In dance, a pirouette is an act of turning on the ball of one foot, typically with the raised foot touching the knee of the supporting leg. In order to perfectly complete a pirouette, it is important to think about the placement of every part of your body. It can be very challenging and takes a lot of time and practice to master, but it is necessary in order to achieve a successful turn. As you master the form of your pirouettes in dance, you can start striving for a higher number of rotations. In the demonstration, the subject will be gracefully completing four pirouettes. The biomechanics of a pirouette are very complex. Biomechanics is the application of the principles of mechanics to the living human body. Studying the kinematics, or the forces associated with the motion of a body, can help a dancer understand what their body needs to do in order to master a pirouette. In this project, I will be analyzing how the body moves and functions while completing this specific action.
To start off a pirouette, the dancer begins in a standing position facing the front with their feet hip width apart and the arms down by their side. Next, they will begin their preparation. To prep, the dancer takes a step forward with their right foot and abducts their arms up into a “T” position. From there, they step forward with the left foot and perform knee flexion to form a bent angle. The left knee should be in line with the left hip and the shin of the right leg in the back is parallel to the floor. As you are stepping with the left foot, keep your left arm in shoulder abduction while horizontally abducting your right shoulder to make your arm and shoulder in a straight line. Once the dancer is in the prep position, she is ready to push off and begin her pirouette.
To start the rotations, the subject uses the right arm to horizontally abduct for momentum and then quickly close both of the arms into first position (shoulder medially rotated while the elbows and wrists are flexed). At the same time the arms are closing, the quad, glute, and hamstring muscles are used to bring the leg into passe, or with the foot against the outside of the supporting leg in plantar flexion. As the first rotation occurs, the dancer will also rise their supporting foot to releve and balance on the ball of the foot. To reach the passe position, the dancer flexes the hip to form a 90 degree angle and then uses the hamstring muscles to connect the left foot which is in plantar flexion to the straight left supporting leg.
While the dancer is rotating, it is important they maintain their body in this position. There are two types forces, static and dynamic. Static forces occur when the body is in balance, or equilibrium, and there is no movement occurring. In other words, this means that everything in the body is lined up properly so you will not fall over. In a pirouette, the body is static from the shoulders and below as the center of gravity is pressed down into the floor and evenly distributed in the base. The center of gravity is the balance point and falls within the base of support. In the principles of body mechanics, the larger the base of support and the lower the center of gravity goes toward the base of support, the more stable the dancer can be. In dance, it is difficult to achieve this balance because it such a small base to balance on, opposed to standing on two feet. While balancing on the ball of the left foot while rotating, strong ankles are needed to keep the foot stable. If the ankle is weak, it can give out and cause multiple injuries. A dynamic force is when the body is in motion. In this force your body is not only acted on by gravity, but also momentum. The gravity and momentum are pulling in different directions. When completing the turn, the body needs to be completely in line with the base. To balance while completing the series of pirouettes, it is important to evenly distribute the body weight and have the forces in your body acting against each other. For example, it is important to lift the back of the neck, underneath the leg in passe, underneath the arms, and the releve, while pushing your shoulders down and grounding yourself in the ball of your foot. These opposite forces create the dancer to be balanced straight up and down. In order to prevent leaning back, the dancer must engage their abdomen and to prevent leaning forwards, the dancer must tuck their pelvis under. Dancers are always taught this when practicing pirouettes. If the trunk (shoulders to hips) are in a straight line, it will be much easier for the dancer to balance and complete a larger number of turns. Balancing plays a huge role in pirouettes. The semicircular canals of the inner ear, vision, touch, and kinesthetic sense all contribute to the balance of the dancer. To prevent getting dizzy while turning, dancers are trained to “spot” their heads. To spot, it means to keep your eyes on a fixed position straight in front of you and leave them in the same position while circulating. When you rotate to the back, the dancer whips the head back to the front. As the dancer rotates, there is no way to increase the base of support for stability, which means the dancer must perform balancing exercises to train their bodies to stay in equilibrium. Equilibrium can be enhanced by increasing the friction between the body and the surfaces it contacts. This happens between the foot and the floor. Balance and its components of equilibrium and stability are essential in completing pirouettes and it is affected by the constant force of gravity as well as by inertia.
A pirouette consists of many forces including Newton’s Laws. Newton’s First Law states that bodies at rest tend to stay at rest and bodies in motion tend to stay in motion unless acted upon by an outside force. While you are in your prep position, your body is still until you build up the momentum to rotate yourself around. The outside force will cause the dancer to push into the floor and complete the turn. In the preparation, the net force is zero since the body is at rest and the force of gravity is pulling her down as the equal force in the floor is pushing her up. The dancer could continue to pirouette but eventually stops due to the outside force, friction. The friction occurs between the floor and her shoe. This concept also applies to the Law of Inertia. Another way the body can slow down while turning is to grip the floor with the toes. The next law that is present in a pirouette is Newton’s Third Law. This law explains that for every reaction, there is an equal and opposite reaction or when an object applies a force to a second object, the second object simultaneously applies an equal force of magnitude and in the opposite direction as the first object. As the dancer completes her rotations, she needs to ground her foot into the floor as the floor pushes back in the opposite direction to the ball of the foot. This also can be known as the ground reaction force or the Law of Reaction. The Law of Acceleration, also known as Newton’s Second Law, is always applied in a pirouette. The greater the mass of the dancer, the greater the force he or she has to use to accelerate the body. Therefore, in order to do more than one pirouette at a time, the dancer must apply a greater force with his or her arms and the force in which he or she pushes off the floor.
To complete a pirouette the dancer needs to understand the kinematics, which is the branch of mechanics concerned with the motion of objects without reference to the forces that cause the motion. A pirouette takes place in a vertical axis since the entire body makes the rotation. The transverse plane is involved because it is perpendicular to the longitudinal axis and it can not occur throughout any other planes since the arms are internally rotated to the midline and the leg in passe is brought up to the medial side of the knee. In this plane, we can see lateral rotation, pronation of the forearms to face down, rotation of the head and neck while spotting, and horizontal adduction of the arms during the preparation. A movement that occurs in the sagittal plane includes plantar flexion (i.e. calf raise), since it is a forward and backward movement. The depression of the scapula in the frontal plane occurs in the frontal plane during a pirouette. The secondary planes which run parallel to the cardinal differ, because they do not pass exactly through the center of the body. They describe functional movements where different body segments are moving in the planes which are parallel to the cardinal planes. As dancers complete their rotations, they are moving through kinematic chains, which are joints that link body segments and bones. There are two types of kinematic chains, open and closed. An open chain is when the distal segment moves in space, the motion in another segment can be isolated and can move either independently or together. For example, the arms in a turn can be placed differently in a pirouette as the dancer links the segments to reach the desired position. A closed kinematic chain is when the distal segment is fixed while the proximal segments are in motion. An example for this is when the knee slightly flexes in the preparation. As the knee is bending, it causes motion to occur through the hip and ankle.
A pirouette consists of a complex force system, where the forces acting upon the body in motion must be identified. When the dancer completes the turn, they move through a series of levers. There are three types of levers which are rigid bars that turn about an axis of rotation or fulcrum. Its movement is caused by a resistance force. A first class lever, designed for balance, has the axis somewhere between the force and resistance arms. These levers are designed best for balance. An example of this lever in a pirouette is when the elbows extend down by your side after completing the rotations. The triceps are applying force to the olecranon in extending the non-supported forearm at the elbow. A second class lever is when the resistance lies between the axis and force. The second class lever is used in plantar flexion and when the dancer rises up on the toes. This action produces force movements, since a large resistance arm can be moved by a small force. The third class lever has the force between the axis and resistance arms and is designed for mobility. An example of this lever is when the knee flexes as it is coming into the passe position. In levers, the longer the force arm, the less force is required to move the lever if the resistance and the resistance arm remain constant. Another aspect of force is torque. Torque is the turning effect of an eccentric force; when a force acts on a rigid bar it may cause a rotary motion around the fixed point. Torque is applied in the motion of a pirouette because the farther the distance of the feet, the greater the lever arm which makes the greater torque for creating the rotation.
There are many ways to do a pirouette incorrectly. Completing this action the wrong way can lead to injuries and it will not look as elegant as it should be. In the incorrect video in the presentation, the subject has a bent knee, and occasionally drops there releve and turns on a flat foot. The dancer is also off her center which means she is not balanced. The most common injuries caused by pirouettes include ankle sprains, ankle tendonitis, knee pain, back strains, and bunions. Dancers need to know how to properly execute this turn to prevent injuries. Pirouettes can be so complicated and there is so much to think about which is one of the reasons why so many dancers become injured. The supporting leg, especially the ankle, must be very strong, since it is holding the dancers entire body weight. Everything needs to be in line to keep the ankle from rolling. Knee pain is very common in dancers and is caused by the supporting knee not straightened all the way. Bunions, or bony bumps, form on the big toe when it rubs up against the next toe. Dancers wear tight shoes that are somewhat slippery on the bottom to help with turns and the two toes constantly rubbing together forms the bunions.
Pirouettes are very complex dance tricks and contain many aspects of biomechanics and kinesiology throughout them. It is important for dancers to know all of this information in order to correctly execute this move. While knowing the details, it decreases the chance of getting an injury. If a dancer practices pirouettes incorrectly for a long period of time, for example if they bend their knee in every turn, it will eventually become a chronic injury. Chronic injuries will prevent the dancer from doing their best and may cause affect their ability to dance. The biomechanics of a pirouette are the key to turning perfectly.