The study subjects included 12 students majoring in Korean dance, 13 students majoring in ballet, eight students majoring in contemporary dance, and 12 nondance majors at Kyung Hee University located in Seoul through simple random sampling. Thus, a total of 45 students (age range, 18–20 yr) participated in this study after they volunteered to participate and signed an informed consent form. None of the participants had any physical defects or diseases and were not on any medication. The participants’ characteristics are shown in Table 1.

Nutritional intake was self-recorded over 24 hr on a dietary record. Nutritional intake was recorded for a total of three days, including two weekdays and one weekend day. The survey employed the Computer Aided Nutrition Analysis Program generated by The Korean Nutrition Society and aimed to investigate the intakes of total calories, the three major nutrients, calcium, phosphorus, iron, and zinc.

Body composition was measured using dual X-ray absorptiometry (DXA; QDR-4500W; Hologic, Marlborough, MA, USA) to investigate lean tissue and body fat percentage.

BMD was measured with DXA assessing whole body BMD and it was recorded in g/cm².

Isokinetic dynamometry (Cybex 770-NORM, Cybex International, Medway, MA, USA) was performed to evaluate flexion and extension of the right and left knees. Each test included three maximal contractions at 60°/sec for muscle strength. Each isokinetic contraction was performed through a full range of motion, and data were normalized to each participant’s body weight and calculated as torque (N·m/kg) × 100.

Statistical analyses were performed by using SAS ver. 9.2 (SAS Institute Inc., Cary, NC, USA), and mean and standard deviation for each variable were computed using descriptive statistics. One-way analysis of variance was performed to test the statistical significance of body build, nutritional intake, body composition, BMD, and isokinetic muscular function of the four groups according to sport type. Post hoc testing was performed using Duncan multiple range test. For all statistical tests, a P<0.05 was considered as statistically significant.

The nutritional intake analysis results for each group are listed in Table 2. There was no statistically significant difference in mean total calories, protein, fat, carbohydrate, calcium, phosphorus, or iron intake among the different groups of dance majors. There was also no statistically significant difference between the dance students and controls.

The body composition analysis results in each group are summarized in Table 3. No statistically significant difference in mean lean tissue was observed among the dance student groups or between the dance students and controls. However, mean percentage body fat was significantly different between the groups (F=5.20, P<0.004). Based on post hoc test results, the Korean dance group did not exhibit a statistically significant difference from the other three groups (27.7% ± 4.64%), whereas the ballet (24.8% ± 3.12%) and contemporary dance (24.5% ± 4.57%) groups had a statistically significantly lower mean body fat content than the control group (30.0% ± 3.09%). On the other hand, there was no statistically significant difference between the Korean dance, ballet, and contemporary dance groups.

The results comparing whole body BMD among groups are shown in Table 4. No statistically significant difference was observed in mean whole body BMD among the different dance type groups or even between dance majors and nondance majors in the control group.

The comparison result of isokinetic muscular function by group is shown in Table 5.

No statistically significant difference was detected on the right or left side of the mean isokinetic extensor at 60°/sec among the dance groups or between any dance group and the control group. No statistically significant difference was detected on the right or left side of the mean isokinetic flexor at 60°/sec among the dance groups or between any dance group and the control group.

Although it is necessary for dancers to obtain sufficient nutrition to ensure their best performance, dancers experience limited nutritional intake to maintain their body image and shape because dance is an art expressed through body motions. Thus, dancers are at risk of minimal nutritional intake, which can lead to deficiencies of micronutrients such as iron, calcium, and vitamin D (Sousa et al., 2013).

No difference was observed in any of the nutritional intake values among participants in this study. However, while the Korean National Health and Nutrition Examination Survey (KNHANES V-3) (Ministry of Health & Welfare, Korea Centers for Disease Control and Prevention, 2013) revealed a total energy intake of 1,779 kcal from similar age groups, the mean caloric intakes were 1,454.1 ± 478.59 kcal in the contemporary dance group, 1,213.4 ± 390.32 kcal in the ballet group, and 1,100.9 ± 472.89 kcal in the Korean dance group in the present study, while that in the control group was 1,306.9 ± 332.53 kcal. These results indicated that total nutritional intake expenditure is insufficient for female nondance majors and dance majors, highlighting the need for an increased nutritional intake for all groups surveyed in this study. In this regard, Lagowska et al. (2014) provided nutritional treatment to ballet dancers for 9 months. The study results showed that the treatment improved nutritional intake from 1,640 ± 412 to 2,368 ± 182 kcal, while fat mass showed no statistical significant increase. Total energy expenditure increased significantly (P<0.05), whereas fat mass did not. Based on their results, nondance and dance majors should avoid limiting their intake because of body image concerns. Furthermore, to decrease nutritional imbalances and related diseases, dancers require a minimum of 30 kcal of fat free mass as per kg of body weight daily as well as the necessary energy expended during training. In terms of macronutrients, the daily recommendation per kg of body weight is 3–5 g for carbohydrate, 1.2–1.7 g for protein, and 20%–35% for fat (Sousa et al., 2013). This study showed that mean carbohydrate intake was 151.9 ± 63.5 g for the Korean dance group followed by 176.7 ± 46.17 g for the control group, 177.8 ± 63.7 g for ballet group, and 196.3 ± 67.99 g for the contemporary dance group, which was converted to 2.8, 3.3, 3.4, and 3.5 g of intake level per kg of body weight, respectively, showing Korean dance group slightly did not meet the daily recommendation. In addition, mean protein intake was 43.3 ± 17.92 g for the Korean dance group, 45.4 ± 15.31 g for ballet group, 50.9 ± 15.37 g for the control group, and 55.3 ± 18.95 g for the contemporary dance group, which was equivalent to intake per body weight of 0.8, 0.9, 1.0, and 1.0 g for individual groups when converted to daily recommendation per body weight, suggesting that all four groups experienced remarkably insufficient protein intake.

Lagowska et al. (2014) reported that the nutritional intake of ballet dancers was 342.0 ± 33.2, 85.3 ± 9.3, and 73.2 ± 15.9 g for carbohydrate, protein, and fat, respectively, values that are much higher than those of the students surveyed in this study. Thus, as shown in Łagowska et al. (2014), it is essential to have treatment or approaches to elevate macronutrient intake level up to the daily recommended intake. It is also important to change perception of dancers about dietary intake for their health and future and to build a system that allows continuous management through nutritional intake monitoring.

Systemic and proper body composition and its maintenance are essential for dancers to perform challenging and high-quality repetitive movements (Rafferty, 2010). However, most dancers pay more attention to their body shapes than body compositions. In this regard, the mean body fat contents of the participants of the present study were 30% ± 3.09% for the control group, 27.7% ± 4.64% for the Korean dance group, 24.8% ± 3.12% for the ballet group, and 24.5% ± 4.57% for the contemporary dance group, and the values of the contemporary dance and ballet groups were significantly different from that of the control group (P<0.05). Friesen et al. (2011) revealed 25.9% ± 4.2% and 32.0% ± 5.9% as the body fat contents of contemporary dancers and nondancers, respectively, while Yang et al. (2010) showed that adolescent dancers and nondancers had body fat contents of 25% ± 0.05% and 34% ± 0.04%, respectively. These studies showed a similar tendency to the results of the present study for the contemporary dance and ballet groups but not the Korean dance group.

However, in the case of lean tissue, no statistically significant difference was observed compared to the control group, showing 39,329.7 ± 2,997.67 g/cm² for the contemporary dance group, 36,772.4 ± 3,004.82 g/cm² for the Korean dance group, 36,503.1 ± 2,849.29 g/cm² for the ballet group, and 35,421 ± 4,631.5 g/cm² for the control group. This result suggests that nondance and dance majors have similar levels of lean tissue. Therefore, it is necessary for dancers to increase their lean tissue to better their performance, for which weight training or weight-bearing exercise programs are highly recommended. When this training is pursued, dancers’ capacities to execute challenging movements that require artistic components and professional dancing techniques are expected to improve.

Eating disorders, menstruation disorders, and low BMD, either alone or in combination, are risk factors for female dancers (Hincapié and Cassidy, 2010). Some studies related to BMD reported that dancers had decreased BMD (Hoch et al., 2011), leading to the risk of osteoporosis, whereas other studies reported opposite results that the weight-bearing movements improved dancers’ BMD (Amorim et al., 2015). This study did not show any difference in BMD among participants; in fact, all four groups maintained a normal BMD range level (1.1 ± 0.06–0.09 g/cm²) despite a low nutritional intake. These results were consistent with those of Yang et al. (2010) in which Chinese adolescent dancers showed a relatively higher BMD despite a low nutritional intake and menstrual disorder. The study mentioned that the results could be due to their high levels of weight-bearing physical activity.

In this study, we also observed a normal BMD range despite a continuous diet restriction and low nutritional intake, which is thought to be because dancing movements such as kicking, leaping, hopping, turning, jumping, and twisting apply intense mechanical stress to the bones through weight-bearing.

However, Friesen et al. (2011) showed a left hip BMD of 1.2 ± 0.11 g/cm² and 1.1 ± 0.10 g/cm² for collegiate contemporary dancers and nondancers, respectively, indicating a statistically significant difference between the groups (P<0.05), a finding that was inconsistent with those of this study. However, BMD could vary among body parts and dance types and levels. Thus, the measurement of BMD in different body parts as well as the whole body is recommended to obtain more accurate data.

The evaluation of muscular function using isokinetic measurement equipment can be a useful indicator to assess the efficacy of sports injury prevention and recovery and is a reliable measurement method for muscular strength and endurance (Cools and Geerooms, 2007). From the analysis of isokinetic strength, no statistically significant difference was observed between the extensor and flexor at 60˚/sec for the left or right sides. This result means that female nondance and dance majors have similar muscular strength, which might limit the ability of the latter to perform active and accurate movements such as standing, locomotion, or dynamic jumping or turning. Thus, it was reported that plyometric training would be proper for dance major students to efficiently improve quadriceps femoris strength, which is critical to dance performance (Sáez-Sáez de Villarreal et al., 2010; Trzaskoma et al., 2010). It is also important that they maintain balanced muscle strength of the biceps femoris, which plays an important role as a flexor in the lower limbs, and resistance exercises such as leg curls are required to improve flexor strength. In addition, if professional approaches such as weight training can be used to overcome difficulties executing active movements and technical challenges, the oxidative function of slow muscle fibers will develop and improve mitochondrial function within the cells, leading to a potential increase in muscular function (Johnston et al, 2008) and more efficient execution of dance performance.