In competitive DanceSport, also known as recreational ballroom

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1 Contributions of Muscle Fatigue to a Neuromuscular Neck Injury in Female Ballroom Dancers Teri Riding McCabe, MS, ATC, J. Ty Hopkins, PhD, ATC, Pat Vehrs, PhD, and David O. Draper, EdD, ATC OBJECTIVE: To investigate the etiology of a loss-of-control neck injury in international modern (IM) dancesport dancers. A comparison to identify if dancers with neck injury have a greater decrease in median frequency in electromyography (EMG) than non-injured dancers. SUBJECTS: Twenty female subjects (mean age 21.6 ± 3.0 yrs, height ± 4.3 cm, weight 59.1 ± 5.2 kg, mean BMI 21.1 ± 1.2) with minimum 1-year experience in competitive IM dancesport. MEASUREMENTS: EMG activity from the left upper trapezius, left splenius capitius, and right sternocleidomastoid muscles before and after dancing the five IM dances. Extension, lateral flexion, and neck length were also measured. RESULTS: There was no significant difference in all measurements. CONCLUSIONS: Although we did not find the etiology of this neck injury, this was the first research into this injury. Future research could study the different IM dances, compare different competition levels, or the amount of force placed on the neck when dancing. Med Probl Perform Art 2013; 28(2): In competitive DanceSport, also known as recreational ballroom dancing, dancers can compete in different classifications and styles of dancesport according to each country s association rules. 1 The only injury research in dancesport has been performed with international modern (IM) and international Latin (IL) style dancers Injury studies have found that the most commonly injured sites are the neck, back, shoulder, knee, lower leg, ankle, and foot Because competitive couples train together, their training duration is equal; however, their dancing techniques are gender specific. 3 The female dancer s technique in IM involves keeping the upper body and head poised slightly back and a little to the left The female dancer begins with an erect and supported spine, then softly flexes the knees forward and upward to carry the body weight over the front of the feet, and lastly stretches up to the left. 18 A correctly held dance frame utilizes all the muscles of the trunk or core to carry the arms and neck. 19 While competing, some female dancers are unable to maintain this position, and the head falls into a paralysis-like condition. 20 The cause of this Ms. McCabe is a doctoral student at the Research Centre for Exercise, Sport and Performance, University of Wolverhampton, Walsall, UK; and Dr. Hopkins is Professor, Dr. Vehrs is Associate Professor, and Dr. Draper is Professor at the Department of Exercise Science, Brigham Young University, Provo, UT, USA. Funding provided by the Ira and Mary Lou Fulton Grant, Exercise Science Department, Brigham Young University. Address correspondence to: Ms. Teri Riding McCabe, University of Wolverhampton, WH224 Walsall Campus, Walsall WS1 3BD, UK. Teri.Riding2@wlv.ac.uk Science & Medicine. loss-of-neck control is unknown at this time. This injury might be due to an acute onset of fatigue in the cervical flexor and lateral rotation muscles, resulting in an inability to sustain static posture of the neck. During a major competition, a dancer can go through six to eight rounds of competition in 1 or 2 days, which means they would be dancing up to 10 minutes per round and 80 minutes per day. 21 In dancesport, the female s shoulder position is at 90º of abduction, with the elbow bent for the hand to be on the male partner s right arm near the shoulder. 17,22 It could be speculated that during ballroom dancing, blood flow to the neck muscles could be slowed because of this arm position. Hagberg 23 examined arm elevations and found a decrease in muscle action potentials because of a decrease in blood flow. This decrease in blood flow would prevent the muscles from receiving the nutrients for muscle contractions and removal of lactic acid. 23,24 This would then cause muscle fatigue. Järvholm et al. 25 has suggested that intramuscular pressure exceeding 30 to 50 mm Hg reduces local muscle blood flow, and when the arms are elevated during highintensity working conditions, obstructed blood flow can cause localized muscle fatigue. Research has shown in dancesport that the heart rate will range between 153 to 193 bpm. 8,11 This research also has shown that the Viennese waltz and quickstep are the most physiologically demanding dances in IM. 2,8,9,11 According to Åstrand et al., 26 dancesport would be classified into the very heavy to extremely heavy category in energy expenditure. The approved competition choreography of the Viennese waltz, in IM, is limited compared to that in the other four dances included in the IM category, and the female dancer holds her neck in the same static position, slightly back and a little to the left, in all the Viennese waltz choreography. 17,22,27 This head position could be considered an isometric contraction with a constant force output. Moritani et al. 28 suggested that an isometric contraction can be influenced by the excitationcontraction coupling, which can decrease the ph from lactate production. During the other four dances in IM, the female dancer starts with her head a little to the left, but the dancer may move the head in response to the partner s lead, whereas in the Viennese waltz the head is held in a constant position. 17 This shoulder elevation position may be enough to cause localized muscle fatigue and cause the inability to hold the neck in position. It may be possible to determine a contributing cause of this loss-of-neck-control injury using electromyography (EMG). Several researchers have used EMG to identify which muscles are active during specific dance motions However, they have not utilized EMG during fatiguing muscle 84 Medical Problems of Performing Artists

2 contractions in dance movements. The median frequency from an EMG signal has been found as a reliable and valid method to estimate muscle fatigue Muscular fatigue is measured as a decrease in the median frequency during a sustained contraction. 28 This can possibly be credited to a slowing of muscle conduction velocity. 40 Gogia and Sabbahi 41 observed that median frequency can be measured in the cervical paraspinal extensor muscles. For female dancers to accomplish correct technique in IM dancesport, they need to use the neck muscles that execute extension (EXT), left lateral flexion (LLF), and left rotation. The oblique capitis superior, rectus capitis posterior, spinalis cervicis, illiocostalis cervicis, trapezius, and sternocleidomastoid (unilaterally) perform EXT. 42,43 The longus colli helps limit hyperextension. 42 The oblique capitis superior, rectus capitis lateralis, illiocostalis cervicis, and trapezius perform LLF. 42,43 The rectus capitis posterior, sternocleidomastoid (unilaterally), multifidus, rotatores (to opposite side), longus capitis (to same side), and longus colli perform left rotation. 42,43 The longissimus capitis and cervicis (unilaterally), semispinalis capitis, and splenius capitis muscles perform all three motions. 42,43 Even though many muscles perform these three motions, only a few are available to measure with surface EMG electrodes. Therefore, the left splenius capitis and left upper trapezius were chosen to measure fatigue in the action muscles, and the right sternocleidomastoid was chosen to measure fatigue as the stabilizing muscle. The aim of this study was to determine if female ballroom dancers with a history of this loss-of-control neck injury will have a greater decrease of median frequency or fatigue in the left upper trapezius, left splenius capitus, and right sternocleidomastoid muscles than dancers with no history of this injury. METHODS Female dancers with at least 1 year experience in competitive IM dancesport were recruited to participate from a university ballroom dance program. The participants must have competed in either in the novice, pre-championship, and/or amateur IM classifications according to National Dance Council of America (NDCA) rules. 27 A questionnaire asking about dance history, injury history, and partner history was used to assign participants into injured and non-injured groups. The injured group consisted of participants who identified themselves as having had the loss-of-control neck injury in the past. Height and weight were measured. Brigham Young University IRB approval was obtained and the participants and their male dance partners provided informed consent prior to participation. Instruments Electromyography. The Biopac MP150 system (BIOPAC Systems, Inc., Santa Barbara, CA) was used to measure muscle activity. Signals were amplified from side-by-side, circular, 1- cm-diameter, pregelled silver-silver chloride (Ag-AgCl) surface electrodes with a fixed interelectrode distance of 2 cm (Product # 272 Noraxon Dual Electrodes, disposable, self-adhesive, Noraxon USA, Inc., Scottsdale, AZ). The ground electrode was also a circular, 1-cm-diameter, pregelled Ag-AgCl surface electrode (Type M-00-S Blue Sensor disposable electrodes, Medicotest, Inc., Rugmarken, Denmark). The EMG measurements were collected at 1,000 Hz. The input impedance of the amplifier was 1.0 MΩ, with a common mode rejection ration of 90 db, bandpass filter of 5 to 500 Hz, a signal-to-noise ratio of 70 db, and a gain of 1,000. Raw EMG signals were processed using a root mean square (RMS) algorithm with a 5-msec moving window. A Microsoft Visual Basic 6.0 (Microsoft Corp., Redmond, WA) custom program identified the median frequency curve for each trial (data set) in the data analysis. The equation used to calculate the median frequency (MF) was: x Median x 2 MF = S(x)dx = S(x)dx x 1 x Median Where S(x) is the spectral density of the EMG signal, x 1 is the lowest frequency of the spectrum, x 2 is the highest frequency in the spectrum, and x median is the median frequency of the spectrum. An average of seconds or 4,979 samples of the 5 seconds of collected data was used in data reduction. Goniometer. Active neck extension (EXT) and right and left lateral flexion (RLF and LLF) range of motion was measured with a fluid goinometer (Medical Research Ltd., Leeds, UK) prior to and after completion of the dance routine. The participants were reminded to stand up straight. Measurements. Neck length was measured as the distance between the following structures: 1) external occipital protuberance (EOP) to 7th cervical spinous process (C7); 2) C7 to acromioclavicular joint (AC), and 3) AC to inferior angle of the scapula. The inferior angle to the scapula is the approximation of where the male partner s hand is placed while dancing. Testing Procedures The participants did not wear their competition costumes, but they did wear their competition shoes. The participants also did not use competition hair styles, which can be elaborate and may affect the extension (EXT) or lateral flexion of the neck. The electrode sites were cleansed with isopropyl alcohol and gauze. Surface electrodes were placed on the following four locations: Left upper trapezius (UT) just lateral to and horizontal with the 2nd cervical vertebra spinous process (C2). Left splenius capitis (SPL) between the UT and upper sternocleidomastoid (SCM) below the occipital bone. Middle half of the right SCM muscle. The ground electrode was over the 7th cervical vertebra spinous process (C2). June

3 TABLE 1. Participants Height, Weight, and Age Correct placement was confirmed with manual muscle testing and visual inspection of the raw EMG signal. After the electrodes were attached, they were outlined by black marker to be sure of correct placement if they fell off while dancing. EMG recordings were taken prior to and immediately after each round of dancing. A total of six EMG recordings were obtained from each female dancer. Participants were instructed to stand in dance position with their partners while muscle activity was recorded for 5 seconds. Dance Routine Non-Injured Injured Height (cm) ± ± 4.1 Partner height (cm) ± ± 5.8 Weight (kg) 58.9 ± ± 5.4 Partner weight (kg) 78.0 ± ± 8.5 Age (yrs) 22.2 ± ± 2.9 Partner age (yrs) 23.1 ± ± 3.5 Data given as mean ± SD. Participants and their dance partners watched a video to learn the standardized novice-level choreography that was performed for each dance. The participants and their partners practiced the choreography in the lab and dance studio before they performed it. Each couple performed to the same timed music. The five IM dances are (in order) the waltz, tango, Viennese waltz, slow foxtrot, and quickstep. All couples performed all five dances with a 30-second break between dances for each round. Each dance was 1:30 (minute:seconds) long with a fade out, except for the Viennese waltz which was 1:15 long. The tempo (measures per minute, mpm) for the waltz, tango, Viennese waltz, slow foxtrot, and quickstep were 28, 32, 56 58, 28, and mpm, respectively. To simulate competition, the participants performed three rounds of the five dances with a 20-minute break between each round. During the 30-sec break between dances, the participants walked to their next starting position. For the 20- min break between rounds, the dancers were told to do what they normally do during competition. Some participants ate, hydrated, practiced routines, or sat and rested. Statistical Analysis Descriptive statistics are expressed as mean ± standard deviation (SD). A 2 6 factorial ANOVA with repeated measures on time was performed to compare the independent and dependent variables. The independent variables were group and time and the dependent variables were median frequency, range of motion, and neck length. A Tukey s honestly significant differences test was used to detect specific changes post hoc. An independent t-test was performed to compare neck length and ballroom dance experience in both groups. For comparative statistics, p<0.05 determined significance. RESULTS There were a total of 20 (10 injured, 10 non-injured) participants. The heights, weights, and ages of both groups were similar (Table 1). The participants ballroom experience was similar (Table 2) except in years ballroom dancing and years competing in IM, where the injured group had been dancing a mean 3 years longer than the non-injured group and significant differences were found (Table 3). Neck range of motion and length were similar in both groups with no significant differences (Tables 3 and 4). There were also no significant differences in median frequency for any of the muscles (Table 5, Fig. 1). In the injured group, six dancers (60%) had competed in ten dance. Ten dance is to compete in all five IM dances (waltz, tango, Viennese waltz, slow foxtrot, and quickstep) and all five IL dances (cha cha, samba, rumba, paso doble, and jive) and then the scores are combined to give the ten dance champion. 1,17 Eight (80%) of the injured group had danced other styles of dancesport, for example American smooth and rhythm, social, swing, and theatre arts/cabaret. All of the injured dancers had experience in other dance genres, such as ballet, jazz, and contemporary. Two (20%) of the injured group were injured at the time the study took place, which included the neck and shin splints. One participant reported that the current injury occurred while competing, and the other participant reported doing something other than dancing when the injury occurred. Six (60%) had been injured in the last 6 months, which included the neck, low back, pelvis, and ribs. The injured group had the loss-of-control neck injury a mean of 2.5 ± 1.7 times, with eight (80%) occurring with their cur- TABLE 2. Participants Ballroom Experience Non-Injured Injured How long have you been ballroom dancing? (yrs) 4.4 ± ± 2.8 How long have you been competing IM? (yrs) 3.0 ± ± 2.4 What level* are you currently competing? 2.9 ± ± 0.7 How long have you been at this level? (yrs) 1.7 ± ± 2.0 How many dance partners have you had? 4.5 ± ± 1.5 How long have you been dancing together? (yrs) 0.9 ± ± 2.1 How many times have you had this neck injury? 2.7 ± 1.7 *Competition level: 1, novice ; 2, novice/pre-champ; 3, pre-champ ; 4, pre-champ/amateur ; 5, amateur. Data given as mean ± SD. 86 Medical Problems of Performing Artists

4 TABLE 3. ANOVA of Muscle Median Frequency and Range of Motion and Independent t-test Results of Ballroom Experience df F 2 Upper trapezius 1, Sternocleidomastoid 1, Left splenius capitis 1, Left lateral flexion 1, Right lateral flexion 1, Extension 1, Yrs ballroom dancing 1, Yrs competing in IM 1, TABLE 4. Participants Neck Lengths and Range of Motion Non-Injured Injured O to C7 (cm) 10.9 ± ± 1.1 C7 to AC (cm) 19.5 ± ± 1.0 AC to IA (cm) 22.4 ± ± 1.6 Pre LLF (º) 55.3 ± ± 18.6 Pre RLF (º) 52.7 ± ± 16.9 Pre Ext (º) 84.7 ± ± 9.8 Post LLF (º) 54.1 ± ± 12.9 Post RLF (º) 55.4 ± ± 9.6 Post Ext (º) 86.8 ± ± 13.6 rent partner and seven (70%) with another dance partner (Table 2). Only one participant reported having numbness or tingling with this neck injury. In the non-injured group, one (10%) had competed in ten dance. Seven (70%) of the non-injured group had danced other styles of dancesport, such as country, social, swing, American smooth, and cabaret. All ten the non-injured dancers had experience in other dance genres. Four (40%) of the non-injured group were injured at the time the study took place, which included the neck, rib, knee, shoulder, ankle, and gluteal area. The participants reported that these current injuries occurred while rehearsing, competing, or doing something other than dancing. Seven (70%) had been injured in the last 6 months, which included the ribs, feet, shoulder, ankle, lower leg, and knee. DISCUSSION The results showed that fatigue in the right sternocleidomastoid, left upper trapezius, and left splenius capitis muscles did not cause the acute loss-of-control neck injury in these female ballroom dancers. The results showed there was a decrease in median frequency; however, this fatigue was found in both the injured and non-injured groups and there was no significant difference in fatigue rates between groups (Tables 3 and 5, Fig. 1). This is the first research on the loss-of-control neck injury in dancesport. A search in medical databases produced only one occurrence of a neck injury of a ballroom dancer. It was a case study of cervical radiculopathy in a 52-year-old female who had been ballroom dancing for 3 years. 15 Cervical radiculopathy is produced by compression and inflammation of a cervical spinal root. 15,44 Wainner and Gill 45 defined cervical radiculopathy as a lesion or disease of the cervical nerve root, regardless of the etiology. Radicular distribution in one or both upper extremities occurring in episodes often lasting for a few weeks can occur with varying degrees of sensory, motor, and reflex changes. 46 The most common level is at C6 and C7, the latter being the level that the dancer sustained. 15,44 47 Since this occurred at the C7 nerve root level, symptoms include tingling or numbness down the 3rd and 4th fingers. 44 Other manifestations may include a decrease in the triceps reflex, pain in the interscapular forearm, chest, and ulnar hand areas, motor weakness in the elbow, wrist, and fingers, and possible scapular winging bilaterally or only on the affected side. 44 In this case study, 15 the female dancer had symptoms only in her left arm which consisted of intermittent numbness and tingling in the second, third, and fourth fingers with little shoulder and arm pain. The dancer complained of mild weakness in the hand with the sensation that the arm felt heavy. The dancer s occupation consisted of duties that involved typing for several hours a day. Malanga 47 suggested that cervical radiculopathy can be present in younger and older athletes. However, Wainner and Gill 45 reported that most occur in 40 to 50-year-olds. Radhakrishnan et al. 46 concurred, with an epidemiologic study finding a higher frequency between ages 40 to 59 years old. The case study subject was 52 years old and had been dancing for 3 years. 15 The subjects in this study had an average age of 22 years and had been dancing an average of 5 years (Tables 1 and 2). This may suggest that senior beginning ballroom dancers run the risk of sustaining a cervical radiculopathy injury, especially if their occupations enhance the risk. It may also be speculated that former dancers could be at risk for cervical radiculopathy later in life. TABLE 5. EMG Median Frequency for Each Muscle Pre Post Non-Injured Injured Non-Injured Injured Upper trapezius 12.0 ± ± ± ± 7.6 Sternocleidomastoid 9.2 ± ± ± ± 3.6 Left splenius capitis 8.5 ± ± ± ± 5.5 All pre trials were averaged together, and all post trials were averaged together. Data given as mean ± SD. June

5 FIGURE 1. EMG median frequency for each muscle, normalization and before (pre) and after (post) each round of dancing. UT, upper trapezius; SCM, sternocleidomastoid; SPL, left splenius capitis. This is the only documented case of a neck injury in dancesport. 15 However, neck injuries in female dancers probably occur more often than they are reported due to a lack of medical professionals who supervise competitions. Only one participant included in this study reported numbness and tingling in the arm, but no other symptoms typical for cervical radiculopathy. The participants in the current study stated that the most common manifestation of this loss-of-control injury occurred during competitions. This might mean that during performances or rehearsals, the choreography may not have the dancers necks in the dancing position (EXT and LLF) for the same amount of time as during competitions and/or the dances may not be in the same order. The number of years ballroom dancing differed significantly between the injured and non-injured groups, with the injured group dancing for longer than the non-injured group (Tables 2 and 3). This also reflected the competition level of each group. The injured group was competing at a prechamp/amateur level, whereas the non-injured group was competing at the lower level of novice/pre-champ. The choreography for this study was at a novice level; therefore, the injured group danced below their competition level and was not physiologically challenged enough. A few of the injured group s partners asked if they could add more demanding choreography into the routine. In the injured group, the participants described having the loss-of-control injury with their current partner a minimum of once to a comment of all the time. The injured group also reported having this injury for a mean of 2.7 times with their partner (Table 2). Howse and McCormack 48 suggested that when determining the etiology of an injury in dancers, technique should be considered first. Faulty technique is one of the primary causes of dance injuries. 49 Technique errors can occur because of fatigue, anatomical causes, lack of knowledge, bad teaching, not applying correct technique, and environmental causes. 48 The neck length was measured to determine if it could contribute to faulty technique (Table 4). Dancesport instructors have expressed that incorrect technique may cause this loss-of-control injury. 18,19 The ballroom experience questionnaire did not ask how old the dancers were when this neck injury first occurred. By knowing when this injury started, it might be possible to identify which previous instructor taught the dancer incorrect technique. Another theory in the dancesport community as to why female ballroom dancers lose control of their neck during competition may be the amount of centripetal force during turns. It is possible the turns in the Viennese waltz (VW) produce a greater amount of centripetal force on the neck than in other dances. This is why the right sternocleidomastoid was chosen; the idea was that the sternocleidomastoid would fatigue more because of its stabilizing the head during dance, especially the VW turns. However, in this study the sternocleidomastoid did not fatigue at a significant rate. The dancesport community knows the music of the VW is faster, 3/4 timed music instead of 4/4 time like the other four dances; therefore the time is shorter for competitions. 22,27,50 The VW can be described as continuous and swift rotations. 22 It is danced at 60 measures per minute, and one revolution of a turn is performed for every 2 measures, which is every 2 seconds. 27 Currently, the amount of force placed upon the head is unknown; because of the speed at which the VW turns are performed, the velocity could be enough for the dancers to lose control of the neck. Besides utilizing choreography that was not challenging enough for the dancers, another limitation could be having only 10 dancers in each experimental group with a total of 20 participants. Previous EMG research in dancers has ranged from 3 to 18 dancers. 29,31,33-35,51 There is a history of low 88 Medical Problems of Performing Artists

6 sample size in dance medicine research. With low participant numbers, a type II error is possible, but it should be noted that actual values (Table 3) are reported to help determine if a type II error is possible. Suggested future research would be to compare median frequency for all five dances to each other, this would reveal the contribution of each dance to the occurrence of this neck injury. Another scheme could have the dancers perform their own choreography or choreography at their level and only use one competition level. An alternative would be to compare competition levels, such as amateur to professional. Another suggestion for the next study may be to see how many former or older dancers have cervical radiculopathy. Additional research could be to use biomechanical analysis to evaluate amount of force natural and reverse turns in the Viennese waltz produce on the neck. 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