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Effects of a modified ballet class on strength and jumping ability in college ballet dancers.

Abstract

The ability to jump high with precision is an important component of the ballet dancers technique. The aim of this study was to evaluate the effect of a modified ballet class on strength and jumping ability in high level female dancers. Seventeen female ballet students were divided into two groups, experimental and control, and tested before and after an 8-week, 2 times/week intervention for peak torque of knee extensors and flexors at 60[degrees] and 180[degrees], and jumping ability (squat jump, countermovement jump, countermovement with arm swing jump, saute in first position, and saute in first position with port de bras). Statistical analysis was performed using Analysis of Variance (Anova 2x2) with repeated measure of factor time (pre and post). T-test with Bonferroni adjustment was used to assess any differences between groups. The experimental group showed improvement in height (7.7%), takeoff velocity (4.0%), and power (5.1%) of the squat jump. In addition, increases were revealed in peak (60[degrees], 11.9%; 180[degrees], 7.8%) and relative peak torque (60[degrees], 13.2%; 180[degrees], 9.2%) of the right knee flexors. Moreover, enhancements of the knee flexor-extensor strength ratio in both angular velocities were found (60[degrees], 10.4%; 180[degrees], 9.7%). These outcomes suggest that the proposed program could help ballet dancers improve the height of their vertical jumps and leg strength.

Inevitably, the ability to jump high with precision is an important requirement for professional ballet dancers to advance in rank. (1-4) The need for good jumping ability is underscored by the fact that soloists tend to have greater jump height than members of the corps de ballet. (1) Ballet dancers must be able to jump high in order to execute the difficult maneuvers in the air that are a significant component of the ballet aesthetic. (5) Jumps and leaps of sufficient distance and height require the control of great push-off and landing forces. It is surprising, therefore, that these authors have found no reporting on improvement in the jumping ability of ballet students, even after up to 14 weeks of dance training. (6-8) This may be due to the established structure of ballet classes, which places jumping exercises at the end of the technique class. Although it has been suggested that if the aim of the work is to improve the height of jumps, the jumping exercises should be moved to the beginning of the workout (9,10); there are no studies that have examined the potential effect of that modification. The aim of this study was to evaluate the effects of a modified ballet class on strength and jumping ability in high level female dancers.

Methods

Subjects

Seventeen female college dancers (mean age: 22.88 [+ or -] 3.10 years) from the same institution volunteered to participate in this study They were randomly assigned to an experimental group (N = 9), which refers to individuals who undertook a specifically designed training program, and a control group (N = 8) that consisted of dancers who performed their usual ballet class. Their basic demographics are described in Table 1. The project was approved by the Ethics Committee of Aristotle University of Thessaloniki, and all of the subjects provided written consent to participate in the study.

Test Procedures

Prior to and immediately following the end of an 8-week training period, all participants were tested for isokinetic strength of knee extensors and flexors, and their jumping ability was evaluated. All tests were conducted in the order described below.

Evaluation of Isokinetic Strength

A Cybex NORM isokinetic dynamometer (Cybex, division of Lumex, Inc., Ronkonkoma, New York, USA) was used to assess knee extensor and flexor peak torques at 60[degrees] and 180[degrees] in both legs. Prior to testing, each subject was given an 8-minute jogging warm up and 5 minutes of stretching. The measurement protocol included 3 repetitions at 60[degrees] and 5 repetitions at 180[degrees].

Jumping Ability

A force plate (Bertec Type 4060, Bertec Corporation, Columbus, OH, USA) was used to assess the height, takeoff velocity, force, and power of squat jump (SJ--i.e., vertical jump from deep plie in parallel position with hands on hips), counter movement jump (CMJ), counter movement jump with arm swing (CMJh), saute in first position, and saute in first position with port de bras. A camera was used for assessing trajectory of the jumps. Efforts that were not in vertical trajectory were considered to be invalid. The jumping height was calculated using take-off velocity with the following equation: Jump Height = Take-Off [Velocity.sup.2] /2g (where g = 9.81 m x [sec.sup.-1]). (11-13)

Intervention Program

The intervention program was applied 2 days per week for 8 weeks. The control group did the regular ballet class according to the Vaganova system (Table 2), while the experimental group reduced the duration of barre exercises from 45 minutes to 20 minutes and moved the petit and grand allegro exercises to the beginning of the center work (Table 2). The type, tempo, and duration of exercises were similar between groups. The experimental group did the modified classes two days per week and regular classes on the other days.

Statistical Analysis

Statistical analysis was performed utilizing Analysis of Variance (ANOVA 2x2) with repeated measure of factor time (pre and post). T-test with Bonferroni adjustment was used to assess any differences within and between control and experimental groups before and after the intervention program. Alpha was set at [less than or equal to] 0.0125.

Results

No statistically significant differences were found between the two groups at baseline level in any of the studied parameters. After completion of the program the experimental group did show improvement in height (pre: 23.48 [+ or -] 2.31 cm; post: 25.43 [+ or -] 1.91 cm), takeoff velocity (pre: 2.14 [+ or -] 0.11 m/s; post: 2.23 [+ or -] 0.08 m/s) and power (pre: 1,719.32 [+ or -] 659.81 W; post: 1,810.69 [+ or -] 691.13 W) ofsquat jump (Table 3). In addition, increases were observed in peak (pre: 68.22 [+ or -] 9.43 Nm; post: 77.44 [+ or -] 9.08 Nm) and relative (pre: 1.18 [+ or -] 0.16 Nm/kg; post: 1.36 [+ or -] 0.20 Nm/kg) torque of the right knee flexors at both 60[degrees] and 180[degrees]. Moreover, enhancements of the right knee flexor and extensor strength ratio in both angular velocities were displayed (pre: 53.86 [+ or -] 3.96%; post: 60.11 [+ or -] 7.47%). No significant differences were observed in the control group.

Discussion

The peak torque values of knee extensors and flexors that were recorded by the pre-intervention testing (Table 4) are similar to other research studies' findings. (14-18) Specifically, the measurements at 60[degrees] of knee extensors in previous studies range from 99.9 to 128 Nm, (15-17) and only one study found higher values (151 Nm). (14) The mean value in our study was 127.3 Nm. Regarding the 180[degrees] peak torque of knee extensors, the range of values in other research is 61.7 to 80 Nm, (17,18) while our mean value is 90 Nm. In regard to the measurements of knee flexors at 60[degrees] and 180[degrees] in other studies, (14-18) the values range from 58.6 to 71.1 Nm and AG to 57.4 Nm, respectively. Comparable values in this study are 68.22 Nm and 51.44 Nm, respectively (Table 4).

The mean heights of saute in first position (1-4) and CMJ (6,7) are lower than other researches' findings (Table 3). The mean values of other studies range from 28.3 to 39.2 cm for saute in first position and 28.8 to 32.5 cm for CMJ, whereas the mean values of this study are 25.08 cm and 26.93 cm, respectively. The absence of statistically significant differences from the control group is in agreement with the claim of other researchers that ballet classes cannot improve the physical fitness of ballet dancers. (6-8,19,20)

The enhancement of strength variables was expected in both groups, as it has been shown that jump training improves muscle strength. (21) However, only in the experimental group were the strength variables enhanced. It is widely speculated that, if the aim of a training program is to increase jump height, jumping exercises should be put at the beginning of the class (after a warm up), as fatigue impacts muscular performance and therefore the ability to generate maximal power. (22,23) The augmentation of peak and relative torque of knee flexors induced the improvement of squat jump height and amended the knee flexors to extensors ratio. Although it was beyond the scope of this study, it is worth noting that prior research has shown that the lower the flexors and extensors strength ratio the greater the degree of low back (24) and lower extremity injuries. That is especially true of anterior cruciate ligament injuries. (25,26) The increase in knee flexors torque resulted in a flexors and extensors strength ratio of nearly 60%, which is considered the best for avoiding injuries. (25,27)

The increase in squat jump height was 7.7%, which is in agreement with meta-analysis studies that determined the effects of jump training. (21,28) The improvement in squat jump height is important for dancers' performance, as it has been reported that a 7% to 13% increment in jumping ability affects athletic performance. (21) Although there were no significant improvements in other jump heights, there was a tendency for improvement (CMJh: 3.6% improvement; sautepb: 2.8% improvement; CMJ: 1.5% improvement), (Table 3). A possible cause may be a tendency for the dancers to jump with less effort, as they used up their maximum electromyographic facility during the jump tests. (29) The relatively short duration of the intervention may have been another factor, as it has been shown that jump training programs that last more than 10 weeks have better effects. (30)

The outcomes of this study suggest that the proposed program could help ballet dancers improve the height of their vertical jumps and the strength of their legs without having supplementary workouts or interfering with the components of ballet class.

References

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Aikaterini Tsanaka, M.Sc, Vasiliki Manou, Ph.D., and Spiros Kellis, Ph.D.

Aikaterini Tsanaka, M.Sc, Vasiliki Manou, Ph.D., and Spiros Kellis, Ph.D., School of Physical Education and Sport Science, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Correspondence: Aikaterini Tsanaka, M.Sc, Rethymnou 1, Thessaloniki, Greece; atsanaka@hotmail.com.
Table 1 Subjects' Demographics

                              Experimental Group    Control Group

Age (years)                   23.33 [+ or -] 3.35   22.38 [+ or -] 9.25
Training age (years)          13.33 [+ or -] 5.29   12.25 [+ or -] 7.20
Training hours (hours/week)   20.39 [+ or -] 2.12   19.00 [+ or -] 1.69
Standing height (cm)         165.33 [+ or -] 3.32  167.50 [+ or -] 7.21
Body mass (kg)                58.01 [+ or -] 7.09   59.10 [+ or -] 4.55
% Body fat                    15.97 [+ or -] 3.84   15.24 [+ or -] 2.00

Table 2 Programs for the Control and Intervention Groups

Control Group                 Intervention Group

Warm up (8-10 min)            Warm up (8-10 min)
Barre exercises (40-45 min)   Barre exercises (20-25 min)
Center exercises (30-40 min)  Center exercises (30-40 min)
  Adagio (5-7 min)            Petit allegro (8-10 min)
  Battements (5-7 min)        Grand allegro (5-7 min)
  Pirouettes-tours (8-10 min) Adagio (5-7 min)
  Petit allegro (8-10 min)    Battements (5-7 min)
  Grand allegro (5-7 min)     Pirouettes-tours (8-10 min)
Port de bras (2 min)          Pointes or flexibility
                              Port de bras (2 min)
Total duration: 90 min        Total duration: 90 min

Table 3 Means of the Height, Force, Takeoff Velocity, and Power of
Squat Jump (SJ), Counter Movement Jump (CMJ), Counter Movement Jump
with Arm Swing (CMJh), Saute in First Position, and Saute in First
Position with Port de Bras (Sautepb) Pre and Post Intervention for the
Experimental and Control Groups

                                Experimental Group
                                Pre

SJ height (cm)                     23.48 [+ or -] 2.31
SJ force (N)                    1,132.34 [+ or -] 122.71
SJ takeoff velocity (m/s)           2.14 [+ or -] 0.11
SJ power (W)                    1,719.32 [+ or -] 659.81
CMJ height (cm)                    26.93 [+ or -] 2.78
CMJ force (N)                   1,270.14 [+ or -] 175.19
CMJ takeoff velocity (m/s)          2.30 [+ or -] 0.12
CMJ power (W)                   1,928.84 [+ or -] 752.34
CMJh height (cm)                   29.88 [+ or -] 3.46
CMJh force (N)                  1,253.97 [+ or -] 161.04
CMJh takeoff velocity (m/s)         2.42 [+ or -] 0.14
CMJh power (W)                  2,065.72 [+ or -] 801.83
Saute height (cm)                  25.08 [+ or -] 2.72
Saute force (Nm)                1,354.00 [+ or -] 283.99
Saute takeoff velocity (m/s)        2.22 [+ or -] 0.12
Saute power (W)                 1,825.04 [+ or -] 724.59
Sautepb height (cm)                29.54 [+ or -] 3.24
Sautepb force (Nm)              1,385.13 [+ or -] 227.28
Sautepb takeoff velocity (m/s)      2.40 [+ or -] 0.14
Sautepb power (W)               2,049.24 [+ or -] 779.23

                               Experimental Group
                                Post

SJ height (cm)                     25.43 [+ or -] 1.91 (*)
SJ force (N)                    1,123.92 [+ or -] 123.28
SJ takeoff velocity (m/s)           2.23 [+ or -] 0.08 (*)
SJ power (W)                    1,810.69 [+ or -] 691.13 (*)
CMJ height (cm)                    27.35 [+ or -] 3.06
CMJ force (N)                   1,207.84 [+ or -] 176.08
CMJ takeoff velocity (m/s)          2.31 [+ or -] 0.13
CMJ power (W)                   1,920.26 [+ or -] 738.23
CMJh height (cm)                   30.99 [+ or -] 4.37
CMJh force (N)                  1,237.03 [+ or -] 159.52
CMJh takeoff velocity (m/s)         2.46 [+ or -] 0.18
CMJh power (W)                  2,091.13 [+ or -] 810.83
Saute height (cm)                  25.10 [+ or -] 2.61
Saute force (Nm)                1,356.65 [+ or -] 271.86
Saute takeoff velocity (m/s)        2.22 [+ or -] 0.11
Saute power (W)                 1,812.05 [+ or -] 709.63
Sautepb height (cm)                30.38 [+ or -] 4.02
Sautepb force (Nm)              1,358.20 [+ or -] 205.53
Sautepb takeoff velocity (m/s)      2.44 [+ or -] 0.16
Sautepb power (W)               2,068.17 [+ or -] 798.78

                                 Control Group
                                 Pre

SJ height (cm)                      23.94 [+ or -] 1.80
SJ force (N)                     1,144.53 [+ or -] 141.09
SJ takeoff velocity (m/s)            2.17 [+ or -] 0.08
SJ power (W)                     2,075.75 [+ or -] 272.46
CMJ height (cm)                     27.01 [+ or -] 2.67
CMJ force (N)                    1,362.21 [+ or -] 113.49
CMJ takeoff velocity (m/s)           2.30 [+ or -] 0.11
CMJ power (W)                    2,285.06 [+ or -] 325.66
CMJh height (cm)                    29.40 [+ or -] 3.35
CMJh force (N)                   1,239.52 [+ or -] 110.85
CMJh takeoff velocity (m/s)          2.40 [+ or -] 0.14
CMJh power (W)                   2,399.23 [+ or -] 322.79
Saute height (cm)                   25.09 [+ or -] 3.24
Saute force (Nm)                 1,427.27 [+ or -] 194.18
Saute takeoff velocity (m/s)         2.22 [+ or -] 0.14
Saute power (W)                  2,185 [+ or -] 333.59
Sautepb height (cm)                 29.16 [+ or -] 3.13
Sautepb force (Nm)               1,452.32 [+ or -] 180.60
Sautepb takeoff velocity (m/s)       2.39 [+ or -] 0.13
Sautepb power (W)                2,396.14 [+ or -] 344.78

                                 Control Group
                                 Post

SJ height (cm)                      23.64 [+ or -] 3.10
SJ force (N)                     1,164.44 [+ or -] 141.06
SJ takeoff velocity (m/s)            2.15 [+ or -] 0.14
SJ power (W)                     2,068.82 [+ or -] 271.26
CMJ height (cm)                     27.30 [+ or -] 4.59
CMJ force (N)                    1,337.61 [+ or -] 106.00
CMJ takeoff velocity (m/s)           2.31 [+ or -] 0.19
CMJ power (W)                    2,312.08 [+ or -] 349.90
CMJh height (cm)                    29.90 [+ or -] 4.01
CMJh force (N)                   1,264.75 [+ or -] 130.27
CMJh takeoff velocity (m/s)          2.42 [+ or -] 0.16
CMJh power (W)                   2,253.10 [+ or -] 595.19
Saute height (cm)                   25.75 [+ or -] 4.23
Saute force (Nm)                 1,494.54 [+ or -] 210.01
Saute takeoff velocity (m/s)         2.24 [+ or -] 0.19
Saute power (W)                  2,231.65 [+ or -] 323.91
Sautepb height (cm)                 29.73 [+ or -] 4.89
Sautepb force (Nm)               1,486.59 [+ or -] 208.94
Sautepb takeoff velocity (m/s)       2.41 [+ or -] 0.19
Sautepb power (W)                2,438.35 [+ or -] 346.50

(*) Statistically significant differences, p [less than or equal to]
0.0125.

Table 4 Means of Peak Torque (PT), Relative Peak Torque (RPT), and
Ratios of Extensors (ext) and Flexors (flex) of Right (R) and Left (L)
Legs at 60[degrees] and 180[degrees] Angular Velocities Pre- and
Post-Intervention for the Experimental and Control Groups

                                 Experimental Group
                                 Pre

PT R ext 60[degrees] (Nm)        127.33 [+ or -] 20.34
PT R ext 180[degrees] (Nm)        92.00 [+ or -] 10.34
PT R flex 60[degrees] (Nm)        68.22 [+ or -] 9.43
PT R flex 180[degrees] (Nm)       51.44 [+ or -] 5.68
PT L ext 60[degrees] (Nm)        123.33 [+ or -] 13.77
PT L ext 180[degrees] (Nm)        88.56 [+ or -] 6.08
PT L flex 60[degrees] (Nm)        66.33 [+ or -] 9.34
PT L flex 180[degrees] (Nm)       49.00 [+ or -] 4.47
RPT R ext 60[degrees] (Nm/kg)      2.20 [+ or -] 0.32
RPT R ext 180[degrees](Nm/kg)      1.59 [+ or -] 0.15
RPT R flex 60[degrees] (Nm/kg)     1.18 [+ or -] 0.16
RPT R flex 180[degrees] (Nm/kg)    0.89 [+ or -] 0.06
RPT L ext 60[degrees] (Nm/kg)      2.13 [+ or -] 0.17
RPT L ext 180[degrees] (Nm/kg)     1.54 [+ or -] 0.14
RPT L flex 60[degrees] (Nm/kg)     1.15 [+ or -] 0.17
RPT L flex 180[degrees] (Nm/kg)    0.85 [+ or -] 0.08
R flex/ext 60[degrees] (%)        53.86 [+ or -] 3.96
R flex/ext 180[degrees] (%)       56.17 [+ or -] 5.85
L flex/ext 60[degrees] (%)        54.07 [+ or -] 8.18
L flex/ext 180[degrees] (%)       55.46 [+ or -] 5.20

                                 Experimental Group
                                 Post

PT R ext 60[degrees] (Nm)        129.33 [+ or -] 11.60
PT R ext 180[degrees] (Nm)        90.00 [+ or -] 5.66
PT R flex 60[degrees] (Nm)        77.44 [+ or -] 9.08 (*)
PT R flex 180[degrees] (Nm)       55.78 [+ or -] 3.15 (*)
PT L ext 60[degrees] (Nm)        124.89 [+ or -] 15.37
PT L ext 180[degrees] (Nm)        85.33 [+ or -] 6.65
PT L flex 60[degrees] (Nm)        69.00 [+ or -] 12.36
PT L flex 180[degrees] (Nm)       48.56 [+ or -] 4.45
RPT R ext 60[degrees] (Nm/kg)      2.26 [+ or -] 0.13
RPT R ext 180[degrees](Nm/kg)      1.58 [+ or -] 0.11
RPT R flex 60[degrees] (Nm/kg)     1.36 [+ or -] 0.20 (*)
RPT R flex 180[degrees] (Nm/kg)    0.98 [+ or -] 0.10 (*)
RPT L ext 60[degrees] (Nm/kg)      2.18 [+ or -] 0.20
RPT L ext 180[degrees] (Nm/kg)     1.50 [+ or -] 0.14
RPT L flex 60[degrees] (Nm/kg)     1.21 [+ or -] 0.25
RPT L flex 180[degrees] (Nm/kg)    0.85 [+ or -] 0.10
R flex/ext 60[degrees] (%)        60.11 [+ or -] 7.47 (*)
R flex/ext 180[degrees] (%)       62.19 [+ or -] 5.16 (*)
L flex/ext 60[degrees] (%)        55.90 [+ or -] 10.88
L flex/ext 180[degrees] (%)       57.13 [+ or -] 5.94

                                 Control Group
                                 Pre

PT R ext 60[degrees] (Nm)        124.57 [+ or -] 22.73
PT R ext 180[degrees] (Nm)        85.14 [+ or -] 14.66
PT R flex 60[degrees] (Nm)        72.71 [+ or -] 12.68
PT R flex 180[degrees] (Nm)       51.14 [+ or -]9.30
PT L ext 60[degrees] (Nm)        126.14 [+ or -]20.51
PT L ext 180[degrees] (Nm)        88.86 [+ or -] 16.63
PT L flex 60[degrees] (Nm)        71.43 [+ or -]8.36
PT L flex 180[degrees] (Nm)       51.71 [+ or -]8.28
RPT R ext 60[degrees] (Nm/kg)      2.12 [+ or -]0.33
RPT R ext 180[degrees](Nm/kg)      1.45 [+ or -] 0.24
RPT R flex 60[degrees] (Nm/kg)     1.24 [+ or -]0.23
RPT R flex 180[degrees] (Nm/kg)    0.88 [+ or -]0.18
RPT L ext 60[degrees] (Nm/kg)      2.15 [+ or -]0.32
RPT L ext 180[degrees] (Nm/kg)     1.51 [+ or -]0.22
RPT L flex 60[degrees] (Nm/kg)     1.22 [+ or -]0.16
RPT L flex 180[degrees] (Nm/kg)    0.88 [+ or -]0.13
R flex/ext 60[degrees] (%)        59.72 [+ or -] 11.82
R flex/ext 180[degrees] (%)       60.16 [+ or -]6.68
L flex/ext 60[degrees] (%)        57.20 [+ or -]5.91
L flex/ext 180[degrees] (%)       58.93 [+ or -]8.19

                                 Control Group
                                 Post

PT R ext 60[degrees] (Nm)        116.14 [+ or -] 19.87
PT R ext 180[degrees] (Nm)        88.71 [+ or -] 10.77
PT R flex 60[degrees] (Nm)        68.86 [+ or -] 17.88
PT R flex 180[degrees] (Nm)       50.43 [+ or -] 9.68
PT L ext 60[degrees] (Nm)        114.57 [+ or -] 15.70
PT L ext 180[degrees] (Nm)        88.71 [+ or -] 8.08
PT L flex 60[degrees] (Nm)        70.29 [+ or -] 14.76
PT L flex 180[degrees] (Nm)       51.29 [+ or -] 7.36
RPT R ext 60[degrees] (Nm/kg)      1.97 [+ or -] 0.32
RPT R ext 180[degrees](Nm/kg)      1.50 [+ or -] 0.15
RPT R flex 60[degrees] (Nm/kg)     1.16 [+ or -] 0.28
RPT R flex 180[degrees] (Nm/kg)    0.85 [+ or -] 0.15
RPT L ext 60[degrees] (Nm/kg)      1.94 [+ or -] 0.23
RPT L ext 180[degrees] (Nm/kg)     1.50 [+ or -] 0.06
RPT L flex 60[degrees] (Nm/kg)     1.19 [+ or -] 0.22
RPT L flex 180[degrees] (Nm/kg)    0.86 [+ or -] 0.09
R flex/ext 60[degrees] (%)        59.15 [+ or -] 9.42
R flex/ext 180[degrees] (%)       56.86 [+ or -] 8.57
L flex/ext 60[degrees] (%)        61.65 [+ or -] 10.54
L flex/ext 180[degrees] (%)       57.64 [+ or -] 4.28

(*) Statistically significant differences, p [less than or equal to]
0.0125.
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Author:Tsanaka, Aikaterini; Manou, Vasiliki; Kellis, Spiros
Publication:Journal of Dance Medicine & Science
Article Type:Report
Date:Jul 1, 2017
Words:4518
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