Factors Associated with Musculoskeletal Injuries in Pre-Professional Modern Dancers before and after the COVID-19 Pandemic

Highlights

• The Chester Step Test showed that dancers with higher aerobic fitness were injured less.
• Pre-professional modern dancers who followed a strength exercise regimen were injured less when compared to those who only danced.
• Dance training programs should consider adapting evidence-based sports training methods and integrating aerobic and strength training.
• Mental support for dancers should be considered, at a minimum during times of perceived high stress.

Abstract

The prevalence of dance-related injuries is high, yet risk factors remain unclear in modern dance. The COVID-19 pandemic has affected the continuity and nature of dance programs. The objectives were to investigate factors associated with musculoskeletal injuries in pre-professional modern dancers before and after the pandemic and to qualitatively describe the dancers’ experiences during COVID-19. We examined 31 modern dancers (19.42 ± 1.57 years) pre-COVID-19 and re-examined 21 participants after one-year post-COVID-19, using objective physical tests for upper and lower body strength, aerobic fitness, hip ranges, injury history, and training hours’ data. The injury rate remained mostly unaffected (0.87 ± 0.88 pre-, 0.76 ± 0.83 post-COVID-19), but weekly dance hours were reduced (33 pre-, 21.40 post-COVID-19). Dancers significantly improved their push-up score (p = 0.016) and decreased their compensated turnout (p = 0.022). Notably, non-injured dancers scored higher in the pre-COVID-19 Chester Step Test (p = 0.033) and practiced more strength training independently post-COVID-19 (p = 0.024). No significant differences were found between injured and non-injured dancers in the other parameters. Dancers reported negative thoughts and difficulty maintaining their fitness during the pandemic. In conclusion, strength training and aerobic fitness were identified as potentially important factors related to injury risk in modern dance and should be examined further for their injury prevention value.

1. Introduction

Professional dancing requires heavy physical exertion, fine motor control for technical skills, and physical fitness. Modern dancers depend on choreographic requirements, which often vary in character and combine floor-based movements, partner maneuvers, and frequent use of weight bearing on the upper extremities [1]. Modern dance is mainly an interval type exercise [2] involving short periods of activity, but the overall duration of classes and rehearsals is often extended, which is why good aerobic fitness seems important for dancers to endure long hours of activity. Moreover, a high anaerobic threshold can limit the harmful effects of lactate accumulation during dance activities [3].

Thus, professional dance significantly affects the dancers’ physical requirements [3]. Pre-professional programs in Israel include full-time dance training, designed to resemble the technical demands and intensity in professional dance companies. These programs in Israel are similar to non-academic college programs, include auditions, and are attended by dancers who wish to become professional dancers. These programs extend over one to two years, with nine months of annual activity. This includes daily high-level classes of ballet and modern, as well as repertoire classes, rehearsals, and performances. However, the physical demands of ballet and modern dance differ, and research on ballet dancers cannot be generalized to all dancers [1].

Despite the high physical demands imposed on both dancers and athletes, it seems that the nature of dance training lacks the application of training principles that are well established in sports [4]. Dance lessons focus on technique and choreography, while sports aim to combine skill training with strength training and aerobic (i.e., cardiorespiratory) fitness. The reported incidence of injuries among dancers is higher when compared to elite artistic gymnasts and varies greatly between studies (0.77–4.71 vs. 2.63 injuries per 1000 training hours, respectively) [5,6,7]. The most common areas of injury reported in modern dance students were the ankle/foot (30%), lower back (15%), and the knee (14%) [8]. Similar frequencies were reported among pre-professional ballet dancers [9]. Above 75% of injuries were in the lower limb, with more than half of them in the ankle/foot, and 16% involved the trunk (mainly the lower back).

Previous studies suggest several risk factors for injuries in dance. These include lower vertical jumps in pre-professional and professional female modern dancers [10] and low aerobic fitness in female ballet dancers [11]. During modern dance classes and rehearsal, heart rates (HR) rarely reach the aerobic training zone [2], and HR indices are significantly lower in class than during dance performances. Professional female modern dancers reached higher levels of VO₂max than their counterparts in ballet, reflecting higher aerobic fitness. Yet, this was not shown for male dancers at any level in modern or ballet dance [3]. A systematic review reported the history of injuries in pre-professional ballet and modern dancers as a risk factor [5], but aerobic capacity, training hours, and demographics were not shown to be risk factors. Greater compensated turnout and greater functional turnout were found in injured dancers when compared to non-injured dancers [12].

Functional turnout is the angle between the feet in the first position of ballet [13]. Hips are externally rotated when standing, while thighs, knees, and heels are close together. Compensated turnout is the difference between the functional turnout and the total range of passive hip external rotation motion for both hips [13]. If a dancer externally rotates their hips alone without compensating from adjacent joints, the compensated turnout range is zero.

There are various methodological limitations to research of injury risk factors in modern dancers. Methodological differences exist between studies, and most research regarding risk factors exclusively investigates ballet [1,7,12]; research is scant in modern dance [10]. The population is partly non-homogeneous, and the use of objective tests and uniform definitions of injury is lacking [5,12]. Therefore, knowledge regarding injury prevention in modern dance is needed [5,12,14] to advance the development of pre-season screening and training planning.

The pandemic caused by the novel coronavirus disease (COVID-19) had begun to spread in Israel in March 2020, which coincided with this study’s first data collection. Gathering restrictions and lockdowns interrupted the daily routine in the cultural and creative sector, including professional and pre-professional dance. To maintain some continuity, dance programs began conducting online classes; however, the activity varied in scope throughout the year, and dancers frequently experienced transitions between the studio and online classes. It is clear that this pandemic has damaged dance dramatically, but the exact effects of activity changes on dance injuries following this period remains unknown. To the best of our knowledge, this work is the first attempt to shed light on this by targeting two objectives: (a) to investigate which self-reported and physical measures are associated with musculoskeletal injuries among pre-professional modern dancers; and (b) to compare these measures before and after the COVID-19 pandemic.

Further, this study provides a qualitative description of the physical, mental, and artistic effects on dancers due to COVID-19 restrictions, and the self-reported reasons for injuries by dancers. Findings from this work may highlight the missing physical components in structured dance training and may further our understanding of the multifaceted effect of the COVID-19 pandemic on dancers.

2. Methods

2.1. Participants

The inclusion criteria for participants were as follows: (1) Pre-professional modern dancers, (2) between 18–25 years of age, (3) who regularly trained over 20 h per week in a formalized modern dance program during the period of the study. For the follow-up, dancers who continued to dance in any setting (e.g., the original training program, a professional dance company, or independently) were assessed one year later.

The exclusion criteria comprised: (1) Dancers who were ill or otherwise unavailable on the assessment date, and (2) those with significant medical issues (e.g., surgery, a medically required break from dance, neurological disorders, rheumatologic, cardiopulmonary or metabolic disease). In addition, dancers who participated in the baseline assessment but quit dancing afterwards were excluded from the one-year follow-up.

2.2. Procedure

Recruitment was based on the Maslool Bikurey Ha’Itim professional dance program in Tel-Aviv, Israel. All participants were initially contacted by phone to screen for inclusion and exclusion criteria. Prior to their physical exam, dancers provided informed consent. This study was approved by the University of Haifa ethics committee (#406/19).

The study consisted of two 45 minute physical assessments conducted by two certified physiotherapists visiting the dance studio: A baseline assessment (pre-COVID-19) and a one-year-later follow-up assessment (post-COVID-19).

The objective physical tests were followed by a one-on-one interview based on Dance UK’s injury questionnaire [15] to collect self-reported data on demographics, anthropometrics, physical activity, and injury history. The physical tests were conducted prior to the injury information collection to avoid bias from the two examiners while assessing the objective metrics.

Injury data collection was conducted at five different time points: (T1) Baseline assessment (pre-COVID-19), during which the dancers were asked about injuries in the past year. (T2, T3) Monthly record after the first and second months of dance activity via an online questionnaire. (T4) Monthly record after the third month of activity via a 20–30 min long video conference due to COVID-19 restrictions, which reviewed the physical activity and injuries of the last three months. When dancers reported an injury, they were requested to provide any medical documentation available [12]. Monthly injury data collection was halted due to the COVID-19 outbreak and the lockdowns. Finally, (T5) was a one-year in-person follow-up assessment (post-COVID-19) to gather injury information from the third follow-up (T4) to this point. In T5, dancers were re-examined according to the first session protocol. To capture the effect of the pandemic on the dancers, they were asked a new open question: “How did the COVID-19 pandemic affect you as a dancer?”

2.3. Primary Outcome Measure

• Dance injury (Yes/No) was defined as a traumatic or non-traumatic physical disorder that impaired dance activity in at least one lesson, rehearsal, or performance, either partially or fully limiting participation [16].
• Dance injury rate was defined as the number of injuries during the activity period in hours. Dance injury frequency was calculated as number of injuries divided by total dance hours.

The above were collected pre-COVID-19 at T1, T2–T4, and post-COVID-19 at T5.

2.4. Secondary Outcome Measures

Validated physical tests were conducted to evaluate strength and aerobic fitness and are described below. Additional data were collected, including demographics, weekly training hours, physical activities other than dance, and injury history. Dance experience and participants’ years in the program were examined and negated as potential modifiers in the preliminary statistical analysis.

2.5. Physical Tests

1.

The Sargent Jump Test is a valid and reliable test (Cronbach’s alpha = 0.96, ICC = 0.96) for explosive power in the lower limbs, which measures jumping height in centimeters from a standing position [17]. The test was performed according to the protocol described by Harman et al. [18].

2.

The Heel-Raise Test assesses functional ankle strength by the number of heel-raise repetitions for each leg [19,20]. The test was found reliable (ICC = 0.78–0.84) with similar reliability as in isokinetic tests [19]. Test protocol was conducted as described by Hébert-Losier et al. [20], with the dancers standing barefoot on the floor.

3.

The Push-Up Test assesses upper limb strength by the number of push-up repetitions to fatigue, based on Baumgartner et al.’s protocol [21]. The dancers’ feet were placed together, and palms were positioned at approximately shoulder width. One push-up was counted when the dancers’ chests touched the five-centimeter height cone in the lower position and then raised up to the straight arms position. The test was found to be valid and highly reliable [21].

4.

The Chester Step Test is a valid test for aerobic capacity in healthy adults, highly correlated to VO₂max [22]. In the test we measured HR during stepping on and off a 30-centimeter step to exertion [22]. We followed Sykes and Roberts’ protocol [22], using an audio file to dictate the cadence. We used a Polar H7 chest strap and the smartphone application Beat to monitor HR. The Polar H7 sensor was found to be in agreement with the electrocardiogram (r_c = 0.996) for assessing HR metrics during aerobic exercises [23].

5.

Hip Range of Motion (ROM) was measured in degrees using a goniometer, which was found reliable in healthy adults (ICC = 0.76–0.97) [24,25]. Hip ROM measures are known dance injury risk factors [12]. We measured passive and functional ROM for this study:

(a)

Passive range for hip external rotation was measured for each leg when sitting on a firm table [25].

(b)

Functional turnout was measured standing on a piece of paper in ballet’s first position. The functional turnout consisted of the angle formed by the longitudinal bisection of the feet [13].

(c)

Compensated turnout was calculated as the functional turnout minus the bilateral passive hip external rotation ROM [13].

2.6. Statistical Analysis

A priori power analysis using the software G*Power (version 3.1.9.7, Kiel, Germany) indicated that a total sample size of 54 people would be needed to detect a medium effect size, with 0.7 power, for a t-test to compare injured to non-injured dancers.

We used Paired t-tests to evaluate the pre- to post-COVID-19 change. Comparison of subjective and physical measures between injured and non-injured dancers was performed using a two-sample T-test, and a Pearson chi-square test, both pre- and post-COVID-19.

We conducted a series of univariate Poisson regression models [26] in which period rate of injury (pre- or post-COVID-19) was related to each single physical test (taken in the relevant period). Following these univariate analyses, if any of the test results significantly predicted the rate of injuries, a multivariable model was applied to explore whether the significant factor remained significant when adjusted for demographic measures, such as dance years, past injury, and gender. Statistical analysis was performed using the SAS software (version 9.4, Raleigh, NC, USA).

3. Results

Participants at T1 included 31 modern dancers (21 female and 10 male). A total of 17 dancers were in their first year in the program and 14 in their second year of training. The mean age was 19.42 ± 1.57 years, and the mean body mass index (BMI) was 21.02 ± 1.98 kg/m². Mean dance experience was 6.81 ± 3.28 years, during which participants danced at least ten hours per week prior to their enrolment in the pre-professional training program.

At T5, 21 of the 31 dancers were reassessed. Twelve dancers had continued in the original training program, four joined a new training program, and five joined professional dance companies. Four dancers had tested positive for COVID-19 during that one year, suffered from mild symptoms, and continued their activity routine without difficulty after recovery. Eighteen dancers reported having been in one or two quarantines, and three dancers reported never having experienced a COVID-19 quarantine.

We had planned to continue recruiting from other programs but had to cancel due to the first lockdown in Israel. Hence, we were unable to reach the expected sample size. Figure 1 presents the chronological sequence of events throughout the study in terms of the pandemic’s effect on life in Israel, on the nature of dance activities throughout 2020–2021, and, accordingly, on the data collection of this study.

T (1–5): Injury data were collected at five different time points. T1: Baseline assessment; T2, T3, T4: End of first, second, and third month of studio dance activity; T5: One-year follow-up assessment.

3.1. Pre-Versus Post-COVID-19 Dance Activity

Before the pandemic outbreak, dancers danced 33 weekly hours in addition to rehearsals and performances, which was at least six hours per day. Since the pandemic, the nature and intensity of the dance activity were changed dramatically (Figure 1). Participants danced 21.4 hours per week on average, which was ~65% of their regular extent. To accommodate the curriculum, training programs introduced online classes including ballet, modern, Pilates, or yoga for 2.5–3.75 hours per day. Dancers did not participate in strength and aerobic training pre-COVID-19, whereas 13 dancers (61.9%) reported they participated in aerobic training and seven (33.3%) in strength training in post-COVID-19.

Table 1. Physical test results pre- and post-COVID-19.

a. Physical Test Results for All Dancers
Variable		Pre-COVID-19 (N = 31)		Post-COVID-19 (N = 21)		Difference (N = 21)
		Mean	SD	Mean	SD	Mean	SD
Sargent Jump	Height (cm)	38.48	7.42	39.81	7.47	0.48	6.54
	% of height	22.84	3.90	23.38	3.71	0.19	3.96
Heel-Raise	Right (repetitions)	21.58	6.18	22.14	4.81	−0.86	4.43
	Left (repetitions)	23.74	6.10	22.90	3.94	−1.81	4.14
Push-Up (repetitions)		8.65	8.97	12.38	9.87	2.00 *	3.49
Chester Step Test	Total score (ml O2/kg/min)	50.31	6.22	49.43	6.73	−1.21	5.35
	Fitness rating (3, 2, 1)	2.14	0.69	2.05	0.59	−0.16	0.50
Hip ROM (degrees)	Passive right	47.97	7.64	48.24	7.32	0.81	2.02
	Passive left	48.16	7.81	48.62	7.27	1.14 *	1.71
	Functional TO	119.19	15.56	114.81	14.40	−4.52	10.50
	Compensated TO	23.06	19.25	17.95	19.25	−6.48 *	11.99
b. Physical test results by gender
Variable		Pre-COVID-19			Post-COVID-19
		Female	Male	Difference	Female	Male	Difference
		(N = 21)	(N = 10)		(N = 12)	(N = 9)
		Mean (SD)	Mean (SD)		Mean (SD)	Mean (SD)
Sargent Jump	Height (cm)	36.43 (4.62)	42.8 (10.28)	0.09	35.92 (4.64)	45.00 (7.55)	0.008 *
	% of height	22.24 (2.62)	24.1 (5.72)	0.35	21.92 (2.54)	25.33 (4.24)	0.05
Heel-Raise	Right (repetitions)	22.05 (6.37)	20.6 (5.97)	0.54	23.25 (4.43)	20.67 (5.15)	0.25
	Left (repetitions)	23.48 (6.02)	24.3 (6.57)	0.74	23.25 (3.14)	22.44 (4.98)	0.68
Push-Up (repetitions)		3.76 (3.25)	18.9 (8.50)	<0.001 *	6.08 (5.07)	20.78 (8.32)	<0.001 *
Chester Step Test	Total score (ml O2/kg/min)	48.21 (5.00)	54.3 (6.58)	0.02 *	47.58 (5.30)	51.89 (7.93)	0.18
	Fitness rating (3, 2, 1)	2.11 (0.66)	2.2 (0.79)	0.75	2.08 (0.29)	2.00 (0.87)	0.79
Hip ROM (degrees)	Passive right	47.86 (7.40)	48.2 (8.52)	0.91	48.58 (7.04)	47.78 (8.09)	0.81
	Passive left	48.48 (7.42)	47.5 (8.95)	0.77	49.50 (6.92)	47.44 (7.97)	0.55
	Functional TO	118.71 (14.38)	120.2 (18.61)	0.83	116.75 (14.34)	112.22 (14.91)	0.49
	Compensated TO	22.38 (20.07)	24.5 (18.33)	0.77	18.67 (23.18)	17 (13.62)	0.84

Pre- and post-COVID-19 refers to the period before and after the COVID-19 pandemic outbreak; it does not refer to the virus infection and its effect on a specific dancer, but to the pandemic effect on the overall training program for all dancers. Chester Step Test fitness rating: 3—Excellent, 2—Good, 1—Average; ROM—range of motion; Functional TO—turnout in first position; Compensated TO—functional minus bilateral passive turnout (TO). * p < 0.050.

a presents the pre- and post-COVID-19 results, with only a few significant changes in push-ups and hip ROM. Dancers managed to perform two additional push-ups in the post-COVID-19 assessment as compared to the pre-COVID-19 assessment (p = 0.016), which is a 23.1% improvement. The compensated turnout was found to be smaller on the post-COVID-19 examination, compared with the pre-COVID-19 examination (p = 0.022). Dancers used a smaller compensated angle by an average of −6.48° when they stood in the first position. A significant statistical difference was shown in the passive left hip ROM (p = 0.006), but this difference of 1.14° has no clinical significance.

Table 1b presents the pre- and post-COVID-19 test results by gender. Significant differences were found between males and females in push-up score both at pre- and post-COVID-19 (p < 0.001), in the Chester Step Test total score pre-COVID-19 (p = 0.02), and in the Sargent Jump Height post-COVID-19 (p = 0.008), all in favor of the males.

3.2. Dance Injuries

Dance injuries data for all time points is presented in

Table 2. Number of dance injuries during study time points.

Injuries per Dancer	T1 (Pre-COVID-19) (N = 31)		T2–4 (N = 30)		T5 (Post-COVID-19) (N = 21)
	No.	%	No.	%	No.	%
0	12	38.71	15	50.00	10	47.62
1	13	41.94	10	33.33	6	28.57
2	4	12.90	5	16.67	5	23.81
3	2	6.45	0	0	0	0
Total injuries	27		20		16
	Mean	SD	Mean	SD	Mean	SD
Injury rate	0.87	0.88	0.67	0.76	0.76	0.83
Dance activity duration (hours)	731.32	48.27	335.50	81.80	520.40	112.78
Injury frequency (injury rate/duration)	0.0012	0.0183	0.0020	0.0093	0.0015	0.0074
Clinically diagnosed dance injuries	T1 (Pre-COVID-19)		T2–4		T5 (Post-COVID-19)
Number of injuries	16		9		4
Participants	No.	%	No.	%	No.	%
Non-injured	12	38.71	15	50	10	47.62
Injured	19	61.29	15	50	11	52.38
Injuries by body region	Foot/toes	Ankle	Knee/shin	Hip/thigh	Spine	Upper limb
%	16	21	27	6	16	14

Injury data were reported at five different time points: (T1) Baseline assessment; (T2–4) end of first, second, and third month of studio dance activity; (T5) one-year follow-up assessment. Note: There was one dancer who did not respond to the dance injury questionnaire at T2–4 but returned and responded at T5. The number of clinically diagnosed dance injuries was determined by an external physician or a physiotherapist, according to the medical documentation provided by the dancers. Upper extremity injury distribution was as follows: 13% shoulder and 1% wrist.

. The percentage of injured dancers pre-COVID-19 during regular dance routines was somewhat higher than in post-COVID-19 (61.3% vs. 52.4%, respectively), but was not statistically significant. Seventy percent of the injuries originated in the lower extremities, with the knee and ankle being the most common site for dance injuries.

Associations between injury (Yes/No) and demographics and physical tests were performed using two-sample t-tests and a chi-square test. These associations were assessed pre- and post-COVID-19. There was no statistical difference between the injured and the non-injured dancers in age, sex, BMI, belonging to the first/second year of activity in the program, training hours, years of dance experience, and previous injury. Only three factors were statistically different for injured dancers and non-injured dancers: heel raises, aerobic fitness, and strength training.

3.3. Heel-Raises and Injuries

The post-COVID-19 assessment demonstrated a statistically significant difference between the injured and the non-injured dancers in heel raises. The injured performed more heel raises in the right leg compared to the non-injured (Mean = 24.4 ± 2.66 vs. Mean = 19.7 ± 5.56, p = 0.032, respectively). This was not shown at the pre-COVID-19 assessment.

3.4. Aerobic Fitness and Injuries

Aerobic fitness among the non-injured (Mean = 2.40 ± 0.63) was significantly higher than among the injured (Mean = 1.86 ± 0.66) in the pre-COVID-19 assessment (p = 0.033). The non-injured dancers’ aerobic fitness was rated good and excellent, while the injured were rated good and average. Accordingly, there seemed to be a similar trend for non-injured dancers to practice more aerobic training post-COVID-19 than injured dancers (p = 0.080).

3.5. Strength Training and Injuries

In comparing strength training in injured vs. non-injured dancers, it was found that all the injured dancers throughout the study did not practice strength training, except one dancer in the post-COVID-19 period (pre-COVID-19 p = 0.007, post-COVID-19 p = 0.024).

3.6. Physical Tests Associated with Rate of Injuries

Poisson’s univariate regression models, in which the injury rate of the period (pre- or post-COVID-19) was predicted by a single physical test, did not yield any significant relationships.

3.7. Qualitative Part

3.7.1. Dancers’ Views on Pandemic Effects

In our one-year follow-up assessment, we conducted an interview to cover the dancers’ experience during the pandemic.

Table 3. Self-reported perception of the COVID-19 pandemic’s impact on the dancers.

	Positive Views	No. of Reports	Negative Views	No. of Reports
Physical perceived effects	Independent practice helped to stay in shape	1/21	Independent practice, online classes, and dancing in small spaces led to poor fitness	7/21
	Return to the studio was gradual and felt physically positive	4/21	Return to the studio was intensive, lack of sufficient graduated training scale made it difficult as fitness was impaired, intermittent activity did not allow adjustment	14/21
	Improved flexibility, feeling improvement as a dancer	6/21	Delayed the improvement as a dancer	2/21
	The decreased intensity of activity assisted in recovery	4/21
	More attentive to their own body	2/21
	Started to practice yoga and Pilates	2/21
Mental perceived effects	Raised passion, motivation, and confidence after declining during the intense work	6/21	Negative feelings: loneliness, depression, detachment, loss of confidence, missed dancing	8/21
	Mental resilience and body-mind connection improved	6/21	Mentally difficult to stop and return each time, damaged resilience	3/21
	There was energy to engage in other interests as well	1/21	This period led to a change in wanting to become a professional dancer	1/21
			Raised questions about the uncertainty of the profession: personal outlook, probability of auditions and steady income, likelihood of being a dancer	9/21
			Difficulty integrating in a new dance company	2/21
			Decided to repeat the first year in the program	2/21
Artistic perceived effects	Provided space for creativity, improvisation, and mind development	7/21	Lack of inspiration	1/21
	Understood the vitality of art, and the joy it brings	1/21	Realization that dance is not essential in life	1/21
	Learned to work with a new media	1/21	The inability to perform and share the art with an audience was difficult, it was not the same through screens	5/21

summarizes the dancers’ responses to: “How did COVID-19 affect you as a dancer?” Answers were both positively and negatively categorized into physical, mental, and artistic effects. Responses given by more than a third of the dancers are bolded.

3.7.2. Dancers’ Self-Perception of Injury Causes

In the fourth injury data collection (T4), dancers answered an open-ended question about the cause of their injuries. Their answers are detailed in

Table 4. Self-reported perceived causes of injury.

Self-Perceived Causes of Injury	No. of Reports
Incorrect body work and investing more power than necessary	12/24
High and intensive workload	8/24
Lack of strength as a result of inadequate independent training	6/24
Previous injury leading to weakness, overcompensation from other body parts, and decreased confidence in their body	5/24
Specific repertoire	4/24

Note: Responses given by more than a third of all dancers are bolded.

.

This study provides a qualitative description of self-reported mental, emotional, and professional effects on dancers during the COVID-19 period. A total of eight out of 21 dancers reported negative feelings of loneliness, depression, and lowered self-confidence. This impression is in line with reports of common mental health complaints reported among performing arts students in the Netherlands during COVID-19 [27].

Insufficient mental coping skills were identified by previous studies as a risk factor for dance injuries [5,28], and pre-professional dancers already face high physical and psychological demands during regular times. In addition, COVID-19 confronted dancers with a serious threat to their professional future. We hope these reported effects might raise awareness of the insecure status dancers have encountered recently and ideally emphasize the need for mental support.

The dancers also reported some specific positive aspects. They felt more at ease with the decrease in dance intensity and reported that it helped in recovery [27], improved flexibility, and opened new opportunities for creativity. The lower injury incidence post-COVID-19 can be explained by allowing more recovery time in a less demanding period. The dancers related injuries to a high and intensive workload, to working their bodies too hard, and to not practicing strength training outside of dance classes. Accordingly, it can be assumed that the dancers themselves identified a connection between injuries and fatigue [29] as well as reduced strength, and that they may have understood the importance of adequate rest and strength training. Similar COVID-19 effects were reported in students from China and the Netherlands, who self-reported a decrease in stress and an improvement in sleep time and quality [27,29].

4. Discussion

This prospective study monitored dance injuries in relation to strength, aerobic fitness, hip mobility, injury history, and training hours, and followed the effects of the pandemic on dancers. To the best of our knowledge, this is the first study following objective measures in pre-professional modern dancers, before and after the COVID-19 outbreak.

Our main findings demonstrate that participation in strength training and higher baseline aerobic fitness differentiated non-injured from injured dancers. In other words, dancers who practiced strength training independently and in addition to dance during the pandemic were not injured pre- or post-COVID-19. In addition, dancers who showed higher aerobic performance in the pre-COVID-19 Chester Step Test reported no injuries pre-COVID-19, with a similar trend post-COVID-19. The dancers who practiced cardiovascular training independently apart from dance were less injured.

These findings are in agreement with a systematic review examining elite female ballet dancers [30]. Reduced strength in the lower limbs and poor aerobic fitness were found to be risk factors for lower limb injury. Other studies in pre-professional and professional contemporary dancers conducted strength and aerobic exercise programs ranging from 1.5 to 6 months, with 2–3 sessions of 1–1.5 h/week [31,32,33]. These programs demonstrated a positive response to the training in the measures of aerobic fitness and improved lower body muscular power and strength [31,32,33]. Two studies were controlled [31,33], and neither investigated injuries [31,32,33]. In contrast, Roussel et al.’s [16] randomized controlled trial did not find a positive effect of a four-month aerobic and strength intervention program for pre-professional dancers on injuries, apart from a reduction in pain and lower-back injuries, when compared to educational sessions [16].

Aerobic training for dancers has some evidence to support its benefits. Aerobic exercise accelerates recovery [34], decreases pain perception, and improves mood [35]. Dance is heterogenic in its aerobic demands. In modern and ballet classes, HR was mainly below the aerobic training zone [36]. During center-class work, HR and oxygen uptake were higher than in the warm-up [37]. Performances demanded the highest HR levels. Professional modern dancers who often engaged in performances demonstrated lower HR in recovery, lower peak HR, and better aerobic fitness when compared to pre-professional modern dancers [38]. Therefore, there is a functional and physiological need for performing dancers to acquire aerobic fitness.

Dance classes do not seem sufficient to improve dancers’ aerobic fitness and strength [36,39], let alone prepare them for the high demands of performances [2,38]. Physical and mental fatigue may play a role in injury propensity [10,29]. Current results suggest that better strength and aerobic capacity potentially elevates the threshold for fatigue in dancers [10]. Further research, including high-quality randomized controlled trials, is needed to specify aerobic and strength training recommendations in relation to injuries [36,38].

The decrease in dancing time during the COVID-19 pandemic enabled dancers to add aerobic and strength training, but not all utilized this opportunity. We found no association between the number of dance hours and injuries post-COVID-19, which aligns with previous studies in professional contemporary dance companies [40,41].

Overall, our findings align with previous results [21,42], demonstrating that modern dancers are weaker than other athletes in the upper limbs. Moreover, ~30% of this study’s injuries involved the shoulders and spine. This highlights the need to examine upper limb strength and endurance as reflected in the Push-Up Test.

Limitations

This study has limitations. We did not reach the planned sample size due to the initial lockdown in Israel, which was due to the onset of the COVID-19 pandemic, which caused a lack of continuity and uncertainty of the dance programs’ existence. Participation changed throughout the study. Initially, dancers were happy to participate and examine their physical condition, but during the pandemic we experienced multiple dropouts due to uncertainty and instability in the professional dance world.

We found that training programs did not have a designated clinician on board. Each dancer has a different health insurance cover and investigators cannot access medical records. Therefore, the dancers’ injury data were mostly self-reported, similar to previous research [14]. Moreover, future studies should reconsider the definition of injury in this context. Many dance injuries stem from overuse and may not always lead to a loss of dancing time, and injury that did not lead to reduced dance time was not counted in our study.

Due to the changes throughout the year in dance activity and heterogeneity in the dancers’ participation, a full report of the additional activity the dancers practiced beyond dance is limited. Still, strength training and aerobic fitness significantly differentiated in injured and non-injured dancers.

5. Conclusions

The main two findings of this original study in dancers showed that non-injured participants demonstrated higher aerobic capacity and performed more strength training than injured dancers. Therefore, pre-professional dance programs should consider adapting their methods and integrating aerobic and strength training in their curriculum. Future research should explore how evidence-based sports training methods aid in reducing injury rate.