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MOVT ANALYSIS > Dynamics of Sporting Movements > Flashcards

Dynamics of Sporting Movements Flashcards

1
Q

Pitching: Phases of motion

A
  • Wind-up
  • early-cocking
  • late-cocking
  • acceleration
  • follow-through
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2
Q

Conservation of Momentum: Linear Motion
∑ρ = 0

A

∑ρ = 0
- Linear Momentum (ρ) = Mass (m) x Velocity (v)
- Vector quantity
- Law of Conservation of Momentum
○ Σρ = 0
- The momentum before an impact is the same than that after a collision or event

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3
Q

Conservation of Momentum: Linear Motion
∑ρ = 0

A

∑ρ = 0
- Linear Momentum (ρ) = Mass (m) x Velocity (v)
- Vector quantity
- Law of Conservation of Momentum
○ Σρ = 0
- The momentum before an impact is the same than that after a collision or event

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4
Q

Conservation of Angular Momentum

A
  • Angular Momentum depends on
    ○ Angular velocity
    ○ Mass of object
    ○ Moment of Inertia
    § Location of centre of mass with respect to the axis of rotation
    • Angular Momentum = Moment of Inertia x Angular Velocity
    • Conservation of Angular Momentum
    • E.g. discus = large angular momentum generated with lower body/large segments
    • Feet apply torque using GRF to twist hips at high velocity to develop a large angular momentum –> that will slow down but angular momentum has to be conserved –> so passed on to thorax, then to the arms = each of these have lower MOI = what happens is the MOI of those segments is lower, the angular velocity must be higher

Total Momentum of the System Remains Constant
* ρ = Σmv = MOMENTUM
* H = ΣIω = ANGULAR MOMENTUM

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5
Q

FORCE: Stretch Shortening Cycle

A
  • If you pre-stretch a muscle, generally pre-stretching during eccentric phase = what happens
    • Muscle force / power output is higher = during the following or subsequent muscle contraction
  • Using the eccentric phase wisely

DEFINITION: SSC - active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle

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6
Q

Stretch-shortening Cycle: Muscle Pre-stretching

A
  • During eccentric phase = muscles becoming more taut = are pre contracted to slow you down = so they start off at the end of the eccentric stretch = start off at a high level of force = so therefore it’s much more efficient when you act in the concentric phase = starting from a much higher force, higher force applied through the displacement of the joints = work is higher so going to jump higher = produce higher energy
  • Can’t go down + stay for 10 mins = have to make it quick otherwise its not an eccentric pre-stretch = effect is attenuated w/ time
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6
Q

Hip-shoulder Loading (Pre-stretching): shoulder-hip angle

A
  • Muscles start to stretch as rotate shoulders –> as you move towards end of ROM, muscle has to pre-activate to slow you down
  • Generally during the pre-stretching phase + therefore get a higher force in the subsequent concentric muscle phase
  • X factor = shoulder + hip alignment = if have a greater separation b/w these two = greater activation of the pre-stretching cycle
  • Pre-stretched the trunk rotators = + therefore the shoulders + thorax are going to rotate much more quickly
  • Hips slow down as the shoulders accelerate = action-reaction
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7
Q

Hip-shoulder Loading (Pre-stretching) = COMPONENTS

A
  • Segmental Lag
  • Activation of SSC
  • Torque (Muscle Force Generation)
    • What happens next?
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8
Q

Hip-shoulder Loading (Pre-stretching) - DESCRIBE WHAT HAPPENS + WHY

A
  • Hip-shoulder separation almost maximum
  • Trunk rotation musculature pre-stretched
  • Describe what happens next:
    ○ 1. Shoulder segment angular velocity increases, reducing hip-shoulder separation angle
    ○ 2. Throwing shoulder anterior muscles pre-stretched
  • Why do the above occur?
    ○ 1. Concentric contraction of trunk rotators causes shoulder segment to angularly accelerate
    ○ 2. Inertial lag of throwing arm, pre-stretching anterior shoulder muscles (eccentric + isometric contraction
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9
Q

The Answer: Shoulder Acceleration (Shoulder-Arm Loading)

A
  • What happens next? i.e. after hip-shoulder loading
    ○ = Shoulder-Arm Loading Phase
    § Concentric contraction of trunk rotators
    § Shoulder (trunk) rotation angular acceleration
    ○ Pre-load shoulder anterior musculature (Eccentric + Isometric)
    ○ Followed by: Arm-acceleration phase
    § Concentric contraction of anterior shoulder musculature
    § Shoulder adduction acceleration causing discus to accelerate
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10
Q

What is the Generic Phase of Motion?
End of Hip-shoulder Loading Phase/Start of Shoulder Arm Loading

A
  • How was this phase achieved?
    ○ 1. Proximal to distal sequencing = the larger segments are going first = the more proximal ones i.e. the hips then the shoulders then the arms
    ○ 2. Hip angular velocity reaches maximum velocity before shoulder segment angular velocity
  • What happens next?
    ○ 1. Throwing shoulder adducts (very slightly), humeral external rotation, wrist extension
    ○ 2. Shoulder-arm loading, pre-stretching shoulder anterior musculature
  • Why?
    ○ 1. Accelerating shoulder segment causes inertial lag of throwing arm
    ○ 2. Shoulder anterior musculature eccentrically controls inertial lag
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11
Q

Pre-stretch and injury

A
  • Pre-stretch is going to improve perf + also reduce injury as protects the shoulder joint = some research showing if this phase is activated correctly it decompresses the gleno-humeral joint = maintaining the integrity of the shoulder during throwing, reducing distraction forces
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12
Q

Shoulder-arm Loading (or Arm-cocking in Baseball Pitch)

A
  • Phase includes increase in humerothoracic external rotation angle
    ○ Arm-cocking phase completed at maximum humeral external rotation
  • Invoke stretch-shortening cycle: eccentric prior to concentric contraction
    ○ Pre-loading of shoulder-arm musculature = arm abducted + externally rotated –> then get arm acceleration = humeral internal rotation + shoulder adduction
  • Maximum loading of shoulder-arm musculature in throwing occurs at maximum humero-thoracic external rotation
  • Pre-stretching the anterior shoulder musculature + shoulder internal rotators
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13
Q

Shoulder-arm Pre-stretching
= most important things

A

Most important thing:
* Is the humeral internal /external rotation
* Arm cocking phase
* And shoulder abduction
* There is scapulothoracic motion

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14
Q

End of Shoulder-Arm Loading/Start of Arm-Acceleration Phase DESCRIBE + WHY

A
  • Describe what happens?
    ○ 1. Shoulder anterior musculature, elbow extensors, wrist flexors concentrically contract
    ○ 2. Shoulder adduction, humeral internal rotation, elbow extension, wrist flexion causes ball to accelerate
  • Causal mechanisms (why?)
    ○ 1. Pre-stretched musculature concentrically contracts powerfully
    ○ 2. Arm-segment motion coordinated to achieve high ball release velocity
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15
Q

Athletics Movement Sequence: Baseball Pitching

A
  • Pelvis starting to increase = get shoulder-hip separation starting
  • After the separation going to get shoulder acceleration
  • When the shoulders accelerate = going to get arm lagging = shoulder-arm loading phase
  • Maximal external humeral rotation = end of phase
  • Shoulder abductors pre-stretched + all the ones mentioned before
  • KINETIC LINK PRINCIPLE = MOMENTUM TRANSFERRED
  • Leg lags behind to counter-balance
16
Q

Hip-shoulder Loading = TENNIS

A
  • Pre-stretching the anterior shoulder musculature – tennis forehand
  • Pre-stretching the posterior shoulder musculature – tennis backhand
17
Q

Kinetic Link Principle: Why doesn’t the distal segment accelerate first in most powerful movement sequences?

A

Downswing Phase (includes Pre-Stretching + Acceleration Phases)
* Biomechanics principle mostly applied to motions that generate high end-effector speeds, such as fast bowling, goal kicking, etc.
* Kinetic Link principle generally advocates PROXIMAL TO DISTAL SEQUENCING to
○ Optimise PRE-STRETCHING PHASES:
§ Increase Hip-shoulder Pre-stretching
§ Increase Shoulder-arm pre-stretching through dynamic inertial loading
○ Powerful ACCELERATION PHASE
§ Muscle force-velocity r/s
§ Conservation of Momentum
§ Summation of segmental velocities = the velocities of the preceding segment are added to the next segment

18
Q

Stretch Shortening Cycle: In throwing, wouldn’t it be a good option to accelerate the hands first?

A

Force-Velocity Relationship Under External Load
* Inertial Lag operates strongly in lengthening region of Muscle Tension- Length Curve
* Muscle concentric contraction is stronger + more powerful preceding period of eccentric contraction through activation of stretch shortening cycle
○ Stretch reflex
○ Elastic energy storage (elastic recoil)
○ Force-velocity curve
○ Impulse-momentum relationship (longer time)
○ Increased metabolic activation
* Increased ROM w/ higher Force
* Why is the pre-stretch effect so effective = because get higher force at an increased operating ROM

* Muscles are smaller at the hand = can't do the job anyway 
* But also would be working at high velocities + according to graph = low force 
* Would also put tremendous strain on the joint
19
Q

Segment Inertial Lag

A
  • Distal segments lag corresponding proximal segments
  • The larger more “proximal” segments of the whip travel first
  • The weightless tip lags behind
  • Whip-like mechanics
20
Q

Hip-shoulder Loading - pre-stretching: Hips rotate before shoulders

A

Proximal to distal sequencing
* Hips rotate before shoulders, + humerus + forearm before hand
* Hip-shoulder separation angle increases

21
Q

Shoulder-arm Loading (Arm-cocking): Segment Inertial Lag

A

Extreme pre-stretching humeral internal rotators
* Shoulder segment accelerates (angular acceleration)
* Hip-shoulder separation angle decreases
* Inertial lag of throwing arm
* Maximum humero-thoracic external rotation
* Arm-cocking phase completed at maximum humeral external rotation

22
Q

Segmental Sequencing: Order of Movement

A

General proximal to distal sequence
* Move segments in proximal to distal sequence to achieve the following:
○ Pre-stretch musculature for maximum concentric contraction
○ Transfer Angular Momentum
○ Summate segmental velocities

  • Theoretically from this concept of summating segmental velocities = we want each segment to start to be activated at the max velocity of the preceding segment
  • Because then the adjacent segment = is added from its immediate proximal segment
  • Too early = less velocity actually summed + also less pre-stretch effect as well = same thing as too late
23
Q

Segmental Sequencing CONT

A

Proximal to Distal Sequencing
* Relatively large muscles actuate proximal segments, generating high angular momentum
○ High moment of inertia
○ Low angular momentum
* Angular momentum is sequentially passed on the kinetic link chain in proximal to distal order
* Each smaller distal segment has smaller moment of inertia, and therefore rotates w/ higher angular velocity to maintain angular momentum
* Muscles connected to distal segments are relatively small, unable to generate high velocities required in athletics
* Muscle force-velocity curve constrains the muscle force, its magnitude diminishing w/ segment velocity (or corresponding joint angular velocity)

24
Q

Muscle Sequencing: Ideal Only

A

Idealistic Action
* Muscles attached to distal segments cannot apply large torques, because of a) smaller size + strength of these muscles + b) force velocity r/s of muscular contraction
* After muscular contraction achieves maximum angular velocity in proximal segments, these muscles relax.
* Sequentially, muscles attached to more distal segments should initiate contraction at the point of maximum angular velocity + zero angular acceleration of the preceding segment

  • Clearly if everything is starting at its maximum velocity of the preceding segment = when you expect the muscles to activate
    = ideally speaking
  • Want them to activate at zero angular acceleration of the preceding segment
25
Q

Summary: Kinetic Link Principle

A

General proximal to distal sequence
* Move segments in proximal to distal sequence to achieve the following Generic Phases of Motion:
○ Loading Phase 1: Backswing Loading: Hip-shoulder Loading (Hip-shoulder pre-stretching)
§ Hip-shoulder separation angle increases
§ Hips (or pelvis) leads the shoulders because of proximal-to-distal sequencing
○ Loading Phase 2: Inertial Loading: Shoulder-arm Loading (Shoulder acceleration)
○ Note: Loading Phase 2: Called Arm-cocking in throwing events where HIR is on maximum pre-stretch (e.g. over-arm throwing, javelin, tennis serve, etc). Call Leg-cocking for kicking.
§ Shoulder segment accelerates
§ Hip-shoulder separation angle reduces
§ Shoulder-arm pre-stretching (i.e. inertial segmental lag: eccentric + isometric contraction)
○ Arm-Acceleration Phase (Distal segment acceleration)
§ Pre-stretch musculature for maximum concentric contraction of musculature connected to segment that makes large velocity contribution during acceleration phase
§ Optimise transfer of angular momentum
§ Summate segmental velocities
○ Objective: High end-effector velocity! This cannot be obtained directly.

26
Q

KINETIC CHAIN sequence

A
  • The kinetic chain sequence is as follows: stride, pelvis rotation, trunk rotation, shoulder rotation, elbow extension, and wrist flexion (Fleisig, Barrentine, Escamilla, & Andrews; 1996)
27
Q

Phase of Motion: Instep Kicking

A
  • A-B: Backswing or Hip-Loading Phase
  • B-D: Leg-cocking or Knee-Loading Phase
  • D-E: Leg-acceleration Phase
  • Why does the knee flex during this phase (B-D) = one thing inertia, the knee extensors are pre-stretched but also when this is eccentrically flexing in D, the ankle joint is closer to the hip so the hip flexion angular velocity increases = everything works together
  • Thigh ang vel at impact relatively stationary

Leg-cocking Phase
(i) Pre-stretching the Knee Extensors (ii) Reducing Moment of Inertia

28
Q

Segment Velocity Contribution

A

The amount a segment motion contributes to end-effector velocity

29
Q

Internal Rotation Velocity Contribution

A
  • Longer the radius of rotation (d) the greater the velocity contribution
  • Need bending of the elbow

MOVT ANALYSIS (8 decks)

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