Introduction

Ballet dancers are at high risk of sustaining musculoskeletal injuries, especially due to the multitude of technical movements they perform repetitively at extreme ranges of joint motion. Combining both the professional and pre-professional levels, overuse accounts for 65.9% of dance injuries.¹ Smith et al.¹ indicated that amateur and professional dancers have a combined incidence of 1.09 injuries per 1000 dance hours. While several authors have indicated that dance injuries most commonly affect the foot and ankle,^1–6 the next most commonly injured regions were the lumbosacral spine,⁷ knee,⁸ and hip.^9,10 These injuries create a substantial burden for dancers and companies alike; the costs of time-loss due to injury, medical expenses, risk of premature retirement, and increased risk for chronic musculoskeletal conditions impact all constituents of the dance community.

Despite the traditional reputation of ballet as an “art,” professional dancers are commonly regarded as athletes based on the physical demands they sustain through long hours of technical training, rehearsals, and performances.¹¹ Dancers must possess a high level of fitness, strength, coordination, agility, speed, and motor control to perform at the elite level with minimal injury risk.¹² However, professional ballet dancers are less likely than other athletes to specifically train these areas of fitness.¹² Dancers commonly teach and work outside of their company dancer positions in order to supplement their limited income from dancing alone.¹² The additional time, financial and physical constraints associated with their supplemental work limit the feasibility of adding further training to their schedules.¹² Many dancers may avoid strength and agility training due to the belief that these fitness activities may cause hypertrophy of muscle, negatively impacting their aesthetic appearance.¹³ Subsequently, dancers have been deemed “not as well-conditioned” as other athletes.^12,14,15 Similar to other sports, the high prevalence for overuse injuries in dance has been linked to strength, aerobic fitness, and motor control deficits.^12,13 Training programs have been shown to improve such impairments in this population.¹⁶

Although injury prevention and screening programs for lower extremity injuries have been commonly utilized in sports such as soccer,^17,18 similar programs have only recently been proposed for professional dancers.^12,13,19,20 Though initially recommended three decades ago,²¹ the literature regarding the effects of ballet injury prevention programs remains limited, and no studies have sought to standardize the elements of such programs. Initial investigations regarding the benefits of supplemental fitness training showed positive results for decreasing pain,¹³ mixed results for improving aerobic capacity,^12,22 and no significant strength improvements.¹² Mistiaen et al. reported positive effects on fitness without affecting aesthetic appearance.¹³ Although dysfunctional movement patterns have been associated with injury,²³ the effects of motor control training in the professional dance population have not been thoroughly studied.

The purpose of this study was to examine the effects of a supplemental conditioning program on professional and pre-professional contemporary ballet dancers. The authors hypothesized that those participating in a training program would reduce injury rate by improving their motor control, stability, balance and physical function. The secondary purposes were to : (1) determine whether professional ballet dancers’ motor control, stability, balance, and physical function improved by participating in a conditioning and injury prevention program, (2) determine if motor control, balance and stability were related to injury incidence, (3) determine if subjective dance-specific function, as measured with the Dance Functional Outcome Survey (DFOS),²⁴ correlated with injury in professional and pre-professional contemporary ballet dancers, and (4) observe the feasibility and qualitative phenomena related to a conditioning program from the dancer’s perspective.

Methods

Participants

This sample of convenience included uninjured adult dancers from a small professional contemporary ballet company who were recruited through word of mouth and a brochure that was shared with the company. The initial sample consisted of 11 dancers: eight professionals, one apprentice and two trainees. Participation was voluntary. All subjects who elected to participate granted informed consent. Anonymity and confidentiality were maintained throughout the study. Two dancers from the initial sample were excluded due to sustaining dance-related injuries prior to the start of the training program.

Study Design

The study was a mixed methods quasi-experimental design with a volunteer sample of professional dancers from one company. The project was approved by the Cleveland State University Institutional Review Board. The final sample consisted of six dancers who were informed that data would be submitted for publication. Subject confidentiality was protected. A power analysis to determine sample size was not possible in this study. Dancers are a unique athletic population. Previous data with estimates of difference or variance for dancers and these outcome measures were not available to perform a power analysis prior to this feasibility study.

Demographics and dance experience

Characteristics of the sample were collected via survey on the day of baseline testing. Dancers were asked for their age, gender, highest level of education, and years of dance experience.

Dance Functional Outcome Survey

All dancers completed the DFOS at baseline, immediately post-conditioning class, and at the four-month follow-up. The DFOS is currently the only dance-specific subjective functional outcome measure and focuses on general activities of daily living and dance-specific technique. Very recent investigations²⁵ regarding the psychometric properties of this tool revealed high test-retest reliability, internal responsiveness over time, sensitivity and internal consistency. The DFOS demonstrated strong construct validity (vs. SF-36 PCS), scale uni-dimensionality, and the absence of both floor and ceiling effects.²⁵

Physical performance tests

A battery of physical performance tests (PPTs) was performed at baseline prior to beginning the conditioning class, within the week following completion of the last class, and at a four-month follow-up. The PPTs selected were previously validated as effective measures of balance, stability, and motor control.^23,26–28 They were performed as described by the authors listed in Table 1, with testing completed by the same raters at baseline and each subsequent testing period.

Neuromuscular conditioning and injury prevention class

The conditioning and injury prevention class was performed in the studio twice a week for 30 minutes over the course of five weeks, with the first session each week taught by a licensed physical therapist who was board certified in orthopedics. The second supplemental session each week was led by one dancer liaison who attended the class earlier in the week. The selected dancer had experience teaching group exercise classes. She reviewed the exercises with the dancers with the guidance of a handout outlining the program.

The neuromuscular conditioning and injury prevention class was developed together by the board certified orthopedic physical therapy specialist who taught the class, and the physical therapist specialty-trained in strength and conditioning. Similar to previous programs,^12,13 this course began with basic movement pattern injury prevention exercises known to be effective in other sport populations.^29,30 It initially emphasized mechanics and correction of movement faults with basic exercises such as bridges, planks, single leg deadlifts, lunges, squats, step ups, and jumping. The program then progressed to more dance-specific movement system patterns as the course advanced (Appendix 1). The full program consisted of a dynamic warm-up, agility training, plyometrics and strength training (Table 2). Previous authors have recommended that injury prevention programs include these components.^18,31,32 As suggested previously,^18,31 verbal and tactile feedback to correct faulty movement patterns were given concurrently while performing each exercise. Dancers were educated regarding the targeted anatomical regions, desired movement patterns, typical compensations, likely mechanisms for injury, intervention rationale, and how the techniques might both reduce injury and enhance performance. Dancers were taught how basic component training was relevant to and translated to improving their traditional ballet combinations.

Statistical Analysis

Inferential statistics. Changes between baseline and post-conditioning PPTs were assessed using the Wilcoxon signed-rank test, which is a paired difference test of mean rank used for single sample, repeated measurements. Statistical significance was set at p<0.05. This non-parametric test is inherently conservative and is used with small sample sizes to reduce assumptions about data distribution normality.³³

Qualitative Analysis

Phenomenological interview. The purpose of this mixed methods phenomenological analysis was to understand the experience or phenomenon from the dancers’ point of view. The researchers were interested in learning if dancers felt a cross training program had benefits and value. If conditioning was beneficial, what recommendations were there for other dancers? This information was obtained through structured interviews by one researcher four months after the conditioning program. The 30-minute interview consisted of eight open-ended qualitative questions. All interviews were audio recorded and transcribed by a member of the research team who did not teach the program, interview dancers, or develop the study design.

Phenomenological analysis. To maximize credibility of the study, several methods were used: triangulation of researchers’ interpretations, sampling for diverse perspectives, and rich descriptions to support thematic categories. First, each transcript was reviewed by the authors individually to look for key phrases in each interview question. Next, the authors met as a group to confirm the key phrases found in each interview question and compile the results. Then, the authors reviewed the key phrases individually to look for main themes in each question across all subjects. The main themes that each individual determined for each interview question were placed in a table organized by the eight guiding questions. The group agreed upon the main themes.

Injury tracking. Injury tracking within the study period was conducted via survey at the four-month follow-up interview. Dancers indicated any time lost from dance¹¹ or time requiring modified activity³⁴ during the course and four-month follow-up period.

Results

Subjects

Of the 11 dancers initially tested, five dancers did not complete the program. Two were excluded prior to the start of the study. Three additional dancers dropped out for the following reasons: (1) concern regarding previous surgeries, (2) a leave of absence from the company, and (3) schedule constraints. Thus, the final sample consisted of six dancers. Descriptive statistics for participating subjects were calculated (Table 3).

Inferential Findings

Post-conditioning. Results from the Wilcoxon signed-rank tests for baseline to post-conditioning change in the DFOS and PPTs are included in Table 4. Statistically significant changes for the DFOS and three of the six PPTs were found. Immediately following the conditioning program, the DFOS was significantly improved (p = 0.04). Dancers also showed improved balance on the composite Modified Star Excursion Balance Test (mSEBT) bilaterally (p = 0.03 for both the right and left lower extremity), improved Single Leg Hop for Distance (p = 0.04), and improved performance on the Upper Extremity Closed Kinetic Chain Test (p = 0.04). No statistically significant changes were noted with the KLAT, Standing Bow Test, or the Medial Triple Hop Test.

Four-month follow-up. Statistically significant changes from initial testing to the four-month follow-up remained for the following tests: (1) DFOS (p = 0.03), (2) Single leg hop for distance (p = 0.03), and (3) mSEBT composite maximum reach for the left lower extremity (p = 0.03). The Upper Extremity Closed Kinetic Chain test (p = 0.08) and the mSEBT composite reach right (p = 0.08), and anterior reach right (p = 0.12) and left (p = 0.23) were not statistically significantly different from baseline (Table 4). Furthermore, none of the tests found non-significant at the initial follow-up became statistically significant at the four-month follow-up.

Qualitative findings

Findings from the phenomenological analysis of the follow-up interview were categorized into common themes across the questions (Table 5). Half of the participants reported they were motivated to participate in the conditioning course to improve their performance. With respect to strengths and limitations, 83.3% of dancers believed their leg strength and endurance were their strongest attributes, and 66.7% reported their stability, balance and landing technique with jumping were their greatest limitations. The dancers found exercises targeting core stability (66.7%), upper body strength (50%) and leg strength (50%) to be the most beneficial exercises, while 66.7% of those same participants reported they no longer continued doing core exercises, specifically bridges and planks, after the course ended.

The dancers did express concern regarding several barriers which may preclude their participation in similar conditioning classes. Most notably, 83.3% of those interviewed reported that time was their greatest barrier. The convenience of this course being brought to them made it more feasible to fit into their schedules. Money and scheduling were also major concerns, with 66.7% of dancers reporting these obstacles to participating. Even with these barriers considered, the participants unanimously agreed that the course was beneficial for both professional and pre-professional dancers. This group was evenly split, with 50% reporting it would be most beneficial for dancers before 8^th grade, while the other 50% noted it would be best suited to target older dancers in 8^th grade or above. All 6 dancers reported no time loss due to injury. None of the participants reported a need to modify their dance activity secondary to injury.

Discussion

Many authors have proposed the need for supplemental conditioning programs to improve dancers’ fitness and decrease injury risk factors.^{12,13,19–21} However, minimal research exists outlining conditioning program design, or the effects of such programs on injury risk factors. It was hypothesized that using a conditioning program similar to other injury prevention programs for mainstream athletics, with some dance-specific components, would improve physical function in areas previously identified as predicting injury in other sports, as well as dancers’ perception of their function. Investigating the effects of risk-factor specific conditioning on validated physical performance measures is crucial for determining how such programs may or may not influence injury risk factors. It is a necessary preliminary step to determining the effects of such conditioning programs on injury incidence and attempting to design a program that might be utilized by dance companies to minimize overuse injuries.

This study is the first to investigate the impact of neuromuscular conditioning on dance function, motor control, stability and balance in professional and pre-professional ballet dancers. A mixed-methods model was used to gain a more thorough understanding of the results and how the proposed conditioning program influenced the dancer participants. Following the dance-specific conditioning program, improvements were noted in dance function, knee/ankle stability and balance, but not in lumbo-pelvic motor control or hip stability. The phenomenological analysis provided insight into perceived benefits of the program, motivation for and barriers to participation in similar conditioning programs. For example, dancers reported which conditioning exercises were perceived as most beneficial, and which exercises were continued independently after the program. They were most motivated to learn of their strengths and weaknesses, and methods to improve upon their limitations. The most common barriers to such programs are time and money. All dancers would recommend similar conditioning classes to other dancers.

Previous research investigated the effects of a conditioning program, which included motor control training, endurance, and strength training, on aerobic capacity and strength.¹² The chosen interventions did not yield significant improvements with the study’s included objective test measures, but their measures did not examine the effect of the program on motor control. The same lead author²³ previously described the KLAT and standing bow test as motor control measures which could predict injury in the lower extremities and lumbar spine. A similar lack of improvement with these same tests was noted here. While the KLAT and Standing Bow Test were validated for predicting injury in the original study,¹² baseline measures in the current sample showed much less pressure variation (Table 6) and higher performance, respectively.

These findings indicate that these measures may have an inherent ceiling effect and may not be sensitive-enough for professional dancers. It is possible that, because of their initially superior scores and lack of injury incidence during the study period, the dancers in this study also had a decreased injury risk compared to those studied previously.¹² If such is the case, further development of more sensitive dance-specific PPTs for motor control and stability in professional-level dancers may be warranted. Improvements were noted in balance and knee/ankle stability, as evidenced by improvements in the mSEBT and the Single Leg Hop for Distance test, respectively. While the SEBT and Y-balance tests have been widely studied, only four publications prior to 2016 used one of these tools to investigate injury risk in sport.¹⁷ These studies demonstrated that a mSEBT combined score of less than 94% of the contralateral lower extremity increased lower extremity injury odds by 6.5 in high school female athletes, and injury odds were 2.7 times more likely with greater than a 4 cm asymmetry difference with anterior reach in male and female high school athletes.^17,26,35 Hegedus et al.²⁶ also reported moderate evidence that the Single Leg Hop for Distance test can discriminate between athletes who do and do not have ankle/knee instability. Considering these previous findings, the current improvements in the mSEBT and Single Leg Hop for Distance following conditioning may indicate decreased injury risk due to gains in balance and ankle/knee stability, respectively. Despite a very small sample size, dance and general function as indicated by the DFOS were also improved following the program, demonstrating the strong responsiveness of this new tool, which was validated recently in a larger-sample study.²⁵ The findings in the current study support the previous idea that applying sports medicine principles may decrease injury risk in the dance population.¹⁹ Continued participation in injury prevention programs throughout a season has been recommended in traditional athletics including, but not limited to, soccer.³¹ Similar independent continuation of the conditioning program may have better maintained the physical performance test improvements into the four-month follow-up period.

Previously, the utility of dance screening programs for injury prediction and prevention was questioned,³⁶ mainly because standard measures from an orthopedic setting (i.e., subjective history, flexibility and strength testing) did not detect between injured and non-injured dancers and were considered too generic for this population. Similar to previous recommendations,^37,38 we focused our screening on functional PPTs measuring complex interactions of movement and evaluated function with the only currently validated dance-specific subjective outcome measure. Further, dancers in this study identified their jump/landing strategies as limitations. Many indicated this was a beneficial aspect of the program, but several also recommended limiting the jump/landing focus in future conditioning programs. These findings suggest that emphasis on these strategies was meaningful, but some dancers were uncomfortable with the dosage implemented in training. Allen indicated that training for jump/landing strategy can decrease injury risk, but that too much fatigue from jumping may increase injury risk.³⁴ Many of the dancers also reported that they often do not participate in cross-training as much as they would like secondary to time and money constraints. They indicated that bringing the current program to their studio and offering it without a charge increased their willingness to participate, even though it was an additional time commitment. Past researchers suggested that dance companies should be aware of and consider the financial consequences resulting from injuries.³⁹ Perhaps appreciating this impact and implementing similar conditioning programs within dance company schedules may serve as a tool to decrease overall long-term costs and improve dancers’ career longevity. Financial resources are typically more readily available in larger companies, increasing their likelihood of adopting supplemental training. More overuse injuries are often found in smaller companies with limited budgets, where dancers are more frequently encouraged to dance through injury due to a lack of understudies.²⁰ Perhaps adopting a sports medicine approach to preventing injuries is most important in these small companies where injuries are more prevalent. Finally, all the dancers suggested that similar conditioning programs begin at least by the pre-professional level, consistent with previous recommendations to begin with adolescent dancers.⁴⁰

While the first objective was analyzed thoroughly, the second and third secondary purposes could not be investigated because none of the dancers reported injury, based on the “time loss” and “modified activity” injury definitions.¹¹ However, additional questioning revealed that while these dancers denied injury and reported an average 0-1/10 pain on a visual analog scale at rest, all reported between 3-6/10 average pain with activity during the study period. The data imply that the dancers consistently work through pain, and that moderate levels of pain do not necessarily signify injury to this sample. These results further support the need to develop an improved consensus definition to track injury,¹¹ and suggest the need to investigate further the implications of the “dancer mentality”^11,41 on pain and injury perception in dancers. Russel et al.¹¹ expressed that injury risk is increased in dancers whose personalities allow them to dance through pain, and that this characteristic typically coincides with the dancer’s level of success. This thought may implicate the need for further focus on injury prevention for those dancers most likely to fill principle roles.

Limitations

This study had inherent limitations due to the self-reported nature of injury tracking with the DFOS, and the test-retest design. The within-subjects design eliminated the possibility of inferring causation from the conditioning intervention. While the study did not include a control group for comparison and evaluated relatively short-term outcomes, these design elements eliminated between-groups differences and reduced maturation bias.⁴²

The four-month follow-up was chosen to assess the dancers’ performance at the farthest period from the intervention, prior to going on a month-long holiday layoff. The authors did not want the results to be skewed due to variance in training with regards to how the dancers chose to use their vacation time. Further follow-up at the end of the season was unattainable secondary to the company touring internationally. Further follow-up beyond that time was impossible due to turnover of company dancers between seasons. The benefit of a short-term follow-up is that it reduces bias due to other training effects and can show if any short-term effects directly following the training program were no longer sustained at a relatively short-term follow-up, thus suggesting the possible need for continued performance of the conditioning program to maintain training effects. A longer follow-up period would be desirable to better determine sustainability of training effects from the program over a longer period of time. Such a follow-up would be easier attained in a larger company. For small companies such as the one studied, it is unfeasible.

Additionally, the dancers self-selected whether or not to participate, potentially causing selection bias.⁴² However, this type of selection is typical when studying such a specific population as a professional ballet company. Also, because the small sample size was possibly underpowered,⁴² the Wilcoxon signed-rank tests may not have yielded effect sizes as great as the true magnitude of change resulting from the program. Nevertheless, this limitation may not have drastically affected the results as numerous positive changes in physical performance and function following the conditioning class were demonstrated with very conservative testing.

Suggestions for future research

Evaluating how a conditioning series may influence dancers’ short-term physical function is only the first step in determining the effectiveness of a conditioning class for reducing injury. Future research should focus on evaluating the long-term stability of balance, stability and functional improvements with and without continued conditioning, if the conditioning program physical improvements directly influence injury risk, and if the physical performance changes reported in this study may serve as mediators to injury incidence. Randomized controlled trials with larger sample sizes and reflective of a larger geographical population of dancers may improve validity and generalizability of the results, respectively.

More detailed injury tracking using injury definitions more sensitive than “time-loss”¹¹ or “modified activity”³⁴ may capture additional physical impairments for better testing the effects of conditioning on injury. While these are standard definitions across the current dance medicine literature, the “dancer’s mentality,”^11,41,43 and the lack of a consensus definition for dance injury^1,34 are well-known challenges for appropriately studying injuries in this population. Future research should focus on streamlining, validating, and possibly standardizing neuromuscular conditioning programs, with a goal of maximizing physical performance benefits and reducing injury risk in the shortest time, with the least financial resources and equipment.

Conclusion

Improvement in multiple PPTs and dance function were noted following the implementation of a neuromuscular conditioning program, but many of the physical gains no longer remained at a four-month follow-up. The loss in improvement at follow-up advocates the potential need for continued conditioning for maintenance of optimal physical performance. The results suggest that conditioning classes may improve professional dancers’ physical performance in areas that are related to injury risk. Subsequently, utilizing such programs may serve to decrease injury risk, but more controlled research with larger sample sizes is needed to determine if a cause-effect relationship of neuromuscular conditioning on dance function and injury exists. The results here support the previous recommendation¹⁹ that dance performance may be improved, and injury risk decreased, by applying principles of sports science to professional dancers’ training regimens.

Conflict of Interest

The authors report no conflicts of interest.