A motor unit is a motor neurone and all the muscle fibres it supplies. The fibres in one motor unit are all of the same type.

State the all-or-none law.

A motor unit contracts fully once its impulse reaches the stimulus threshold. A stimulus below the threshold produces no contraction at all.

What is gradation of contraction?

Gradation of contraction is the ability of a muscle to produce varying levels of force. The force depends on how many motor units are recruited and how often they are stimulated.

How does the number of motor units recruited affect force?

The recruitment of more motor units brings more fibres into action. The muscle then produces more force.

Define wave summation.

Wave summation happens when impulses arrive so rapidly that a fibre cannot fully relax between them. Each twitch builds on the last, producing a stronger contraction.

What is a tetanic contraction?

A tetanic contraction is a smooth, sustained contraction produced by a rapid stream of impulses. The individual twitches fuse, with no relaxation between them.

Edexcel A-Level Physical Education 9PE0

The Musculo-Skeletal System

Topic overview Muscles, bones and movements of the upper body Muscles, bones and movements of the lower body and trunk Contraction types and the stretch-shortening cycle Muscle roles and the acute response to a warm-up

Levers, Newton's Laws and Stability

Topic overview Lever systems in the body Mechanical advantage and disadvantage of levers Newton's laws of motion and force calculations Centre of mass and stability

The Respiratory System

Topic overview Structure of the airways and alveoli The mechanics of breathing Gas exchange, partial pressure and diffusion Lung volumes and capacities

The Cardiovascular System

Topic overview Heart structure and the conduction system Blood vessels, circulation and vascular shunting Heart rate, cardiac output and bradycardia Exercise responses and the effects of an unhealthy lifestyle

The Neuromuscular System

Topic overview Muscle fibre types and their characteristics Motor units, recruitment and gradation of contraction Muscle structure and the sliding filament theory Neuromuscular transmission and the response to warming up

Adaptations to Training

Topic overview Heart and lung adaptations to training Muscle and bone adaptations to training Nervous system and muscle fibre adaptations

Energy Systems

Topic overview Forms of energy and ATP The ATP-PC and glycolytic systems The aerobic system and fuel use The energy continuum and priming exercise

Fatigue and Recovery

Topic overview Fatigue from energy depletion and dehydration Lactic acid, hydrogen ions and fatigue Oxygen deficit, EPOC and the fast component The slow component and recovery windows

Diet, Nutrition and Supplements

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Fitness Testing

Topic overview Gas analysis and aerobic field tests Lactate and functional threshold testing Anaerobic capacity and power tests Strength, agility and sprint tests

Components and Principles of Training

Topic overview Aerobic, anaerobic and muscular fitness Speed, agility, balance and coordination Principles of training and FITT Measuring intensity, Karvonen and monitoring technology

Training Methods and Periodisation

Topic overview Periodisation cycles and recovery strategies Continuous, fartlek, interval, circuit and cross training Flexibility, resistance, plyometric and SAQ training Training at altitude and in heat and humidity

Injury Prevention and Rehabilitation

Topic overview Classifying injuries and acute injuries Overuse injuries: shin splints, tendonitis and stress fractures Preventing sports injuries Rehabilitation methods, POLICE and RICE

Linear and Angular Motion

Topic overview Distance, displacement, speed and acceleration Distance–time, speed–time and velocity–time graphs Angular motion and moment of inertia Conservation of angular momentum

Projectile Motion and Fluid Mechanics

Topic overview Forces acting on a projectile in flight Release velocity, height and angle Drag, streamlining and technology Lift, the Bernoulli effect and spin

Coaching and Skill Classification

Topic overview Mosston's coaching styles Tactics and strategies in competition Analysing a skill in phases Classifying skills on continuums Transfer of skills

Learning Theories

Topic overview Classical and operant conditioning Reinforcement, punishment and the S-R bond Thorndike's laws of learning Fitts and Posner's stages of learning

Practice and Guidance

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Feedback and Motor Control

Topic overview Purposes and effectiveness of feedback Types of feedback Feedback technology and performance analysis Open and closed loop control

Information Processing and Memory

Topic overview Welford and Whiting's information processing models The sensory store and short-term memory Long-term memory and the multi-store model Reaction time, Hick's law and the psychological refractory period Schmidt's schema theory

Personality and Attitudes

Topic overview Sport psychology and the nature–nurture debate Trait theory: Eysenck and Cattell Interactionist theory and personality structure Attitudes, Wood's triadic model and cognitive dissonance

Arousal and Anxiety

Topic overview Arousal and the optimal level for performance Drive, inverted-U and catastrophe theories Anxiety, stress and stressors Cognitive and somatic stress management strategies

Aggression

Topic overview Aggression and assertion in sport Types of aggression Theories of aggression: Lorenz, Bandura, Dollard and Berkowitz Causes of aggression and strategies to reduce it

Motivation

Topic overview Types of motivation Internal, external, tangible and intangible rewards Achievement motivation: NACH and NAF Developing a need to achieve

Social Facilitation

Topic overview Social facilitation, social inhibition and types of others Zajonc's dominant response and evaluation apprehension Home advantage, distraction, proximity and coping with an audience

Group Dynamics and Cohesion

Topic overview Groups, teams, and task and social cohesion Carron's four factors of cohesion Steiner's model and the Ringelmann effect Social loafing and building team cohesion

Goal Setting

Topic overview SMARTER targets Outcome, performance and process goals Goal timescales and the benefits of goal setting

Attribution Theory

Topic overview Weiner's attributions for success and failure The three dimensions of attribution Attribution retraining

Confidence and Self-Efficacy

Topic overview Self-confidence and its effect on performance Vealey's model of sport confidence Bandura's four sources of self-efficacy Learned helplessness

Leadership

Topic overview Qualities and impact of an effective leader Autocratic, democratic and laissez-faire styles Fiedler's and Chelladurai's leadership models Trait, social learning and interactionist theories of leadership

The Emergence of Modern Sport

Topic overview Popular recreation in pre-industrial Britain The Industrial Revolution and recreation Rational recreation, Arnold and athleticism Factory teams, the sporting press and the first governing bodies

Equality, Diversity and Migration in Sport

Topic overview Corporate and geographically based teams Disability sport and opportunities for women Migration of sporting labour

The Globalisation of Sport

Topic overview What globalisation means for sport Colonial diffusion of sport across the British Empire National and international governing bodies Bidding for and staging world events

The Commercialisation of Sport

Topic overview Commercialisation and sport as a commodity Broken time, spectatorism and the media The Olympic Games and the 1984 commercial blueprint Franchises, Americanisation and global stars

Ethics and Deviance in Sport

Topic overview Ethics, sportsmanship and gamesmanship Performance-enhancing drugs from early use to today Simulation, bribery, bungs and match fixing Responses to deviance and the role of WADA

Sport and the Media

Topic overview The two-way relationship between sport and the media Live and social media coverage Viewing technology, sports packages and pay-per-view

Talent Identification and Elite Development

Topic overview Talent identification programmes in the UK The pathway from novice to elite performer East German and Australian influences on UK sport

Participation and the Health of the Nation

Topic overview Barriers to participation and the benefits of mass participation Mass participation initiatives in the UK Participation trends in the 21st century

The Neuromuscular System

Motor units, recruitment and gradation of contraction

3 things to know
Component 1

Overview

Motor units and the all-or-none law, gradation of contraction, wave summation and tetanic contraction, the order of recruitment in a marathon and a vertical jump, the darts player and the scrum, and training recruitment patterns.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

In what order are motor units recruited, and how are they used in a marathon?

Key term

Why does recruitment change late in a marathon, and why do darts and scrummaging use different motor units?

Key term

Define a motor unit.

Questions from this subtopic

Each one with the model answer underneath.

1
Define a motor unit.
Model answer
A motor unit is a motor neurone and all the muscle fibres it supplies. The fibres in one motor unit are all of the same type.
2
State the all-or-none law.
Model answer
A motor unit contracts fully once its impulse reaches the stimulus threshold. A stimulus below the threshold produces no contraction at all.
3
What is gradation of contraction?
Model answer
Gradation of contraction is the ability of a muscle to produce varying levels of force. The force depends on how many motor units are recruited and how often they are stimulated.
4
How does the number of motor units recruited affect force?
Model answer
The recruitment of more motor units brings more fibres into action. The muscle then produces more force.
5
Define wave summation.
Model answer
Wave summation happens when impulses arrive so rapidly that a fibre cannot fully relax between them. Each twitch builds on the last, producing a stronger contraction.
6
What is a tetanic contraction?
Model answer
A tetanic contraction is a smooth, sustained contraction produced by a rapid stream of impulses. The individual twitches fuse, with no relaxation between them.

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The Musculo-Skeletal System

Levers, Newton's Laws and Stability

The Respiratory System

The Cardiovascular System

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AThe training zone is 136 to 158 bpm.

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