Review Article

The Significance of Muscular Strength in Dance Yiannis Koutedakis, Ph.D., Antonis Stavropoulos-Kalinoglou, M.Sc, and Giorgos Metsios, M.Sc.

Abstract The physical demands placed on dancers make their physiology and fitness just as important as skill development. However, dancers' muscular strength and bone and joint integrity seem to suffer as a result of the dance-only selection and training system. This partly reflects the unfounded view that exercise training that is not directly related to dance would diminish dancers' aesthetic appearances and destroy muscle flexibility. Nevertheless, data on male and female dancers have demonstrated that supplemental strength training can lead to better dancing and reduced incidents of dance injuries without interfering with key artistic and aesthetic requirements. An awareness of these factors will assist dancers and their teachers in improving training techniques, employing more effective injury prevention program, and in determining better physical conditioning strategies.

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rofessional dancers are normally involved in daily classes followed by several hours of rehearsal or stage performances. Demanding timetables can also be found in most dance schools. Such conditions, however, are also associated with sport, which perhaps led the former

Artistic Director of Birmingham Royal Ballet, Sir Peter Wright, to introduce the term "performing athlete" for his dancers. Sir Peter was among the first to recognize that as the physical demands placed on today's dancers continue to grow, their physiology and fitness becomes just as important as skill development. Although differences do exist between one dance form and another and between dance and other forms of athletic activity, it is the similarities between sport and dance that are the focus of this article. As in sport, dance performance is a rather complex phenomenon depending on a large number of elements.' At the professional level, dancers must be experts in the aesthetic and technical side of the art and psychologically prepared to handle critical situations and, to do so, they must be free of injury. Tbey must also be physically "fit." Physical fitness may be defined as the individuals' ability to meet the demands of a specific physical task. In dance, fitness incorporates elements of body composition,^'^ joint mobility,'* and cardiorespiratory fitness.^''' Dance fitness also depends on the dancer's ca-

Yiannis Koutedakis, Ph.D., is in the Department of Sport and Exercise Science, Thessaly University, Trikala, Greece, and the School of Sport, Performing Arts and Leisure, Wolverhampton University, England. Antonis Stavropoulos-Kalinoglou, M.Sc, and Giorgos Metsios, M.Sc, are in the School of Sport, Performing Arts and Leisure, Wolverhampton University, England. Correspondence: Yiannis Koutedakis, Ph.D., Department of Sport and Exercise Science, Thessaly University, 42100 Trikala, Greece.

pacity to develop high levels of muscle tension (i.e., on muscular strength).'''^ Nevertheless, research has revealed that certain forms of dance elicit limited stimuli for fitness enhancement''" and that dancers, in general, are not physically as well conditioned as equivalent athletes,'^ particularly with respect to strength.'^'' In dance, strength training has not been generally considered necessary for a successful career. This partly reflects the tentative view that increased muscular strength would diminish dancers' aesthetic appearances. Anotber such view, shared by sections of tbe dance profession, is that strength and strength training would negatively affect muscle flexibility, the development of wbich is a long and demanding process. It is, therefore, not surprising that relatively little published data exist that are directly relevant to dancers' strength and its training. The aim of this brief review is to discuss relevant information from botb dance and sport, to discuss the signiftcance of strength for tbe dance student and professional dancer, and to correct some ofthe misunderstandings around strength training. The bodyconditioning techniques of Pilates, Alexander, and Feldenkrais will not be discussed as they have generally attracted little scientific attention.'^ However, a brief introduction to skeletal muscle physiology is necessary, as muscle is the basis of all

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physical fitness parameters, iticluding strength.

Muscle Fiber

Skeletal Muscle Most movements of the body are the result of the contraction or shortening of skeletal muscle cells. Muscle is capable of causing very large variations in force, speed, power, and range of movement, as it very elegantly converts chemical energy from food directly to mechanical energy. In dancers, skeletal muscle accounts for somewhere between 38% to 45% of body weight, contains about half of the body's water, and during exercise can raise their metabolic rate more than 20 times.' Muscle consists of long (up to 10 cm) and thin (30 to 60 micrometers) cells, which appear striated or striped under the microscope, due to ordered arrays ofthe contractile protein rods, actin, and myosin. Skeletal muscle itself consists of three main types of muscle fiber, graded on two main abilities; their speed of contraction (ranging from the "slow," 140, to "fast," 70 milliseconds) and their major energy source. Muscles tend to be described as "slow" or "fast," with two types of fast twitch fibers."^ Humans have genetically determined mixtures of fast and slow fibers. Most people have a ratio of around 50:50 fast to slow muscles, although gifted individuals may have a muscle profile distinguishably different from that. In great sprinters up to 90% of their muscle cells are fast, while more than 90% ofthe fibers in successfial marathon runners are ofthe slow variety. Those who can jump well have a varying preponderance of fast fibers."^ The limited data on dancers' muscle profiles have shown that (ballet) dancers have predominately slow fibers. "< Although the slow-to-fast muscle fiber profile appears not to be altered (except possibly with age) with training, the cross-sectional area of both types of fibers may be changed, especially that of fast. Hence, when undergoing a similar training regimen, "muscular" dancers (who probably have a higher percentage of fast fibers to begin with) will hypertrophy their

Myofilaments

Myosin Figure 1 Various stages of magnification of muscle fiber. muscle more than their "slimmer" counterparts. Cell for cell, fast fibers are 30% to 40% larger than slow fibers. Dancers witb more fast fibers will tend to look more "muscular" than dancers with more slow fibers. The sarcomere, the unit of contraction ofthe muscle cell, is the part of muscle wbere dance — and all other physical actions - originates. It is bounded at each end by a "Z-line," and contains parallel arrays of the protein filaments actin and myosin (Fig. 1). For maximal performance, the sarcomere has to be at about twothirds of its longest length. In terms of a whole muscle, that is often about two-thirds of its fully extended length. This is why the sprinter starts from a crouch position, with all muscles set to about two-thirds of their resting length, to maximize the force at tbe start. The force a muscle generates is proportional to its cross-sectional area, rather than to its length." But the speed of sbortening is also dependent on length. The longer the muscle, all else being equal, the quicker it shortens. Power, the rate of generating tension, is the product of force multiplied by velocity, and as force is proportional to area, and velocity to length, then power is proportional to length times area, which is volume. So, a short thick muscle will produce high force at low speed, and a long thin muscle will produce low force at higher speed. In both cases the power

may be tbe same, whicb is why dancers of different physiques can achieve the same elevation. Most muscle contraction, of the type known eitber as isotonic ("same tension") or concentric (ends move toward tbe center), does indeed shorten the muscle fiber. However, isometric ("same length") contraction is the name given when a lot of force is developed with no obvious movement. Just as in bolding a partner aloft. And there is a tbird mode of "contraction," wbich is where a muscle may exert a strong force wbile it is lengthening. This is termed an eccentric contraction (ends moving away from tbe middle). This happens every time a dancer lands from a jump or leap; tbe landing leg(s) flexes, yet is generating forces much greater than bodyweigbt to absorb the impact. Muscle can generate 30% to 40% greater force eccentrically tban concentrically.^"

Strength and Dance Strength training has been a part of atbletes' preparation for at least 2,500 years. Archaeological reports have confirmed tbat the carved stones of varying sizes found in the ancient stadium of Olympia were used by Greek athletes for tbeir strengtb training. Strength is generally understood to be tbe ability of an atblete to overcome external resistance, or to counter external forces, by using muscle. Therefore, muscle strength can be simply defined as tbe maximum force tbat

Journal of Dance Medicine ef Science can be exerted in a single voluntary contraction. However, since many of the individual movements in dance last for up to a few seconds, the entire force-time continuum, and not just the force at an instant of time, is the information required by dancers and their trainers. Improvements in muscles' ability to generate force seem to be a way for dancers to enhance their performance' and reduce career hazards.^' Soloist ballerinas are characterised — inter alia — by increased muscular strength,'" while an early study indicated that muscular strength, together with agility, balance, and flexibility, are positively associated with modern dance performance.^^ Nevertheless, isokinetic measurements have repeatedly indicated lower torque values in dancers than in other athletes^^'^"* and even untrained individuals.''^ Ballerinas have the least muscular strength, demonstrating only 77% of the weight-predicted strength values based on normal values." This may be partly explained by the fact that, in these dancers, skeletal muscle accounts for just 38% to 4 3 % of their body weight^^ and consists of predominately slow fibers.'* It should be added here that sub-optimal loading of the neuromuscular system may result in muscular strength decreases in both males and females,^*' which may explain why young female dancers demonstrate lower hip flexors strength than control subjects.'^ However, male and female modern dancers are generally stronger than their counterparts in ballet, and in many cases can easily compare in strength with other athletes.' Unlike most professional ballet dancers, individuals involved in modern dance often have a multidisciplinary background (e.g., former gymnasts) which may explain certain elements of "athleticism."

Strength and Dance Injuries It has been generally assumed that dancers' movements are not capable of generating sufficient power to cause the muscular injuries seen in sports. However, dancers do get injured^^ and the effects of these injuries can

be detrimental. The lower back seems to be the most frequently injured site, which together with the pelvis, legs, knees, and feet, account for more than 90% of the reported dance injuries.^**'^' The young age at which serious dance training begins, the long and rigorous hours of practice, the thin ballet slipper, dancing en pointe, unusual dietary regimens, difficult choreography, and insufficient warm-up may all contribute to injury patterns to varying degrees.'^''" Levels of physical fitness, particularly strength, have also been recently added in this list. An investigation on dancers' thigh strength in relation to lower extremity injuries indicated that the lower the thigh strength levels, the greater the degree of injury.^* Supplementary strength training might circumvent such problems and provide a relatively cost-effective way of reducing dance injuries.

Strength and Osteoporosis Skeletal fragility caused by osteoporosis represents a major health problem with growing social and economic implications. The foundations for the condition can frequently be traced at an early age.^' Low bone mass — which may lead to osteoporosis — occurs in young females with amenorrhea and delayed menarche regardless whether they are classed as exercisers or non-exercisers.^^ However, secondary amenorrhea has been linked to certain external factors such as type and volumes of physical exertion. For example, secondary amenorrhea is more common in females participating in endurance-type training, compared to females in strength or weight training programs.•'•' Indeed, strength training has been suggested as a way to defuse the world's osteoporosis time bomb.^"* Muscular strength and strength exercise have been recommended as a means of increasing bone health and preventing osteoporosis in both female athletes-" and dancers,^'' as well as in elderly females.^^ These authors reported that bone density was normal or elevated at weightbearing sites whereas deficits were observed at non-weightbearing sites.

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This was supported by another study involving aerobic dancers indicating that exercise that includes versatile movements and high peak forces are more effective in bone formation than training with a large number of lowforce repetitions.^**

Strength Training Strength training entails exposing muscle to exercise stimuli of sufficient intensity and duration to produce a desirable and lasting training effect. In the case of dance, these stimuli should also derive from exercises that are mechanically as similar as reasonably possible to the specific form of dance. Overloading is perhaps the single most important strength training principle.^' The Greek athlete Milon of Croton was the first who, perhaps unwittingly, implemented the principle of progressive muscle overloading as early as the late sixth century BC. He carried a bull calf on his back each day until the animal reached maturity. This practice was resurrected in the 1940s by practitioners who advocated that exercise resistance (or load) must be periodically increased. By ensuring that the magnitude of the training load is above the habitual level, the overload principle is also applicable to untrained individuals and novice dancers. It has been argued that conventional dance studio exercise alone confers few strength benefits."*" This hypothesis has been tested by examining the effects of supplementary strength training programs in professional male and female dancers.'^'*'"'*'' Unlike the experimental group, "control" dancers showed no differences in peak torques after the monitoring period, while strength training seems to be more beneficial to weaker dancers than to their stronger colleagues. However, matters are slightly different with younger individuals; 12 months of dance activities demonstrated greater improvements in muscular strength in females who ranged in age from 8 to 11 years compared to controls."*' Whether these results were confounded by aspects such as baseline strength

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levels and dance training regimens remain to be confirmed. Mtiscle hypertrophy is an anathema to the dance profession. However, it is encouraging to notice that significant increases in muscle strength may occur without the presence of proportional changes in muscle size.'*'' This reinforces the belief that resistance training is followed by changes within the nervous system, which play an active role in strength development.''^ An elevated neural involvement may account for some of the exercise-induced increases in muscular strength,^^ suggesting that, at least in the early stages of such training, hypertrophy is not a condition for strength gains. Women and men respond to strength training in very similar ways to their individual pre-training baselines,^' and there is no evidence that women should train differently than men. Women, on average, display approximately two-thirds of the overall strength and power of men. However, unit for unit, female muscle tissue is similar in force output to male muscle tissue and demonstrates proportional increases for the sexes in strength performance and hypertrophy of muscle fiber relative to pre-training status. In a study designed to test whether different modes of activity and forms of preparation affect selected strength and muscle contractile characteristics, no differences were found between professional dancers, Olympic bobsledders, and Olympic rowers.'*' This finding tentatively suggests that regardless the type of physical training or levels of fitness, the basic muscle contractile properties remain the same and that - on the muscular level - there are no differences between dancers and other athletes.

Strength Training and Body Aesthetics Significant anatomical differences separate elite dancers of both sexes from the normal population.'" Even at school level, dancers are moderately lean and have a relatively small body size.' 'These distinctive body characteristics form part of the overall dance aesthetics, from which no performer

Journal of Dance Medicine & Science wants to be detached. However, it has been found that strength training reduces body fat in trained" and untrained'^'" men and women. When appropriately conducted, strength training does not affect the dancers' aesthetic appearances.'" Koutedakis and Sharp"" demonstrated that a 12weeks supplementary strength training for hamstrings and quadriceps is beneficial to professional ballerinas and their dancing and that this training did not alter selected thigh aesthetic components. The findings are supported by previously published data that demonstrated that resistance training can lead to improvements in leg strength without interfering with key artistic and physical performance requirements in male''^ and female"*^ ballet dancers. Strength Training and Muscle Flexibility Despite popular thought, there is no scientific evidence to support the view that strength and strength training would negatively affect muscle flexibility. In contrast, it has been advocated that resistance training does not affect gains developed through flexibility training,''* that strength levels are positively associated with flexibility scores in adolescent athletes," and that strength and flexibility are simultaneously present as predictors of folk dancing in 11-year-old girls."^ Some investigators even recommend: "Strengthen what you stretch, and stretch after you strengthen!"''' The reason for this recommendation may be that flexibility training on a regular basis causes connective tissues to loosen and elongate. When the connective tissue of a muscle is weak, it is more likely to become damaged due to overstretching, or sudden, powerful muscular contractions. The likelihood of such injury can be reduced by strengthening the muscles bound by the connective tissue. However, when working on increasing (or maintaining) flexibility, it is very important that strength exercises force muscles to take the joints through their full range of motion.'*"

Repeating movements that do not employ a full range of motion in the joints (e.g., cycling) can cause shortening of the muscles surrounding the joints. This is because the nervous control of length and tension in the muscles are set at what is repeated most strongly and most frequently. Some relatively new training methods (e.g., superimposed vibrations on target muscles) have been specifically designed to allow for gains in both maximal strength and flexibility.'^ Nevertheless, as to whether flexibility in young dancers can improve with further training or is confounded by genetic factors remains to be confirmed.'^ Coexistence of optimal muscular strength and flexibility have also been suggested as factors to prevent low back pain in athletes," including young rhythmic gymnasts.^" On similar lines, it has been suggested that coaches should introduce strength and flexibility training to counteract specific weaknesses and, therefore, prevent injuries in pediatric*^' and collegiate female^^ athletes, as well as in elite junior figure skaters.^^ In fact, concurrent pain-free stretching and strengthening exercises (beginning with isometrics and progressing to isotonics and isokinetics) are essential in regaining flexibility and preventing injuries."^

Conclusions Dancers remain subject to the same unyielding physical laws as athletes. However, although muscular strength has been part of the athlete's life since classical times, this physical fitness component has not been considered as a necessary ingredient for success in dance. We presented published data demonstrating that supplementary exercise training can increase muscular strength without interfering with artistic and dance performance requirements. There is little indication that an appropriate strength training regimen would diminish body aesthetics and muscle flexibility. However, any change in the traditional training regimens must be approached cautiously to insure that

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