copyright © 2012 american college of sports medicine chapter 3 neural adaptations to training

Copyright © 2012 American College of Sports Medicine

Chapter 3Neural Adaptations to Training

Chapter 3Neural Adaptations to Training


Functions of the Nervous SystemFunctions of the Nervous System

• Receives sensory information

– Pain

– Pressure

– Hot/cold temperatures

– Joint position

– Muscle length

• Integrates information in appropriate places

• Controls output or response from tissues, glands, organs

• Controls emotions, personality, & other cerebral functions


Functional Organization of the Nervous SystemFunctional Organization of the Nervous System

I. Central nervous systemA. Brain

B. Spinal cord

II. Peripheral nervous system (31 pairs of spinal nerves)A. Sensory division

B. Motor division

1. Somatic nervous system

2. Autonomic nervous system

a. Sympathetic nervous system

b. Parasympathetic nervous system


Divisions of the Nervous SystemDivisions of the Nervous System


Nerve CellsNerve Cells

• Supporting Cells

– Play stability roles throughout CNS

• Neurons

– Actual nerve cells

– Communicate with other tissues & nerves

– Sensory neurons: unipolar

– Motor neurons: multipolar


Nerve Cells (cont’d)Nerve Cells (cont’d)

• Key Features of Neurons– Dendrites: receive input form other nerve cells

– Cell body

• Contains organelles

• Plays critical role in integrating stimuli from other neurons

– Axons: long processes that communicate with target tissues

– Axon hillock: area where action potential is initiated

– Myelin sheath: wraps axons, increases transmission speed

– Presynaptic terminal: end of axon branches


Motoneuron AnatomyMotoneuron Anatomy


Nerve Cells (cont’d)Nerve Cells (cont’d)

• Neural Communication

– Action potential: generation of an electrical current (signal)

• Integration: cell body integrates charges from other neurons

• Propagation: ion movement down axon at nodes of Ranvier

• Neurotransmitter release: from nerve terminal, allowing communication


The Action PotentialThe Action Potential


The BrainThe Brain


Higher Brain Centers: BrainstemHigher Brain Centers: Brainstem

• Components

– Medulla oblongata

– Midbrain

– Pons

– Reticular formation

• Functions

– Cardiac heart rate & force of contraction

– Blood pressure

– Blood vessel diameter

– Breathing

– Hearing

– Vision

– Sleep

– Consciousness


Higher Brain Centers: DiencephalonHigher Brain Centers: Diencephalon

• Components

– Thalamus

– Hypothalamus

– Pineal body

• Functions

– Relay area of brain

– Release of hormones

– Homeostasis

– Autonomic control

– Body temperature

– Emotions

– Most functions in body


Higher Brain Centers: CerebrumHigher Brain Centers: Cerebrum

• Components

– Cerebral cortex

• Primary sensory area

• Premotor cortex

• Primary motor cortex

• Functions

– Sensory integration

– Voluntary muscle contraction

– Memory bank for skilled motor activities


Higher Brain Centers: CerebellumHigher Brain Centers: Cerebellum

• Functions

– Integrates sensory information

– Coordinates skeletal muscle activity

– Provides blueprint of how motor skill should be performed


Higher Brain Centers: Basal GangliaHigher Brain Centers: Basal Ganglia

• Functions

– Planning & control of:

• Muscle function

• Posture

– Controlling unwanted movements


Descending Corticospinal TractsDescending Corticospinal Tracts

• Collection of axons linking cerebral cortex to spinal cord

• Motor Pathway

– Neurons in brain form synapses with other nerves

– Nerves exit spinal cord for innervation of skeletal muscle

– Site of many potential neural changes


Motor UnitsMotor Units

• Definition

– Functional unit of nervous system

– A single alpha motor nerve & all muscle fibers it innervates

• Location

– Cell bodies & dendrites: in spinal cord

– Axons

• Extend beyond spinal cord

• Innervate skeletal muscles in periphery


The Motor UnitThe Motor Unit


Motor Units (cont’d)Motor Units (cont’d)

• Recruitment

– Voluntary activation of motor units during effort

– Based on size principle: smaller to larger

– Selective recruitment

• Preferential recruitment of type II motor units

• Can occur during change in direction of exerted forces & explosive muscle actions

– Muscle mass activation

• Depends on magnitude of muscle hypertrophy

• May decrease when muscle size increases


The Size PrincipleThe Size Principle



• Recruitment (cont’d)

– Postactivation potentiation

• Time after maximal or near-maximal muscle contraction when it is easier to recruit type II motor units

• Examples:

• Swinging a weighted bat prior to batting in baseball

• Performing a few sets of squats prior to vertical jump

• Using weighted vest prior to speed or agility events

• Performing a few sets of weight training prior to sport



• Firing Rate

– Number of times per second a motor unit discharges

– Affected by nerve’s conduction velocity

– Conduction velocity higher in power than in endurance athletes

– Lower at rest

– Positive relationship with amount of force produced

– Role of increasing firing rate depends on muscle size



• Motor Unit Synchronization

– Occurs when two or more motor units fire at fixed time intervals

– May be advantageous for bursts of strength or power needed in a short period of time

– Occurs in greater measure after resistance training (RT)

– May be advantageous for timing of force production



• Antagonist Muscle Activation

– Increases joint stability & movement coordination

– Reduces risk of injury

– May counteract effects of agonist muscles

– Magnitude affected by:

• Muscle group

• Velocity & type of muscle action

• Intensity

• Joint position

• Injury status


Communication With Skeletal Muscle: The Neuromuscular JunctionCommunication With Skeletal Muscle: The Neuromuscular Junction

• Neuromuscular Junction

– Gap between nerve & muscle

– Crossed by neurotransmitter, allowing action potential to reach muscle

– Acetylcholine

• Key neurotransmitter

• Released between motor nerve & skeletal muscle


The Motor Unit and Neuromuscular JunctionThe Motor Unit and Neuromuscular Junction


Sensory Nervous SystemSensory Nervous System

• Golgi Tendon Organs (GTOs)

– Proprioceptors located at muscle-tendon junction

– Convey information regarding muscle tension to CNS

– Amount of stretch to GTOs increases with increased muscle tension

– Cause agonist muscle relaxation & antagonist muscle excitation

– Defense mechanism to protect body from excessive damage


Golgi Tendon OrganGolgi Tendon Organ


Sensory Nervous System (cont’d)Sensory Nervous System (cont’d)

• Muscle Spindles

– Proprioceptors located within muscle fibers

– Consist of nuclear chain & nuclear bag fibers

– Respond to:

• Magnitude of change in muscle length

• Rate of change of length

– Convey information to CNS regarding static changes in muscle length or joint angle

– Enhance human performance

– Initiate stretch reflex


Muscle SpindleMuscle Spindle


Training StudiesTraining Studies

• EMG, or neural activation, has been shown:

– To be higher for high-intensity muscular effort vs. low-intensity

– To be higher during ballistic or explosive resistance exercise compared with slower velocities

– To be higher for concentric (CON) vs. eccentric (ECC) muscle actions when matched for intensity

– To increase as fatigue ensues in CON & ECC muscle actions

– To be reduced following a workout compared with preworkout

– To be lower for high-volume, high-intensity training

– To be reduced during periods of detraining


Training Studies (cont’d)Training Studies (cont’d)

• Unilateral Training

– Cross education: strength & endurance gained in nontrained limb during unilateral training

– Adaptations are carried over to opposite limb

– Induces novel stimulus to nervous system

– Improves functional performance

– Useful in injured individuals due to partial training effect in injured limb

• Bilateral Deficit

– Max force produced in bilateral contraction is smaller than sum of limbs contracting unilaterally


Autonomic Nervous SystemAutonomic Nervous System

• Controls:

– Heart rate

– Force of contraction

– Respiration rate

– Digestion

– Blood pressure & flow

– Fuel mobilization

• Sympathetic Branch (“Fight or Flight”)

• Parasympathetic Branch: Returns body to normal


Autonomic Nervous System (cont’d)Autonomic Nervous System (cont’d)

copyright © 2012 american college of sports medicine chapter 3 neural adaptations to training

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