United States Sports Academy - "America's Sports University"

Introduction

One question that many dancers ask is, “How can I get my jumps higher?” The repetitive execution of demi-plie is used to improve timing, alignment, strength, torso stability, coordination of joint movement, and finally, as a first component of other movements such as pirouette, releve’, and all aerial movements (Trepman, et al., 1998). There are four principles that must be applied when executing jumps of any kind (Kraines & Pryor, 2001): (1) all jumps must begin in demi-plie, (2) in order to get the jump into the air, dancers must press off the floor by fully pointing the foot, (3) the dancer must land on the balls of the feet and roll through to the heels, and (4) the jump must end in demi-plie.

There is little information available analyzing the way dancers use their muscles to perform highly trained movements such as leaps and jumps. Most studies focus on the treatment of specific injuries sustained by dancers (Trepman, et al., 1998). “The type of training dancers undergo places specific demands on their bodies which can result in muscle imbalances” (Hobby & Hoffmaster, 1986, p. 39). Incorrect training can produce undeveloped or overdeveloped muscle groups. In a study conducted by Simpson and Kanter (1997), researchers indicated that lower extremity injuries are common among dancers of various forms of dance such as modern dance, jazz dance, and ballet. The study concluded that chronic dance injuries are linked to the improper landing techniques of jumping.

Many of the skills required for dance are also used in sports such as figure skating and gymnastics (McQueen, 1986). “Therefore, training techniques that have become prominent in sport may also be applicable to dance” (McQueen, 1986, p. 43). “Jumping exercises and plyometrics enhance performance in strength-speed sports because they increase leg power and train the nervous system to activate large muscle groups when you move” (Fahey, 2000, p. 76). In a study conducted by Hutchinson, Tremain, Christiansen, and Beitzel (1998), researchers suggested that leap training utilizing a swimming pool and Pilates safely improved the leaping ability of elite gymnasts. In the study, after one month of training, gymnasts improved their explosive power by 220%, ground reaction time by 50%, and leap height by 16.2%.

The objective of plyometrics is to generate the greatest amount of force in the shortest amount of time (Seabourne, 2000). Plyometrics trains the nervous system and metabolic pathways to increase explosiveness, giving the athlete the extra push needed to go higher and faster. Plyometrics requires acceleration through a complete range of motion and then relaxation into a full stretch. The quick stretch the athlete applies to the muscle during the initial push-off is thought to increase muscle contraction, therefore increasing power. Sportsmetrics, a plyometrics-based program developed by the Cincinnati Sportsmedicine and Orthopaedic Center, is scientifically proven to increase jump height and decrease harmful landings (Hewett & Noyes, 1998). Hewett, Stroupe, & Riccobene (1999) analyzed the effects of the six-week Sportsmetrics program in female athletes. The authors found that peak landing forces decreased 22 percent, lateral and medial forces at the knee decreased 50 percent, and there was a 10 percent increase in jump height. “The hamstring-to-quadriceps strength ratio increased from 50 percent to 66 percent, a more favorable condition for the ACL” (Boden, Griffin, & Garrett, 2000, p. 57). Because the use of plyometrics training has been shown to be beneficial in generating greater strength output with fewer injuries, the purpose of this study was to assess the effects of a seven-week plyometrics program on college dancers’ vertical jumps and leaps.

Method

Subjects

With approval of the Human Subjects Review Board, twelve female members of a Division I college dance team were used as subjects for a plyometrics training program.

Methodology

The Cincinnati Sportsmetric Program was used for seven weeks. Vertical jumps were measured using a Vertec Vertical Height Measuring Device. Strength measurements were evaluated using a Cybex II Isokinetic Testing Rehabilitation Center System utilizing the Humac Cybex Software by CSMI.

Testing Procedure

The pretest consisted of a five-minute warm-up and a five-minute stretch. Height and weight was established for each subject. A standing reach measurement was determined while the subjects stood with their feet hip-width apart, eyes forward, and reaching vertically the dominant hand on top of the other hand using the Vertec Vertical Height Measuring Device. Using the Vertec Vertical Height Measuring Device, subjects executed a standing two-leg jump. The best of three efforts was recorded.

Using the same device, a two-step leap off of the right leg and a two-step leap off of the left leg were evaluated. Subjects stood behind the Vertec and attempted a run, run, leap, off of the right leg with the left leg flexed at the knee, reaching up with the right hand. The foot was plantar flexed and placed against the medial side of the knee in “passe’” position. The same leap was executed on the left side.

The subjects were taken to the Sports Medicine Lab where they were evaluated. Each subject was familiarized with the Cybex II equipment. Standard protocols for measuring thigh strength with the Cybex II were used. All post-test measurements were taken after seven weeks of training.

Training

Subjects were called to a meeting where the Cincinnati Sportsmetric Program was explained in detail. The subjects were told that the program would be used for seven weeks, three times a week. The Cincinnati Sportsmetric Program consisted of approximately forty minutes of various jumping exercises. The subjects kept record of how many repetitions they completed as each week the amount of time increased for each exercise. After completing the session, subjects continued with a one- to two-hour rehearsal. Every two weeks, a new program was taught with increased difficulty to the subjects. The plyometrics program carried the subjects into the beginning of regular season workouts and game performances.

Data Analysis

Pre- and post-test data was analyzed using a paired t-test with alpha set at 0.05.

Results

The biometric data for the participants were as follows: age (yrs) 19.7 + 1.5; height (m) 1.65 + 0.06; weight (kg) 57.4 + 6.38. There were five freshmen, one sophomore, four juniors, and two seniors on the dance team. After seven weeks of plyometric training, the post-test right quadriceps peak torque at 180 degrees/second (M=57.9 Ft. pounds) was significantly higher (t(11)= -2.435, p<.05) than the pre-test (M=54.3 Ft. pounds). Although not significant (t(11)= -1.904, p>.05), the left quadriceps peak torque 180 degrees/second post-test means (M=57.8 Ft. pounds) and pre-test means (M=54.2 Ft. pounds) differences indicated improvement.

Results from the vertical jump indicated a significant difference (t(11)= -4.59, p<.05) after seven weeks of plyometric training. Also noted was significant improvement in the two-step jump off of the right foot (t(11)= -2.5, p<.05) but not the left foot (t(11)= -1.05, p>.05).

Discussion

After seven weeks of plyometrics training, there were increases in strength in the right leg at 180 degrees/second. Although not significant, the left leg showed improvement in peak torque performance at 180 degrees/second. There was significant improvement in vertical jump and the two-step jump off of the right foot. Most teachers teach leaps off of two feet, off of the left foot, and off of the right foot. However, because many dancers jump off of the left foot when executing leaps in classroom combinations at center or in performance, there may be an imbalance in lower limb strength in most dancers. The seven-week plyometrics program may have improved the imbalance of strength in these dancers.

Future investigation is warranted in this area with other dancers. It may prove useful to test dancers in middle school, high school, and college. In addition, it may be beneficial not only to take isokinetic strength measures, but also to include an isometric strength measurement. Future research is needed to investigate the possibility that dancers’ training may develop lower limb muscle imbalances. If so, it may prove useful to incorporate plyometrics training into dance classes at a younger age in order to prevent lower limb muscle imbalance.

References

Boden, B. P., Griffin, L. Y., & Garrett, W. E. (2000). Etiology and prevention of noncontact acl injury. The Physician and Sportsmedicine, 28(4), 53-50.

Fahey, T. D. (2000). Super fitness for sports, conditioning, and health. Needham Heights, MA: Allyn & Bacon.

Hewett, T. E. & Noyes, F.: Cincinnati Sportsmetrics: A jump training program proven to prevent knee injury, videotape. Cincinnati, Cincinnati Sportsmedicine Research & Education, 1998.

Hewett, T. E., Stroupe, A. L., & Nance T. A. (1996). Plyometric training in female athletes: A prospective study. American Journal of Sports Medicine,24(6), 765-773.

Hobby, K. & Hoffmaster, L. (1986). The medical aspects of dance. (Peterson, D., Lapenskie, G., & Taylor, A. W.) London, Ontario: Sports Dynamics.

Hutchinson, M. R., Tremain, L., Christiansen, J., & Beitzel, J. (1998). Improving leaping ability in elite rhythmic gymnast. Medicine and Science Sports Exercise, 30, 1543-1547.

Kraines, M. G. & Pryor, E. (2001). Jump into jazz: The basics and beyond for the jazz student. (4th ed). Mountain View, California: Mayfield Publishing Company.

McQueen, C. (1986). The medical aspects of dance. (Peterson, D., Lapenskie, G., & Taylor, A. W.) London, Ontario: Sports Dynamics.

Seabourne, T. (2000). The power of plyometrics. American Fitness, 18, 64-66.

Simpson, K. J. & Kanter, L. (1997). Jump distance of dance landings influencing internal joint forces: I. axial forces. Medicine and Science Sports Exercise, 29, 916-927.

Biographical Information

Brenda Griner is currently a graduate student and adjunct instructor in the Department of Health and Kinesiology and the Department of Music, Theater, and Dance at Lamar University.

Douglas Boatwright is currently a professor in the Department of Health and Kinesiology at Lamar University.

Dan Howell is an adjunct instructor in the Department of Health and Kinesiology at Lamar University and an athletic trainer at Beaumont Bone and Joint in Beaumont, Texas.