Dynamics of Sporting Movements Flashcards
Pitching: Phases of motion
- Wind-up
- early-cocking
- late-cocking
- acceleration
- follow-through
Conservation of Momentum: Linear Motion
∑ρ = 0
∑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
Conservation of Momentum: Linear Motion
∑ρ = 0
∑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
Conservation of Angular Momentum
- 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
FORCE: Stretch Shortening Cycle
- 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
Stretch-shortening Cycle: Muscle Pre-stretching
- 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
Hip-shoulder Loading (Pre-stretching): shoulder-hip angle
- 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
Hip-shoulder Loading (Pre-stretching) = COMPONENTS
- Segmental Lag
- Activation of SSC
- Torque (Muscle Force Generation)
- What happens next?
Hip-shoulder Loading (Pre-stretching) - DESCRIBE WHAT HAPPENS + WHY
- 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
The Answer: Shoulder Acceleration (Shoulder-Arm Loading)
- 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
What is the Generic Phase of Motion?
End of Hip-shoulder Loading Phase/Start of Shoulder Arm Loading
- 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
Pre-stretch and injury
- 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
Shoulder-arm Loading (or Arm-cocking in Baseball Pitch)
- 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
Shoulder-arm Pre-stretching
= most important things
Most important thing:
* Is the humeral internal /external rotation
* Arm cocking phase
* And shoulder abduction
* There is scapulothoracic motion
End of Shoulder-Arm Loading/Start of Arm-Acceleration Phase DESCRIBE + WHY
- 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
Athletics Movement Sequence: Baseball Pitching
- 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
Hip-shoulder Loading = TENNIS
- Pre-stretching the anterior shoulder musculature – tennis forehand
- Pre-stretching the posterior shoulder musculature – tennis backhand
Kinetic Link Principle: Why doesn’t the distal segment accelerate first in most powerful movement sequences?
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
Stretch Shortening Cycle: In throwing, wouldn’t it be a good option to accelerate the hands first?
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
Segment Inertial Lag
- Distal segments lag corresponding proximal segments
- The larger more “proximal” segments of the whip travel first
- The weightless tip lags behind
- Whip-like mechanics
Hip-shoulder Loading - pre-stretching: Hips rotate before shoulders
Proximal to distal sequencing
* Hips rotate before shoulders, + humerus + forearm before hand
* Hip-shoulder separation angle increases
Shoulder-arm Loading (Arm-cocking): Segment Inertial Lag
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
Segmental Sequencing: Order of Movement
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
Segmental Sequencing CONT
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)
Muscle Sequencing: Ideal Only
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
Summary: Kinetic Link Principle
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.
KINETIC CHAIN sequence
- The kinetic chain sequence is as follows: stride, pelvis rotation, trunk rotation, shoulder rotation, elbow extension, and wrist flexion (Fleisig, Barrentine, Escamilla, & Andrews; 1996)
Phase of Motion: Instep Kicking
- 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
Segment Velocity Contribution
The amount a segment motion contributes to end-effector velocity
Internal Rotation Velocity Contribution
- Longer the radius of rotation (d) the greater the velocity contribution
- Need bending of the elbow
