The Role ofBiomechanics in Understanding Dance Movement

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The Role of Biomechanics in Understanding

Dance Movement A Review Margaret Wilson, Ph.D. , and Young-Hoo Kwon, Ph.D.

Abstract This review introduces different tech­ niques used in biomechanics that have been used in analyzing dance movement. Biomechanics provides information not only for analysis of motion, but for un­ derstanding muscle use, forces acting on the body, issues of motor control, and the interaction between anyone body part and the body as a whole. The goal of this review is to highlight the role that biome­ chanical analysis plays in understanding dance movement, with applications for teaching, skill enhancement, and injury prevention.

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mponent ofthe emerging field of dance science, biomechanics rovides analytical description and quantification of components of a given movement, as well as measure­ ment of associated forces acting on the body. In dance biomechanics, a mecha­ nistic focus on the body is adopted for analysis; the dancer's body is viewed as a collection of rigid segments link ed at the joints. These joint motions are the building blocks for investigation; thus, a ny dance movement can be divided into component joint motions for analysis. Biomechanics observes both kine­ matic and kinetic aspects of a dancer's

movemen t . JG n em atics p rovides a description of motion: h ow far, how fast, how much change, and what type of motion is involved. It describes a dancer's motions and allows the re­ searcher to identifY key events in the performance of a skill. In kinematics, quantification of component jo int motions and identification of the ranges of motion of individu al joints provides a foundation for understand­ ing how these elements contribute to the dancer's total motion. Kine tics, on the other hand , focuses on the ca use-and-effect relationship seen in movement: the force involved and the resultant motion . The primary mechanical quantities in kinetics are forces and moments (torques) acting w ithin the body (im ernal) and those that origina te in the environment (external). A dancer's environ m e nt includes anything that is in contact wich the body: other dancers , train­ ing spaces, performance sp aces, and the footwear in which dancers train and perform. The internal forces and mom ents acting on the bones, joints, m uscles, and other connective tissues are de te rmi ned by the a mount of muscle activation required to create the desired movement or are in response

Margaret Wilson, Ph.D ., is in me Department of Theatre and Dance, University of Wyoming, Laramie, Wyoming. Young-Hoo Kwon, Ph.D ., is in the Biomechanics Laboratory, Texas Woman's University, Denton, Texas. Correspondence: Margaret Wilson, Ph.D., Department of Theatre and D ance, University of Wyoming, Dept. 3951, 1000 East Un iversity Avenue, Laram ie, Wyoming 82071-395 1; [email protected]

. to external forces coming from the environment. Identifying these internal and external forces and moments can lead to a greater understanding of how movement is produced. In addition, understanding the intetaction a dancer has with these factors and the resultant muscle activation patterns is viral ro preventing injury and supporting the development of skilled performance. Biomechanical analysis of move­ ment involves th e use of spec ific m easuremen t tools. Electromyogra­ phy (EMG) , force measurement, and video motion analysis are employed to describe m uscular activity, understand forces acting on the body, and to ob­ serve movement of the center of mass and movement in both segmental and global meas ures . Employing technol­ ogy provides not only for sophisticated analysis of movement, but also for an il nderstanding of the componenrs o f skill, artistry, and expression. Accord ing co M idgert, biomechan­ ics can help "close the gap between the rea li ty of movement a nd our understan d ing of it. I Kwo n echoes this point by advocating for inclusion of a mechanical perspective in train­ ing dancers that addresses issues of safety and introduces the mechanical principles of dance movements while at the same time honoring dance as a performing arc2 This review highlights early biome­ chanical research in dance that laid

rhe foundarion for furrher analysis; it inrroduces the an alytical ools used

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in current research and it reviews bio­ mechanical studies in dance following five lines of in ui : understandin motion, m uscle actio n, ancer-envi­ 'ffi'riffient interaction, mo;;-r con trol, and segment motion.

Early Research in Dance

Biomechanics

At the Dance: Verities, Values, Vi­ sions: Binational Dance Conference in Waterloo, O ntario (1971 ), several papers introducing a biomechanical perspective fo r dance were presented. The "Verities" section included an introduction to electromyography by Joh n Basmajian and an overview of neurophysiologic development of dancers by Douglas Camp belP4 Research in dance biomechanics conducted in the mid-1970s focused on descriptive analyses of dance movements (kinematics). Observing six grand allegro jumps based on a frame by frame analysis of 16 mm film, Ryman identified segmental Contributions of different body parts in each jump.5 Hinson conducted a similar study of tour-jete, and Wiley analyzed saut de basque using qualita­ tive and kinematic data. G.? Filming in slow motion allowed these researchers to observe movement in detail and understand how the body segments work together to create movement. Nichols looked at the effect ofwork­ ing at the barre on vertical alignment during plie; Bannister analyzed the relationship between dance training and pelvic angle, lwnbar angle, hip mobil­ ity, and low back pain; and Ryman and Ranney observed pelvis and lumbar spine movement in grand battement devam .8 - 1o Becker, using forc e plate technology and cinematographic pro­ cedures, recorded kinetic and kinematic parameters oflandings from jumpS.ll He found that landing with the leg in exter­ nal rotation, a requirement that concen­ trates on the enhancement of style and artistic appearance, did not result in low impact landings. His recommendation was that the focus in jwnping should be on landing as well as preparation, or take off. Murgia described kinematic and kinetic variables in three selected

achieved, and amount of time spent in the air.12 Most of this research was con­ ducted as part of graduate degree work on dancers in university dance programs. L ater resear ch would incl ude informatio n gathered from professional dancers. While most of the early research involved ballet dancers, Krasnow identified impor­ tant studies using modern dancers.13 Finally, as dance science developed as a discipline, Ranney's chapter on dance biomecha.nics in Clarkson and Skri­ nar's Science ofDance Training (1988) became a primer for many educators, as it clearly described biomechanical principles in accessible language. 14 Physicist Kenneth Laws applied his scientific expertise to the analysis and description of dance movement. His original text, 1he Physics ofDance, was published in 1984. 15 Looking at dance from a biomechanical perspec­ tive, Laws' mission was (and still is) to help dancers understand the physics of movement as a way of learn in g more about techniq ue . H e has p ubl ished numerous articles related to specific movements in dance. For example, he has discussed the biomechanics of using the barre, fouette turn, grand jete, pirouettes, mom entum transfer and vertical jumps. 16-21 In 1994 Laws published Physics, Dance, and the Pas de Deux, and his most recent book Physics and the A rt of Dance (2002) is an expanded version of the 1984 original. 22,23 He has collaborated with many dancers and researchers, wor k­ ing speCifically toward an understand­ ing of how the physical properties of movement can be directly applied to dance technique.24-28 By introducing concepts of veloci ry, acceleration, trajectory, friction, and torque to the analysis of dance movement, a clearer understanding of the forces acting on and in the body is achieved.

Components of Biomechanica1 Analysis The fi eld of biomechanics uses many d ifferent techniq u es for ana lysis, generally classified into three catego­ ries; 1. analysis of muscle action, 2.

techn iques can be used in co mbina­ tion or employed separately. As many of the studies cited in thi s review use o ne or more of these techniques, a brief explanation of the fundamental pri ncipl es and applications of each techniq ue is in order.

Analysis ofMusde Action Muscle action can be measured by looking at the electrical activity in the muscle _Electromyography (EMG) de­ tects elecrrical activity elicited by the muscle cells during contraction, using either electrodes placed on the surface of the skin or needles inserted into the muscles. While the needle technique provides valuable information about the state of the neuromuscular system, it is highly intrusive; therefore, most electromyographic studies conducted wi th dancers use surface electrodes. These electrodes provide in forma­ tion regarding the firing patterns of specific m uscle groups. More recently, ultrasound imaging has been used to monitor muscle action, particularly in the trunk and ankle. 29 Both ultrasound and EMG provide a broad picture of movement, which is useful for understanding the muscle action that produces dance move­ m ent. In addition, recent research in electromyography and motor control has re vealed muscular minimums , that is, low intensity muscular activity operating in balance with maximal muscular contractions. This informa­ tion confirms that complex human movement occu rs in a geometri­ cally balanced neuromuscular system , which provides for both specific and global phenomena.30 ­32 Analysis of Forces Acting on the Body In any movement, a dancer is mediat­ ing different forces acting in and upon the body: gravity, the weight and ac­ celeration oflim bs, and torque created in the joines . In any vertical excursion away from, and returning to, the fioo r, these forces are mul tiplied by incre­ ments of the dancer's mass. Ground reaction force (GRF) measures identify external forces acting on the body in

dance leaps and identified differences in

analysis ot forces acting on the body,

its interaction with the ground. The

peak angular velocity at the knee, height

an d 3, ana lysis of m otion. T h ese

ground reaction force is measured with

Journal of Dance Medicine 6- Science' Vol ume 12,

the dancer standing or moving on a force plate and reveals changes in me dancer's center of mass as wdl as the forces transmitted to the body through interaction wim the plate. 33 -41Ground reaction force data has many applica­ tions. For example, it can be used in modeling, or understand ing, forces acting on the body; information re­ garding stress on individual joints dur­ ing movement can be described as net moments.42.43 G ro un d reaction force data can be used to understand and ad­ dress the effects of the different types of footwear. surfaces, and environmen ts dancers train on and in.44 Finally, GRF data provides in formation on force s generated in me body by movements, such as jumping, to better understand and help prevent unnecessary injuries in dance training.35,37 New technological advances furmer both biomechanical research and an understand ing of dance movement. For example, Srinivasan and colleagues have designed a pressure-sensing floor constructed from modular mats that are easily configured to different sized spaces. The real-time data generated by this system provides information about the amou nt and distribution of force being exerted on the floor mat can be integrated with other external systems in motion analysis and EMG.45 Analysis of Motion Three-dimensional (3D) video mo­ tion analysis is an effective tool for understanding co m plex movement. It allows th e research er, dance teacher, and dancer to look at mov-emen[ in a modeled form , yet also reveals precise details that are not available to the unaided eye. The visual information is quantified with regard to general and specific body position, joint angles, accelerations, and u ajectories. M o­ tion analysis p rovides a me ans for understanding movem nt at any body scale or time scale, and this informa­ tion can be used to identifY skill and efficiency or risk and inefficiency. The data generated can be applied to un­ derstanding and enh anci ng teaching, learning, and performance. Three-dimensional motion capture uses m ultiple cameras (2 to Gor more) that are lin ked with direct output to

m arker tracki ng software. Ie locates the dancer in a general r ference frame, but also identifies specific reference frames for analysis of individual body segmen ts. For example, a glo bal refer­ ence frame determines movement of the body in space, whereas m ovem em of a particular part of the body, relative to me whole body, is identified through a local reference frame. The kinematic data gathered in this way can be com­ bined with inertial data an d integrated with EMG, body segment modeling, or GRF data for a more com prehensive understanding of movement . Data from motion analysis is developed quantitatively, but is also converted into visual representation of the body in a modeled form: a stick fig ure that can be viewed from any angle. Both the quantitative data and pictorial represemation provide insight fo r the researcher. H owever, the model speCifically simplifies the movem ent to reveal key components for analysis. M otion analysis has been used to re­ veal patterns of efficiency and skilled performance in arabesque,46.47 rond de jambe,43.4 8 grand battement paSSe ,49'51 and port de bras.52

Understanding Motion: Grand

Plie D ance training is characterized by the use of repeated motions. U nderstand­ ing the pattern of recruitment of the muscles used, as well as practicing good mechanical execution of these motions, not only increases skill but also mi nimizes the potential for in­ jury. One of the most controversial movements in a dancer's vocabulary is grand plie; grand plie has been the su bject of biomechanical an alysis to determine the net balance between posit ive attri b utes of the movement and poss ible negative consequences. Plie and grand plie have been stud­ ied from a biomechanical perspective to understand the forces ac ting on the body, particularly at the joints, and identifY risk potential . One of the first studies to look at the impact of perform ing grand plie was con­ ducted by W oodruff, who observed angular disp lacement of the center of gravity duri ng a dancer's execution of the movement. Noting the potential

um ber 3, 2008

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for injury to the knee, she made the recommendation to limit repetitions in second position.53 Trep man and colleag ues , usin g EMG analysis, identifi ed variation in patterns of muscle use related to different training modali ties (ballet and m odern). In a follow-up study, ballet dancers exhibited lower patel­ lofemoral joint reaction force at the deepest pan of a grand plie than d id modern d ancers . T he investigators concluded that the ballet barre dis­ places some of the force at the knee for the ballet dancers, whereas the greater quadriceps strength in the mod ern dancers increased the patellofemoral forces and put them at greater risk for . injury, particularly if they performed the grand plie without being properly warmed up.54.55 Barnes looked at external longi­ tu di n al rotation (ELR) in d an cers executing grand plie in all five ballet positions and concluded that while ELR always increased at the dep th of the p Ue it was greatest in third and fourth positions. 56 Barnes noted mat grand pUe is more dangerous to the knees than d emi-plie because it increases patella r compression and comprom ises knee joint stab ility. Fo r th is reason she recommended caution when executing repeated grand plies. W hile m any ed ucators feel th at grand plie is potentially dangerous, it remains a vital part of a dancer's vocab­ ulary. Using biomechanical analysis, a more comprehensive understanding of grand plie has been generated. TIle results of the research conducted have confirmed the importance of grand plie for developing srrength in a dancer. Specifi cally, o bserving the freq uency and scheduling of grand plie within me dance class can provide maximum benefit from the movement without crea ting un balanced pressure in the patellofemoral joint.

Muscle Actions: Releve Part of any dancer's repertoire is the releve: rising to demi-pointe or full pointe. This action can be described as a sec ond-class lever, whe re the weigh t of the body is being moved at a fulcrum (the an kle) by the muscles of the lower leg and foot. Unders tand ing

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Volume 12, Number 3, 2008 • Journal of Dance Medicine & Science

the muscle activity in this movement may co ntribute to an appreciation of how best to increase effectiveness and minimize the risk for injury in train­ ing dancers. Researchers have focused on mus­ cular activi' in rising to demi-pointe and point( or releve . Yoshida and associates k Jked at EM G activity in the triceps surae, comparing dance students and non-dancers. 57They iden­ tified a training effect in the dancers revealed as a delayed onset of fatigue in a heel-rise (releve) test. Masso and colleagues found variation in muscle activiry in different positions of th n legs (parallel vs. external rotation).' I Distinct patterns were seen in the gastrocnemius and peroneous longus firing relative to pronation in the foot. Specifically, they identified low activ­ ity in the abductor haUucis muscle as a risk factor for injury. Kadel observed differences in muscular responses to different positions and conditions en pointe using electromyography. 59 She identified the gastrocnemius as the key muscle in achieving demi-pointe and the soleus as the key muscle used in going en poin teo Lin and coworkers studied differen t joint moments between the dominant and n on-dominant ankles in re/eve en pointe, CI rrelating the significant dif­ ferences Jetween sides with injury.4 ! They found a higher peak moment in releve for the dominanr leg, indicating that it was more skilled at controlling the ankle, while the non-dominant leg had a po orer reaction to rapid move­ ments in particular. The information from each of these srudies is useful to dance educators in terms of understanding how to pre­ pare a dancer for work on dem i-pointe and pointe. Whereas dance training is often considered a means unto itself, identifying areas for focused trainin g is useful in promoting skilled perfor­ mance and preventi ng injury.

on jumping. Simpson and colleagues published a series of articles on inter­ nal joint moment forces in landing from a jump.3 5.37 Greater patello­ femo ral forces were seen wi th longer jump displacements due to increased eccentric forces. In add ition, these investigators found th at increased quadriceps force contributed to axial forces more than joint reaction axial forces. For example, as . he jump dis­ tance increased, so did r Ie shear forces at the ankle, kn ee, a d quadriceps muscle group; in fact, ~he quadriceps shear force exceeded the knee joint force. It has been pointed out that this exc~ssive use of the quadriceps relat ive to underutilized posterior leg musculature is an "arypical impact force" that might be a predisposing factor for injury. D ance is characterized by spectacu­ lar jumps and leaps, wi th seem ingly effortless landings. O fte n the jump is used fo r musical or aesthetic affect, or to h ighlight the ath leticism of the dancer. M easuring and q uantifying forces acting o n the body thro ugh biomechanical research has led ro a greater understanding of the need to clarify information regarding the take off phase and landi ng of jumps, identify m uscle imbalances that are risk facto rs for injury, and train danc­ ers to jump as a function of the whole body. Footwear

Biomechan~search has illumi­ nated forces acting on the body in

Dancers interact with unique foot­ wear, depending on the dance fo rm . The un iq ue ness of a dancer's shoe requires a very specific form of analy­ sis, which biomechanical tools can provide. The shoe design for many genres of dance follows an aesthetic principle rath er than a functional one; therefore, understanding the re­ lationship between dancers and their footwear is an important area ofstudy in dance biomechanics. T he po inte shoe worn in ballet has received the most attention. Th is footwear must be supportive and pliable, yet the dancer's foot absorbs large forces when en poi nre. Teitz and associates used transducers to

dancer-envi ro nment in teraction s.

look at pressures in pointe shoes on

Most not bly, the research has focused

the first and fifth metatarsals, and as

Dancer-Environment Interactions Forces in Jumping

a result they recommended the use of padding ro diStribute these forces througho ut th e whole foo r. 60 G alea found high muscle forces en pointe, which, she warned, could lead to structural changes and pro blems in a dancer's feet and an kles. 6 ! Albers and coworkers recorded peak pressures in pointe shoes for releve and eleve, and recommen ded minimizing use of the pointe shoe in training. G2 Doni and Winters found pressures on the metatarsophalangeal joints in ballet dancers en pointe, determi ning that the work load on the in trinsic muscles of the foot was 2.5 to 3 times greater than for the extrinsic muscles.43 Miller and colleagues and C un­ ningham and associates, looking more specifically at the pointe hoe design and construction, found differences berween shoe manufacturers for stiff­ ness, strength , and fatigue .G4 •65 How­ ever, M iller and colleagues' conclusion was that dancers select the shoe that best sui ts their individual needs fo r fi t and shape, not based on whether it is the strongest or most durable option available. Dance forms featuring a stiff soled shoe, such as flamenco and tap, have also been the subject of biomechani­ cal investigation. O f unique interest in fl amenco and tap is the percussive and auditory requirement for the feet. While much of the research on these forms has looked at injury profiles, Voloshin and Bejjani analyzed the stress of flamenco dancing on the body and examined the use of insoles for shock absorption in injury prevention. 44 •GG Wilmerding and coworkers used mo­ tion analysis (0 explore postural adapta­ tions in young dancers wearing heeled footwear in flamenco dance, no ting that children who dance in a heeled shoe might be at greater risk fo r inj ury because of the changes in posture as­ sociated wi th persistent plantar flexion. The recommendation from this study was that increasing core strength and lower exuemity flexibility, as well as develo ping postural awareness and proprioception, was important for preparing young dancers for the rigors of flamenco training 67 Looking at tap dancers in a retro­ sp~ctive study, M ayers and Bronner

Jo urnal of Dance Medicine & Science found a relatively low rate of stress­ related injury.68 Based on this infor­ mation, these investigators examined ground reaction and lower extremity forces, finding low vertical component (Fz) values in professional tap danc­ ers. They concluded that the amount of force used contributed pri marily to creating the sound required in the dance form and had relatively little influence on stress-related injury. 69 Force pl ates, electromyog raphy, pressure transducers, and mo ti on analysis are biomechanical tools that have been used to understand the effect that a dancer's footwear has on the foot and leg. In addition, the effect of the interaction of the foot and shoe on the rest of a dancer's body h as been studied. As dance shoes are not nec­ essarily designed to rr,r:et functional specifications, but rather address an aesthetic requirement, understan d ­ ing how to work with footwear in enabling dancers to perform safely is of utmost importance.

Motor Control lssues of balance and counterbal­ ancing maneuvers are of interest in understanding strategies that dancers use in performing particular m ove­ ments. Video analysis and ground reaction force technology have al­ lowed researchers to understand subtle panerns in a dancer's movement profile relating to body orientation and balance. It is clear that balancing strategies consritute an intrinsic skill that dancers develop, but they shed more light on the neuronal and reflex adjustments that accompany dance training in general than on a specific movem ent. M o uchnino and colleagues found that dancers' training established mo­ tor programs that allowed them to maintain vertical orientation of the head using a counter-rotational trans­ lation strategy of the trunk, pivoting around the hip joint, to compensate for the movement of the leg. 70 Mon­ asterio looked at postural adjustments made in voluntary leg m ovements relative co postural muscle recruit­ ment prior to the leg motion, and M ouchnino and colleagues looked at spine m otion duri ng leg movem ent

an d fo und different strategies for fa­ cUitating movement of the leg to the side using the tru nk for baiancing.7I.72 More recen d y, Ojofei t imi studied lateral disp lacement of the center of pressure (CP), revealing that skilled dancers maintained m ore vert ical trunk alignment than beginners dur­ ing a weight shift task. 73 She equated the ability to understand the effects of dance training with understand­ ing rehabilitation for balance-related problems in general . Another compone n t o f motor control has to do with muscle recruit­ ment. Electromyography documents patterns of muscular re cru itment that illuminate an individual d ancer's strategy for performing movement. These individual patterns of m uscle recruitm ent often demonstrare vari­ abil ity between dancers perform ing the same