Chapter 21: Locomotion: When Suspended and Free of Support

Chapter 21:Locomotion:When Suspended and Free of Support KINESIOLOGY Scientific Basis of Human Motion, 10th edition Luttgens & Hamilton Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University

Objectives 1. Explain the major factors that influences the action of swinging bodies 2. Describe how to initiate pendular action, increase the height of a swing, alter the period, change grips, and dismount safely 3. Explain the major factors the influences the flight path of unsupported bodies 4. Describe how to initiate and control rotation of unsupported bodies 5. Analyze the performance of a suspension and a nonsupport movement

SUSPENSION ACTIVITIES • Climbing, hanging, swing, and other suspension activities were more commonly engaged in by our early ancestors Fig 21.1

Principles Related to Hanging and Hand Traveling Activities 1. Muscles of the arm and shoulder girdle must contract to protect the joints 2. Hand traveling is a locomotor pattern governed by the principle of action and reaction 3. The action used in hand climbing activities is essentially a chinning action 4. Sequential hand support movement should be continuous, then momentum of one action contributes to the next action

Principles Related to Swinging Movements 1. The movement of a pendulum is produced by the force of gravity 2. As the pendulum swings downward, gravity causes its speed to increase; as it swings upward, gravity counteracts its speed 3. The upward movement of a pendulum is brought about by the momentum developed in the downward movement

Principles Related to Swinging Movements 4. The potential energy of the pendulum is greatest at the height of the swing and zero at the bottom 5. The centripetal-centrifugal force in pendular movements increases as the mass or velocity increases and decreases as the radius increase

Principles Related to Swinging Movements 6. When a pendulum reaches the end of its arc, it reaches a zero point in velocity 7. The height of a swing may be increased by lengthening the radius or rotation on the downswing and decreasing it on the up swing

Principles Related to Swinging Movements 8. To increase height, the decrease in radius should be initiated at the moment that the center of gravity of the body is directly under the axis of rotation 9. The time taken by the pendulum to make a single round trip excursion (know as its period) is related to the length of the pendulum 10. The period of the pendulum is not influenced by its weight

Principles Related to Swinging Movements 11. When a body consisting of two segments reaches the vertical, with the proximal segment leading on the downswing, the distal segment will accelerate relative to the other segment and precede it into the upswing Fig 21.3

Principles Related to Swinging Movements 12. The rotation of the hands about a bar is opposed by frictional forces 13. In all mounting exercises involving swinging, the center of gravity must be brought as near as possible to the center of rotation 14. In support swings the center of gravity should be at the point of support

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht Dismount • Fig 21.4

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht DismountMechanical Essentials • Starting down swing form the handstand, push against the bar • Reactive force pushes back in opposite direction • The backward push and stretch increase the distance between center of gravity and the axis of rotation • Increases torque on the downswing

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht DismountMechanical Essentials • Time for gravity to act on the downward swinging body is also increased • Half-twist is performed at the beginning of the downswing when the forces acting on the hands are minimal and the grip change can be accomplished with ease • At the bottom of the swing gymnast flexes the hips, shortening the radius of rotation and increasing angular velocity on the upswing

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht DismountMechanical Essentials • The piked position also enable her to “wrap” around the low bar as she moves into the back hip circle • As hands leave the high bar, she pushes up and forward, causing the reactive force to add to the downward trunk rotation • Hip circle should be accomplished with the hip close to the bar

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht DismountMechanical Essentials • Near the end of the hip circle the gymnast forcefully extends by lifting the upper trunk and arms forward and upward • This action has several effects • Legs also extend so body is straight • Moment of inertia is increased • Rate of Rotation decreases

Suspension Analysis ExampleHalf-turn Flying Hip Circle with Hecht DismountMechanical Essentials • The body pushes down and back against the bar causing the bar to push the body forward and up • All of this results in the body rotating up and away form the bar for the dismount • Once the body has left the bar the back should be arched to decrease the radius and aid in rotation of the body, allowing feet to move slightly ahead of the center of gravity at the moment of landing

Anatomical Essentials • Strength of shoulders, arms, and hands are important in swinging movements • Range of motion is also needed for these movements, particularly in the shoulder during the swing and in the hip and lower back during the pike of the hip circle

NONSUPPORT ACTVITIES • The unsupported body moves through the air along a pathway determined prior to the beginning of flight • Principles governing the flight path of the body relate to those of the projectile

Principles Related to Nonsupport Activities 1. The path of motion of the body’s center of gravity is space is determine by the angle at which it is projected into space, the force of the projection and the force gravity

Principles Related to Nonsupport Activities 2. The time a body remains unsupported depends on the height of its projection, which is governed by the vertical velocity of the projection Fig 21.5

Principles Related to Nonsupport Activities 3. Most rotary movements are initiated before the performer leaves the supporting surface Fig 21.6

Principles Related to Nonsupport Activities 4. The angular momentum of an unsupported body is conserved 5. When a body is free in space, movement of a part in one direction results in movement of the rest of the body in the opposite direction Fig 21.7

Principles Related to Nonsupport Activities 6. A performer who is rotating about a horizontal axis in the air may initiate a twist about a vertical axis by tilting the body to one side Fig 21.8

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 Twist • Diver starts the dive facing the end of board • Performs a reverse spinning somersault about a transverse axis in a layout position completing a one-half revolution • At the same time, he twits one-half of a revolution about the vertical axis

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistMechanical essentials • Diver must end the forward approach by pushing backward toward the back end of the board with the feet • The rebounding board will push back, causing the legs to move forward • This action of the board causes the reverse spin to develop in the body • It also causes the entire body to move forward away from the board

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistMechanical essentials • The amount of rotation (spin) about the transverse axis must be determined at take off • The angular momentum of the dive is determined and conserved at take off and cannot be altered • The twist is this dive is accomplished through the use of two method on initiating twists

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistMechanical essentials • As the diver leaves the board, he also pushes slightly to the right to initiate a twist to the left • As diver twists to the left the left arm is brought across the chest, causing his body to move in the opposite direction (left) in reaction • Head is kept in line with the body and the right arm straight overhead decrease the moment of inertia of the rotating body and increases the speed of the twist

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistMechanical essentials • Turning the head to the left toward the water helps in the turn and the diver’s orientation • In spite of the spin about the vertical and horizontal axis, the center of gravity follows a parabolic curve controlled only be the velocity and angle of projection ant the downward acceleration of gravity

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistMechanical essentials • At entry, body is stretched with arms overhead to create the greatest moment of inertia and therefore the slowest rotation • But there still is some rotation • The diver should continue to turn underwater in the same direction • The angle of entry should be a continuation of the parabolic path of the center of gravity

Nonsupport Analysis ExampleThe Reverse Dive Layout with 1/2 TwistAnatomical essentials • Dive requires good strength, flexibility, and control • Good range of motion in the ankle joint • Strength in the extensors of the hip and knee is important in lifting the body • Strength of abdominals and back extensors is important to control vertical alignment • Flexibility of the back and hips for full flexion in tuck and pike positions

Free Fall • Body will reach terminal velocity between 100 & 200 mph • Depending on surface area presented to air flow • By manipulating body shape velocity can be partially controlled Fig 21.9

Weightlessness • The laws of motion still apply • Objects still possess inertia based on mass or momentum • Acceleration is still directly related to force and mass • Every action has an equal and opposite reaction • The only difference is NO gravity

Chapter 21: Locomotion: When Suspended and Free of Support