Why do some dancers perform such a perfect and effortless looking Feather step like Luca and Lorraine in this video? Why is the Latin- American style more suitable for some people than Ballroom or vice versa? What makes for a good hip action? What creates a better swing in Waltz? How about a powerful and quick movement?
Although the answers to these questions may be rooted in physiological, psychological, or other areas, the problems identified are biomechanical. This article will provide a foundation for identifying, analyzing, and solving problems related to the biomechanics of the dancer’s movement.
What is Biomechanics?
The term biomechanics combines the prefix bio, meaning "life," with the field of mechanics, which is the study of forces' actions. The international community of scientists adopted the term biomechanics during the early 1970s to describe the science involving studying the mechanical aspects of living organisms. Within kinesiology and exercise science, the living organism most commonly of interest is the human body. The forces analyzed include both the internal forces produced by muscles and the external forces that act on the body.
Biomechanists use the tools of mechanics, the branch of physics involving analysis of forces' actions, to study the anatomical and functional aspects of living organisms. For example, how does a bird fly or a dancer leaps across the floor?
There are two main branches of Biomechanics- kinematics that deals with the geometry of the motion of objects, including displacement, velocity, and acceleration, without taking into account the forces that produce the motion while kinetics is the study of the relationships between the force system acting on a body and the changes it produces in body motion. In terms of this, there are skeletal, muscular, and neurological considerations we also need to consider when describing biomechanics.
How Does it Impact Dance?
Essentially Biomechanics is the science of movement techniques and, as such, tends to be most utilized in sports where technique is a dominant factor rather than the physical structure or physiological capacities.
Biomechanics incorporates a detailed analysis of dance movements to minimize the risk of injury and improve sports performance. The following are some of the areas where biomechanics is applied, to either support the performance of athletes or solve issues in sport or exercise:
- The identification of optimal technique for enhancing dance performance in terms of linear and angular movement
- The analysis of body loading to determine the safest method for performing a particular dance movement
- The assessment of muscular recruitment and joint loading
- The analysis of dance and exercise equipment e.g., shoes, surfaces and costumes.
Isaac Newton’s Laws of Motion
Newton’s motion laws are vital for understanding how our bodies move through space and what influences that movement. There are four laws, and the main concepts that are core to those laws are mass and force. The laws describe in a nutshell how an object that has mass or weight can move around in space as a result of the forces applied to it.
In our case- a dancer has a mass/ weight, and we move. The only way we can move in dance is through internal or external forces. Internal being our muscles, and external being gravity, the floor, or our partner.
1st Law- Inertia
Isaac Newton's First Law of inertia explains that for the dancer to move we need some force to act on the dancer's body for it to move.
It also states that objects tend to resist changes in their state of motion. An object in motion will tend to stay in motion, and an object at rest will tend to stay at rest unless acted upon by a force.
Example - The body of a dancer who dances scattered chasses around the floor will tend to want to retain that motion unless muscular forces can overcome this inertia and either transition to another step, change direction or stop. Similarly, a skater gliding on ice will continue gliding with the same speed and in the same direction, barring an external force's action.
2nd Law- Acceleration
Newton's Second Law precisely explains how much motion a force creates. The acceleration (the tendency of an object to change speed or direction) an object experiences is proportional to the force's size and inversely proportional to the object's mass.
Force= Mass x Acceleration (F = ma)
Example - When a ball is thrown, kicked, or struck, it tends to travel in the direction of the applied force's line of action. Similarly, the greater the amount of force applied, the greater the speed the ball has.
Suppose a dancer improves leg strength through training while maintaining the same body mass. In that case, they will have an increased ability to accelerate the body using the legs, resulting in better agility and speed. This also relates to the ability to rotate segments, as mentioned above.
3rd Law- Action and Reaction
The Third Law tells us that for every action (force), there is an equal and opposite reaction force. This means that forces do not act alone, but occur in equal and opposite pairs between interacting bodies.
Example - The force created by the legs “pushing” against the ground results in ground reaction forces in which the ground “pushes back” and allows the dancer to move across the floor (As the Earth is much more massive than the dancer, the dancer accelerates and moves rapidly, while the Earth does not accelerate or move at all).
This action-reaction also occurs when we try to stand on our toes. By pushing through the calf muscles to the floor, the ground reacts on our bodies with equal and opposite force causing us to get up on the toes much like a balerina on point.
Friction is another important force for dancers. The friction between a dancer's feet and the floor is an example of a horizontal ground reaction force. For a dancer to move forward, the dancer pushes backward into the floor.
Providing that there is enough friction between the dancer's foot and the floor, the horizontal ground reaction force of friction then pushes the dancer's mass forward. This can be a little confusing that a dancer needs to push back to move forward, but it is no different to a jump where the dancers push down into the ground, and the ground reaction force pushes the dancer into the air.
Similarly, when we need to stop moving or change direction, the friction from the floor is needed. The dancer pushes forward to stop moving forward, and the reaction force from the friction pushes backward, stopping the dancer.
Dancers use different methods to change the friction from the floor, such as shoes or oil.
Newton's law of gravitation states that any particle of matter in the universe attracts any other with a force varying directly as the product of the masses and inversely as the square of the distance between them.
A dancer standing on the floor has the ground reaction force from the earth, which is produced by gravity from the earth, puling the dancer into the floor. This is a derivative of the 3rd Law of Action and Reaction.
Center of Gravity
The Center of Gravity (COG) is an imaginary point around which the dancers' body weight is evenly distributed. The center of gravity of the human body can change considerably because the segments of the body can move their masses with joint rotations. This concept is critical to understanding balance and stability and how gravity affects sport techniques.
The direction of the force of gravity through the body is downward towards the center of the earth and through the COG. This line of gravity is important to understand and visualize when determining a person's ability to successfully maintain balance. When the line of gravity falls outside the Base of Support (BOS), a reaction is needed to stay balanced.
In the next part, we will observe how those laws directly correlate to the dancers' body movement in space and get familiar with concepts such as displacement and velocity.