Footwear in classical ballet: a study of pressure distribution and related foot injury in the adolescent dancer.
Progressive training is desirable so that the anatomical structures involved can be gradually strengthened in preparation for the greater loading demands of pointe work. (3) Tissue breakdown may occur, with a resultant predisposition to overuse injury, if the feet are exposed to repetitive loads without adequate preparation and sufficient recovery time. (3,4) In this regard, increased underfoot pressure has been shown to be a strong predictor of overuse injury in active young people. (5)
Shoes used during high physical demand on the feet generally incorporate shock absorbing materials, which help increase flexibility of the sole, reducing plantar pressure. (6) Pointe shoes require materials that are stiff and durable in order to support the dancer when balancing on the tips of her toes. These materials have low shock absorbent properties; consequently, the demands on the foot structures are heightened in comparison to training in the flexible soft shoe.
The aim of this study, therefore, was to examine the pressure characteristics of different shoes used in ballet. Specifically, the objectives were to 1. compare the pressure profile of the demi-pointe shoe with those of the soft and pointe shoes, and 2. examine current practice in order to test whether the use of demi-pointe shoes may help prevent overuse injuries in the adolescent dance community.
Materials and Methods
All procedures were approved by the local Research Governance and Ethics Committee, and all participants gave their written informed consent. The study conformed to the declaration of Helsinki.
Pressure Distribution Measurement
The study utilized a repeated measures same subject design. Eight female dancers (age: 19.63 [+ or -] 1.06 years; height 163.00 [+ or -] 7.42 cm; weight 54.88 [+ or -] 8.95 kg) were recruited from university undergraduate dance degree programs. All had trained in ballet to a level equivalent to RAD Intermediate, with at least two years of experience dancing in pointe shoes and were free of lower limb injury and abnormalities. Pressure data were collected with an emed[R]-x high-speed high-scan pressure platform (Novel, Munich, Germany) sampling at 100 Hz. Participants were asked, while standing in first position on the pressure platform, to rise from demi-plie onto demi-pointe (Fig. 1) in four footwear conditions: barefoot, soft shoes (Sansha Tutu Split--standard style across manufacturers), demi-pointe shoes (Grishko 2007), and pointe shoes (Grishko 2007). The conditions were tested in random order, and plantar pressure measurements were taken from the demi-plie to completion of the rise onto demi-pointe (the participants were not required to go onto full pointe while in pointe shoes, as these data would not have supported the repeated measures design required to compare each footwear condition).
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Pointe shoes were fitted to the participants a week prior to data collection by a trained fitter and were sufficiently broken in to allow the participants to feel comfortable in them when rising through demi-pointe to en pointe. While wearing the shoes, rises and releves with support were permitted. No toe pads were used during testing, as they might influence the observed differences in footwear.
After a 15 minute warm-up (consisting of ankle circles, rises, releves and small jumps), contact area, peak pressure, pressure time integrals, and relevant force values were obtained in each condition over four areas: total foot, forefoot (consisting of the first to fifth metatarsal heads and all toes), midfoot, and hindfoot (heel). (7) Mean values were calculated for four trials in each condition. The data were then analyzed for statistical significance (p < 0.05) with repeated measures ANOVA and Bonferroni corrected post hoc pairwise comparisons.
Questionnaire Data Collection
Sixty-seven female vocational dance pupils (age 13.49 [+ or -] 1.42 years) were recruited from vocational schools of dance to complete a questionnaire regarding dance training, injury, and shoe use. These subjects had all begun pointe work (mean starting age = 11.15 [+ or -] 0.43 years), and their main dance discipline was ballet. Two questionnaires were discarded due to incompletion. All reported injuries were then categorized as either relevant or irrelevant. "Irrelevant" comprised any injury that was located in the upper limb, had a non-dance-related mechanism, or occurred prior to the onset of pointe training. These injuries were not used during further analysis. A "Relevant" injury that occurred or was first noticed during ballet practice was designated as a "ballet injury," and any relevant injury located below the knee, not inclusive of the knee, came under the heading "lower leg, ankle, and foot injury." Injury, age, training frequency, and pointe experience (years since beginning, and frequency of, pointe work) were correlated with current shoe use and shoes used for training prior to pointe onset. Relationships were explored between injury prevalence, ballet-related injury, lower leg, ankle, or foot injury, and shoes used prior to the onset of pointe work, as well as the shoes currently used.
Pressure and force data were obtained for the total foot in each footwear condition (Table 1), and pressure was recorded for specific areas of the underfoot for each shoe condition (Table 2). Intraclass correlation values for barefoot, soft shoe, demi-pointe shoe, and pointe shoe data collection were 0.81, 0.78, 0.79, and 0.76, respectively.
Significant differences in pressure were found between barefoot and pointe shoe (p < 0.01) and soft and pointe shoe conditions (p < 0.01). No significant pressure difference was found between demi-pointe and pointe shoes or demi-pointe and soft shoes, indicating overall that the demi-pointe shoe provides a transitional stage in pressure between soft shoes and pointe shoes. Progression can be observed from soft to demi-pointe to pointe shoes, the latter having significantly higher pressure values. Except at the midfoot, the shoe conditions significantly (p < 0.01) decrease in contact area progressively from barefoot to soft shoes, to demi-pointes, to pointe shoes (Table 2). Figures 2-5 illustrate the pressure distribution in each of the conditions. Differences in force can also be observed in Table 1 between soft shoes and pointe shoes.
Each participant was grouped as either 1. an individual who wore demi-pointes prior to starting pointe (N = 9), or 2. one who did not wear demi-pointes prior to starting pointe (N = 56). Participants were also grouped according to their current shoe use during ballet class: soft shoes (N = 12), demi-pointe shoes (N = 34), or a combination thereof (N = 19).
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Of the sample, 82% (53) had trained in demi-pointe shoes (mean starting age 11.96 [+ or -] 0.91yrs), and of those individuals, 83% (44) did so after the onset of pointe work (mean starting age 11.18 [+ or -] 0.46 years).
Dancers who wore demi-pointes before starting on pointe were more likely to report their first dance-related injury at an older age (Fig. 6A) than those who did not wear them beforehand (Fig. 6B), the occurrence of which had a distinct peak at age 13.
Relevant injury was reported by 55% (36) of the total sample (65). Forty-two percent (21) of injuries reported were localized to the ankle, foot, and lower leg: 20% (10), 12% (6), and 10% (5), respectively. Forty-five percent (21) of injuries occurred during ballet class, 17% (8) in other dance classes or exercise, and 38% (18) were reported as "unsure." An individual was found to be more likely to sustain a ballet-related injury or a lower leg, ankle, or foot injury, if she had not worn demi-pointe shoes prior to starting pointe work (Fig. 7A). This was also the case with those who currently wore demi-pointe shoes during class rather than soft shoes or a combination of soft and demi-pointe shoes (Fig. 7B).
Pressure time integrals, peak, and mean pressures recorded demonstrated a consistent contrast among the various footwear conditions. Soft shoes impose the least pressure on the plantar surface of the foot and pointe shoes the most, with demi-pointe shoes between the two. In addition, a reverse trend was found to be significant with regard to contact area of each of the shoe conditions: pointe shoes had the least contact and soft shoes the most.
The pressures recorded in pointe shoes were significantly greater than the other footware conditions (Tables 1 and 2), an indication of much greater demands of the foot and related structures in this condition. Similar to pointe shoes, but to a far lesser extent, demi-pointe shoes impose greater plantar pressures than in the barefoot condition, unlike soft shoes. The structure and stiff nature of the pointe shoe materials contribute to the restricted contact area and therefore heightened pressure in this condition. The less resilient materials used for the soft and demi-pointe shoes result in larger contact areas and reduced pressures in comparison. This illustrates the potential advantage of demi-pointe shoes over soft shoes in preparation for pointe work. It has already been established that high plantar pressure is a strong predictor of exercise-related lower leg pain, specifically overuse injury in adolescents. (5) It follows, then, in the context of ballet footwear, that one way to decrease the likelihood of this type of injury is to introduce the demi-pointe shoe prior to pointe work, so as to achieve a load progression from that of a soft shoe.
Young dancers train using one of three shoe progression scenarios:
1. Wearing soft shoes only prior to the onset of pointe work, then continuing to practice in soft shoes only when not in pointe shoes;
2. Wearing soft shoes, then demi-pointe shoes for a period prior to the onset of pointe work; or
3. Wearing soft shoes only prior to the onset of pointe work and then, at onset or shortly thereafter, also training in demi-pointes.
The results of this study's questionnaire support the suggestion that when demi-pointe shoes are worn prior to the onset of pointe work (progression 2), the relevant soft tissues are strengthened through exposure to a gradually increasing load and therefore are less likely to become injured once pointe work begins. However, many dancers begin to wear demi-pointes at the same time as, or shortly after starting pointe training (progression 3). This further increases training loads rather than creating the desired transitional step, as the dancer must withstand the additional load of training in both demi-pointe and pointe shoes after previously wearing only soft shoes.
It is likely that, due to the structural similarities of demi-pointe and pointe shoes, proprioceptive training may also be developed in advance of pointe training to help the dancer become accustomed to pointe shoes. However, it has not been determined whether the dancers in this study who wore demi-pointes prior to starting pointe work were better adapted, stronger, had better proprioceptive awareness, or sustained fewer injuries as a result of having done so. Such findings were beyond the scope of the questionnaire, as the preparatory pointe training regimen of the participants was not in all cases at their vocational school and therefore could not be accurately assessed by this method. Further consideration and research are required in these areas.
As may be anticipated, older dancers who participated in the present study reported a higher training frequency and were more experienced in pointe work. When correlated with injury, training frequency was generally lower among injured dancers, which would be the expected result of time lost to recovery. The lower incidence of ballet and lower leg, ankle, or foot injuries reported among dancers who currently train in a combination of soft and demi-pointe shoes may be due to the flexibility of the soft shoe. This possibly allows for better recovery from stress in the tissues surrounding the sites of potential overuse injury. (3)
The pressures recorded in the different sections of the foot indicate that the footwear conditions' pressure was highest in the hindfoot; however, in soft shoes the highest pressure recorded was in the forefoot (Table 2). This difference in the focus of pressure relative to footwear condition may well influence shoe choice to protect the local structures of the forefoot and hindfoot during daily training. This is particularly relevant during busy training periods and injury rehabilitation, when load is of specific concern. Similarly, the lower pressures throughout the foot in soft shoes in comparison to demi-pointe shoes is relevant to injury prevention and rehabilitation, as use of the soft shoe may help to offload the forefoot and hindfoot when necessary.
Compared to previous injury surveys with reports of ankle and foot injuries accounting for 53%, (1) 54%, (7) and 65% (8) of all injuries, the corresponding figures obtained in this study were low. Those other studies all investigated injury occurrence in professional dancers, who were unquestionably exposed to a greater number of previous training hours and therefore more likely to have sustained a training-related injury. (9)
The peak of first reported injury at 13 years of age (Fig. 6) may be explained by a combination of factors. This time frame coincides with the rapid adolescent growth spurt among females; however, when compared with other sport training in this age group, it appears to be only among female dancers that this injury peak occurs. (2) The present study suggests a specialized explanation for this anomaly. It found that the majority of young dancers had not worn demi-pointe shoes prior to pointe work; however, after the onset of pointe, they mainly used demi-pointe shoes for class work. The mean pointe onset age is 11.18 [+ or -] 0.46 years, and for demi-pointes it is 11.96 [+ or -] 0.91 years. Thus, dancers who had worn demi-pointe shoes prior to starting pointe were somewhat older than those who had not. When they first sustained an injury, however, the peak at 13 years was still present in this group. For both groups, the time lapse to the injury peak at 13 years corresponds with the amount of time required for consistent sub-maximal gradual loading to produce the related microfailure of structures that may be above the tolerated threshold in some individuals. (10) This may be attributed to the increased demand of accepting the additional loads of wearing both demi-pointe and pointe shoes without prior progression, possibly leading to overuse injury.
In addition, it was seen that a number of dancers had started pointe prior to beginning vocational training (i.e., at their local dance schools). As should be apparent by now, in these authors' opinion, it is particularly important that demi-pointes be worn at this stage of a young dancer's career in order to potentially reduce the risk of lower limb overuse injury, and such was likely not the case with these dancers. After the onset of pointe work dancers are most likely to benefit from wearing a combination of soft and demi-pointe shoes for class work.
This study identifies a possible contributing factor to overuse injuries in adolescent female dancers and proposes an applicable approach to dancers' training aimed at reducing the injury rate. The study suggests that demi-pointe shoes have a clear impact on injury risk, and their use should be a consideration in dance practice and injury research. A progressive integration of appropriate footwear at the onset of pointe training in adolescent females may not only reduce injury in individuals but also promote more efficient and accurate technique.
We thank Amanda Hill at IDS/ Grishko for her kind support.
Caption: Figure 1 A, Demi-plie in first position, B, first position, and C, demi-pointe in first position.
Caption: Figure 2 Barefoot: pressure and center of gravity.
Caption: Figure 3 Soft shoes: pressure and center of gravity.
Caption: Figure 4 Demi-pointe shoes: pressure and center of gravity.
Caption: Figure 5 Pointe shoes: pressure and center of gravity.
Caption: Figure 6 A, Age at first related injury with wearing demi-pointe shoes prior to pointe work. B, Age at first related injury without wearing demi-pointe shoes prior to pointe work.
Caption: Figure 7 A, Previous shoe use in relation to injury incidence. B, Current shoe use in relation to injury incidence.
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Stephen J. Pearson, Ph.D., and Alison F. Whitaker, M.Sc.
Stephen J. Pearson, Ph.D., and Alison F. Whitaker, M.Sc., are from Centre for Health, Sport and Rehabilitation Sciences Research, University of Salford, Greater Manchester, United Kingdom.
Correspondence: Alison F. Whitaker, M.Sc., Centre for Health, Sport and Rehabilitation Sciences, University of Salford, Greater Manchester M6 6PU, United Kingdom; email@example.com.
Table 1 Pressure and Force Data with Variation of Footwear Barefoot Soft Shoes Mean pressure 249.41 [+ or -] 52.23 * 240.94 [+ or -] 59.55 * (kPa) Mean force (N) 567.06 [+ or -] 126.08 579.29 [+ or -] 119.10 * Mean contact 22.80 [+ or -] 2.57 24.84 [+ or -] 5.29 * area * ([dagger]) ([cm.sup.2]) Pressure time 747.36 [+ or -] 157.71 * 722.82 [+ or -] 178.65 * integral (kPa.s) Force time 1701.19 [+ or -] 378.24 1737.86 [+ or -] 357.30 * integral (N.s) Total contact 216.38 [+ or -] 27.19 199.38 [+ or -] 21.76 * area * ([dagger]) ([cm.sup.2]) Demi-pointe Shoes Pointe Shoes Mean pressure 279.50 [+ or -] 81.11 436.51 [+ or -] 152.69 (kPa) Mean force (N) 565.40 [+ or -] 113.72 524.99 [+ or -] 116.24 Mean contact 20.84 [+ or -] 3.39 * 12.93 [+ or -] 4.24 area ([cm.sup.2]) Pressure time 838.49 [+ or -] 243.32 1309.50 [+ or -] 458.07 integral (kPa.s) Force time 1696.20 [+ or -] 341.16 1574.97 [+ or -] 348.72 integral (N.s) Total contact 182.13 [+ or -] 19.19 * 148.00 [+ or -] 19.25 area ([cm.sup.2]) * Significant difference to pointe shoe group (p [less than or equal to] 0.01). ([dagger]) Significant difference to demi-pointe shoe group (p [less than or equal to] 0.01). Table 2 Peak Pressure and Contact Area of the Different Sections of the Foot with Variation of Footwear Barefoot Soft shoes Forefoot Peak pressure (kPa) 306.88 [+ or -] 130.49 379.38 [+ or -] 166.29 ([double dagger]) Total contact area 59.88 [+ or -] 9.34 55.50 [+ or -] 5.88 ([cm.sup.2]) * ([double dagger]) ([double dagger]) Midfoot Peak pressure (kPa) 63.75 [+ or -] 28.00 107.50 [+ or -] 34.12 ([double dagger]) ([double dagger]) Total contact area 22.88 [+ or -] 12.25 33.13 [+ or -] 13.81 ([cm.sup.2]) Hindfoot Peak pressure (kPa) 436.25 [+ or -] 70.29 373.13 [+ or -] 99.42 Total contact area 132.75 [+ or -] 17.35 110.50 [+ or -] 18.42 ([cm.sup.2]) ([double dagger]) ([double dagger]) ([section]) Total foot Peak pressure (kPa) 462.50 [+ or -] 60.83} 449.38 [+ or -] 134.36 ([double dagger]) ([dagger]) Total contact area 216.38 [+ or -] 27.19} 199.38 [+ or -] 21.76 ([cm.sup.2]) ([double dagger]) ([double dagger]) ([section]) Demi-pointe shoes Pointe shoes Forefoot Peak pressure (kPa) 372.50 [+ or -] 246.69 493.75 [+ or -] 166.56 Total contact area 52.88 [+ or -] 9.00 43.38 [+ or -] 6.05 ([cm.sup.2]) Midfoot Peak pressure (kPa) 141.25 [+ or -] 33.57 236.25 [+ or -] 125.58 Total contact area 35.13 [+ or -] 8.69 32.88 [+ or -] 7.59 ([cm.sup.2]) Hindfoot Peak pressure (kPa) 418.13 [+ or -] 182.87 709.38 [+ or -] 294.59 Total contact area 93.88 [+ or -] 11.08 71.13 [+ or -] 11.13 ([cm.sup.2]) ([double dagger]) Total foot Peak pressure (kPa) 543.13 [+ or -] 241.56 764.76 [+ or -] 321.22 Total contact area 182.13 [+ or -] 19.19 148.00 [+ or -] 19.25 ([cm.sup.2]) ([double dagger]) * Significant difference to demi-pointe shoe group (p = 0.03); ([dagger]) Significant difference to pointe shoe group (p = 0.02); ([double dagger]) Significant difference to pointe shoe group (p [less than or equal to] 0.01); ([section]) Significant difference to demi-pointe shoe group (p < 0.01).
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|Author:||Pearson, Stephen J.; Whitaker, Alison F.|
|Publication:||Journal of Dance Medicine & Science|
|Date:||Apr 1, 2012|
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