Ground Reaction Forces in Ballet Dancers Landing in Flat Shoes Versus Pointe Shoes

Original Article Ground Reaction Forces in Ballet Dancers Landing in Flat Shoes 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 shoe 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 footwear 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 Dcareers, 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.

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