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The Biomechanics of Dance is the functional study of the biology and mechanical physics behind artistic dance. Dance is an art form which demands the extremes of human movement. The dancer’s body appears to glide with effortless grace across the floor, whilst constantly challenging the laws of balance, force and motion. Biomechanics is simply the study of the mechanics of human movement. In order to dance we must create motion, maintain balance and overcome certain forces which affect the way that we move. Each of these concepts, balance, force and motion can be studied through biomechanics. An understanding of these concepts should assist the dancer to understand and improve the fundamental skills of dance.
A body is considered to be balanced when it reaches a state of equilibrium. This may occur when the body is at rest or whilst the body is moving. In order for equilibrium to be achieved the following must occur • the body’s centre of mass must fall within the boundaries of the base of support • the net sum of the forces acting on the body must equal zero (see forces)
Mass refers to the total amount of matter in a body. Centre of mass (CofM) or centre of gravity is defined as the point through which the entire mass of the body may be considered to act. In reality, mass is distributed throughout the entire body, however for simplicity, the location of centre of mass can be estimated to enable analysis of movement and balance. In objects which demonstrate 3 dimensional symmetry such as a ball or square box, the centre of mass is located at the exact centre of the object. In non-uniform bodies (ie humans) the centre of mass changes depending on the shape made by the body. Base of support is a two dimensional area bounded by the points of contact of the body with the ground. The larger the area of the base of support the easier it is to achieve and maintain balance. During motion, the centre of mass may fall outside of the base of support. In order to maintain balance, however, the dancer must be easily able to return the centre of mass over the base of support if desired.Center of Mass Figure 1
Stability specifically relates to a dancer’s ability to maintain balance. When the base of support is large a dancer is very stable, yet whilst balancing on pointe a dancer is easily disrupted from this position and therefore highly unstable. Balance is achieved when the centre of mass and base of support are aligned vertically, whereas stability is a measure of how difficult balance is to maintain. Greater stability is achieved when the base of support is large and the centre of mass is lowered. A larger base of support means that the area over which the centre of mass must fall is enlarged. For example, it is easier to balance standing in second position than on pointe. Curriculum Council - Biomechanical Principles of Dance - Balance, force and Motion. 5 When the centre of mass is lowered, stability is more easily sustained because the body has less potential energy when the centre of mass is closer to the Earth’s core. Potential energy is energy stored within the body to create movement. This concept is fairly complex and will be examined during the practical tasks, however in simple terms, increasing the distance of the body from the centre of the Earth increases the effects of gravity making it less stable. Rotational stability is required for movements such as twisting, turning and spinning. Stability during turns is improved by increasing the rate of turn, the mass of the body and the distribution of mass around the axis of rotation. Notice that ice skaters spin faster wStability Figure 2hen they tuck their limbs in close to their bodies.
Stability Figure 1
Force may be described as a push or pull applied to a body. Force has magnitude and direction. Two equal forces applied to a stationary body in opposite directions results in no motion. However, if a single force is applied, it will cause an effect on that body which will result in a change of motion. Forces may be external such as friction with the ground, or the influence of gravity (which pulls us towards the Earth’s core), or they may be internally applied by the muscles within our own bodies. The effects of force on the motion of a body can be summarised by the laws of motion described by Newton.
First Law A body which is at rest will remain at rest. A body in motion will continue to move in a straight line with constant velocity. Newton’s first law describes inertia, which is the body’s resistance to a change in the state of motion. If a body is at rest it will stay at rest until a force is applied to move it. Similarly, a body in motion will continue to move unless a force is applied to stop it. When performing a slide across the floor, the body is stopped because of friction between the dancer and the surface of the floor. If the surface is very slippery (minimal friction), the slide will go much further because the forces which are decelerating the motion are reduced. If the body is at rest or moving with constant velocity the body is said to be in equilibrium.Physics Figure 1

Second Law A body with a net force acting upon it will accelerate in the direction of the force. The net force is the sum of all the forces acting simultaneously on a body. If force in one direction is greater than the forces in the opposite direction, the body will accelerate in the same direction as the strongest force. In order to perform a leap or a jump the dancer must be able to overcome the force of gravity which pulls the body towards the ground. The dancer will accelerate and leap off the ground when the force created by the body is greater than the force of gravity. When the net sum of the forces acting on the body equals zero and the centre of mass lies within the base of support, the body is said to be balanced.
Third Law For every action there is an equal and opposite reaction. This law is self-explanatory. The reaction may come from an internal source, such as a counterbalance movement from within the body to ensure maintenance of equilibrium, or an external source, such as the reaction of the floor as the dancer lands from a jump. Physics Figure 2

The motion or movement of a dancer may be linear (in a straight line), angular (in a circle) or a combination of both. Within the body, movement occurs by way of forces applied to levers. Levers work by moving rigid objects (bones) around a fulcrum or joint. This is achieved by the contraction of muscles which create the forces required for movement. Muscles act by pulling on bones rather than pushing them. During dancing, many lever systems are working together simultaneously to create the desired motion.
A long lever is more difficult to move and accelerate than a short one. For example, we know that is much easier to hold the leg out to the side when the knee is bent rather than straight. You can also swing the leg from front to back much more quickly when the knee is bent because the straightened leg represents a longer lever. A heavy body part is also more difficult to move than a lighter one. Try swinging your arm compared with your leg. We can therefore see that the choreography can be designed to make the dance movements strenuous or easy to perform. Unfortunately, the aesthetics of dance applauds lengths in the limbs, meaning that dance is usually harder to perform than it looks.Motion Figure 1
When a body moves through the air in any direction other than vertical, it moves in a curved path under the influence of gravity which pulls the body towards Earth. The shape of the path is influenced by the speed and direction of the body during take off. A more vertical take off produces a well rounded path whereas as the flight path is more flattened with a horizontal take off.Projectile Motion Figure 1

INJURIES: Foot/Ankle

The ankle joint connects the lower leg to the foot and, in dance, allows for pointing the toe (plantar flexion) and flexing the foot during plié (dorsiflexion). The ankle also allows for inversion and eversion, producing turn-in and turn-out, respectively. The 26 bones in the foot work in concert with ligamentous support and muscular force to create three separate arches, critical for shock absorption during jumps. Structurally, the ideal foot for ballet is considered to be a flexible “square foot”, which has equal-length first and second toes.
Dancer’s Fracture
“I landed badly from a jump and now it hurts to walk.” Biomechanics of Dance Home - Biomechanics of Dance

This is the most common acute fracture seen in dancers. This fracture occurs along the 5th metatarsal, the long bone on the outside of the foot. The typical method of injury is landing from a jump on an inverted (turned-in) foot. The dancer will usually experience immediate pain and swelling. He or she may or may not be able to walk.

Treatment typically consists of ice, elevation, and limiting weight bearing activities. Consulting with a physician to confirm a fracture will be necessary. A dancer’s fracture will require a period of immobilization while the injury heals. Rehabilitation should follow to rebuild foot and ankle mobility and strength.
“I have pain underneath my big toe, particularly while walking without shoes.” Sesamoid bones are unique in that they are not connected to any other bones in the body. There are two very small bones (about the size of a kernel of corn) on the underside of the forefoot near the big toe. These two sesamoids provide a smooth surface over which tendons controlling the big toe are located.

The sesamoids provide a support surface while the dancer is on demi-pointe. The tendon that runs between the sesamoids can become inflamed, causing sesamoiditis, a form of tendinitis. Pain is focused under the big toe on the ball of the foot. With sesamoiditis, pain may develop gradually. There may be pain while bending and straightening the big toe.

The dancer may be required to rest and take time off from rehearsals while the pain and inflammation from sesamoiditis decreases. A consult with a physician is indicated to rule out a sesamoid fracture. A physical therapist or athletic trainer consult is also helpful to identify and correct muscle imbalances and assist with acute symptom relief. The use of a J-shaped pad around the area of the sesamoid to relieve pressure may be helpful, as is taping the toe so that it remains slightly downward (plantarflexed). It may take several months for the pain associated with sesamoiditis to be completely relieved. Surgical intervention to remove the sesamoid bones should only be considered after all conservative measures have been exhausted.
Hallux Valgus and Bunion
“My big toe points inward and is painful.” Hallux valgus and bunion can be seen in the public at large; however, dancers generally develop this condition at a younger than typical age. This injury usually has a gradual onset and is often associated with other postural and or biomechanical faults involving other joints (most often a tendency to pronate, or roll-in, during turned-out positions). It is characterized by medial movement of the first metatarsal head (big toe), where a bunion bump will gradually form. Consequently the phalanges of the great toe will shift towards the other toes.

Signs and Symptoms
The dancer will notice a gradual onset of foot pain at the area of the big toe or ball of the foot. Pain will be greatest with weight bearing and particularly jumping activities. Typically, dancers will notice pain with excessive pressure to the affected area, sometimes to the point where the slightest contact causes exquisite pain.

The best course of action is to identify a hallux valgus condition as early as possible and clarify its structural and/or biomechanical causes. Conditions that are caught early on can be treated with either strengthening exercises, stretching and/or orthotic prescription. Often, a toe spacer between the first and second toes can help with alignment and prevent further progression of the injury. Conditions that develop into significant structural changes can be very difficult to manage and may require surgical intervention. It is imperative that the clinician treating the dancer looks at the ankle, knee, and hip joints to identify any proximal impairments. Finally, attention to a dancer’s technique with plié, relevé, and jumping is essential to limiting the progression of hallux valgus identified.
Hallux Rigidus (or Limitus)

“I have pain with full relevé.”

This condition is characterized by pain and/or restriction of movement at the joints of the big toe. To achieve full demi-pointe the metatarsal phalangeal joint must be able to make a 90 degree angle. Dancers who start later in life may lack this much mobility. A dancer without mobility who forces a high demi-pointe will cause the bones in the joint to impinge on each other. If this is done repeatedly, bone spurs will develop leading to even further decreased motion in the joint, inflammation and eventual degeneration of the joint.

Compensations for lack of full mobility include sickling. This position will decrease impingement but it is not an esthetically acceptable line and puts the dancer at risk for ankle sprains. An acceptable and safe compensation for this condition is a half demi-pointe position. The dancer must learn to rise onto the ball of the foot without forcing the foot into full demi-pointe.
Biomechanics of Dance Home - Biomechanics of DanceBiomechanics of Dance Home - Biomechanics of DanceBiomechanics of Dance Home - Biomechanics of Dance

Full Demipointe Half Demipointe Sickling

During the acute stages, rest and ice are helpful to reduce pain and inflammation. A good way to ice this injury is with an ice massage for 5 minutes. Stretching of the foot can be done to help improve flexibility. The stretch into a demi-pointe position can be done in a non-weight bearing position, in a pain free range and should be held for 30 seconds. The dancer should assess the available pain free range of the joint and learn to work within that range. Taping the great toe to restrict full demi-pointe can be effective in relieving symptoms. The tape should be applied so that the toe remains slightly downward (plantarflexed). Mobilization of the metatarsal phalangeal joint by an experienced clinician is also quite effective.

Biomechanics of Dance Home - Biomechanics of DanceBiomechanics of Dance Home - Biomechanics of Dance
Ice Massage Stretching of big toe and sole of the foot

Plantar Fasciitis
“My foot hurts when I walk barefoot, especially first thing in the morning.”

Plantar Fasciitis is an overuse injury affecting the sole of the foot. The tough, fibrous band of tissue (fascia) connecting the heel bone to the base of the toes becomes inflamed and painful. Most often people will experience pain first thing in the morning when they step out of bed. Dancers will often experience an increase in pain after class, or following lengthy weight bearing activities. Plantar fascia pain can also be influenced by tightness in the calf or the Achilles tendon, or dancing on a hard surface or a non-sprung floor.

The earlier plantar fasciitis is treated, the quicker it can be resolved. Rest and ice are the first treatments for plantar fasciitis. Anti-inflammatory medication can also be helpful. For persistent conditions, physical therapy or athletic training treatments to assist with tight tissues and identify weakness is indicated. Chronic conditions respond well to the use of an overnight splint (issued by your physician or clinician) to provide a long duration stretch to the affected tissues.

“I have pain over the balls of my feet.”

Metatarsalgia is characterized by pain and tenderness along the ball of the foot. For dancers, this is commonly caused by instability in the joints of the smaller toes. Repeated sprains and overstretched ligaments can lead to laxity, or increased flexibility in these joints. For a dancer, years of overwork and forcing of extreme motion in the foot can increase laxity and may cause subluxation of these joints.

As with all acute inflammatory conditions, ice and rest are appropriate. Strengthening the muscles that control toe flexion can be helpful. This can be done with towel scrunches (using your toes to grab a towel placed on the ground and drawing it towards you). A metatarsal pad just behind the balls of the feet can help prevent subluxations and may relieve pain.

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