- Email: [email protected]
The effect of textured ballet shoe insoles on ankle proprioception in dancers
Accepted Manuscript The effect of textured ballet shoe insoles on ankle proprioception in dancers Dr. Nili Steinberg, Gordon Waddington, Roger Adams, Janet Karin, Oren Tirosha PII:
S1466-853X(15)00031-0
DOI:
10.1016/j.ptsp.2015.04.001
Reference:
YPTSP 661
To appear in:
Physical Therapy in Sport
Received Date: 11 February 2014 Revised Date:
18 February 2015
Accepted Date: 13 April 2015
Please cite this article as: Steinberg, N., Waddington, G., Adams, R., Karin, J., Tirosha, O., The effect of textured ballet shoe insoles on ankle proprioception in dancers, Physical Therapy in Sports (2015), doi: 10.1016/j.ptsp.2015.04.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The effect of textured ballet shoe insoles on ankle proprioception in dancers
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Running headline: Texture insoles and ankle proprioception in dancers
Nili Steinberg A, B, Gordon Waddington C, Roger Adams D, Janet Karin E, Oren Tirosh A
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A. Institute of sport exercise and active living (ISEAL), Victoria University, Victoria,
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Australia.
B. Zinman College of Physical Education and Sports Sciences, Wingate Institute, Netanya, Israel.
C. Faculty of Health, University of Canberra, Australia.
D. School of Physiotherapy, University of Sydney, Australia.
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Corresponding author:
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E. The Australian Ballet School, Melbourne, Australia.
Dr. Nili Steinberg,
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Institute of sport exercise and active living (ISEAL), Victoria University, Victoria, Australia.
Email: [email protected]
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The effect of textured ballet shoe insoles on ankle proprioception in dancers ABSTRACT
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Background: Impaired ankle inversion movement discrimination (AIMD) can lead to ankle sprain injuries. The aim of this study was to explore whether wearing textured insoles improved AIMD compared with barefoot, ballet shoes and smooth insoles, among dancers.
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Methods: Forty-four adolescent and mature male and female dancers, aged 13-19, from
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The Australian Ballet School were tested for AIMD while barefoot, wearing ballet shoes, wearing smooth insoles, and wearing textured insoles.
Results: No interaction was found between the four different footwear conditions, the two genders, or the two levels of dancers in AIMD (p>.05). An interaction was found between the four different footwear conditions and the three tertiles when tested in
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ballet shoes (p=.006). Although significant differences were found between the upper tertiles and the lower tertiles when tested with ballet shoes, barefoot and with smooth
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insoles (p<.001; p<.001; p=.047, respectively), when testing with textured insoles dancers in the lower tertile obtained similar scores to those obtained by dancers in the
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upper tertile (p=.911).
Conclusion: Textured insoles improved the discrimination scores of dancers with low AIMD, suggesting that textured insoles may trigger the cutaneous receptors in the plantar surface, increasing the awareness of ankle positioning, which in turn might decrease the chance of ankle injury. Key Words: dancers, ankle discrimination, proprioception, injuries.
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ACCEPTED MANUSCRIPT INTRODUCTION Ballet dancers require high levels of postural and balance control to achieve better performance (Kiefer et al., 2011; Bronner, 2012; Lobo da Costa et al., 2013). Postural balance can be defined as the ability to maintain the body’s center of mass
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within its base of support, with the mechanisms controlling postural control consisting of visual, vestibular and somatosensory/ proprioceptive feedback (Hrysomallis, 2007). Somatosensory feedback refers to the proprioceptors located at the skin, muscles,
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tendons, ligaments, and joint capsules (McKeon & Hertel, 2007; Li et al., 2009; Höhne et al., 2011), which are integrated to determine the body position and movements in
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space. The sensory information from the proprioceptors contributes to providing feedback to the central nervous system regarding any change in foot position, in order to maintain balance and prevent loss of balance and potential injuries (Höhne et al., 2011).
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To achieve excellence in a dance performance, dancers must have an outstanding proprioceptive ability to optimally represent limb position in space (Jola et al., 2011; Kiefer et al., 2013). Enhanced proprioceptive feedback may allow for
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improved movement smoothness, with better coordination and accuracy, which reflect
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the aesthetical values of dance (Smitt & Bird, 2013). Moreover, as professional dancers depend on the reliable functional stability of their ankle and foot joints to exercise their profession, better ankle and foot proprioception has been attributed to prolonged periods of training and decreased risk of injuries (Hertel et al., 2002; Arnold et al., 2009; Li et al., 2009; Marmeleira et al., 2009; Muaidi et al., 2009; Lin et al., 2011; Rein et al., 2011; Han et al., 2013a; Hutt & Redding, 2014). Any disruption of the proprioceptive system at the ankle may result in the generation of postural instability, ineffective application of muscle force, decreased
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ACCEPTED MANUSCRIPT detection of inversion movements, or a delay in the motor response of the peroneal muscles. Poor ankle movement control, especially over the medial-lateral direction, may place the ankle joint in inversion positions at increased risk for ankle and foot injuries (Hiller et al., 2004; Corbin et al., 2007; Hrysomallis, 2007; Batson, 2009;
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Hrysomallis et al., 2011; Lin et al., 2011).
Previous studies have already attempted to increase plantar sensory and
proprioceptive feedback, with the aim of protecting the athlete/dancer from injury (e.g.,
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Batson et al., 2009; Li et al., 2009; Muaidi et al., 2009; Witchalls et al., 2013). Since
the plantar sole of the foot has previously been shown to provide important information
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about the disposition and movement of the body (Waddington & Adams, 2003), the rationale for inserting textured insoles into athletes’ shoes was that performance might be improved by enhancing afferent information from the plantar sole to the central nerve system (Waddington & Adams, 2003; Cameron et al., 2008; Pearson & Whitaker,
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2012). The ability of textured insoles to improve the proprioception feedback from the sole of the foot and to provide an avenue for further reducing lower limb injuries, has been measured previously in athletes such as soccer and netball players, but not among
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dancers wearing ballet shoes (Waddington & Adams, 2000; Waddington & Adams,
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2003; Salles & Gyi, 2013).
In the current study, we hypothesized that proprioceptive insoles inserted in the
ballet shoes would enhance proprioceptive feedback, providing more accurate information about foot position. This hypothesis was based on the assumption that wearing textured insoles would increase afferent information and improve ankle discrimination ability (Corbin et al., 2007). Furthermore, insoles have been shown to be well tolerated by athletes/dancers as an intervention for balance improvement and injury prevention (Waddington & Adams, 2000; Salles & Gyi, 2013).
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ACCEPTED MANUSCRIPT An accurate way to evaluate the ability of the somatosensory system around the ankle joint to detect changes in foot position, is by measuring the ankle inversion movement discrimination ability (Waddington & Adams, 2003). It should be noted that although inversion movement occurs anatomically at the sub-talar joint, most ankle
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injuries have been found to be associated with false functional inversion movement at the ankle joint (Ashton-Miller, 2000; Waddington & Adams, 2003). Hence, in the
current study ankle discrimination refers to inversion movement at the ankle joint.
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There is a general consensus in the dance literature that proprioception and
postural balance vary between dancers and non-dancers, between different dance levels
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(e.g., professional vs. amateur dancers), and when tested with different types of dance shoes (e.g., pointe shoes vs. demi-pointe shoes) (Nunes, 2002; Fong Yan et al., 2011; Rein et al., 2011; Kiefer et al., 2013; Smitt & Bird, 2013; Wyon et al., 2013; Hopper et al., 2014; Hutt & Redding, 2014); No previous study has examined the effect of the
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different construction of dance shoe linings on enhancing proprioception that may contribute to injury prevention. Therefore, the purpose of the current study was: 1) To examine the influence of textured insoles inserted into the ballet shoes
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compared to other conditions (barefoot, ballet shoes without insoles, and smooth
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insoles inserted into the ballet shoes) on AIMD among adolescents and mature dancers of both genders.
2) To determine whether AIMD in dancers with different footwear conditions
changes over time.
METHODS A group of 44 dancers, aged 13-19 years (mean age= 16.32 ± 1.625), from the Australian Ballet School (ABS), were included in the current study. The study was
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ACCEPTED MANUSCRIPT approved by the Ethics Committee of Victoria University, Australia. All dancers and one of their parents (for dancers under the age of 18) provided written informed consent for participation. All participants were full-time elite classical ballet students at the ABS. Their
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ages ranged from 13 to 19 and their dance levels ranged between Levels 4-5
(adolescent dancers aged 13 to 16) and 6-7 (mature dancers aged 17 to 19) (Table 1). ABS students are selected by an extensive audition process. Students are
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predominantly from throughout Australia and New Zealand and from Asian countries, particularly Japan and China.
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For inclusion in the present study, participants had to be students that were participating in a full-time programme of vocational dance training at the ABS. Participants were excluded from the study if they were suffering from any current lower extremity or lower back injury.
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Equipment:
Ankle Movement Extent Discrimination Apparatus (AMEDA): The AMEDA provides discrimination scores representing each participant’s sensitivity to small differences in
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the degree of ankle inversion (Waddington & Adams, 1999) (Figure 1).
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The AMEDA device consists of a hinged plate which rotates around an axle under the long axis of the foot being tested. With their feet placed shoulder-width apart, standing with both legs in a weight bearing position, subjects were asked to stand in a relaxed posture on the platform of the AMEDA, with the foot of the limb being tested centered over the axis of movement of the movable base plate. The participant made an active inversion movement which moved the plate and the outer side of the foot down until contact was made by the rim of the plate on an adjustable metal stop. The participant then returned the plate to the horizontal stopped position at
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ACCEPTED MANUSCRIPT the same steady pace, and made a judgment as to the degree of inversion achieved during the movement. The AMEDA uses a set of 5 predetermined available end positions for ankle inversion movements. The 5 predetermined displacements, from smallest to largest,
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were: 10.49˚, 11.84˚, 12.55˚, 13.27˚ and 14.52˚ from the horizontal position. A
position number (1, 2, 3, 4 or 5) was assigned to each movement displacement in order from the smallest/shallowest angle (10.49˚- position number 1) to the
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largest/deepest angle (14.52˚- position number 5). Participants were provided with three familiarization trials during which they experienced all of the available
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movement degrees in sequence. A trial consists of each of the 5 movement degrees being presented to the participant 10 times in a random order (a total of 50 ankle movements), with the participant judging each movement degree as it is undertaken and reporting the appropriate position number.
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Four footwear conditions: The ability to discriminate differences in the degree of ankle inversion movements was measured in four different footwear conditions. The order in which each dancer was tested with the four different types of footwear
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was randomized using a Latin square.
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1. Ballet shoes: Each dancer was tested using his/her personal ballet shoes. 2. Barefoot: The dancers were tested standing barefoot on the AMEDA device.
3. Textured insoles: We used rubber insoles with four nodules (3 mm high and 1 mm diameter) per square centimeter, similar to the textured rubber compound described previously by Waddington and Adams (2000, 2003). The rubber was cut-to-fit for each dancer and was inserted into the dancer’s own ballet shoe (Figure 2).
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ACCEPTED MANUSCRIPT 4. Smooth insoles: 3mm PVC Vinyl upholstery “Expanded – Slate” insole. The smooth insoles were cut to fit for each dancer and were inserted into the dancer’s own ballet shoe. Testing protocol:
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All dancers were asked to identify their dominant leg, which was defined as
the dominant weight-bearing leg, the leg for take-offs and landings, and the preferred hopping leg (for a pirouette, for example) (Hiller et al., 2004; Kiefer et al., 2011; Rein
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et al., 2011). The dancers were tested on their dominant side under four (randomized) conditions (barefoot, wearing their ballet shoes without insoles, wearing smooth
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insoles in their ballet shoes, and wearing textured insoles in their ballet shoes). The dancers were tested in two different conditions on one day (with a 10-min rest between the two foot-wear conditions), and in the two additional conditions on the following day (again, with a 10-min rest in between). The tests were undertaken on
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separate days and with 10-min rest in between, so as to avoid fatigue of the tested leg in the four different foot-wear conditions.
Pre-test: Participants were given a brief pre-test of three series of trial movements to
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familiarize them with the feel of the plate at each of the inversion distances, prior to
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data collection. In the pre-test, they experienced the five inversion movement distances, in order, from the smallest (moving to position 1) to the largest (moving to position 5), three times (15 in total). Test: Participants then undertook 50 trial blocks, without feedback. The trials were presented in a random sequence, 10 at each of the 5 different movement displacements. The test protocol provides a score reflecting the participant’s ability to discriminate between the adjacent inversion angles (Maher & Adams, 1996). The
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ACCEPTED MANUSCRIPT accuracy with which the participant distinguishes between each adjacent pair of angles (1-2, 2-3, 3-4, 4-5) is calculated, using the area under the curve (AUC) of the receiver operating a characteristic curve for each adjacent pair. The total score is the mean of the AUC scores for the 4 degrees of freedom between the 5 stop positions.
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AUC values range from 0.5, which is equivalent to chance responding, to 1.0,
representing a perfect ability to discriminate between the 5 different movement degrees (Han et al., 2013a, b; Witchalls et al., 2013).
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Each dancer received a final AUC score for each test condition (barefoot,
ballet shoes, textured insoles and smooth insoles). Based on the ballet shoes’ AUC
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score (mostly relevant for their daily dance training), all dancers were subdivided into three tertiles. This division could further represent the dancers with "better" discrimination ability and the dancers with "worse" discrimination ability. Reliability of the scores (Inter-class Correlation Coefficient) generated by the
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AMEDA tests has been determined as ranging from 0.82 to 0.96. (Waddington & Adams, 2004; Han et al., 2013a, b). The AMEDA device fulfills the validity criteria for assessing active movement function, with sufficient trials to determine the
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participants’ ability to use proprioceptive information when they discriminate a set of
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movements (Ashton-Miller, 2000; Han et al., 2013a). Data Analysis:
Analysis of variance (ANOVA) with repeated measures was used to compare
the four different footwear conditions, in the two levels (adolescent dancers – levels 4-5; mature dancers – levels 6-7), and two genders (male, female) of dancers. To further examine the effect of footwear on the ankle discrimination score, the participants were subdivided into tertiles based on the score they obtained in ballet shoe testing. ANOVA with repeated measures was used to compare the four different
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ACCEPTED MANUSCRIPT foot-wear conditions, in the upper and lower tertiles. The analysis was performed using SPSS software version 21.0 (SPSS Inc., Chicago, Illinois). The level of significance for all statistical tests was set at 0.05. RESULTS
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Table 2 presents the mean scores ( X ± SD) of ankle inversion movement
discrimination under four different testing conditions (barefoot and three types of footwear), among adolescent and mature males and females.
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No interaction was found between the four different footwear conditions and the two genders tested (p>.05); no interaction was found between the four different
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footwear conditions and the levels of dancers (adolescence/mature) (p>.05); and, no interaction was found between the four different footwear conditions, the two genders tested and the two levels of dancers (p>.05).
Tertiles: All dancers were divided into three tertiles, based on the score they obtained
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when testing with ballet shoes. An interaction was found between the four different footwear conditions and the upper tertile and lower tertile of dancers when tested in ballet shoes (p=.006), indicating significant differences between the upper tertiles and
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the lower tertiles of dancers when tested with ballet shoes, barefoot and smooth
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insoles (p<.001; p<.001; p=.047, respectively). However, when tested while wearing the textured insoles, no differences were obtained by the dancers in the upper tertile and the dancers in the lower tertile (p=.911), suggesting improved scores by the lowest tertile of dancers when wearing the textured insoles (Figure 3). Learning effect: Significant improvement was found between the second testing compared to the first testing (p=.025) and between the third testing compared to the first testing (p=.011). No significant improvement was found between the third testing and the second testing. Furthermore, no significant improvement was found between
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ACCEPTED MANUSCRIPT the fourth testing and the first testing, or between the fourth testing and the third testing (Figure 4).
DISCUSSION
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The main findings of the current study demonstrated that dancers with lower discrimination scores significantly improved their ability to judge inversion
movements, up to the level of dancers with good ability, by wearing textured insoles.
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Dancers with lower discrimination ability appeared to significantly benefit from the
enhanced stimulation of cutaneous receptors of the plantar surface, which appears to
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have enhanced the afferent input received by the central nerve system (Cameron et al., 2008), leading to an improved movement discrimination capacity in this group. In previous studies, it was demonstrated that additional proprioceptive stimuli to the foot when insoles are worn show greater improvement in subjects with lower
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proprioception ability to begin with, or those with a history of injury (Newcomer et al., 2001; Cameron et al., 2008). The sensitivity of the plantar surface is related to differences in the stiffness, roughness texture and flexibility of the contact surface.
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Inserting insoles into the ballet shoes of dancers with low discrimination ability may
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have increased the level of information available from the contact surface up to that of dancers with high sensitivity levels (Mundermann et al., 2001). Another explanation might be that different groups of dancers have different
foot types, with different sensation ability. The major limitation of the current study is that no screening for sensory ability or for foot type was made for our participants prior to commencing the testing. It might be that wearing the textured insoles differently affected dancers with high/low foot sensation and dancers with a different foot shape. Subjects with pes planus feet, for example, may have had more plantar
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ACCEPTED MANUSCRIPT cutaneous surface area contact compared with subjects with pes cavus feet (Corbin et al., 2007). These differences in foot types may have resulted in different discrimination abilities among the different groups of dancers. The negative effect of wearing textured insoles in dancers with pre-existing
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higher discrimination ability may be due to the additional enhancement of afferent stimulation provided by the insoles having overloaded their sensorimotor system (Newcomer et al., 2001). Similar to our results, Cameron and colleagues (2008)
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investigated the effect of wearing close-fitting neoprene shorts on swinging leg
movement discrimination scores in elite level Australian football players. The authors
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found that high ability participants were worse at the discrimination task when wearing neoprene shorts, but low ability subjects performed better in neoprene shorts. It might be that for dancers with good proprioceptive ability, additional textured insoles confuse the sensory system, for which information is important, resulting in
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increased error and poorer performance. Furthermore, McNair and Heine (1999) examined the effects of a neoprene lumbar brace on proprioceptive ability and found that although bracing can improve proprioception, subjects with poor proprioception
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improve more by wearing lumbar braces, compared to subjects with good
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proprioception.
When all dancers with different ranks of proprioception ability (combined
three tertiles) were considered, no interaction was found between the four different footwear conditions, the two genders or the two levels of dancers, in their ankle inversion movement discrimination ability. This suggests that the initial proprioception ability of the dancers is the only parameter that can define the importance of wearing textured insoles, rather than their dance level or gender.
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ACCEPTED MANUSCRIPT Reducing plantar cutaneous afferent input (through surface cooling, for example) has been found to change the base of support and impair postural control (McKeon & Hertel 2007; Wang & Lin, 2008). It may be that increasing the afferent input by wearing textured insoles only during the time of testing does not provide
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sufficient time for dancers with existing higher level discrimination to improve their discrimination ability. In a previous report, it was indicated that when a textured
insole was added to the athletic shoes of elite netball players (for testing only), their
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discrimination score was not significantly different from the score obtained in
barefoot testing (Waddington & Adams. 2000). Further research is required to
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determine the association between wearing textured insoles over an extended period and changes to proprioception ability, especially given that it has been reported that enhanced proprioceptive and balance ability is an outcome of years of sport-specific training (Daneshjoo et al., 2012; Han et al., 2013b).
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The textured insoles used in this study did not seem to cause significant discomfort to the participants, with few of the dancers reporting issues with comfort when wearing the textured insoles for the first time. Salles and Gyi (2013), who
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attempted to evaluate the use of personalized insoles versus non-personalized insoles
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in terms of comfort, found that both types of insoles were defined as causing discomfort. The authors explained that the changed foot capturing position of the insole and the insole thickness may have contributed to the higher ratings of discomfort, with increased rigidity restricting the natural movement of the feet. The proprioceptive ability of the dancers in the current study might have been altered by insertion of the additional textured material that changed the normal foot position during motion (Lin et al., 2011; Fong Yan et al., 2011). Xiong and colleagues (2011) found that the medial plantar arch has a lower pain pressure threshold in comparison
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ACCEPTED MANUSCRIPT to the other plantar regions of the foot, which can cause increased pressure discomfort thresholds. Moreover, Robbins et al. (1995) examined the hypothesis that lower judgment of foot position is due to a change in plantar tactile sensibility, and that footwear itself will further impair position judgments. These researchers found that
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wearing footwear impaired foot position awareness compared to being barefoot, and that reduced information about foot position may worsen postural balance in both
young and elderly subjects. The insertion of textured insoles into the ballet shoes of
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the dancers tested here might have increased the stiffness around the foot tissue and increased the pain pressure threshold and arch discomfort which may interfere with
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proprioception ability in the ankle/foot area (Salles & Gyi, 2013).
Finally, these results suggested a "learning effect" among the dancers during the first three repetitions, which had stabilized by the fourth test. In a test requiring movement of a cursor to a target using ankle movements of plantar/dorsi-flexion and
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inversion/eversion, Morris and colleagues (2009) looked for a learning effect and observed that the early trials exhibited the worst performance, meaning that errors decreased from the first to last task. Witchalls and colleagues (2013) found similar
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results among healthy university students over three test repetitions on the AMEDA.
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Comparing healthy students with students suffering from chronic ankle instability, these authors found that healthy students improved their scores between the first and second test, after which their performance stabilized for the third test. Clinical implications:
The risk of ankle injuries is of great concern to dancers. An important implication of the current study is that further evaluation of effective assessment of proprioception ability is needed to evaluate its role in the dancer's fitness profile. Dancers with low inversion movement discrimination scores (such as those in the
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ACCEPTED MANUSCRIPT lower tertile of the current study) may benefit from additional proprioceptive training, as it has been demonstrated to be a component of better performance ability, in preventing lower extremity injuries, as well as in reducing recovery time and providing additional protection against re-injury (Batson, 2009; Waddington &
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Adams, 1999). CONCLUSIONS
Insertion of textured insoles into the ballet shoes of dancers with low
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discrimination scores may enhance their movement discrimination ability to the level of dancers with good discrimination scores. This might be due to the textured insoles
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triggering increased activity in the cutaneous receptors in the plantar surface of the foot, which increases plantar sensitivity, and in turn, might decrease their risk of injury.
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30. Mundermann, A., Stefanyshyn, D.J., & Nigg, B.M. (2001). Relationship between footwear comfort of shoe inserts and anthropometric and sensory factors. Medicine & Science in Sports & Exercise, 33(11), 1939-45.
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ACCEPTED MANUSCRIPT 31. Newcomer, K., Laskowski, E.R., Yu, B., Johnson, J.C., & An, K.N. (2001). The effects of a lumbar support on repositioning error in subjects with low back pain. Arch Phys Med Rehabil, 82, 906-10. 32. Nunes, N.M., Haddad, J.J., Bartlett, D.J., & Obright, K.D. (2002).
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Musculoskeletal injuries among young, recreational, female dancers before and after dancing in pointe shoes. Pediatr Phys Ther, 14, 100-6.
33. Pearson, S.J., & Whitaker, A.R. (2012). Footwear in classical ballet: A study
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of pressure distribution and related foot injury in the adolescent dancer. J Dance Med Sci, 16(2), 51-6.
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34. Rein, S., Fabian, T., Zwipp, H., Rammelt, S., & Weindel, S. (2011). Postural control and functional ankle stability in professional and amateur dancers. Clin Neurophysiol, 122, 1602-10.
35. Robbins, S., Waked, E., & Rappel, R. (1995). Ankle taping improves
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proprioception before and after exercise in young men. Br J Sports Med, 29, 242-7.
36. Salles, A.S., & Gyi, D.E. (2013).
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An evaluation of personalised insoles developed using additive manufacturing.
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J Sports Sci, 31(4), 442-50. 37. Smitt, M.S., & Bird, H.A. (2013). Measuring and enhancing proprioception in musicians and dancers. Clin Rheumatol, 32, 469-73.
38. Waddington, G., & Adams, R. (1999). Discrimination of active plantarflexion and inversion movements after ankle injury. Aust J Physiother, 45(1), 7-13. 39. Waddington, G., & Adams, R. (2000). Textured insole effects on ankle movement discrimination while wearing athletic shoes. Phys Ther Sport, 1, 119-128.
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ACCEPTED MANUSCRIPT 40. Waddington, G., & Adams, R. (2003). Football boot insoles and sensitivity to extent of ankle inversion movement. Br J Sports Med, 37(2), 170-4. 41. Waddington, G., & Adams, R.D. (2004). The effect of a 5-week wobble-board exercise intervention on ability to discriminate different degrees of ankle
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inversion, barefoot and wearing shoes: a study in healthy elderly. J Am Geriatr Soc, 52, 573-6. 42. Wang, T.Y., & Lin, S.I. (2008).
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Sensitivity of plantar cutaneous sensation and postural stability. Clin Biomech (Bristol, Avon), 23(4), 493-9.
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43. Witchalls, J.B., Waddington, G., Adams, R., & Blanch, P. (2013). Chronic ankle instability affects learning rate during
repeated proprioception testing. Phys Ther Sport, [Epub ahead of print]. 44. Wyon, M.A., Cloak, R., Lucas, J., & Clarke, F. (2013). Effect of midsole
Art, 28, 195-8.
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thickness of dance shoes on dynamic postural stability. Med Probl Perform
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45. Xiong, S., Goonetilleke, R.S., & Jiang, Z. (2011). Pressure thresholds of the human foot: measurement reliability and effects of stimulus characteristics.
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Ergonomics, 54(3), 282-93.
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ACCEPTED MANUSCRIPT Table 1: Number of dancers, mean age, and hours of practice per week, for adolescent and mature dancers.
Adolescent dancers
Males
N
Mean age
10
15.6±1.1
Dance hours per week
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18
(Level 4+5)
Females
16
15.2±.98
Mature dancers
Males
10
18.1.±1.2
24 - 29
Females
8
17.4±1.2
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(Level 6+7)
Table 2: The mean scores ( X ± SD) of ankle inversion movement discrimination (AUC values) under four different testing conditions (barefoot, ballet shoes, smooth
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insoles, textured insoles).
Adolescent
Mature
females
females
males
males
.687±.066
.690±.045
.682±.064
.721±.090
.687±.067
.690±.051
.698±.068
.715±.074
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Ballet shoes
Mature
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Barefoot
Adolescent
Smooth insoles
.699±.061
.693±.062
.696±.069
.656±.101
Textured insoles
.689±.065
.694±.047
.693±.040
.664±.067
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Figure 1: The AMEDA device.
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Figure 2: Textured insoles inserted to the ballet shoes
ACCEPTED MANUSCRIPT Figure 3: Mean score (±SE) for dancers in the upper tertile and lower tertile (when tested with ballet shoes) in the four different footwear conditions.
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Upper tertile Lower tertile
0.75
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0.7
0.65
*
0.6
balletshoes
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(AUC) values
Ankle inversion movement discrimination
0.8
*
*
barefeet
smoothins
Textureins
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* Significant differences between the upper tertile and the lower tertile (p<.05).
ACCEPTED MANUSCRIPT Figure 4: Mean score (±SE) of ankle discrimination score, by testing order.
0.72 0.71 0.7
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0.68 0.67 0.66 0.65 0.64 0.63 0.62
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Test_3
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Test_2
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Test_1
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AMEDA score
0.69
Test_4
ACCEPTED MANUSCRIPT Highlights: •
Textured insoles enhanced discrimination ability of dancers with low ability.
•
Dancers with low ability improved up to the level of dancers with good ability. Textured insoles increased the activity of receptors in the plantar surface.
•
Increased plantar sensitivity might decrease the risk of ankle injury.
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•
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ACCEPTED MANUSCRIPT • Ethical Approval: The research was approved by the Ethics Committee of Victoria University, Australia. All dancers and one of their parents (for dancers under the age of 18) provided written informed consent for participation. • Funding: No.
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• Conflict of Interest: No
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S1466-853X(15)00031-0
DOI:
10.1016/j.ptsp.2015.04.001
Reference:
YPTSP 661
To appear in:
Physical Therapy in Sport
Received Date: 11 February 2014 Revised Date:
18 February 2015
Accepted Date: 13 April 2015
Please cite this article as: Steinberg, N., Waddington, G., Adams, R., Karin, J., Tirosha, O., The effect of textured ballet shoe insoles on ankle proprioception in dancers, Physical Therapy in Sports (2015), doi: 10.1016/j.ptsp.2015.04.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The effect of textured ballet shoe insoles on ankle proprioception in dancers
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Running headline: Texture insoles and ankle proprioception in dancers
Nili Steinberg A, B, Gordon Waddington C, Roger Adams D, Janet Karin E, Oren Tirosh A
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A. Institute of sport exercise and active living (ISEAL), Victoria University, Victoria,
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Australia.
B. Zinman College of Physical Education and Sports Sciences, Wingate Institute, Netanya, Israel.
C. Faculty of Health, University of Canberra, Australia.
D. School of Physiotherapy, University of Sydney, Australia.
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Corresponding author:
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E. The Australian Ballet School, Melbourne, Australia.
Dr. Nili Steinberg,
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Institute of sport exercise and active living (ISEAL), Victoria University, Victoria, Australia.
Email: [email protected]
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The effect of textured ballet shoe insoles on ankle proprioception in dancers ABSTRACT
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Background: Impaired ankle inversion movement discrimination (AIMD) can lead to ankle sprain injuries. The aim of this study was to explore whether wearing textured insoles improved AIMD compared with barefoot, ballet shoes and smooth insoles, among dancers.
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Methods: Forty-four adolescent and mature male and female dancers, aged 13-19, from
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The Australian Ballet School were tested for AIMD while barefoot, wearing ballet shoes, wearing smooth insoles, and wearing textured insoles.
Results: No interaction was found between the four different footwear conditions, the two genders, or the two levels of dancers in AIMD (p>.05). An interaction was found between the four different footwear conditions and the three tertiles when tested in
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ballet shoes (p=.006). Although significant differences were found between the upper tertiles and the lower tertiles when tested with ballet shoes, barefoot and with smooth
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insoles (p<.001; p<.001; p=.047, respectively), when testing with textured insoles dancers in the lower tertile obtained similar scores to those obtained by dancers in the
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upper tertile (p=.911).
Conclusion: Textured insoles improved the discrimination scores of dancers with low AIMD, suggesting that textured insoles may trigger the cutaneous receptors in the plantar surface, increasing the awareness of ankle positioning, which in turn might decrease the chance of ankle injury. Key Words: dancers, ankle discrimination, proprioception, injuries.
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ACCEPTED MANUSCRIPT INTRODUCTION Ballet dancers require high levels of postural and balance control to achieve better performance (Kiefer et al., 2011; Bronner, 2012; Lobo da Costa et al., 2013). Postural balance can be defined as the ability to maintain the body’s center of mass
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within its base of support, with the mechanisms controlling postural control consisting of visual, vestibular and somatosensory/ proprioceptive feedback (Hrysomallis, 2007). Somatosensory feedback refers to the proprioceptors located at the skin, muscles,
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tendons, ligaments, and joint capsules (McKeon & Hertel, 2007; Li et al., 2009; Höhne et al., 2011), which are integrated to determine the body position and movements in
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space. The sensory information from the proprioceptors contributes to providing feedback to the central nervous system regarding any change in foot position, in order to maintain balance and prevent loss of balance and potential injuries (Höhne et al., 2011).
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To achieve excellence in a dance performance, dancers must have an outstanding proprioceptive ability to optimally represent limb position in space (Jola et al., 2011; Kiefer et al., 2013). Enhanced proprioceptive feedback may allow for
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improved movement smoothness, with better coordination and accuracy, which reflect
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the aesthetical values of dance (Smitt & Bird, 2013). Moreover, as professional dancers depend on the reliable functional stability of their ankle and foot joints to exercise their profession, better ankle and foot proprioception has been attributed to prolonged periods of training and decreased risk of injuries (Hertel et al., 2002; Arnold et al., 2009; Li et al., 2009; Marmeleira et al., 2009; Muaidi et al., 2009; Lin et al., 2011; Rein et al., 2011; Han et al., 2013a; Hutt & Redding, 2014). Any disruption of the proprioceptive system at the ankle may result in the generation of postural instability, ineffective application of muscle force, decreased
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ACCEPTED MANUSCRIPT detection of inversion movements, or a delay in the motor response of the peroneal muscles. Poor ankle movement control, especially over the medial-lateral direction, may place the ankle joint in inversion positions at increased risk for ankle and foot injuries (Hiller et al., 2004; Corbin et al., 2007; Hrysomallis, 2007; Batson, 2009;
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Hrysomallis et al., 2011; Lin et al., 2011).
Previous studies have already attempted to increase plantar sensory and
proprioceptive feedback, with the aim of protecting the athlete/dancer from injury (e.g.,
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Batson et al., 2009; Li et al., 2009; Muaidi et al., 2009; Witchalls et al., 2013). Since
the plantar sole of the foot has previously been shown to provide important information
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about the disposition and movement of the body (Waddington & Adams, 2003), the rationale for inserting textured insoles into athletes’ shoes was that performance might be improved by enhancing afferent information from the plantar sole to the central nerve system (Waddington & Adams, 2003; Cameron et al., 2008; Pearson & Whitaker,
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2012). The ability of textured insoles to improve the proprioception feedback from the sole of the foot and to provide an avenue for further reducing lower limb injuries, has been measured previously in athletes such as soccer and netball players, but not among
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dancers wearing ballet shoes (Waddington & Adams, 2000; Waddington & Adams,
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2003; Salles & Gyi, 2013).
In the current study, we hypothesized that proprioceptive insoles inserted in the
ballet shoes would enhance proprioceptive feedback, providing more accurate information about foot position. This hypothesis was based on the assumption that wearing textured insoles would increase afferent information and improve ankle discrimination ability (Corbin et al., 2007). Furthermore, insoles have been shown to be well tolerated by athletes/dancers as an intervention for balance improvement and injury prevention (Waddington & Adams, 2000; Salles & Gyi, 2013).
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ACCEPTED MANUSCRIPT An accurate way to evaluate the ability of the somatosensory system around the ankle joint to detect changes in foot position, is by measuring the ankle inversion movement discrimination ability (Waddington & Adams, 2003). It should be noted that although inversion movement occurs anatomically at the sub-talar joint, most ankle
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injuries have been found to be associated with false functional inversion movement at the ankle joint (Ashton-Miller, 2000; Waddington & Adams, 2003). Hence, in the
current study ankle discrimination refers to inversion movement at the ankle joint.
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There is a general consensus in the dance literature that proprioception and
postural balance vary between dancers and non-dancers, between different dance levels
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(e.g., professional vs. amateur dancers), and when tested with different types of dance shoes (e.g., pointe shoes vs. demi-pointe shoes) (Nunes, 2002; Fong Yan et al., 2011; Rein et al., 2011; Kiefer et al., 2013; Smitt & Bird, 2013; Wyon et al., 2013; Hopper et al., 2014; Hutt & Redding, 2014); No previous study has examined the effect of the
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different construction of dance shoe linings on enhancing proprioception that may contribute to injury prevention. Therefore, the purpose of the current study was: 1) To examine the influence of textured insoles inserted into the ballet shoes
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compared to other conditions (barefoot, ballet shoes without insoles, and smooth
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insoles inserted into the ballet shoes) on AIMD among adolescents and mature dancers of both genders.
2) To determine whether AIMD in dancers with different footwear conditions
changes over time.
METHODS A group of 44 dancers, aged 13-19 years (mean age= 16.32 ± 1.625), from the Australian Ballet School (ABS), were included in the current study. The study was
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ACCEPTED MANUSCRIPT approved by the Ethics Committee of Victoria University, Australia. All dancers and one of their parents (for dancers under the age of 18) provided written informed consent for participation. All participants were full-time elite classical ballet students at the ABS. Their
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ages ranged from 13 to 19 and their dance levels ranged between Levels 4-5
(adolescent dancers aged 13 to 16) and 6-7 (mature dancers aged 17 to 19) (Table 1). ABS students are selected by an extensive audition process. Students are
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predominantly from throughout Australia and New Zealand and from Asian countries, particularly Japan and China.
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For inclusion in the present study, participants had to be students that were participating in a full-time programme of vocational dance training at the ABS. Participants were excluded from the study if they were suffering from any current lower extremity or lower back injury.
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Equipment:
Ankle Movement Extent Discrimination Apparatus (AMEDA): The AMEDA provides discrimination scores representing each participant’s sensitivity to small differences in
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the degree of ankle inversion (Waddington & Adams, 1999) (Figure 1).
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The AMEDA device consists of a hinged plate which rotates around an axle under the long axis of the foot being tested. With their feet placed shoulder-width apart, standing with both legs in a weight bearing position, subjects were asked to stand in a relaxed posture on the platform of the AMEDA, with the foot of the limb being tested centered over the axis of movement of the movable base plate. The participant made an active inversion movement which moved the plate and the outer side of the foot down until contact was made by the rim of the plate on an adjustable metal stop. The participant then returned the plate to the horizontal stopped position at
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ACCEPTED MANUSCRIPT the same steady pace, and made a judgment as to the degree of inversion achieved during the movement. The AMEDA uses a set of 5 predetermined available end positions for ankle inversion movements. The 5 predetermined displacements, from smallest to largest,
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were: 10.49˚, 11.84˚, 12.55˚, 13.27˚ and 14.52˚ from the horizontal position. A
position number (1, 2, 3, 4 or 5) was assigned to each movement displacement in order from the smallest/shallowest angle (10.49˚- position number 1) to the
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largest/deepest angle (14.52˚- position number 5). Participants were provided with three familiarization trials during which they experienced all of the available
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movement degrees in sequence. A trial consists of each of the 5 movement degrees being presented to the participant 10 times in a random order (a total of 50 ankle movements), with the participant judging each movement degree as it is undertaken and reporting the appropriate position number.
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Four footwear conditions: The ability to discriminate differences in the degree of ankle inversion movements was measured in four different footwear conditions. The order in which each dancer was tested with the four different types of footwear
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was randomized using a Latin square.
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1. Ballet shoes: Each dancer was tested using his/her personal ballet shoes. 2. Barefoot: The dancers were tested standing barefoot on the AMEDA device.
3. Textured insoles: We used rubber insoles with four nodules (3 mm high and 1 mm diameter) per square centimeter, similar to the textured rubber compound described previously by Waddington and Adams (2000, 2003). The rubber was cut-to-fit for each dancer and was inserted into the dancer’s own ballet shoe (Figure 2).
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ACCEPTED MANUSCRIPT 4. Smooth insoles: 3mm PVC Vinyl upholstery “Expanded – Slate” insole. The smooth insoles were cut to fit for each dancer and were inserted into the dancer’s own ballet shoe. Testing protocol:
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All dancers were asked to identify their dominant leg, which was defined as
the dominant weight-bearing leg, the leg for take-offs and landings, and the preferred hopping leg (for a pirouette, for example) (Hiller et al., 2004; Kiefer et al., 2011; Rein
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et al., 2011). The dancers were tested on their dominant side under four (randomized) conditions (barefoot, wearing their ballet shoes without insoles, wearing smooth
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insoles in their ballet shoes, and wearing textured insoles in their ballet shoes). The dancers were tested in two different conditions on one day (with a 10-min rest between the two foot-wear conditions), and in the two additional conditions on the following day (again, with a 10-min rest in between). The tests were undertaken on
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separate days and with 10-min rest in between, so as to avoid fatigue of the tested leg in the four different foot-wear conditions.
Pre-test: Participants were given a brief pre-test of three series of trial movements to
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familiarize them with the feel of the plate at each of the inversion distances, prior to
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data collection. In the pre-test, they experienced the five inversion movement distances, in order, from the smallest (moving to position 1) to the largest (moving to position 5), three times (15 in total). Test: Participants then undertook 50 trial blocks, without feedback. The trials were presented in a random sequence, 10 at each of the 5 different movement displacements. The test protocol provides a score reflecting the participant’s ability to discriminate between the adjacent inversion angles (Maher & Adams, 1996). The
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ACCEPTED MANUSCRIPT accuracy with which the participant distinguishes between each adjacent pair of angles (1-2, 2-3, 3-4, 4-5) is calculated, using the area under the curve (AUC) of the receiver operating a characteristic curve for each adjacent pair. The total score is the mean of the AUC scores for the 4 degrees of freedom between the 5 stop positions.
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AUC values range from 0.5, which is equivalent to chance responding, to 1.0,
representing a perfect ability to discriminate between the 5 different movement degrees (Han et al., 2013a, b; Witchalls et al., 2013).
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Each dancer received a final AUC score for each test condition (barefoot,
ballet shoes, textured insoles and smooth insoles). Based on the ballet shoes’ AUC
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score (mostly relevant for their daily dance training), all dancers were subdivided into three tertiles. This division could further represent the dancers with "better" discrimination ability and the dancers with "worse" discrimination ability. Reliability of the scores (Inter-class Correlation Coefficient) generated by the
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AMEDA tests has been determined as ranging from 0.82 to 0.96. (Waddington & Adams, 2004; Han et al., 2013a, b). The AMEDA device fulfills the validity criteria for assessing active movement function, with sufficient trials to determine the
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participants’ ability to use proprioceptive information when they discriminate a set of
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movements (Ashton-Miller, 2000; Han et al., 2013a). Data Analysis:
Analysis of variance (ANOVA) with repeated measures was used to compare
the four different footwear conditions, in the two levels (adolescent dancers – levels 4-5; mature dancers – levels 6-7), and two genders (male, female) of dancers. To further examine the effect of footwear on the ankle discrimination score, the participants were subdivided into tertiles based on the score they obtained in ballet shoe testing. ANOVA with repeated measures was used to compare the four different
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ACCEPTED MANUSCRIPT foot-wear conditions, in the upper and lower tertiles. The analysis was performed using SPSS software version 21.0 (SPSS Inc., Chicago, Illinois). The level of significance for all statistical tests was set at 0.05. RESULTS
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Table 2 presents the mean scores ( X ± SD) of ankle inversion movement
discrimination under four different testing conditions (barefoot and three types of footwear), among adolescent and mature males and females.
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No interaction was found between the four different footwear conditions and the two genders tested (p>.05); no interaction was found between the four different
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footwear conditions and the levels of dancers (adolescence/mature) (p>.05); and, no interaction was found between the four different footwear conditions, the two genders tested and the two levels of dancers (p>.05).
Tertiles: All dancers were divided into three tertiles, based on the score they obtained
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when testing with ballet shoes. An interaction was found between the four different footwear conditions and the upper tertile and lower tertile of dancers when tested in ballet shoes (p=.006), indicating significant differences between the upper tertiles and
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the lower tertiles of dancers when tested with ballet shoes, barefoot and smooth
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insoles (p<.001; p<.001; p=.047, respectively). However, when tested while wearing the textured insoles, no differences were obtained by the dancers in the upper tertile and the dancers in the lower tertile (p=.911), suggesting improved scores by the lowest tertile of dancers when wearing the textured insoles (Figure 3). Learning effect: Significant improvement was found between the second testing compared to the first testing (p=.025) and between the third testing compared to the first testing (p=.011). No significant improvement was found between the third testing and the second testing. Furthermore, no significant improvement was found between
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ACCEPTED MANUSCRIPT the fourth testing and the first testing, or between the fourth testing and the third testing (Figure 4).
DISCUSSION
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The main findings of the current study demonstrated that dancers with lower discrimination scores significantly improved their ability to judge inversion
movements, up to the level of dancers with good ability, by wearing textured insoles.
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Dancers with lower discrimination ability appeared to significantly benefit from the
enhanced stimulation of cutaneous receptors of the plantar surface, which appears to
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have enhanced the afferent input received by the central nerve system (Cameron et al., 2008), leading to an improved movement discrimination capacity in this group. In previous studies, it was demonstrated that additional proprioceptive stimuli to the foot when insoles are worn show greater improvement in subjects with lower
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proprioception ability to begin with, or those with a history of injury (Newcomer et al., 2001; Cameron et al., 2008). The sensitivity of the plantar surface is related to differences in the stiffness, roughness texture and flexibility of the contact surface.
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Inserting insoles into the ballet shoes of dancers with low discrimination ability may
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have increased the level of information available from the contact surface up to that of dancers with high sensitivity levels (Mundermann et al., 2001). Another explanation might be that different groups of dancers have different
foot types, with different sensation ability. The major limitation of the current study is that no screening for sensory ability or for foot type was made for our participants prior to commencing the testing. It might be that wearing the textured insoles differently affected dancers with high/low foot sensation and dancers with a different foot shape. Subjects with pes planus feet, for example, may have had more plantar
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ACCEPTED MANUSCRIPT cutaneous surface area contact compared with subjects with pes cavus feet (Corbin et al., 2007). These differences in foot types may have resulted in different discrimination abilities among the different groups of dancers. The negative effect of wearing textured insoles in dancers with pre-existing
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higher discrimination ability may be due to the additional enhancement of afferent stimulation provided by the insoles having overloaded their sensorimotor system (Newcomer et al., 2001). Similar to our results, Cameron and colleagues (2008)
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investigated the effect of wearing close-fitting neoprene shorts on swinging leg
movement discrimination scores in elite level Australian football players. The authors
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found that high ability participants were worse at the discrimination task when wearing neoprene shorts, but low ability subjects performed better in neoprene shorts. It might be that for dancers with good proprioceptive ability, additional textured insoles confuse the sensory system, for which information is important, resulting in
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increased error and poorer performance. Furthermore, McNair and Heine (1999) examined the effects of a neoprene lumbar brace on proprioceptive ability and found that although bracing can improve proprioception, subjects with poor proprioception
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improve more by wearing lumbar braces, compared to subjects with good
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proprioception.
When all dancers with different ranks of proprioception ability (combined
three tertiles) were considered, no interaction was found between the four different footwear conditions, the two genders or the two levels of dancers, in their ankle inversion movement discrimination ability. This suggests that the initial proprioception ability of the dancers is the only parameter that can define the importance of wearing textured insoles, rather than their dance level or gender.
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ACCEPTED MANUSCRIPT Reducing plantar cutaneous afferent input (through surface cooling, for example) has been found to change the base of support and impair postural control (McKeon & Hertel 2007; Wang & Lin, 2008). It may be that increasing the afferent input by wearing textured insoles only during the time of testing does not provide
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sufficient time for dancers with existing higher level discrimination to improve their discrimination ability. In a previous report, it was indicated that when a textured
insole was added to the athletic shoes of elite netball players (for testing only), their
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discrimination score was not significantly different from the score obtained in
barefoot testing (Waddington & Adams. 2000). Further research is required to
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determine the association between wearing textured insoles over an extended period and changes to proprioception ability, especially given that it has been reported that enhanced proprioceptive and balance ability is an outcome of years of sport-specific training (Daneshjoo et al., 2012; Han et al., 2013b).
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The textured insoles used in this study did not seem to cause significant discomfort to the participants, with few of the dancers reporting issues with comfort when wearing the textured insoles for the first time. Salles and Gyi (2013), who
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attempted to evaluate the use of personalized insoles versus non-personalized insoles
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in terms of comfort, found that both types of insoles were defined as causing discomfort. The authors explained that the changed foot capturing position of the insole and the insole thickness may have contributed to the higher ratings of discomfort, with increased rigidity restricting the natural movement of the feet. The proprioceptive ability of the dancers in the current study might have been altered by insertion of the additional textured material that changed the normal foot position during motion (Lin et al., 2011; Fong Yan et al., 2011). Xiong and colleagues (2011) found that the medial plantar arch has a lower pain pressure threshold in comparison
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ACCEPTED MANUSCRIPT to the other plantar regions of the foot, which can cause increased pressure discomfort thresholds. Moreover, Robbins et al. (1995) examined the hypothesis that lower judgment of foot position is due to a change in plantar tactile sensibility, and that footwear itself will further impair position judgments. These researchers found that
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wearing footwear impaired foot position awareness compared to being barefoot, and that reduced information about foot position may worsen postural balance in both
young and elderly subjects. The insertion of textured insoles into the ballet shoes of
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the dancers tested here might have increased the stiffness around the foot tissue and increased the pain pressure threshold and arch discomfort which may interfere with
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proprioception ability in the ankle/foot area (Salles & Gyi, 2013).
Finally, these results suggested a "learning effect" among the dancers during the first three repetitions, which had stabilized by the fourth test. In a test requiring movement of a cursor to a target using ankle movements of plantar/dorsi-flexion and
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inversion/eversion, Morris and colleagues (2009) looked for a learning effect and observed that the early trials exhibited the worst performance, meaning that errors decreased from the first to last task. Witchalls and colleagues (2013) found similar
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results among healthy university students over three test repetitions on the AMEDA.
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Comparing healthy students with students suffering from chronic ankle instability, these authors found that healthy students improved their scores between the first and second test, after which their performance stabilized for the third test. Clinical implications:
The risk of ankle injuries is of great concern to dancers. An important implication of the current study is that further evaluation of effective assessment of proprioception ability is needed to evaluate its role in the dancer's fitness profile. Dancers with low inversion movement discrimination scores (such as those in the
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ACCEPTED MANUSCRIPT lower tertile of the current study) may benefit from additional proprioceptive training, as it has been demonstrated to be a component of better performance ability, in preventing lower extremity injuries, as well as in reducing recovery time and providing additional protection against re-injury (Batson, 2009; Waddington &
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Adams, 1999). CONCLUSIONS
Insertion of textured insoles into the ballet shoes of dancers with low
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discrimination scores may enhance their movement discrimination ability to the level of dancers with good discrimination scores. This might be due to the textured insoles
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triggering increased activity in the cutaneous receptors in the plantar surface of the foot, which increases plantar sensitivity, and in turn, might decrease their risk of injury.
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ACCEPTED MANUSCRIPT Table 1: Number of dancers, mean age, and hours of practice per week, for adolescent and mature dancers.
Adolescent dancers
Males
N
Mean age
10
15.6±1.1
Dance hours per week
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18
(Level 4+5)
Females
16
15.2±.98
Mature dancers
Males
10
18.1.±1.2
24 - 29
Females
8
17.4±1.2
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(Level 6+7)
Table 2: The mean scores ( X ± SD) of ankle inversion movement discrimination (AUC values) under four different testing conditions (barefoot, ballet shoes, smooth
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insoles, textured insoles).
Adolescent
Mature
females
females
males
males
.687±.066
.690±.045
.682±.064
.721±.090
.687±.067
.690±.051
.698±.068
.715±.074
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Ballet shoes
Mature
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Barefoot
Adolescent
Smooth insoles
.699±.061
.693±.062
.696±.069
.656±.101
Textured insoles
.689±.065
.694±.047
.693±.040
.664±.067
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Figure 1: The AMEDA device.
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Figure 2: Textured insoles inserted to the ballet shoes
ACCEPTED MANUSCRIPT Figure 3: Mean score (±SE) for dancers in the upper tertile and lower tertile (when tested with ballet shoes) in the four different footwear conditions.
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Upper tertile Lower tertile
0.75
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0.7
0.65
*
0.6
balletshoes
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(AUC) values
Ankle inversion movement discrimination
0.8
*
*
barefeet
smoothins
Textureins
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* Significant differences between the upper tertile and the lower tertile (p<.05).
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0.72 0.71 0.7
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0.68 0.67 0.66 0.65 0.64 0.63 0.62
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Test_3
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Test_2
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Test_1
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AMEDA score
0.69
Test_4
ACCEPTED MANUSCRIPT Highlights: •
Textured insoles enhanced discrimination ability of dancers with low ability.
•
Dancers with low ability improved up to the level of dancers with good ability. Textured insoles increased the activity of receptors in the plantar surface.
•
Increased plantar sensitivity might decrease the risk of ankle injury.
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•
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ACCEPTED MANUSCRIPT • Ethical Approval: The research was approved by the Ethics Committee of Victoria University, Australia. All dancers and one of their parents (for dancers under the age of 18) provided written informed consent for participation. • Funding: No.
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• Conflict of Interest: No
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