While technical dance, such as ballet, is the epitome of visually effortless movements, have you wondered how dancers are able to turn on a small bodily area without falling over? It turns out there is much more to a dancer’s execution of a turn than the elegant movement the audience sees.
To turn, dancers face the dichotomy of stabilizing their center of mass, the concentration of their bodily weight, above their base of support, the ball of their turning foot, while constantly moving. If misaligned, then gravity acting at their center of mass generates a moment, which is a force acting at a horizontal distance from the point of rotation. With nothing inherently countering this moment, the dancer will topple over and potentially hurt themself. Understanding the biomechanical principles throughout a dancer’s turn is therefore imperative to inform personalized training methods, improve performance, and decrease risks of injury from improper techniques.
Two studies conducted by Dr. Antonia Zaferiou, a former dancer and current biomechanics researcher, analyzed the motion of piqué turns of experienced dancers. The dancer begins standing on one leg (the “push” leg), translates to the side by stepping onto their other leg (the “turn” leg), and then rotates about their bodily axis. See the diagram below or this video for an illustration of a piqué turn.
The first study investigated the turn initiation phase and how dancers generated angular and linear impulse, which are moments and forces, respectively, throughout a period of time. Reaction forces between the dancers’ feet and the floor generated angular impulse, which peaked at the end of the phase when both feet contacted the floor. These forces simultaneously rotated the dancer clockwise, as demonstrated by the arrows in the image above. The push leg contributes linear impulse by providing force to propel the dancer in the horizontal direction of travel. Executing proper biomechanical technique in the preparation sets the rotation up for success.
The second study explored balance retention strategies while turning. They found that dancers used their limbs to apply forces and moments in opposing directions to those necessary to turn. While seemingly contradictory, the opposition worked to decrease the horizontal speed of the dancers’ center of mass so it did not overshoot their base of support while rotating. When dancers are trained to properly balance themselves, they reduce the chances rolling their ankles or falling. The figure below illustrates challenges and strategies of maintaining vertical alignment while turning.
If the goal of a turn is to remain balanced, then why don’t dancers stay perfectly rigid? To test the feasibility of this, a study in the Journal of Dance Science & Medicine modeled the dancer as a composition of rigid bodies completely balanced throughout a pirouette turn (no translational motion). It calculated that the angle from the dancers’ foot to their center of mass in the preparation phase would need to be less than 1° to maintain balance while turning – an impossible precision. Thus, methods for making necessary balance adjustments while turning must be taught to dancers.
These impulses, forces, moments, and more contribute to completing successful turns in dance! Check out this article or watch this video to learn about other factors and tips that maximize turning performance and prevent injuries.