Muscle Mechanics and Relative Age Effect in Sports

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Questions and Answers

What does the relative age effect refer to in sports selection?

The tendency to favor athletes born earlier in the year (correct)

The impact of age-related physical growth on athlete performance

The influence of training programs on athlete selection

The preference for selecting athletes born later in the year

In a complex reaction task, how is the stimulus typically presented?

As multiple stimuli where all are relevant

As multiple stimuli where only one is relevant (correct)

As a visual-only stimulus without a response

As a single irrelevant cue

Which of the following best describes the mechanical properties of muscles?

Muscles contribute to movement through their unique mechanical properties (correct)

Muscles are solely responsible for generating speed in movement

Muscles can function independently of the nervous system

Muscles have no influence on the coordination of movement

What could be a consequence of the relative age effect during athlete selections?

Disparities in competition levels among similarly categorized athletes Signup and view all the answers

When reacting to a complex stimulus, what is the expected response?

To respond only when the designated relevant stimulus is present Signup and view all the answers

What occurs at the optimal length (Lo) of a muscle?

Greatest active force is generated due to full cross-bridge formation. Signup and view all the answers

What happens to active force when a muscle is understretched?

Few actin-myosin bindings occur. Signup and view all the answers

Which statement best describes passive force?

It is the resistance of relaxed muscle to stretch. Signup and view all the answers

What is the main factor contributing to the total force in a muscle?

Active force plus passive force. Signup and view all the answers

What condition leads to reduced muscle force due to too much overlap?

Muscle is overstretched. Signup and view all the answers

What primarily limits force production when a muscle is at its shortest length?

Too few active cross-bridge formations. Signup and view all the answers

Which term describes the length at which passive force begins to develop?

Resting length. Signup and view all the answers

In the context of muscle contraction, what is the significance of the sarcomere?

It is the basic unit that generates contractile force. Signup and view all the answers

Which enzyme is crucial for the interaction between actin and myosin in muscle contraction?

ATPase. Signup and view all the answers

What is the primary function of contractility in skeletal muscle?

To shorten and produce force Signup and view all the answers

What are the two types of elastic elements present in muscle properties?

Parallel elastic elements and serial elastic elements Signup and view all the answers

How does the nervous system regulate the mechanical properties of skeletal muscles?

By altering the timing and amount of muscle contraction Signup and view all the answers

During which type of contraction is energy stored in the elastic elements of the muscle-tendon complex?

Eccentric contraction Signup and view all the answers

What does the force-length relationship of muscle describe?

The optimal length at which muscles generate maximal force Signup and view all the answers

What is the role of tendons in muscle physiology?

To connect muscle to bone while storing and releasing force Signup and view all the answers

Which mechanical property of muscle refers to its ability to recoil after being stretched?

Elasticity Signup and view all the answers

What is the effect of external forces on the muscle-tendon complex during stretching?

They contribute to energy storage in elastic elements Signup and view all the answers

What is the central nervous system primarily responsible for?

Processing sensory information and issuing commands Signup and view all the answers

Which component is NOT part of the central nervous system?

Peripheral nerves Signup and view all the answers

What happens when muscle length is short during contraction?

Minimal active force is produced Signup and view all the answers

In which direction does information typically flow within the central nervous system?

From the brain to voluntary muscle systems Signup and view all the answers

What does the term 'resting length' refer to in muscle dynamics?

The optimal length for maximum force production Signup and view all the answers

What effect does stretching before strength and power performance have?

It may reduce performance due to stress-induced strength loss. Signup and view all the answers

How does stretching affect muscle stiffness?

It reduces stiffness, making muscles more compliant. Signup and view all the answers

What evidence exists regarding flexibility training and injury prevention?

There is little to no evidence of its effectiveness in reducing injuries. Signup and view all the answers

What is one likely result of resistance training?

Increased muscle-tendon stiffness. Signup and view all the answers

What is the purpose of plyometric training?

To maximize elastic recoil and develop neural coordination. Signup and view all the answers

What is a consequence of increased muscle stiffness in training?

Enhanced ability to store and return elastic energy. Signup and view all the answers

Which of the following best describes ballistic training?

It involves light-load weight-lifting at maximal speed. Signup and view all the answers

In the context of training, how does rapid eccentric movement affect performance?

It enhances explosive rapid contractions. Signup and view all the answers

What changes may occur in muscle-tendon structures with resistance training?

Increased tissue thickness and density. Signup and view all the answers

How does plyometric training contribute to injury prevention?

By maximizing energy return and improving coordination. Signup and view all the answers

Which ion influx is responsible for initiating depolarization in a neuron?

Sodium ions (Na+) Signup and view all the answers

Which neural structures are primarily responsible for receiving signals?

Dendrites Signup and view all the answers

What is the role of neurotransmitters in neuron communication?

Facilitate action potential through summation Signup and view all the answers

What is the purpose of the all-or-none principle in motor units?

To ensure all muscle fibers within a motor unit contract or none do Signup and view all the answers

How is spatial summation achieved in neuronal activity?

By having multiple synapses active at the same time Signup and view all the answers

What effect do inhibitory neurotransmitters have on a postsynaptic neuron?

They prevent depolarization Signup and view all the answers

What indicates that a neuron has reached the threshold for action potential generation?

A depolarization to -55 mV Signup and view all the answers

What can lead to hyperpolarization in a neuron?

Opening of potassium channels Signup and view all the answers

What defines a motor unit's innervation ratio?

The number of muscle fibers activated by one neuron Signup and view all the answers

During the action potential process, what is the role of voltage-gated K+ channels?

They help in repolarization of the neuron Signup and view all the answers

Study Notes

Motor Learning - Week 4

Physical Abilities: Highly modifiable through training (e.g., muscle strength, muscle mass, flexibility, maximal oxygen uptake)
Static Abilities: Limited potential to change (e.g., muscle fiber type, height, lung size). Largely genetic. Not to be confused with static vs. dynamic exercises.

Movement Continuity

Discrete Movements: Throwing a punch (marked in presentation).
Serial Movements: Steering a car (marked in presentation).
Continuous Movements: Playing piano composition, triple jump, running (marked in presentation).

Triple Jump

Phases: Approach run, hop, step, jump.
World Record: (Men) 18.29 m (Edwards, 1995)
Long Jump Record: 8.95m

Reaction Time

Simple Reaction Time: One stimulus, one response (e.g., sprinting after a starting pistol shot).
Complex Reaction Time (choice): Two or more stimuli, specific responses (e.g., choosing the correct response from multiple options).
Complex Reaction Time (discrimination): Two or more stimuli, one response paired with specific stimuli (e.g., pressing a button only when a red light is lit).

Relative Age Effect

Preference: Preference for selecting athletes born earlier in the year.
Example: January 15, 2024 selection for 9-year-olds. April 1, 2014 selection for 9-year-olds.

Unit 3: Peripheral Neuromuscular Mechanisms

Learning Objectives: Understand the basic mechanical properties of muscles, describe the organization of the central and peripheral nervous system, explain functions of neurons and their communication, and describe the physiology and organization of the motor units.

Muscle Properties

Skeletal Muscles: Central area of muscle tissue with tendons on both ends.
Mechanical Properties: Extensibility (stretch and recoil), contractility (shortening to produce force), and elasticity.
Simplified Model: Contractile element (CE), Parallel Elastic Elements (PE), Serial Elastic Elements (SE).
Stretch and Recoil Properties: Vary greatly, depend on shortening/lengthening velocity, and tissue thickness/health. Nervous system regulates mechanical properties (stiffness, force absorption, recoil) by timing/amount of muscle contractions.
External Forces: Body weight and stretching of muscle-tendon complex. Forces are stored in EE (tendon) and released through recoil. Muscle work is reduced.
Tasks: Running, Hopping, Walking.
Muscle Contraction:
Concentric: Muscle shortens, force generated (e.g., jumping, acceleration).
Eccentric: Muscle lengthens (stretched), force absorbed (e.g., declin running, deceleration).

Force-Length Relationship

Passive Force: Resistance of relaxed muscle to stretch (EE).
Resting Length: Length at which passive force begins to develop.
Active Force: Produced by active cross-bridges during contraction (CE). Sarcomere is basic force generating unit.
Total Force: Active + passive force.
Optimal Length (Lo): Length at which the greatest active force occurs.

Stretch-Shorten Cycle (SSC)

Concentric vs. Eccentric Contraction: Contractions occurring simultaneously.
Concentric: Length shortens, force generated.
Eccentric: Lengthens, force absorbed.
SSC Mechanism: Preload effect (build up of stored elastic energy within tissues during eccentric phase, released during concentric phase), Optimal length (muscle stretched during eccentric phase), Excitation or reflex mechanism (e.g., muscle spindle feedback).

Exercise Training and Neuromechanics

Flexibility Training (static stretching): May increase range of motion (ROM) and decrease stiffness, tolerance to stretching (how this impacts SSC?).
Strength Training: May increase muscle-tendon stiffness and tissue density/thickness (hypertrophy).
Plyometric Training: Increases muscle stiffness and maximizes elastic recoil (the energy return). Targets the SSC mechanism; forceful eccentric followed by rapid concentric phase (e.g., box jumps). Ballistic training, light-load, maximal speed of concentric phase. How would that change the force-length relationship?
Considerations: How would this training impact the force-length relationship of specific muscles?

Organization of the Nervous System

Central Nervous System: Brain and spinal cord; integration and command centre for the entire nervous system.
Peripheral Nervous System: Motor/efferent (somatic, autonomic, sympathetic, parasympathetic) pathways; skeletal muscle connections.
Direction of Information: Central nervous system to peripherals.

Neuron Structure

Soma, dendrites: Signal incoming
Axon: Signal out
Classifications: Sensory (afferent), Motor (efferent), Interneurons
- Sensory: Receptors to central nervous system
- Motor: Central nervous system to muscle contractions
- Interneurons: Connect other neurons.

Action Potentials

Bioelectric Signal: Neuron to neurons/muscles
Spread through Synapses: Neurons communicate through changes in charges across the membrane (sodium or potassium ions).
Depolarization: Membrane potential becomes less negative, Na+ channels open (in to out).
Repolarization: Membrane potential returns to resting state, K+ channels open (in to out).
Hyperpolarization: membrane potential becomes more negative.
Overshoot: Period after depolarization where the membrane potential is more positive than the resting potential.

Neuron Function

Neurotransmitters: released from presynaptic neuron to induce depolarization in postsynaptic neuron(s)
EPSP: excites postsynaptic neuron; more likely to fire an action potential
IPSP: inhibits postsynaptic neuron; less likely to fire an action potential
Summation: Multiple EPSPs may summate to a threshold level to generate an action potential; summation can be temporal or spatial
Temporal: Repeated stimuli in short time frame
Spatial: Multiple stimuli at same time
Ratio of EPSPs to IPSPs: Balance determines if a neurons fires an action potential or not.

Motor Neurons

Axons of Motor Neurons Branch Off: Axons branch, affecting multiple muscles.
Motor Unit (MU): Lower motor neuron (found in spinal cord) and all muscle fibres it innervates; Muscle Fibers are found in MU innervation.

Motor Unit (continued)

Innervation Ratio: Number of fibers controlled by one neuron; lower ratio= finer movement.
All-or-none Principle: All muscle fibers within one motor unit contracts or none contract in response to the neuron's action potential.
Fine Movement: Lower innervation ratio (e.g., hand).
Gross Movement: Higher innervation ratio (e.g., gastro-cnemius)

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Description

This quiz explores key concepts related to muscle mechanics, including the relative age effect in sports selection and the physiological properties of muscles. Test your understanding of muscle contraction, force production, and the factors influencing athletic performance. Ideal for students of sports science or physiology.