Biomechanics and Skill Acquisition

3 Types of Forces

1. Gravitational force

2. Air/wind resistance

3. Frictional Force

4 Factors that influence motion

• Mass (kg) - amount of matter

• Velocity (m/s) - rate of object moving 

• Force (N) - push/pull, C.O.D

• Inertia - A body’s reluctance to change its state of motion

Definition of ‘Eccentric Force’

A force that doesn’t act in a line that passes through the centre of mass of an object will cause the object to rotate as well as move in a straight line.

Define ‘Force Reception’

When trying to stop momentum of a projectile

Definition of Newton’s 1st Law - Law of Inertia

A body will remain at rest or in a uniform motion unless acted upon by an external force

Definition of Newton’s 2nd law - Law of Acceleration

Force applied to an object will produce a change in motion (acceleration) in the direction of the force, that is directly proportional to the size of the force and inversely proportional to its mass.

Equation for Law of Acceleration

mass x acceleration = force

Definition for Newton’s 3rd Law - Law of Action and Reaction

For every action has an equal and opposite reaction.

What does D.E.E.P stand for

D - Definition

E - Equation

E - Explanation

P - Performance Link

Definition for Momentum

Amount of motion in an object

Equation for Momentum

mass x velocity = momentum (kg/m/sec)

Definition of Conservation of Momentum

Applies to any collision between 2 objects - the total momentum of the 2 bodies prior to impact is equal to the total momentum after impact.

Definition of Summation of Movement

Refers to correct timing and sequencing of body segments to produce maximal force

What does B.E.S.T stand for

Body Parts

sEquence

Stabilize

Timing  

B - Use as many body parts as possible
E - Move the heavier/slower body parts (legs, trunk)  first, followed by the lighter/faster parts (arm, wrist, fingers)

S - Body parts must stabilize so momentum isn’t lost

T - Move the next body party only when the previous body has reached maximum velocity.

Definition of Impulse

 Impulse measures the change in momentum of a body 

Equation for Impulse

Force x Time = Impulse

What is Linear Momentum

A body or Object moving in a straight line

What is Angular Momentum

Rotation around an axis (fixed point). This can be internal or external e.g. knee joint or door hinge

Definition for Torques

Angular motion caused by an eccentric force

Equation for Torques

Force x Moment Arm  (distance from the centre of gravity to the applied force) 

• When the moment arm is smaller → more force is needed 

Why is the Distribution of mass important?

• Location of the mass is important in reducing or increasing an object's moment of inertia 

• Object whose mass is located closer to the axis of rotation is much easier to rotate than one whose mass is located further away

High moment of inertia = Low angular velocity

Low moment of inertia = High angular velocity 

Definition of Angular Velocity

The rate of change of an object about an axis of rotation (degrees/seconds) 

Definition of Conservation of Angular Velocity

States that when no external force acts on an object, no change of angular momentum will occur

Equation for Conservation of Angular Velocity

Moment of Inertia x angular velocity (AV)

                (mass x radius^2)

              Weight      height/width

Definition of Balance

Is the ability to control equilibrium

Definition of Stability

Resistance to change equilibrium

3 factors of Stability

BOS - Base of Support 

COG - Centre of Gravity

LOG - Line of Gravity

Definition of Equilibrium

When all forces and torques are balanced

2 Types of Equilibrium

• Static (Still)

• Dynamic (moving) - moving at a constant velocity

Definition of Levers

A rigid bar used to increase force or speed

What happens when you have a longer lever

Longer the lever = faster/higher velocity

What are 3rd class levers built for

3rd class levers are built for speed

Where will force always be on a 3rd class lever

Force will always be directly below the axis

Definition for Mechanical Advantage

A measure of how much a lever amplifies force or speed

Equation of Mechanical Advantage

MA = Force arm / Resistance arm

What is Force Arm

Distance from force to axis

What is Resistance Arm

Distance from load to axis

What happens when something has a mechanical advantage less than 1

• When a lever has a mechanical advantage less than 1 its in favor of speed, anything further from 1 amplifies more speed 

Decrease resistance arm = decrease amount of force required to move

Definition of Projectile Motion

Any Airbourne Object

Factors of Projectile Motion

H - Height of Release

A - Angle of Release

V - Velocity of Release

What is Height of Release

The difference between the height that a projectile is released from and the height at which it lands or stops.

What is Angle of Release

Angle of object projected in the air, can depend of objective of sport

What is Velocity of release

The speed at which an object is thrown or kicked 

Greater speed of release = greater horizontal range 

What is a skill

Ability to do something well

What is a motor skill

A voluntary, goal directed activity that we learn through practice and experience 

What is a gross motor skill

Requires recruitment of large muscle groups, or the whole body

What is a fine motor skill

Recruitment of smaller muscle groups

What are the characteristics of Discrete movement

Distinct Beginning and End

What are the characteristics of Continuous movement

No distinct Start or finish

What are the characteristics of Serial Movement

String together several discrete skills to form a continuous performance. Includes a number of distinctly ordered elements

What are the characteristics of Open Skill Environment

• Team games 

• Consistently changing environments

• Unpredictable 

What are the characteristics of Closed Skill Environment

• Pre-learned

• without having to consider environmental changes 

• No stress of quick responsive decision-making

How to answer a Open/Closed Question

1. Stability - Stable or unstable environment 

• How much is an environment changing

2. Timing of skill - Internally or externally paced

• You decide when or players around you decide (pressure)

3. Inter-trial variability - Skill Performed the same or differently each time 

• High or low 

• Hit the shot everytime? Is it different?

What are some characteristics of learners in the Cognitive Stage

• Uncoordinated movements (not fluid)

• Frequent large errors 

• Can’t Detect their own errors

What do learners in the cognitive stage need

• A few simple instructions 

• Demonstrations are the best

• Break down skills into smaller parts

What are some characteristics of learners in the Associative Stage

• Can detect their own errors

• More gradual improvements

• Can start focussing on some tactics

What do learners in the Associative Stage need

• Regular feedback to refine skill, reduce chance of poor habits developing 

• Opportunities to practise with increased variability (random/open)

What are some characteristics of learners in the Autonomous Stage

• Requires less conscious thought 

• Attention given to tactics and opponents 

• Can use anticipation

What do learners in the Autonomous Stage need

• Practise under game like conditions 

• Focus on tactics 

• Practise opportunities with high level variability, open environment 

ERRORS (characteristics of each)

1. Are they making errors

2. Are they big or small errors 

3. How frequent are these errors

What is Whole Practice

• Learning of skills in their entirety 

• If the skill is simple then whole practice is best fit

What is Part Practice

• Learning a skill broken down into parts 

• Most effective when the skill is complex and has clearly defined components 

Definition of Massed Practice

Continuous Practice with little or no rest between repeated rehearsal of skill in the training session

Definition of Distributed practice

More frequent breaks, with opportunities for feedback from coaches and teammates. Suits cognitive learners attempting to grasp a new skill

Advantages and Disadvantages of Massed and Distributed

Massed	Distributed
Advantages	Advantages
Maximises practice time	Greater learner engagement
Suits practicing non-fatiguing, discrete skills	Assists bigger / unmotivated performer
Suits an elite, highly motivated performer	Reduction of mental and physical fatigue during practise
	Suitable when learning complex skills
Disadvantages	Disadvantages
Physically and mentalling fatiguing	More time consuming
Repetitous and monotonous (boring/dull repetition)

Blocked Practice

• Practicing the same skill continuously without changing

• Best for beginners 

• More for closed environment, enables the beginner to quickly replicate the basic foundations of the movement patterns

Random Practice

• Varied sequencing of different motor skills in the same session 

• Suitable for performers in the associative and autonomous stage 

• More of an open environment

Definition of Intrinsic feedback

information gained from inside the body

The ‘feel’ of a movement or action

1. Visual 

2. Auditory 

3. Proprioception

4. Touch 

Definition of Augmented / External feedback

Information from any external source 

Knowledge of results

• Feedback about the outcome of the performance

• Coach, teachers, Video, Spectators, Opponents 

Knowledge of Feedback

• Feedback that you receive about the performance or execution of a movement 

• During performance 

Individual Constraints

• Body Size (height, Weight)

• Fitness level

• Skill level 

• Personal motivation 

• Age, gender

• Cognitive Ability

Environmental Constraints

• Playing Surface

• Noise Level

• Weather 

• Quality of Facilities

Task Constraints

• Rules 

• Equipment 

• Field/Court/Pitch dimensions

• Number of players 

Direct Coaching

• Instructor Directed

• Directed Learning 

• Instructor-centred

• Passive Information Reception

• Good for cognitive learners

Constraints based coaching

• Learnrer Directed

• Discovery learning 

• Learner centred 

• Active problem solving

• Based on Individual, Environmental and Task constraints 

What are the 4 P’s

Peers

Parents

Positive role models

Price

QMA - POEE

Qualitative Movement Analysis Principles	Key Characteristics
Preparation	Research the Sport  Decide movement being analyzed  How will you analyze it?
Observations	Gathering information about the performance using live or recorded footage
Evaluation	Judge the quality of performance and identity areas for improvement
Error Correction	Implementing practise to change technique providing feedback