1. Somersaulting – Angular Kinetics
Angular kinetics is concerned with the generation of rotations and the control of these rotations.
All objects posses inertia and do not wish to begin rotating.
If an external moment of force is applied to the object, it will experience an angular acceleration.
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2. Off-center External Forces
Any external force that acts away from the body’s center of mass will create a moment of force acting on the total body
Usually, the off-center force is a reaction force from the ground or equipment, resulting from the internal muscle forces generated by the athlete
If an athlete has forward momentum and a pivot point is created, then some or all of the linear motion can be transferred into angular motion
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3. Transfer of Momentum Within the Body
Sometimes athletes accelerate specific body parts while in contact with the ground.
Upon leaving the ground, athletes lock these segments to the rest of their bodies.
The joint angles these segments make with the trunk become fixed.
The momentum created by these segments becomes part of the momentum of the total body.
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4. Rotations While Airborne
Rotations cannot be generated when airborne.
Once the body is airborne, only gravity acts on the body.
The angular momentum (the amount of angular motion) is conserved.
Changes in body shape will decrease/increase the moment of inertia about the somersaulting axis.
If the moment of inertia increases, the athlete will have more reluctance to rotating and will have slower angular velocity.
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5. The inverse relationship between moment of inertia (I) and angular velocity (ω)
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6. Qualitative Analysis of Human Motion
The study of human motion, in the absence of measuring, by observing a movement and applying biomechanical principles in assessing performance.
It is subjective and yet systematic evaluation of a movement or skill.
It is based on a direct visual observation of a movement or its video recording.
It is dependent on the constraints or limitations of an event or performer.
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7. Integrative model of qualitative analysis
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8. Skill Objectives An objective can be described for all skills
Secondary objectives refer to the speed of the movement or the accuracy required
Skills with similar overall objectives are governed by similar biomechanical principles
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9. Analyzing a Skill
Divide the skill into phases (preparation, execution, follow-through)
Determine the biomechanical criteria for each phase (in the execution phase, shot putters must maximize the velocity of the shot prior to the takeoff)
Identify the key body movements involved in each phase (in the preparatory phase of the soccer kick, the foot of the stance leg is placed beside the ball)
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10. Observation of Performance
Before going to practice, identify the skill you wish to observe and why.
Be specific regarding the phase, body movements, and related biomechanical criteria.
It is important to keep the surroundings as uncluttered as possible and to minimize distractions.
Estimate how many times you have to view the skill.
Use all your senses to observe a performance.
Ask the athlete questions to confirm your observations.
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11. Good coaching includes asking Athletes if given instructions were
understood correctly, particularly
Under distracting environmental conditions, i.e., noise, distance, low visibility, etc.
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12. Error detection
Visual observation (use direct observation, video, or observe traces left by the athlete)
Observe the outcome or follow-through
Use a checklist
Ask athletes how they felt during the performance
Avoid comparison with an ideal form or mental model
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13. Error Correction
Usually done verbally, with visual feedback, or using mental imagery
Begin with the earliest occurring error
Correct only one or two faults before re-observing the skill
Accept that error correction is an ongoing, multi-step process
Use positive and specific language appropriate to the age, developmental level, and competitive level of the athlete
Ask for feedback
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14. In sports where there is a considerable distance between the coach and the athlete, a walkie talkie or other long-range communication device comes in very handy.
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15. In this chapter you have learned:
How to generate Free Body Diagrams of the body using the particle and stick figure models
Those factors affecting the height and range of a projectile
How the forces of air resistance, drag, and lift affect projectile paths
The role of impulse and impact on many sporting activities
The body actions affecting throw-like and push-like skills
How angular motion is generated when somersaulting
How angular motion is manipulated while airborne
A technique for performing a biomechanical qualitative analysis of a skill
Some tips on performing error detection and correction
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16. Discussion Questions:
Define Biomechanics. Briefly discuss each of the components in the model of Biomechanics presented.
Discuss three ways in which Biomechanics would be helpful to a coach.
Apply each of Newton’s three laws of motion to a skill from your sport. Be specific in identifying forces, masses, accelerations, etc.
Briefly discuss how you would advise an athlete in maximizing impulse and minimizing the harmful effects of impact.
List advantages and disadvantages of the particle and stick figure models.
What factors affect the horizontal distance of a projectile? Which factor is most important?
Differentiate between throw-like and push-like patterns of motion. Give examples of each.
Select a sport skill in which a light object is thrown. Discuss the effects of air resistance on the path of the object.
Identify three ways athletes can decrease drag forces acting on their bodies.
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17. Discussion Questions:
Identify two sport skills in which lift forces have a large effect on the resulting motion.
Differentiate between equilibrium, stability, and balance.
For a skill from your sport, identify how one maintains or loses balance.
Draw a free body diagram of a diver during the takeoff phase with the board. Identify all possible ways the diver may increase the amount of rotation.
Discuss the relationship between moment of inertia and angular velocity.
Analyze a skill from your sport biomechanically.
Prepare an observation plan to observe the above skill from your sport.
Draw a series of free body diagrams to represent the human body during each phase of the above skill.
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