FORCE ATTENUATION PROPERTIES OF PADDED DANCE SUPPORT SOCKS ______
A Thesis
Presented to
The Honors Tutorial College
Ohio University
______
In Partial Fulfillment
of the Requirements for Graduation
from the Honors Tutorial College
with the degree of
Bachelor of Science in Translational Health—Exercise Physiology
______
by
Isabella Mueller
April 2019
Force Attenuation Properties of Padded Dance Support Socks Page 1
This thesis has been approved by
The Honors Tutorial College and the Department of Applied Health Sciences
______
Dr. Jeff Russell Associate Professor, Athletic Training Thesis Adviser
______
Dr. Cheryl A. Howe Associate Professor, Exercise Physiology Director of Studies, Translational Health
______
Cary Roberts Frith Interim Dean, Honors Tutorial College
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PREFACE
Chapter 1 and Chapter’s 4⎼7 contained within the thesis document serve as a prepublication manuscript. This manuscript has been formatted to meet the guidelines set forth by the Journal of Dance Medicine & Science. The reference citation style follows the guidelines provided in the American Medical Association Manual of Style and the
Chicago Manual of Style.
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ACKNOWLEDGEMENTS
I would like to thank Apolla Performance, Inc. for supplying the socks for this study. I would also like to express my gratitude to the Ohio University students and faculty members of the dance department for their time in participating in this project. I am thankful to Dr. Howe for her guidance, expertise, and compassion throughout my academic career at OU and the thesis process. Her assistance to me throughout the past four years is more than I could have asked for. I would also like to thank Dr. Yom for assisting me in identifying ways to analyze and make sense of the data. Dr. Russell for being an exceptional thesis advisor. His enthusiasm, knowledge, and most importantly his confidence in me have been so crucial to my success in not only my thesis project, but also throughout my academic career. His door was always open to help guide me in the right direction. I could not have asked for a better mentor and I cannot thank him enough for all of his encouragement support throughout this process. Finally, I would like to thank my friends and family. I want to especially recognize my mom and dad. You both played a huge role in encouraging and supporting me throughout this project. I am very grateful to have such special people in my life and I would not be the person I am today without you both. This project was funded in part by the Dean’s Research and Travel
Fund.
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Table of Contents PREFACE ...... 3 ACKNOWLEDGEMENTS ...... 4 INDEX OF FIGURES ...... 6 INDEX OF TABLES ...... 7 ABSTRACT:...... 8 CHAPTER 1: INTRODUCTION ...... 10 CHAPTER 2: REVIEW OF THE LITERATURE ...... 12 2.1 DANCE INJURIES ...... 12 2.2 PHYSICAL DEMANDS OF MODERN DANCE ...... 13 2.3 ANALYSIS OF FORCES ACTING ON THE BODY ...... 15 2.4 DANCE FOOTWEAR ...... 16 2.5 PROTECTIVE MEASURES ...... 17 CHAPTER 3: RESEARCH QUESTIONS AND APPROACH ...... 19 3.1 SPECIFIC AIMS ...... 19 3.2 HYPOTHESIS ...... 19 CHAPTER 4: MATERIALS AND METHODS ...... 21
4.1 STUDY DESIGN ...... 21 4.2 PARTICIPANTS ...... 21 4.3 INSTRUMENTATION...... 22 4.4 TEST PROCEDURES...... 23 4.5 DATA COLLECTION AND ANALYSIS ...... 25 CHAPTER 5: RESULTS ...... 26 CHAPTER 6: DISCUSSION ...... 29 CHAPTER 7: CONCLUSION ...... 33 REFERENCES ...... 34 APPENDIX A: RECRUITMENT OF PARTICIPANTS ...... 36
RECRUITMENT EMAIL ...... 36 ANNOUNCEMENT AT DANCE CLASS ...... 37 RECRUITMENT SLIPS ...... 37 APPENDIX B: SCREENING QUESTIONNAIRES ...... 38 APPENDIX C: CONSENT FORM...... 39
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INDEX OF FIGURES
Figure 1. Bertec Force Plate...... 22
Figure 2. Sensors and Transmitters ...... 23
Figure 3. Sensor Placement...... 24
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INDEX OF TABLES
Table 1. Characteristics of Participants ...... 27
Table 2. Force (N) Data for Dance Sequence Across Conditions ...... 27
Table 3. Landing Data from Sauté Jump Across Conditions...... 28
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ABSTRACT:
Foot injuries frequently occur in dancers, and researchers have investigated different protective measures that prevent injuries for this population. Research has primarily focused on ballet dancers, but foot injuries also are common in modern and contemporary dance where footwear is not worn. The purpose of this study is to explore whether the padded dance-support socks can serve as a protective measure for modern dancers by attenuating force on their feet during a dance sequence and when landing from a sauté jump. In this randomized, cross-over designed study, seventeen injury-free dancers (2 M,
15 F; age=21.7±7.3 yrs; height=165.4±6.2 cm, mass=69.5±15.5 kg) volunteered to perform a 40-second modern dance sequence and a sauté jump landing under two conditions: while wearing DS and BF. A 0.5 cm2 Flexiforce A201 445N sensor (Tekscan,
Boston, MA) was affixed under the first metatarsophalangeal joint (great toe); a second was affixed under the heel. The sensors wirelessly recorded foot forces during dancing. A
Bertec 600x1200mm force plate (Bertec Inc., Columbus, OH) measured vertical ground reaction force (VGRF) and time to peak VGRF of the jump landings. A Noraxon MR3.12 biomechanics system (Noraxon, Inc., Scottsdale, AZ) synchronized and recorded the data. Peak toe force, peak heel force, mean toe force, and mean heel force were measured during the dance sequence, while VGRF, time to peak VGRF, peak toe force, and peak heel force were measured during the jump onto the force plate. A dependent samples t- test was used to assess pairwise differences in these measures between the DS and BF conditions. Statistical significance was set to p < 0.05. The peak forces on the heel when dancing and landing from the sauté jump with DS were significantly lower compared
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with the BF condition (Dance Sequence: p=0.005; Sauté Jump: p=0.042). All other variables were not significant between conditions. When considering the high demands of a dance training, results of this study showing the usefulness of these sock as a protective measure may be limited. However, this study does offer evidence that padded dance socks may protect dancers’ feet from forces commonly encountered during modern dance. Further research is needed to determine the use of these socks as an injury- reducing measure for modern dancers.
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CHAPTER 1: INTRODUCTION
Dancers are not only artists, but also high performance athletes who perform rigorous athletic activity.1 Just like other athletes, dancers have a high rate of musculoskeletal injuries because of the intense physical demands placed on the body and the repetitive movements of the activity.1 Dance injuries are commensurable in type, site and rate to athletes participating in traditional sports.2 In the first large-scale study on modern dancers it was found that the incidence of injuries among professional modern dancers (82%) is comparable to incidence of injuries among professional football players
(81%).1 The majority of these injuries affected a dancer’s ability to dance; however, many of them would return to dance in spite of continuing symptoms.1
In dance, dynamic overloads often occur when impacts forces exceed the strength of the bones and muscles of a dancer.3 Modern dancers are more susceptible to injuries because of the high impacts place on their body and the intensity associated with their dance training.4 Modern dance is represented by dynamic and expressive movements such as falls, handstands, unique lifts, and jumps that generate excessive ground reaction forces.4 Such forces are significant factors that lead to an increased risk of injury in modern dance, as high impact forces occur during the landing phase of a jump.4 Further, landing from jumps that they perform may put this population at increased risk for injury because the ankle joint must rapidly accommodate to the high loads placed on the foot.5
Many protective measures, such as athletic taping and bracing, have been used in high risk sports to protect against athletic injuries. Due to the frequency and intensity of injuries suffered by dancers, researchers have found the need to investigate different
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protective measures as well as relationships between different dance footwear and injury rates.6,7 Most of the research conducted to date has primarily focused on ballet dancers,8,9 but foot injuries also are common in modern dance where footwear is not worn. To our knowledge no studies have investigated support measures to reduce the impact forces placed on modern dancers’ feet. Therefore, the purpose of this study is to explore whether the padded dance-support socks can serve as a protective measure for modern dancers by attenuating force on their feet during a dance sequence and when landing from a sauté jump.
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CHAPTER 2: REVIEW OF THE LITERATURE
2.1 Dance Injuries
Dance injuries are commensurable in type, site and rate to athletes participating in traditional sports.2 Dance medicine began to emerge in the early 1980s in the U.S. because of the growing injury problems that many dancers faced, increased concerns within ballet and dance companies about the rates of injuries, and the impact of injuries on a dancer’s career and the companies to perform on their schedule.10 Around the same time in the United Kingdom the National Organisation of Dance and Mime was established to represent dancers, and a medical advisory panel was created to take care of the medical needs and health care of all professional dancers. This medical advisory panel developed a retrospective questionnaire to find out more about dance-related injuries. The questionnaire was administered to 141 dancers from seven professional and modern dance companies in the United Kingdom. It was found that 67 dancers (47%) had experienced a chronic injury and 59 (42%) had an injury within the previous six months that affected their dancing. This study concluded that due to the high rates of injury it was time to initiate discussions about injury prevention for dancers. Shah et al. (2012) conducted the first large-scale study to describe the epidemiology of musculoskeletal injuries in modern dancers.1 They found that the incidence of injuries among professional modern dancers (82%) is comparable to incidence of injuries among professional football players (81%). Shah et al. (2012) also reported that the foot and ankle were the most commonly injured locations. The majority of these injuries affected a dancer’s ability to dance, although many of them would return to dance in spite of continuing symptoms.
Dancers also reported that the main factors contributing to their injuries came from the
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demands of their specific roles, self-pressure to excel, and directions from the choreographer. In recent years, researchers have started to investigate injury rates in amateur or young dancers because of the increased number of children and adolescents participating in dance.2 A 2013 study found that an estimated 113,084 children and adolescents between the ages of 3 and 19 years old were all treated for injuries related to dance in emergency departments between 1991 and 2007 in the United States.2
Adolescents (15-19 years of age) constituted 40.4% of these dance injury cases and sprains and strains were the most common injuries. Roberts et al. (2013) concluded that since the injuries incurred differed by type, more research needs to be done on preventing different injury types. The authors also mentioned that the majority of dance-related injury research focused on ballet, thus emphasizing the need for more research to investigate injuries occurred in other dance styles. Another study investigating injury rates of adolescent dancers at a liberal arts high school dance program over nine months.11 During this time, there were 112 self-reported injuries and 71 physician- reported injuries as assessed by a physical therapist. Lower limb injuries in the ankle, knee, and foot seemed to be the most common injuries for dancers, whether the dancers are professionals or amateurs.1,2,11
2.2 Physical Demands of Modern Dance
Dancers often experience overloads from dynamic movements that happen during impacts with forces exceeding the resistance or strength of healthy bones and muscles.3
In the literature, dynamic overload is defined as “the load exceeding the resistance threshold of muscles, joints, and bones, as well as every mechanical action resulting in damage to the motoric apparatus.”3 (p. 78) Based on this definition, modern dancers are
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more susceptible to injuries because of the loading frequency and intensity associated with their dance training. Modern Dance incorporates all of the techniques of ballet; however, the dancer is not obligated to follow all of the classical rules of ballet.4 Modern dance is represented by dynamic and unique movements such as fall, handstands, and unique lifts, which create many dangerous situations for the musculoskeletal system.
Many of the expressive movements that modern dancers perform consist of jumps that generate excessive ground reaction forces. Such forces are significant factors that lead to injury in modern dance, as high impact forces occur during the landing phases of the excessive jumps. Forces at the knee during some dance jump landings have been measured to exceed 12 times the dancer’s body weight.12 Landing from jumps that they perform may put this population at increased risk for injury because the ankle joint must rapidly accommodate to the high loads placed on the foot.5 During the early stages of the landing cycle, errors in the orientation of the foot may cause excessive tissue stress or decrease stabilization of the ankle joint and may lead to injury. Also on average, professional dancers may train about 8 hours daily and if they are rehearsing for a performance this training duration can extend 12 hours per day.3 This level of overload on the body may result in permanent damage to the tissues. Achilles tendinopathy is a common injury in dancers who perform frequent landing tasks.5 These landing tasks are associated with rapid eccentric contractions of the triceps surae in order to stabilize dorsiflexion at the ankle. Ankle sprains are another common injury in dancers because of the inability of the joint and muscles that make up the ankle to respond to the high mechanical demand of the foot at contact with the floor. Dance floors force reduction values vary between venues and some floors even have different force reduction values
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within the stage.5 These force reduction values can affect loads at the ankle that are associated with ankle tendinopathy and ankle sprains. For example, Hopper et al. (2014) found that dancers in touring companies are regularly required to rehearse and perform at different venues with little consideration for the mechanical properties of the stage floor and potential influences on injury risk. 13 This study aimed to determine the mechanical properties of dance floors at three venues used by a touring professional ballet company compared with injury frequency within the dance company when performing at the three venues. Furthermore, they found that none of the three floors that they were testing fell within the range of force reduction values required by the European Sports Surface
Standards. A significantly greater weekly injury rate was found within the dance company when performing on the floor that had the greatest variability of force reduction magnitudes. These results show that dance floors with higher intra-floor force reduction variability may increase a dancers’ risk for injury then floors that have more uniform intra-floor force reduction. With that said, care should be taken to provide appropriate and uniform flooring for training and performances as a protective measure against musculoskeletal injuries in modern dancers.
2.3 Analysis of Forces Acting on the Body
Jumps and landings are vital components of many activities including dance, but they often fail to receive the attention they deserve both in the literature and by coaches who train athletes to perform these actions.14 The forces acting upon a dancer’s body include gravity, the dancer’s body weight, acceleration of limbs, and the torque created in the joints.15 During a jump these forces are multiplied by the dancer’s mass. Ground reaction forces specify the intensity and duration of stress that the body goes through during the
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landing phase of jumps.14 When landing from a jump, an individual body mass is subject to acceleration due to gravity which results in a ground reaction force every time the foot contacts the ground. Ground reaction forces are measured by an individual either standing, moving, or jumping onto a force plate.15 Ground reaction force can be used to investigate the amount of force generated in the body by different dance movements such as jumps as well as the effects of different types of footwear, surfaces, and environments that dancers utilize. This information can be used by healthcare professionals and dance instructors to better understand the forces acting on the body during certain dance movements in order to prevent injuries.
2.4 Dance Footwear
It is imperative for a dancer to have healthy and pain-free feet regardless of their age, genre they perform, or training level due to the amount of time they spend on their feet during this activity. Accordingly, researchers have explored the effects of different dance footwear on foot motion and injury during dance.6,7 Besides modern and contemporary dancers, all other genres of dance utilize specific shoe types.7 Dance footwear such as jazz shoes, ballet slipper, and Irish dance shoes do not distribute the forces on the feet well due to their structure and makeup.6 A more cushioned dance shoe can be worn during rehearsals and practice to provide greater shock absorption and force distribution in order to reduce the risk of injuries to the lower limb.7 However most dancers would not wear a more cushioned dance shoe during practice because it can compromise their feel of the floor and as well as their confidence during performances since they prefer to practice in the same conditions they will perform in. Dance footwear should try to limit the restriction of foot motion since a greater restriction of foot motion might lead to
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improper technique which can ultimately contribute to injury.6 In a review on dance footwear, the researchers concluded that overall dance footwear could be a risk factor for injuries to the foot and ankle and their ability to protect the foot is limited.
2.5 Protective Measures
Many protective measures, such as athletic taping and bracing, have been used in high risk sports to protect against athletic injuries. Due to the frequency and intensity of injuries suffered by dancers, researchers have found the need to investigate different protective measures that will prevent injuries for this population. So far most of the research conducted to date has only investigated ballet dancers. Hendry et al. (2015) investigated the effect of Mulligan’s and Kinesio taping on knee and hip biomechanics during landing from ballet jumps in different turnout positions.8 Eighteen ballet dancers performed ballet jumps in three turnout positions under the two taping conditions compared with no tape. It was found that Mulligan’s tape at the knee was able to reduce knee and hip forces without affecting the aesthetic performance of jumps. Specifically, when participants were wearing Mulligan’s tape there was significantly less peak posterior knee force when landing in first position compared to the same jump without tape. This was particularly significant because when ballet dancers land in first position there is often forced turnout at the knees and hips which can overload the tissues; these forces can lead to overuse injuries. Mulligan’s tape appeared to provide protection at the knee joint and proximal hip joint. This reduction in hip force will likely have a positive influence on hip injuries related to elevated force absorption in ballet dancers. According to the study, Mulligan’s tape may offer a protective role for overuse knee injuries in ballet dancers.8 Miller et al. (1990) investigated if wearing an orthotic insert in the ballet
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shoe can help distribute the stress more evenly to the foot and reduce stress related injuries for ballet dancers. 9 Eleven out of the twelve shoes that were tested were modified using three different orthotic insoles (PPT, Spenco, and Sorbothane) alone or in combinations as padding for the heel, metatarsals, toes and arch support. The other shoe was just a regular ballet shoe that was not modified with padding. A professional ballet dancer performed a jump by taking a single step on his left foot, jumping and landing with his right foot on the force and pressure plate with each of the modified and normal ballet shoe. The trial shoe that they found was most successful at distributing the pressure most evenly away from the first and second toes, metatarsal heads and heel, to the arch had a high arch support as compared to the standard ballet shoe. This modified shoe increased the area that the pressure from the jump is distributed in, which then decreased the pressure from one part of the foot. However, the authors concluded that a long-term study with a larger group of ballet dancers using the orthotic insert with a high arch support verses a standard ballet shoe is needed to see if stress-related injuries can be reduced. Unfortunately, there has been no studies that have investigated similar protective measures to reduce the impact forces placed on modern dancers’ bodies.
Although this study did not measure injury reduction over a long period of time with wearing the socks, similar to the studies mentioned above, this study determined if padded, dance-support socks, which provide increased arch and ankle support, attenuate force to help protect modern dancer’s feet.
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CHAPTER 3: RESEARCH QUESTIONS AND APPROACH
The research questions guiding the present study are as follows:
1. Is the force (N) on the feet significantly lower when dancing while wearing dance
socks compared to dancing barefoot?
2. Is vertical ground reaction force (N) significantly lower when performing a sauté
landing on the force plate while wearing dance socks compared to being barefoot?
3. Is time to peak VGRF significantly longer when performing a sauté landing on
the force plate while wearing dance socks compared to being barefoot?
3.1 Specific Aims
Due to the lack of research on protective measures for modern dancers, the specific aims of this research were to:
1. Compare the mean toe force, mean heel force, peak toe force, and peak heel force
exerted on the foot in modern dancers while performing a forty-second modern
dance sequence while in bare feet and while wearing the dance socks.
2. Compare the vertical ground reaction force, the time to peak VGRF, peak toe
force, and peak heel force in modern dancers performing a sauté jump while in
bare feet and while wearing the dance socks.
3.2 Hypothesis
The hypothesis for each of these research questions are:
1. Force on the foot will be significantly lower while dancing with dance socks
verses dancing barefoot.
2. Vertical ground reaction force will be significantly lower while performing a
sauté jump with the dance socks versus performing the jump barefoot.
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3. The time to peak VGRF will be significantly longer while performing the sauté
jump with dance socks verses performing the jump barefoot.
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CHAPTER 4: MATERIALS AND METHODS
4.1 Study Design
This study used a randomized cross-over design, with participants performing a dance sequence and sauté jump landing under two conditions: with dance socks (DS) and bare foot (BF). The order of the testing conditions was randomized. Four outcome measurements were recorded during the dance sequence: [1] Mean Toe Force (N), [2]
Mean Heel Force (N), [3] Peak Toe Force (N), [4] Peak Heel Force (N). Mean of three trials were recorded for four outcome measurements from the sauté jump landing: [1]
Vertical Ground Reaction Force (VGRF) in Newtons, [2] Time to Peak VGRF in seconds, [3] Peak Toe Force in Newtons, [4] Peak Heel Force in Newtons.
4.2 Participants
Healthy male and female dancers from Ohio University were recruited to participate in this study. Participants were either students in the dance degree program or faculty members of the dance degree program. The current study was approved by the Ohio
University Biomedical Institutional Review Board, and participants signed consent forms prior to participation. The exclusionary criteria included (1) a lower extremity, non-foot injury in the past month that required the participant to miss at least one day of class, rehearsal, or performance, (2) a foot injury in the past three months that required the participant to miss at least one day of class, rehearsal, or performance, or (3) a sensitivity to tape adherent sprays or athletic tape adhesives. Recruitment of participants occurred via word of mouth in dance classes and via email to all dance majors. Participants kept the padded dance socks that they wore during the testing as compensation for participating.
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4.3 Instrumentation
Flexiforce A201 445N sensors (Tekscan, Boston, MA) were placed under the ball of the foot and heel and attached to wireless transmitters to measure the average toe force, average heel force, peak toe force and peak heel force during the dancing sequence and dance jump. A Bertec 600x1200 mm force plate (Bertec Inc., Columbus, OH) measured the vertical ground reaction forces (VGRF) and time to peak VGRF of the jump landings.
A Noraxon MyoForce MR3.12 biomechanics system (Noraxon, Inc., Scottsdale, AZ) recorded the participants’ movement patterns and synchronized the data so that the position of a participant at specific moments in time could be visually reconciled with the force data generated by the sensors and the force plate.
Figure 1. Bertec Force Plate
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Noraxon wireless transmitter
Flexiforce sensor
Figure 2. Sensors and Transmitters
4.4 Test Procedures
Data collection occurred in the biomechanics laboratory in Grover Center at Ohio
University. Participants attended one session that lasted approximately 45 minutes. On arrival at the laboratory, age, years of dance experience, and preferred landing leg from a sauté́ jump were recorded. Height was then recorded with a stadiometer, while weight was recorded by the force plate during the data collection. Eligible participants watched a video in which they learned a 40-second modern dance sequence phrase from the
Dance-Specific Aerobic Fitness test of the Laban Conservatoire of Dance and Music. A video of a former college dance student performing the sauté jump onto the force plate was also shown and the researchers read the directions on how to perform the sauté jump.
The researchers instructed participants to start the jump off the force plate, perform the sauté jump with their non-dominant leg in arabesque, while their dominant leg landed on the force plate and their non-dominant leg was in coupe during the landing.
Participants had as much time as they needed to practice both the dance sequence and the jump on the force plate. Flexiforce sensors were then placed on the dominant foot of the
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participant by palpating the attachment site, cleaning the attachment areas with alcohol,
applying benzoin to the attachment areas and then lastly placing fabric tape over the
sensors. One sensor was placed under the ball of the foot (first metatarsophalangeal joint)
and another under the center of the heel. Sensors were then attached to a Noraxon
wireless pressure sensor transmitter, which was affixed to the leg with a neoprene Velcro
strap. According to the randomization, the participant performed the dance movement
phrase once and the three trials of the sauté jump onto the force plate with either bare feet
or while wearing the socks first and then repeated the activities in the alternate condition
(BF or DS). Trials were discarded if the participant did not land on the force plate, if they
landed with two feet on the force plate, if they lost their balance on landing, or if the
sensor became disconnected from the wireless transmitter at any point of the trial.
B A
Figure 3. Sensor Placement A. Center of the Heel B. Ball of the Foot (first metatarsophalangeal joint)
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4.5 Data Collection and Analysis
All of the data was exported from the Noraxon Biomechanics System to Microsoft Excel.
Peak toe force, peak heel force, mean toe force, and the mean heel force during the dance sequence were found using formula commands in Microsoft Excel. VGRF, time to peak
VGRF, peak toe force and peak heel force were averaged across the three jump trials for each participant using Microsoft Excel. The data was then transferred to the Statistical
Package for the Social Sciences (SPSS). A dependent t-test was conducted for each of the outcome measurements in order to examine if there was a significant difference between dancing BF versus dancing with the DS. The two samples in this study were: 1) the sample of scores while dancing BF and 2) the sample of scores while dancing with
DS. Means, standard deviation, and 95% confidence intervals were calculated for all of the outcome measures. Statistical significance was set to p < 0.05.
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CHAPTER 5: RESULTS
Seventeen dancers met the inclusion criteria and participated in this study (Means ± SD: age= 21.7 ± 7.3, height: 165.4 ± 6.2 cm, weight: 69.5 ± 15.1 kg). No injury or adverse events were reported during the data collection. The characteristics of the participants are detailed in Table 1. The peak forces on the heel when performing the dance sequence with DS were significantly lower compared with performing the dance sequence BF
(DS=45.0 N vs. BF=36.9 N; p=0.005). There were no significant changes found between dancing in the socks compared to dancing BF or peak force on the toe, mean force on the toe, and mean force on the heel, although it is noteworthy that the padded dance socks were associated with less force than bare feet for all of the outcome variables during the dance sequence (Table 2).
The peak force on the heel when performing a sauté jump onto the force plate with the DS was significantly lower compared with performing a sauté jump on the force plate BF (DS=21.9 N vs. BF=26.5 N; p=0.042). Performing a sauté jump on the force plate with the dance socks slightly reduced vertical ground reaction forces (DS=2.5 N vs.
BF=2.7 N; p=0.058) and peak forces on the toe (DS=45.7 vs. BF=46.5; p=0.650) but, the difference was not significant for either of these outcome measures. While the test revealed no significant difference for time to peak VGRF between the two conditions, the dance sock condition tended to have a slightly greater time to peak VGRF while performing the sauté jump onto the force plate (DS=0.1072 vs. BF=0.1009; p=0.225).
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Table 1. Characteristics of Participants MeanSD Range Minimum Maximum Age (year) 21.7 ± 7.3 31 18 49 Dance Experience (year) 14.9 ± 5.1 23 4 27 Standing height (cm) 165.4 ± 6.2 23 154 177 Body mass (kg) 69.5 ± 15.5 45.8 49.7 95.5
Table 2. Force (N) Data for Dance Sequence Across Conditions Descriptive Statistics: MeanSD (95% CI) Mean Toe Mean Heel Peak Toe Peak Heel
7.0 4.0 3.3 5.6 73.6 41.5 45.0 28.9* BF (4.9⎼9.1) (0.5⎼6.2) (52.3⎼95.0) (29.68⎼60.4)
6.9 3.9 2.5 4.7 68.9 41.1 36.9 25.5* DS (4.91⎼8.95) (0.05⎼4.91) (47.7⎼90.0) (23.8⎼50.1)
Mean Differences 0.1 0.9 4.7 8.1
N, force in Newtons; SD, standard deviation; CI, confidence interval; BF, barefoot; DS, dance sock; *Significantly different (p=0.005)
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Table 3. Landing Data from Sauté Jump Across Conditions
Descriptive Statistics: MeanSD (95% CI) Time to Peak VGRF (N) Peak Toe (N) Peak Heel (N) VGRF (s)
2.7 0.8 0.1009 0.03 46.5 30.5 26.5 22.7* BF (2.3⎼ 3.2) (0.088⎼0.114) (30.8⎼62.2) (14.9⎼38.2)
2.5 0.5 0.1072 0.02 45.7 33.5 21.9 21.6* DS (2.3⎼2.8) (0.097⎼0.117) (28.4⎼ 62.9) (10.8⎼33.0)
Mean Differences 0.2 0.006 0.8 4.6
N, force in Newtons; s, time in seconds; SD, standard deviation; CI, confidence interval; VGRF, vertical ground reaction force; BF, barefoot; DS, dance sock; *Significantly different (p=0.042)
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CHAPTER 6: DISCUSSION
The purpose of this study is to explore whether the padded dance-support socks can serve as a protective measure for modern dancers by attenuating force on their feet during a dance sequence and when landing from a sauté jump. Although the dance sock condition mean force values on the toe and the heel appeared to be associated with less forces on the foot in modern dancers, no significant difference was observed for peak toe force, mean heal force, and mean toe force during the dance sequence. The results might be explained because the Flexiforce sensors only measured the force on a small area of a participant’s foot, and the study was not able to account for differences in the participants’ overall dancing BF and wearing DS.
The DS were associated with significantly less peak force on the heel during the dance sequence and when landing from the sauté jump. There were no significant changes found between BF and DS conditions for time to peak VGRF; however, the DS condition was associated with a slightly longer time to peak VGRF. We would expect this outcome from the DS as previous literature has shown that increasing landing time decreases impact forces on the body.14 The aim of landing is to stop the body’s vertical momentum.14 To minimize this momentum, a force must be applied over time.14 If the dancer applies a large force from landing in a jump over a small amount of time, this can result in a “hard” landing. Applying a large force from landing in a jump over a longer time, a “softer” landing will be the result,14 and the size of the impact forces will be smaller in a softer landing. Further research is needed to determine the extent to which dance socks can reduce the impact forces by increasing the time to peak VGRF. The dance socks were associated with marginally less VGRF when landing from the dance
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jump. VGRF values that were found were normalized by body weight to account for differences in size between participants.
To our knowledge, this is the first study to investigate how padded socks can serve as protective devices for the feet of modern dancers. There has been research on the design of dance footwear and protective measures to minimize impact force in other genres of dance, but this has mainly focused on ballet.6-9 Researchers have demonstrated that is possible to redistribute the pressure of a dancer’s jump across the foot by using an orthotic built into the ballet shoe without compromising the dancers comfort and feel for the floor.8
The success of protective measures in dancers shoes and socks has been mixed.
For example, use of shock absorbing materials in Irish dance shoes were not associated with reduced injury rates in one study.16 However, the use of split sole sneakers during training were associated with reduced injury rates, but these shoes cannot be worn by
Irish dancers for competition. The split sole sneakers provided greater shock absorbency then the insoles and they provide greater support to the foot and ankle.16 Overall it has been found that dance footwear is typically inadequate for protecting the foot and might be a risk factor for foot and ankle injuries.6 With that said, it is necessary for future research to focus on improving dance footwear and protective measures and there influence on preventing musculoskeletal injuries in all types of dance genres.
Although the dance socks were not associated with significantly less force for most of the outcome measurements, it is important to recognize this study only considered data points during a 40-second sequence and across three trials of a sauté jump. On average, professional dancers may train about 8 hours daily and if they are
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rehearsing for a performance, this training duration can extend to 12 hours per day.3
During the artistic season, performers may participate in as many as 20 performances in a month.4 The majority of dancers’ movements consist of jumps that generate very high ground reaction forces.4 The high loads of an impact that occur during the landing phases of numerous jumps performed in modern dance is one of the most significant factors that leads to injuries.4 It has been found that dancers perform more then 200 jumping and landing activities throughout their daily training and practice.5 In practice, then, incremental reductions in force on the feet—such as those provided by the padded socks we tested—may be beneficial. However, further research is necessary to quantify this.
During training and practice, dancers need to quickly transition from one movement to the next.4 This leaves them with little time to prepare for the high loads of an impact during landing.4 Further, dancers must dance on whatever surface is installed in the school, studio, or theater in which they are performing.7 Hopper et al. found that dance venue floors with the greatest intra-surface variability in force reduction were floors that most injuries occurred on and that none of the floors in the present study fell within the range required by the European Sports Surface Standards.13 Therefore, the results of this study showing the usefulness of these socks as a protective measure may be limited when considering both the demanding schedule of the dancers everyday training as well as the high impact placed on their bodies.
The current study had several limitations. First, only one specific dance jump type was investigated. Future studies that might investigate the padded dance socks of this type or other protective measures may want to include a variety of specific dance jumps to best mimic the physical demands dancers typical endure in their actual performance
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and training settings. Second, there was no professional dance instructor watching the participants perform the dance sequence or the dance jump. Subsequent research may consider having a professional dance instructor watch the data collection process to control for any mistakes the participants might make while performing the dance sequence and dance jump. Fourth, this study relied upon a small sample size. A larger sample size would have allowed a broader representation of the force attenuation properties of the socks. Finally, the current study only considered direct impacts to the heel and metatarsophalangeal joint. This is only one mechanism that can lead to foot injuries in dance. Future longitudinal studies would be necessary with a larger group of participants to investigate the relationships among the dance socks, injury rates, and other aesthetic measures.
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CHAPTER 7: CONCLUSION
This study offers evidence that padded dance socks may protect dancers’ feet from forces commonly encountered during modern dance. Results from this study may help dancers, dance, teachers, and dance medicine professionals better understand the role of shock- absorbing socks may play in foot injury prevention for modern dancers. Further research is needed to determine the extent to which padded dance socks can decrease foot injury incidence and what force reduction quantity is clinically relevant for injury prevention.
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REFERENCES
1. Shah S, Weiss D, Burchette R. Injuries in professional modern dancers incidence, risk factors, and management. J Dance Med Sci. 2012;16(1):17-25.
2. Roberts KJ, Nelson NG, Mckenzie L. Dance-related injuries in children and adolescents treated in US emergency departments in 1991−2007. J Phys Act Health. 2013;10(2):143-50.
3. Dworak L, Gorwa J, Kmiecik K, Mączyński J. A study characterizing dynamic overloads of professional dancers. Biomechanical approach. Acta Bioeng Biomech. 2005;7(1):77-84.
4. Michnik R, Jurkojc J, Gorwa J, Dworak L, Michnik R, Jurkojc J. Kinematic analysis of modern dance movement "stag jump" within the context of impact loads, injury to the locomotor system and its prevention. Med Sci Monit. 2014;20:1082-9.
5. Hopper LS, Alderson JA, Elliott BC, Ackland TR. Dance floor force reduction influences ankle loads in dancers during drop landings. J Sci Med Sport. 2015;18(4):480-5.
6. Fong Yan A, Hiller C, Smith R, Vanwanseele B. Effect of footwear on dancers: a systematic review. J Dance Med Sci. 2011;15(2):86–92.
7. Russell JA. Preventing dance injuries: current perspectives. Open Access J Sports Med. 2013;4:199-210.
8. Hendry D, Campbell A, Ng L, Grisbrook T, Hopper D. Effect of Mulligan's and Kinesio knee taping on adolescent ballet dancers knee and hip biomechanics during landing. Scand J Med Sci Sports. 2015;25(6):888-96.
9. Miller C, Paulos L, Parker R, Fishell M. The ballet technique shoe: a preliminary study of eleven differently modified ballet technique shoes using force and pressure plates. Foot Ankle. 1990;11(2):97-100.
10. Bowling A. Injuries to dancers: prevalence, treatment, and perceptions of causes. BMJ. 1989;298(6675):731-4.
11. Luke A, Kinney S, D Hemecourt P, Baum J, Owen M, Micheli L. Determinants of injuries in young dancers. Med Probl Perform Art. 2002;17(3):105-12.
12. Liederbach M, Dilgen FE, Rose DJ. Incidence of anterior cruciate ligament injuries among elite ballet and modern dancers: a 5-year prospective study. Am J Sports Med. 2008;36(9):1779-88.
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13. Hopper L, Allen N, Wyon M, Alderson J, Elliott B, Ackland T. Dance floor mechanical properties and dancer injuries in a touring professional ballet company. J Sci Med Sport. 2014;17(1):29-33.
14. Bressel E, Cronin J. The Landing Phase of a Jump Strategies to Minimize Injuries. J Phys Educ Recreat Dance. 2005;76(2):30-5.
15. Wilson M, Young-Hoo K. The Role of Biomechanics in Understanding Dance Movement. J Dance Med Sci. 2008;12(3):109-16.
16. McGuinness D, Doody C. The injuries of competitive Irish dancers. J Dance Med Sci. 2006;10(l-2):35-9.
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APPENDIX A: RECRUITMENT OF PARTICIPANTS
Recruitment Email
Subject: DANCERS NEEDED FOR RESEARCH ABOUT DANCE SOCKS
Dear dancer,
My name is Isabella Mueller and I am senior in the Translational Health program in Honors Tutorial College. I am currently working on my senior thesis with Dr. Russell that I hope to publish by the end of the year. Dr. Russell and I are investigating the extent to which padded dance support socks made by the Apolla company (https://www.apollaperformance.com/) can reduce the force exerted on the feet during a contemporary dance movement phrase and when landing from a dance jump. Positive results could indicate that dance socks of this type may help reduce the shock on dancers' feet as a measure to reduce the incidence of foot injuries in dancers.
This e-mail is designed to describe the study and give you the chance to participate. If you do participate, you will visit Dr. Russell’s lab in Grover Center, and we will record some basic information about you. Then you will watch a video where you will learn a 30 second dance movement phrase from the Laban Conservatoire of Dance and Music. Then we will apply two pressure sensors to the sole of one of your feet. While you are dancing and jumping the sensors will record the foot pressures. Next, you will complete three trials of a sauté jump. You will perform the routine both wearing the socks and with bare feet, and your dancing will be recorded by video. The whole process will take about 45 minutes. All of your data will be kept strictly confidential. When you are finished, you will be able keep the pair of dance socks you used; they are valued at approximately $30.
Please contact me if you would like to learn more about the study or are interested in being a participant. Thank you for your consideration.
Yours sincerely,
Isabella Mueller [email protected] (845)570-1849
Advisor: Dr. Jeff Russell [email protected] (740)593-4648
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Announcement at Dance Class
Hi, my name is Isabella Mueller and I am senior in the Translational Health program in Honors Tutorial College. I am currently working on my senior thesis with Dr. Russell that I hope to publish by the end of the year. Dr. Russell and I are investigating the extent to which padded dance support socks made by the Apolla company can reduce the force exerted on the feet during a contemporary dance movement phrase and when landing from a dance jump. Positive results could indicate that dance socks of this type may help reduce the shock on dancers' feet as a measure to reduce the incidence of foot injuries in dancers.
Dr. Russell and I are here today to describe the study and give you the chance to participate. If you do participate, you will visit Dr. Russell’s lab in Grover Center, and we will record some basic information about you. Then you will watch a video where you will learn a 40 second dance movement phrase from the Laban Conservatoire of Dance and Music. Then we will apply two pressure sensors to the sole of one of your feet. While you are dancing and jumping the sensors will record the foot pressures. Next, you will complete three trials of a sauté jump. You will perform the routine both wearing the socks and with bare feet, and your dancing will be recorded by video. The whole process will take about 45 minutes. All of your data will be kept strictly confidential. When you are finished, you will be able keep the pair of dance socks you used; they are valued at approximately $30.
We have some slips with contact details to give. Please contact me if you would like to learn more about the study or are interested in being a participant. Thank you for your consideration.
Recruitment Slips
DANCERS NEEDED FOR RESEARCH ABOUT DANCE SOCKS
To learn more about the study or to volunteer to participate, please contact:
Isabella Mueller [email protected] (845)570-1849
Advisor: Dr. Jeff Russell [email protected] (740)593-4648
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APPENDIX B: SCREENING QUESTIONNAIRES
Screening Survey: Highlight Yes or No
Inclusion Criteria: Are you an Ohio University dance major or dance faculty? Yes No
Exclusion Criteria: Have you had a lower extremity, non-foot injury in the past month that required you to miss at least one day of class, rehearsal or performance? Yes No
Have you had a foot injury in the past three months that required you to miss at least one day of class, rehearsal, or performance? Yes No
Do you have sensitivity to tape adherent sprays or athletic tape adhesives? Yes No
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APPENDIX C: CONSENT FORM
Ohio University Adult Consent Form with Signature
Title of Research: Force attenuation properties of padded dance support socks Researchers: Isabella Mueller and Dr. Jeff Russell (advisor) IRB number: 18-X-226
You are being asked by an Ohio University researcher to participate in research. For you to be able to decide whether you want to participate in this project, you should understand what the project is about, as well as the possible risks and benefits in order to make an informed decision. This process is known as informed consent. This form describes the purpose, procedures, possible benefits, and risks of the research project. It also explains how your personal information will be used and protected. Once you have read this form and your questions about the study are answered, you will be asked to sign it. This will allow your participation in this study. You should receive a copy of this document to take with you.
Summary of Study The objective of this study is to determine whether or not APOLLA dance socks reduce pressure on the feet during dance and whether APOLLA dance socks reduce the force on the feet when landing from a dance jump.
Explanation of Study This study is being done to see if there is a reduction in pressure and force on modern dancers’ feet when they are dancing wearing pressure reducing dance support socks versus dancing barefoot. The particular brand of padded dance support socks being used in this study is APOLLA.
If you agree to participate, you will be asked to learn a 30 second modern dance sequence called the “High Intensity Dance Fitness Test.” After you learn this dance, pressure sensors will be placed on the bottom of your foot of your preferred dancing leg. You will perform the dance both with socks on and off and then do a dance jump on to a force plate with the socks on and off. The order in which you do these will be assigned at random by the researchers.
During this process your dancing and jumps will be video-recorded so that the signals collected by the sensors can be matched to the moves you perform on the video. The videos may show your face; however, they will be used only for the purposes of this study, will be stored on a password-protected computer in a locked laboratory, and will destroyed once the study is complete.
You should not participate in this study if you had a lower extremity injury in the last month that has required you to sit out of dance or other physical activity for at least one day, or if you have had a foot or ankle injury in the past three months that has required you to sit out of dance or other physical activity for at least one day.
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Your participation in the study will last a maximum of 45 minutes.
Risks and Discomforts You may stumble and fall during the study. However, you will be performing typical dancing and jumping procedures similar to what you do in your dance classes, rehearsals, and performances. Your skin may be sensitive to the adherent spray or the tape adhesive we use in the study. While hypoallergenic products will be used that are in widespread use in sports medicine and performing arts medicine, if you believe you may have a sensitivity to any of these products you will be excused from the study. If your skin does become irritated from the spray or adhesive, it should last no more than 24-48 hours. You should wash the area with soap and water at the first sign of any irritation. You may wish to apply some over-the-counter allergy cream such as Benedryl (diphenhydramine) cream. If you wish to not participate in the study or wish to stop participating once you have started, you may do so without any consequence whatsoever.
Benefits This study is important to society because the socks could reduce pressure and force on dancers’ feet. By reducing the pressure and force, this could help protect dancers’ feet.
You may not benefit personally by participating in this study.
Confidentiality and Records The video recordings of the Noraxon data collection system may show your face. However, the recordings associated with this project will be kept on a password protected computer in Dr. Russell's lab in Grover E116, which is inside a door that is always locked when the room is not in use. The data and videos will be destroyed following their use in data analysis. This is anticipated to be complete by May 2019.
While every effort will be made to keep your study-related information confidential, there may be circumstances where this information must be shared with Federal agencies, for example the Office of Human Research Protections, whose responsibility is to protect human subjects in research, or with Representatives of Ohio University (OU), including the Institutional Review Board, a committee that oversees the research at OU.
Compensation As compensation for your time/effort, you will receive the pair of padded dance support socks that you use during your testing. These socks are valued at approximately $30.
Future Use Statement Data/samples collected as part of this research, even if identifiers are removed, will not be used for future research studies.
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Contact Information If you have any questions regarding this study, please contact the investigator Isabella Mueller, [email protected] and 845-570-1849] or the advisor [Dr. Jeff Russell, [email protected] and 740-593-4648].
If you have any questions regarding your rights as a research participant, please contact Dr. Chris Hayhow, Director of Research Compliance, Ohio University, (740)593-0664 or [email protected].
By signing below, you are agreeing that:
• you have read this consent form (or it has been read to you) and have been given the opportunity to ask questions and have them answered; • you have been informed of potential risks and they have been explained to your satisfaction; • you understand Ohio University has no funds set aside for any injuries you might receive as a result of participating in this study; • you are 18 years of age or older; • your participation in this research is completely voluntary; • you may leave the study at any time; if you decide to stop participating in the study, there will be no penalty to you and you will not lose any benefits to which you are otherwise entitled.
Signature ______Date
Printed Name ______
Version Date: [09/14/2018]
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