Original Article

Ground Reaction Forces in Dancers Landing in Flat versus Pointe Shoes

Heather L. Walter, M.S., L.A.T., A.T.C., Carrie L. Docherty, Ph.D., L.A.T., A.T.C., and John Schrader, H.S.D., L.A.T., A.T.C.

Abstract injuries in dancers include talar im- perform on resilient floors. Reports in the literature suggest an abun- pingement syndromes, tendonitis, Incorrect technique can also con- dance of lower extremity injuries in ballet stress fractures, problems with the tribute to greater ground reaction dancers; however, few studies have identi- first metatarsophalangeal joint, and, force. Every day dancers participate fied the underlying causes of these inju- perhaps most common of all, acute in a conditioning program that ries. Excessive ground reaction forces and ankle sprains.2 While a great deal of includes elements of strength and type are two potential contributing research identifies the types of inju- flexibility training, muscular and factors. Eighteen collegiate female ballet ries dancers sustain, there is a relative cardiovascular endurance, neuro- majors volunteered for this study. Each lack of information pertaining to muscular coordination, and balance.8 participant performed 12 trials of a basic ballet jump, six trials in flat shoes and 6 why these injuries occur. Forces that The repetition of this program, when trials in pointe shoes, landing on a force the body has to absorb during dance done incorrectly, can contribute to plate. Ground reaction force (Newtons) activities are an obvious causal factor; injuries. Dancers must always be and jump height (centimeters) were as- as a dancer makes contact with the aware of their bodies in space but sessed for each trial. The mean ground re- ground, the ground returns a reaction especially so when jumping and action force and jump height for each shoe force that is absorbed by the dancer’s landing. Much attention is generally condition was used for statistical analysis. body. Excessive ground reaction given to the technique required to go Two dependent t-tests were conducted to forces may be attributed to a variety into the air, but the landing is often determine differences between the shoe of factors including hard landing sur- overlooked. Three phases of landing types, one for ground reaction force and faces,3-5 faulty technique,1 inadequate should occur when a dancer com- one for jump height. Alpha level was set or inappropriate instruction,6 and the pletes a jump correctly.9 In the first at p < .05. We found that the ground reaction force was significantly higher dance involved. phase, the toes make initial contact when landing in flat shoes than in pointe Most dance studios have sprung with the ground. During the second shoes (p = .003). There was no significant wooden flooring, often covered with phase, the ball of the foot contacts difference in jump height between the two linoleum or Marley vinyl. A sprung the ground and the foot begins to shoe conditions. This leads us to believe floor is needed because it is resilient5; descend to a flat position. In the that the increase in ground reaction force the more resilient the floor, the more final phase, the heel has to contact was produced primarily by the shoe type. force it can absorb.5 Some dance the ground. A controlled landing movements, most obviously landings occurs when the dancer completes all ancers tend to be plagued from jumps, can expose the lower phases correctly and the heel stays in with a great number of extremities to loads up to 14 times contact with the ground.9 The dancer injuries throughout their body weight.7 These forces need to be who does not understand correct careers,D nearly 86% of which occur dissipated to reduce the risk of injury. technique for landing jumps is likely in the lower extremities.1 Chronic Thus, it is important that dancers to suffer the effects of higher ground reaction forces. Heather L. Walter, M.S., L.A.T., A.T.C., Carrie L. Docherty, Ph.D., L.A.T., An additional factor, type of A.T.C., and John Schrader, H.S.D., L.A.T., A.T.C., are in the Department of instruction, may also affect ground Kinesiology, Indiana University, Bloomington, Bloomington, Indiana. reaction force. McNair and col- Correspondence: Carrie L. Docherty, Ph.D., .L.A.T., A.T.C., 2805 East 10th Street, leagues6 demonstrated that when Bloomington, Indiana 47408; [email protected]. subjects were given instructions

61 62 Volume 15, Number 2, 2011 • Journal of Dance Medicine & Science on how correctly to position their degree program in ballet performance on a runway and landed on an X in limbs during jumps, ground reaction (19.94 ± 1.16 years of age, 169.12 ± the center of a force plate (AMTI force was reduced. Also, when the 6.40 cm in height, 55.44 ±5 .40 kg in Accugait System Model ACG, Wa- subjects were instructed to decrease weight) volunteered to participate in tertown, Massachusetts). They were the “sounds” they made on impact, this study. All participants had similar instructed to use maximal effort ground reaction force was dimin- activity levels (22.97 ± 8.41 hours of (amplitude) during the test trials. ished.6 This shows that when dancers ballet training a week) and years of ex- To evaluate this, jump height was concentrate on a given task they can perience (14.17 ± 2.92 years). Prior to assessed during each jump. All danc- affect maximal ground reaction force, participating, subjects read and signed ers wore an elastic band around their either positively or negatively. an informed consent form approved waist and performance was recorded The last factor that may affect by the University Institutional Review with a standard video camera (Pana- ground reaction force is type of foot- Board for Protection of Human Sub- sonic PV-GS500). Using a postural wear. To date this factor has received jects, which also approved the study. grid the resulting video footage was minimal attention. Traditionally, analyzed for jump height. ballet dancers use two different shoes. Test Procedures To perform the assemblé, one The first is a flat technique shoe that Subjects were tested at the Athletic foot goes into the air as the dancer is made out of canvas or soft leather Training Research Laboratory on pushes off the floor with the sup- and has no padding or arch support one occasion for approximately 30 porting leg and extends the toes. of any kind. The second is the classical minutes. They performed an assem- Both legs then land simultaneously pointe shoe, made of corset satin on blé (Fig. 1) in both flat shoes (Fig. 2) in fifth position—i.e., with the feet the outside. The toe box of the pointe and pointe shoes (Fig. 3). The shoe completely crossed so that the heel of shoe consists of layers of burlap, card- order was randomized, with half the the front foot touches the toe of the board, paper, or a combination of dancers completing the trials in the back foot, and vice versa. The dancers these materials. There is a shank in the flat shoe first and half in the pointe were instructed to land in a proper sole of the shoe that is made of card- shoe first. Each dancer was allowed fifth position, hold for two seconds, board, leather, or a combination of to practice the jump until she was and then step off the platform. The the two.9 Pointe shoe construction has comfortable with it. trial was repeated if deemed unac- improved dramatically over the years. To standardize test procedures ceptable. An unacceptable trial was It was not until the 1950s that the all dancers started at the same place defined as one in which the dancer modern shoe was constructed.10 When the dancer acquires new shoes, she will usually customize them to her own foot by hitting them with a hammer, slamming them in a door, or steaming them over boiling water.10 This act of fitting the shoe to one’s own foot quickly breaks down the integrity of the shoe. Many times pointe shoes last only one performance, despite the layers of leather and fabric. Dancers wear pointe shoes to achieve a variety of aesthetic and practical advantages.10 As increased ground reaction force may lead to increased injury rates in dancers, investigating the effect of different types of ballet shoes on these forces is a potentially valuable step in determining how injuries may be prevented. Therefore, the purpose of this study was to determine whether the type of dance shoe used affects maximal ground reaction force (GRF- max) during a basic ballet jump. Methods Eighteen healthy female dancers en- rolled in a rigorous bachelor of science Figure 1 Assemblé jump. Journal of Dance Medicine & Science • Volume 15, Number 2, 2011 63

Table 1 Means and Standard Deviations for Each Shoe Condition We believe increased GRFmax in Maximal Ground Reaction Vertical Jump Height the flat shoe could have occurred Force (Newtons) (centimeters) for several reasons. First, the pointe Flat Shoe 1742.9 ± 252.6 33.1 ± 7.7 shoe may have absorbed more forces Pointe Shoe 1612.7 ± 261.5 32.4 ± 7.2 because of the layers of material that make up its sole. Conversely, the lack of any type of padding in the did not land in fifth position, lost her conditions (t = 1.22, p = .24, Effect flat shoe allowed most of the forces balance, landed with a double heel size = .08, Power = .21). to be absorbed by the body. Miller strike, or did not give maximal effort. and associates13 attempted to modify Six acceptable trials were completed Discussion the sole of a flat shoe by using PPT®, in each shoe condition. GRFmax data The primary focus of this investigation Spenco, and Sorbothane materials, were collected at the point when was to determine if a GRFmax differ- all of which are typically used in dancers landed from the jump. ence existed in ballet dancers landing making orthotics. The materials were an assemblé jump in flat shoes versus applied in different ways to produce Statistical Analysis pointe shoes. We were interested in 11 modifications of a flat shoe. Each GRFmax (Newtons) and maximal GRFmax because it may be linked modification allowed plantar pressure jump height (centimeters) were as- to an increase in injury rates.11,12 As to be distributed more evenly across sessed for each jump trial. The mean previously stated, several factors may the foot; thus, it was found that add- GRFmax and mean vertical jump affect GRFmax, including landing ing light layers to a typical flat shoe height for each shoe condition was surface, improper technique, incorrect helped decrease the GRFmax. This used for statistical analysis. Two de- landing, quality of instruction, and finding leads us to believe that extra pendent t-tests were conducted to footwear. Minimal attention has been material in the shoes does indeed determine differences between the given to researching the footwear used help to absorb some of the ground shoe types, one for GRFmax and one in ballet dancing. reaction forces. However, while the for jump height. Alpha level was set We found a significant increase in results of Miller and coworkers13 were at p < .05. GRFmax when dancers wore flat shoes. interesting, it is unlikely that many For this particular task, jump height dancers would be willing to pad their Results may also affect GRFmax. Therefore, flat shoes. Dancers are concerned Means and standard deviations for we also evaluated whether there was with being able to “feel the floor” each condition are displayed in Table a difference in jump height in the two and do not want anything extra in 1. We found a significant difference in shoe types. No significant difference their shoes. Therefore, this laboratory GRFmax between the two shoe condi- was observed in jump height between finding may not successfully translate tions (t = 3.53, p = .003). Specifically, the flat and pointe shoe trials. This to actual dance practice. the GRFmax was higher for landings finding indicates that any difference Another factor that possibly de- in flat shoes (1742.9 ± 252.6 N) than in GRFmax is primarily due to the creased GRFmax is the type of toe in pointe shoes (1612.7 ± 261.5 N). type of shoe used, or more precisely padding used in our subjects’ pointe There was no significant difference in the mechanics involved when landing shoes. Each dancer has a preference jump height between the two shoe jumps in the different types of shoes. for materials to use in covering her

Figure 2 Fifth position in flat shoes. Figure 3 Fifth position in pointe shoes. 64 Volume 15, Number 2, 2011 • Journal of Dance Medicine & Science toes to prevent blisters, ranging from old, broken pointe shoes during by avoiding additional stress on the paper towels, to lambswool, to gel- technique classes where full pointe intrinsic muscles of the foot. filled sleeves. This material may well is not used. They do this to help have helped to disperse the forces perfect working through the foot References more evenly when compared to the and strengthening its muscles. These 1. Simpson KJ, Kanter L. Jump distance flat shoes, but it is a variable that is shoes may provide the added benefit of dance landings influencing inter- extremely difficult to control for. of decreasing GRF . While the nal joint forces: I.axial forces. Med max Sci Sports Exerc. 1997;29(7):916-27. Yet another hypothesized reason reduction of GRFmax may not be as 2. Malone TR, Hardaker W. Rehabili- for the decreased GRFmax in the pronounced with a broken pair of tation of foot and ankle injuries in pointe shoes was related to dance pointe shoes, our study suggests that ballet dancers. J Orthop Sports Phys technique. As the dancers in this the additional material in the shoe Ther. 1990;11(8):355-61. study were quite experienced, they will still help disperse forces away 3. Seals JG. A study of dance surfaces. landed correctly. A correct landing from the body better than a flat shoe. Clin Sports Med. 1983;2(3):557-61. means that the three phases of land- 4. Werter R. Dance floors: a causative ing were achieved, with the tip of the Suggestions for Future factor in dance injuries. J Am Podiatr pointe shoe touching first and the rest Research Med Assoc. 1985;75(7):355-8. of the foot following sequentially. This study raises several questions 5. Fiolkowski P, Bauer J. The effects This technique of rolling through the that might be explored further to the of different dance surfaces on plan- tar pressures. J Dance Med Sci. foot allows the pointe shoe to absorb advantage of ballet dancers, instruc- 1997;1(2):62-6. more of the force and the dancer’s tors, and researchers. First, how does 6. McNair PJ, Prapavessis H, Callender lower extremity less. In flat shoes, on the age of the pointe shoe affect the K. Decreasing landing forces: effect the other hand, the foot contacts the transmission of GRFmax? Does GRF- of instruction. Br J Sports Med. floor in demi-pointe, and this initial max increase or decrease as the pointe 2000;34(4):293-6. impact on the metatarsal heads may shoe is broken in or overused? Second, 7. Shippen JM, Mech MI, Eng C, May 14 increase GRFmax. Chockley looked as there are many manufacturers of B. Calculation of muscle loading and at the time required to progress pointe shoes and all use slightly dif- joint contact forces during the rock through the three phases of landing, ferent components and procedures step in Irish Dance. J Dance Med Sci. and how long the dancer was in each in constructing their shoes, to what 2010;14(1):11-7. of these positions. She found that in extent do the materials used affect 8. Cassella MC, Ploski C, Sullivan E, Micheli LJ. Transition dance class: re- flat shoes initial toe contact had a GRFmax? Third, in this study we ex- habilitation through dance. J Dance mean duration of 0.02 seconds, the amined the effects of only one basic Med Sci. 1999;3(4):139-43. ball of the foot 0.037 seconds, and ballet jump (assemblé). Future studies 9. Cunningham BW, DiStefano AF, the heel contacted the ground for might look at any one of the many Kirjanov NA, et al. A comparative 0.053 seconds.14 It would be interest- other jumps used in ballet to see how mechanical analysis of the pointe ing to compare these times when the the resultant GRFmax compares to shoe toe box. Am J Sports Med. same jump is landed in flat shoes and that in the present investigation. 1998;26(4):555-61. pointe shoes. Also, these data would 10. Contompasis JP. The classical bal- in all likelihood change dramatically Conclusion let shoe. Clin Podiatr Med Surg. with the dancer’s experience level. Results of this study demonstrate a 1986;3(4):631-6. The experienced dancer would be significant decrease in GRF when 11. Ricard MD, Veatch S. Comparison max of impact forces in high and low expected to control her landing much the participants landed a jump in impact aerobic dance movements. better than the inexperienced one. pointe shoes relative to landing the Int J Sports Med. 1990;6(1):67-77. It is important to note that in this same jump in flat shoes. After ana- 12. Seegmiller JG, McCaw ST. Ground study GRFmax force was measured lyzing the two types of shoes used in reaction forces among gymnasts and only during one ballet jump. This ballet, it is understandable that the recreational athletes in drop landings. is, of course, just one component pointe shoe would create a smaller J Athl Train. 2003;38(4):311-4. of a ballet class or performance. The GRFmax. The multiple layers of the 13. Miller CD, Paulos LE, Parker RD, stresses imposed on the body by pointe shoe help to absorb some of Fishell M. The shoe: pointe work in general is a different the forces and disperse them away a preliminary study of eleven differ- issue that needs to be investigated from the dancer’s body. Based on these ently modified ballet technique shoes further. It is possible that pointe findings, we conclude that it may be using force and pressure plates. Foot Ankle. 1990;11(2):97-100. shoes might benefit dancers by de- advantageous to have dancers take 14. Chockley C. Ground reaction force creasing GRFmax if used for dancing technique class in pointe shoes. As comparison between landing on the at all times, even when achieving full they will not be required to achieve full foot and jumps landing en pointe pointe is not required. There are, in full pointe during this class, they may in ballet dancers. J Dance Med Sci. fact, many dancers who wear their benefit from the decreased GRFmax 2008;12(1):5-8.