as the "German Foot Report" has shown, foot morphologies and the foot widths in particular are spread over a wide range, even in slim feet.
Another concern to be expressed is that there is really no "standard width" which the study used as a basis for its ready-to-wear shoes. The widths of ready-to-wear shoes without overwidth vary across a broad spectrum and there is no uniform, standardized width labeling. These reasons make it difficult to understand why only one shoe was selected for the healthy-weight subjects, whereas the obese wearers tested three shoes.
Thirdly, the benchmark assumes that the feet of healthy-weight wearers were shod with a single standard width of properly fitting footwear. In this regard, the “German Foot Report“ however showed that the most common foot widths in the population are not in agreement with the most commonly manufactured widths. The most commonly manufactured widths prove to be too wide for the majority of persons. The fact that foot and shoe matched in the healthy-weight subjects of the present study must therefore be doubted. It would be recommendable for a follow-up study to verify the proper fit of the trial shoe in the healthy-weight subjects using measurement technology, instead of just accepting their self-reported statements.
Notwithstanding the above, and therein lies its merits, this study proposes a critical appraisal of the relationship between obese foot and wide-fit footwear and thereby a critical appraisal relating to the fit of overwide-fit shoes. For this purpose, it would make sense to quantify the relationship of the morphology and dimensions of foot and shoe to one another using a 3D scanner. A comparison with the foot/shoe relationship of healthy-weight subjects can be informative, if it has been previously established how well these shoes actually fit the subjects. We, nevertheless, submit that this comparison could be dispensed with since the relationship between the obese foot and overwide-fit shoe can be regarded as conclusive in and of itself. Whether the room the foot has in its shoe is sufficient can be assessed by applying biomechanical knowledge and fit competency to a comparison of the foot and shoe data. Such an evaluation would look at where the shoe should be made narrower or wider and how much room the foot needs when the subject is walking in the shoe. A questionnaire that additionally surveys patients in more detail about their subjective sense of comfort could supplement the patients’ subjective perceptions with the factually measured data.
We recommend, moreover, that not only the foot be measured statically, but also dynamically given that the shoe has also to fit for the purpose of walking as well. It would also be interesting to not only investigate fa-shionable retail shoes but also comfort shoes designed for the feet of obese wearers.

Prince C., Nester C.: Is retail footwear fit for purpose for the feet of adults who are obese? Footwear Science, 2016, Vol. 8, No.3, 139-146.

Do high heels cause musculosceletal changes? A review by Julia Knaut

They are a symbol for femaleness and the modern woman: high heeled shoes (high heels). But what is about the
association between this favorite accessory and injuries? A systematic epidemiological review from 2016 collected and evaluated international peer-reviewed scientific literature concerning high heels and musculoskeletal injuries.
The authors of the study “High heeled shoes and musculoskeletal injuries: a narrative systematic review” screened seven major bibliographic databases in July 2015 to identify all scholarly articles on high-heeled shoes [1]. Across seven major languages they searched for all articles regarding the association between high-heeled shoewear and hallux valgus, musculoskeletal pain, osteoarthritis and both first-party and second-party injury in human participants without prior musculoskeletal conditions [2].
Initially 644 unique records were identified and 18 studies included in the review. Four studies assessed a relationship with hallux valgus and three found a significant association. Furthermore two studies assessed the relationship with osteoarthritis, but neither found a significant association. Five studies assessed first-party injury and seven found evidence of a significant injury toll associated with high-heeled shoes. One study collected data on second-party injury and the toll was low.
The contributors of the review suggest that the identified body of literature taking an epidemiological approach (18 studies) is smaller than the body of literature taking a biomecha­nical approach (estimated 100 stu­dies).
Summarized high-heeled shoes were shown to be associated with musculoskeletal pain, hallux valgus and first-party injury. The balance of the evidence regarding association with musculosceletal pain is increased by women’s everyday experience as explored in the research of Dilley et al [3]. All but one low quality study identified an association between high heels and hallux valgus. This correlates with biomechanical evidence, for example, an increase in forefoot pressure and loading at the first metatarsal head (4, 5, 6, 7). The body of evidence regarding first-party injury is the largest in the review. The contributors refer to the studies of Nagata and Gabell et al (8, 9). Nagata points out the potential hazard of climbing stairs in high heels, while Gabell et al suggested that high heels wearing habit may predispose women to falling even when not wearing high heels at the time of the fall.
Regarding osteoarthritis and second-­party injury no distinct evidence was found. The lack of association between high heels and osteoarthritis is explained by low study quality, recall bias regarding past shoe exposure and a particularly small sample size in one study [10]. These results contrasts with biomechanical evi­dence suggesting an association between high heels and osteoarthritis of the knee (increased knee flexion, patellofemoral joint pressure et cetera).
A further major finding of the study is the injury toll among underage girls including 4737 injuries to those under the age of 10 [11]. Certainly neither study classified age in a way that
allows precise division of legal adults from those below the legal age of adulthood. The review’s contributors highlights that there are styles of high heels specifically marketed for children, there is no age restriction on the sale of high heels in countries such as England and Australia.

1. Barnish MS, Barnish J. High-heeled shoes and musculoskeletal injuries: a narrative systematic review. BMJ Open 2016;6:e010053.doi:10.1136/bmjopen-2015-010053.
2. English, French, German, Spanish, Italian, Dutch, Portuguese.
3. Dilley R, Hockey J, Robinson V, et al. ­Occasions and non-occasions: identity, femininity and high-heeled shoes. Eur J Women’s Stud 2015; 22:143–58.
4. Cong Y, Cheung JT, Leung AK, et al. Effect of heel height on in-shoe localized triaxial stresses. J Biomech 2011;44:2267–72.
5. Mandato MG, Nester E. The effects of increasing heel height on forefoot peak pressure. J Am Podiatr Med Assoc 1999;89:75–80.
6. Nyska M, McCabe C, Linge K, et al. Plantar foot pressures during treadmill walking with high-heel and low-heel shoes. Foot Ankle Int 1996;17:662–6.
7. Snow RE, Williams KR, Holmes GB Jr. The effects of wearing high heeled shoes on pedal pressure in women. Foot Ankle 1992;13:85–92.
8. Nagata H. Occupational accidents while walking on stairways. Saf Sci 1991;14:199–211.
9. Gabell A, Simons MA, Nayak USL. Falls in the healthy elderly: predisposing causes. Ergonomics 1985;28:965–75.
10. Dawson J, Juszczak E, Thorogood M, et al. An investigation of risk factors for symptomatic osteoarthritis of the knee in women using a life course approach.
J Epidemiol Community Health 2003; 57:823–30.
11. Moore JX, Lambert B, Jenkins GP, et al. Epidemiology of high-heel shoe injuries in U.S. women: 2002 to 2012. J Foot ­Ankle Surg 2015; 54:615–19.

Intra-rater reliability of footwear-related comfort assessment A review by Wolfgang Best

Until recently, the two most commonly studied variables that were thought to be associated with the development of running injuries were foot pronation and impact forces during heel–toe landing.
However, in the last years it has become more and more clear that there is no supporting evidence that vertical impact forces are associated with running injuries. The same applies to pronation, most recently after the study of Nielsen [1], in which he investigated the foot position in relation to running injuries. He showed that a pronated foot position between 7° and 10° was rather a protection from injuries. The group in the study with a foot position in this range had significantly less injuries than all
other groups. Therefore pronation is not regarded as a good indicator of running injuries anymore.
Several other concepts have been proposed like the “preferred movement path”. A good running shoe would help the athlete to stay in the movement path given to him by his individual anatomy. If the preferred movement is disturbed through the shoe, so the theory goes, the athlete needs more muscle activity and is more at risk to be injured.
Another concept that has become very popular is comfort. This concept assumes that shoe conditions that are more comfortable are associated with a lower movement-related injury frequency than shoe conditions that are less comfortable. So different functional groups of athletes need different features in their shoes, e.g. medial support or not, in order to feel comfortable in a shoe.
The first proof of this concept came from the study of Mündermann [2] with military recruits. For the boots that were used during their training, she provided six types of insoles differing in arch height, heel shape, material and elasticity and let 106 recruits select the most comfortable one. A control group, which was exposed to the same military training, wore no insoles. After 4 month of training, the test group had 53% fewer lower-extremity injuries than the control group.
This concept was transferred to running shoes, and was proposed as a new paradigm: “When selecting a running shoe, an athlete selects a comfortable product using his/her own comfort filter. This automatically reduces the injury risk and may be a possible explanation for the fact that there does not seem to have been a trend in running injury frequencies over time.” [3]

How good are athletes at assessing comfort? Will the judgement be the same on different occasions? This was the objective of the study of Hoerzer et al. [4]. Footwear related comfort may be described as an ever changing perception of an individual, which is the result of mechanical, neuro-physiological and psychological factors. Therefore it is quite a challenge to investigate and quantify comfort. Although there seem to be reliable measures such as Visual Analog Scales (VAS), little is known about the reliability of a given individual to assess footwear comfort on different occasions.
Can healthy individuals reliably assess footwear comfort between days by means of VAS and will the results be more reliable by reducing the complexity of the comfort measure by using Yes-No-questions? These were the two hypotheses that were examined.
A neutral running shoe was used with one control insole (default sole of the shoe) and six test insoles, which varied systematically in material and shape characteristics. The shoe was available in different sizes and the insoles were fitted to them accordingly. Three comfort assessment sessions were carried out for each of the ninety participants (physically active male adults).
The time of the day for the testing was kept consistent for each participant. Comfort ratings from previous testing session were not visible for the participants. The footwear comfort was assessed using VAS and Yes-No-questions (Was the insole comfortable?/Was the insole uncomfortable?).

Despite the careful set-up of the testing conditions to keep the mechanical and neurophysiological states constant, and the fact that only the last two sessions were analyzed when the participants were familiar with the procedure, only a minority was able to reliably assess footwear comfort (31.1%) with the VAS. When using only Yes-No-questions, 46.7% of the participants provided reliable comfort assessment. The hypothesis that the majority of healthy individuals can reliably assess footwear comfort between days had to be denied.

The authors offer various reasons for this. Not all factors that might influence the assessment could be checked. The psychological state of mind could have varied across the testing sessions, e.g. the participant could have had a good or a bad day. Also different lengths of the break between the testing days might have influenced the result. Individuals with a low reliability may have a low receptor sensibility on the plantar surface of the feet. Thus the differences between the footwear conditions may have not been big enough for them to feel the difference. Therefore it might be important to understand how much a footwear condition has to change to represent a reliable change. Caution is advised, the authors conclude, when assessing comfort, be it for shoes, orthotic devices or for research purposes.

The authors do not question the comfort concept developed by their own study group here. Yet the results show that we cannot trust the spontaneous comfort assessments by athletes when they try on shoes in a shoe store for example. Obviously there are further factors that influence the comfort assessment. For these factors more scientific tests are needed. The outcome does correspond with the experience in pedorthics. The first assessment is not always the valid one. Whereas soft shoes or soft custom foot orthotics often feel comfortable at first sight, harder and more supporting insoles are frequently assessed as being more comfortable after a longer wearing period.

1. Nielsen RO, Buist I, Parner ET, et al. Foot pronation is not associated with increased injury risk in novice runners wearing a neutral shoe: A 1-year prospective cohort study. Br J Sports Med 2014;48:440–7.
2. Mündermann A, Stefanyshyn DJ, Nigg BM. Relationship between footwear comfort of shoe inserts and anthropometric and sensory factors. Med Sci Sports Exerc 2001;33:1939–45.
3. Nigg BM, Baltich J, Hoerzer S, et al. Running shoes and running injuries: mythbusting and a proposal for two new paradigms: ‘preferred movement path’ and ‘comfort filter’ Br J Sports Med 2015;49:1290–1294.
4. Hoerzer S, Trudeau M B., W. Edwards B, Nigg BM; Intra-rater reliability of footwear-related comfort assessment, Footwear Science, Vol. 8, No. 3 155-163.