Rotation in Sport and Motor Control

Motor Control

Study of how movement is controlled

Expanded Info Processing Model

Angular Momentum

• defintion

• Equation

• quantity of rotational motion

Angular Momentum (L) = Moment of inertia x Angular Velocity

L = I x ω

Moment of inertia

• defintion

• 3 axis

• Which has bigger I and why

• resistance of a body to angular motion

• Measure of distribution of mass about an axis (tucking reduces)

3 axis…

1. Lateral (pole through hips)

2. Frontal (pole through belly button)

3. Longitudinal (pole through head to toe)

I = largest in frontal axis

Conservation of Angular Momentum

• equation

• Definition

Is ωs = It ωt

• If moment of inertia changes, angular velocity changes to compensate

Can Angular Momentum be generated in flight?

• Generating angular momentum around an axis of a joint whilst decreasing inertia = small angular velocity

• CANT generate angular momentum though

How is a somersault generated at takeoff?

• how?

• Equation

• Create torque by shifting COM foward within the base of support

• Generates GRF pointing backwards, then pike at hips and shift COM forward

Torque = Force x Distance

• Force from trampoline

• Distance from landing point to COM

How do long jumpers cope against forwards somersault momentum during flight?

• Circle arms and legs forward = go backwards

High Jumpers

• explain their approach

The Curved Approach

• curve tightens as they near jump to produce somersault rotation

Gymnasts

• how do they maintain rotation

Have to input energy into the bar to keep rotating round

• energy lost through friction and elasticity

• Energy input through muscle and hip flexion, then straighten

Motor Control of Gymnast bar dismount

• Timing

Margin for error in timing of releases is larger due to modified technique

• Change the radius to the COM

• Tangential release = 90° from path

Production of Twist - during takeoff

• name

• How?

• Disadvantage

Contact Twist…

• Makes use of Newtons 3rd Law - every action has equal and opposite reaction force

• Push back of floor, then move arms in to reduce I and Increase ω

HOWEVER…

• taking energy from floor (GRF), so energy in system during the whole movement = less controlled landing

Production of Twist - After takeoff

• name

• How

Ariel Twist…

• Hips rotate in one direction, causing system to maintain angular momentum by rotating in the opposite direction

• Conservation of Angular Momentum

Advantages of Hula - 3

• Don’t have to worry about twist on take off

• Good view of landing spot the entire way

• Twist is stopped when hula is stopped

Disadvantages of Hula - 1

• Limited amount of twist can be produced

2 ways to produce Tilt

• why useful

1. Asymmetrical Arms

2. Asymmetrical Hips

• Can produce tilt during somersault

• Gymnasts use to correct movements in flight

3 Equations for Production of Angular Momentum

1. Angular Momentum = Moment of Inertia x Angular Velocity

   • h = Iω

2. Torque = Force x Distance

   • T = Fd

3. Torque = rate of change in angular momentum