Monday, April 22, 2013

Absorbing the Shock




Jumping, my favorite aspect of dance, is one of the most exciting moves we are capable of making. For me it is the sensation of flight that I enjoy. For animals it is a means of transportation  and often a tool for athletes to score, dive, catch, flip, dodge, etc. Be it a Wide Receiver jumping to catch a football or children jumping at the sight/sound of an Ice Cream Truck, It is exciting to watch and when we are overcome with excitement jumping is a natural outlet for Expression.    

Professional Athlete, or not, it is important to understand the mechanics of Jumps to prevent injury and sustain a long health life. The danger in jumping is landing; which is actually a collision with the floor. There are many physical factors that help our bodies cope with this collision and adsorb the shock.  
Let's Compare the two Images Below: 
Image A: High Speed Head on Collision 
Image B: Fender Bender in a Parking Lot 

It is obvious there is much more damage in Image A than Image B. A big factor in car accidents is the velocity at which the impact occurs.  Mechanical Engineers do there best to design a body that will resist the impact and protect the passengers  but our best way to stay safe is abiding by the speed limits. Another variable is mass the larger vehicles had more damage than the smaller. And the final differential is direction and displacement of Impact. Image A the vehicles hit straight on moved the vehicles off the road.  Image B there was little displacement and the contact is at an angle.


Do you get the picture? we observed how theses variables relate to car crashes, but what does that have to doe with Jumping.  Below we will explore how the same variables above relate to landing of a jump on the basketball court or descending from a grand jete or simply not slipping when you jump to reach for an object off a high shelf. Below we will examine the physics of collisions and analyze the mechanics of Jumping. 
  • Mass is an amount in kilograms of an object relative to the amount of gravitational force applied. Our ability to jump well is related to our weight, or the amount of gravitational force applied to the collision with the ground in landing.   Yes, it is hard to put math in to words that is why we rely on Newton's Second Law of Gravity 
    • Force (weight) = mass * g, where g=9.8m/s^2
    • Healthy eating and exercise go together because our weight effects our Joint's ability to support our bodies during vigorous activity.  Good Nutrition (not starvation) is important to providing the energy for Jumping
    • Our joints are like the suspension system on a vehicle.  Vehicles have there towing limits just as our joints have limits for the weight they carry. 
  • Hooke's Law is a principal of Physics that explains the force need for displacement (extension or compression) of a spring proportional to some distance.  For every material, there is a constant characteristic that represents the Stiffness or elasticity.  
    • Force = kx, where x is the distance and k is the constant characteristic
    • Oppose to an object, our bodies are constantly changing; therefore, our joint's level of elasticity is constantly changing.  Our Skin is the most elastic part of our bodies and is the first line of defense when we collide with the earth.  Second is our joints, a series of springs, that cushion the descent of a jump.
    • A positive change could be managing a healthy weight; have you ever notice after regular exercise you have more spring in your step?  A negative change is from compensating muscles to cope with an injury. 
    • Improper body mechanics will deplete the joint of collagen and may cause serious injury. In physics distance is a vector quality represented by a straight line in a given directions.  Our goal as movers is to keep each joint in a straight line. I like to visualize three parallel: two from ankle to shoulder and one up the spine.  Imaging the middle line longer than the other two, and if it isn't too foreign see it moving infinitely down & up to provide a strong central axis.  
  • Are you familiar with the phrase what goes up must come down? Or maybe you know Newton's says for every action there is an equal and opposite reaction. The same force to accelerate upward must be equal to the force of resistance when colliding with the floor.
    • This concept is from Newton's Third law of motion:  F1 = - F2  
    • Bending and straightening our legs (or Plie), Forces our body upward, slowing down at a rate of 9.85 m/s^2, untile our body reaches a velocity of zero before it changes directions, accelerating downward at the same rate of 9.85 m/s^2. The rate of acceleration due to gravity and our bodies mass is constant; therefore, the force is equal and the direction varies. 
    • While suspended at the peck of the jump, there is a sensation of flight. It is an amazing feeling, yet can be destructive and a distraction.  Eager to fly, I tend to apply as much force as possible, and when finding that suspension I want to linger which results in a rough collision with the floor.  
    • To prevent a high-speed head-on crash with the dance floor, My teachers always coached me that the beginning and end of a jump should have as deep of a plie
Each of these variable and constant in physics can be related to the body's function to jump.  If you struggle with one particular aspect of jumps, the body naturally compensates.  The above description is an ideal demonstration and takes diligent effort to achieve. When practicing your long jump, slam dunk, or jete always remember the landing is a collision. Take care of your body to sustain our natural ability to absorb shock. Practice is not always accomplished by action. The best way to protect our bodies and absorb shock  is from conditioning to strengthen and stretch the muscles around the joints.

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