Essentials of Strength Training & Essentials of Strength Training & ConditioningConditioning

Neuromuscular Anatomy and Neuromuscular Anatomy and Adaptations to ConditioAdaptations to Conditioningning

Chapter 2Chapter 2

Neuromuscular Anatomy Neuromuscular Anatomy & Physiology& Physiology

Motor UnitMotor Unit – a motor neuron and all of the muscle fibers that it – a motor neuron and all of the muscle fibers that it innervates ; the basic functional entity of muscular activityinnervates ; the basic functional entity of muscular activity

Motor NeuronMotor Neuron – nerve that travels from the spinal cord to the target – nerve that travels from the spinal cord to the target muscle; generally has numerous terminal branches to innervate many muscle; generally has numerous terminal branches to innervate many muscle fibers; when a motor neuron fires, all fibers it innervates become muscle fibers; when a motor neuron fires, all fibers it innervates become activatedactivated• Precision muscles may have a ratio of muscle fibers to motor neuron Precision muscles may have a ratio of muscle fibers to motor neuron

that approaches 1:1that approaches 1:1• Large muscle group muscle fibers may have hundreds of fibers Large muscle group muscle fibers may have hundreds of fibers

controlled by one motor neuron controlled by one motor neuron Motor neuron Action Potential arrives at all of the motor end plates Motor neuron Action Potential arrives at all of the motor end plates

innervated by neuron; this causes a release of neurotransmitter innervated by neuron; this causes a release of neurotransmitter Acetylcholine (Ach); Ach diffuses across the neuromuscular synapses Acetylcholine (Ach); Ach diffuses across the neuromuscular synapses and electrochemically excites the sarcolemma, causing contraction of all and electrochemically excites the sarcolemma, causing contraction of all of the muscle fibersof the muscle fibers

All or None PrincipleAll or None Principle – when an action potential has enough strength – when an action potential has enough strength to activate a muscle fiber, it activates all muscle fibers supplied by the to activate a muscle fiber, it activates all muscle fibers supplied by the motor neuronmotor neuron

Neuromuscular Anatomy Neuromuscular Anatomy & Physiology (cont.)& Physiology (cont.)

TwitchTwitch – – a short period of activation of the muscle fibers within the a short period of activation of the muscle fibers within the motor unit, stimulated by an action potentialmotor unit, stimulated by an action potential• If a second twitch occurs before the muscle fiber relaxes, the Force If a second twitch occurs before the muscle fiber relaxes, the Force

generated summatesgenerated summates• Decreasing the time interval between twitches results in greater Decreasing the time interval between twitches results in greater

Force summationForce summation TetanusTetanus – when continued stimulation of a muscle fiber results in – when continued stimulation of a muscle fiber results in

twitches occurring simultaneously without relaxation; this is the largest twitches occurring simultaneously without relaxation; this is the largest amount of Force that the muscle fiber and motor unit can generateamount of Force that the muscle fiber and motor unit can generate• ““Russian Stimulation” is an electrical stimulation training technique Russian Stimulation” is an electrical stimulation training technique

that utilizes an outside electrical charge to generate large amounts that utilizes an outside electrical charge to generate large amounts of Force within a muscle to increase lifting potential, and therefore of Force within a muscle to increase lifting potential, and therefore increasing the training effectincreasing the training effect

SsSs

Muscle Twitch – Summation - TetanusMuscle Twitch – Summation - Tetanus

Major Characteristics of Muscle Fiber TypesMajor Characteristics of Muscle Fiber Types

CharacteristicCharacteristic Type IType I Type IIaType IIa Type IIbType IIb

Contraction SpeedContraction Speed SlowSlow FastFast FastFast

Force productionForce production LowLow IntermediateIntermediate HighHigh

Power OutputPower Output LowLow HighHigh HighHigh

EnduranceEndurance HighHigh Intermediate / LowIntermediate / Low LowLow

Aerobic enzymesAerobic enzymes HighHigh Intermediate / LowIntermediate / Low LowLow

Anaerobic enzymesAnaerobic enzymes LowLow HighHigh HighHigh

FatigabilityFatigability LowLow Intermediate / HighIntermediate / High HighHigh

Capillary densityCapillary density HighHigh IntermediateIntermediate LowLow

Fiber diameterFiber diameter SmallSmall IntermediateIntermediate LargeLarge

Mitochondria densityMitochondria density HighHigh IntermediateIntermediate LowLow

ATPase activityATPase activity LowLow HighHigh HighHigh

MyoglobinMyoglobin HighHigh LowLow LowLow

ColorColor RedRed White (intermediate)White (intermediate) WhiteWhite

Motor Unit Recruitment Patterns During ExerciseMotor Unit Recruitment Patterns During Exercise

Muscle Force output varies over a wide gradation in order to allow for Muscle Force output varies over a wide gradation in order to allow for appropriate use of force to carry out activity in a smooth, controlled appropriate use of force to carry out activity in a smooth, controlled mannermanner

Frequency of ActivationFrequency of Activation – by decreasing the time interval between – by decreasing the time interval between muscle twitches, greater force production is attained; most commonly muscle twitches, greater force production is attained; most commonly used in precision muscles (i.e. hand, eye)used in precision muscles (i.e. hand, eye)

RecruitmentRecruitment – increasing the number of motor units activated to – increasing the number of motor units activated to produce greater Force or carry out a particular movement; most produce greater Force or carry out a particular movement; most commonly used in large muscle groups (thigh, gluteals, arms, trunk)commonly used in large muscle groups (thigh, gluteals, arms, trunk)

Increasing frequency of contraction and increasing recruitment occur Increasing frequency of contraction and increasing recruitment occur simultaneously when great Force production is requiredsimultaneously when great Force production is required

Depending on the physiological need, different types of muscle fibers Depending on the physiological need, different types of muscle fibers are recruited, based on the fibers characteristicsare recruited, based on the fibers characteristics

Relative Involvement of Muscle Fiber Types Relative Involvement of Muscle Fiber Types in Sport Eventsin Sport Events

EventEvent Type IType I Type IIType II

100-m sprint100-m sprint LowLow HighHigh

800-m run800-m run HighHigh HighHigh

MarathonMarathon HighHigh LowLow

Olympic WeightliftingOlympic Weightlifting LowLow HighHigh

Barbell squatBarbell squat HighHigh HighHigh

SoccerSoccer HighHigh HighHigh

Field HockeyField Hockey HighHigh HighHigh

Football wide receiverFootball wide receiver LowLow HighHigh

Football linemanFootball lineman HighHigh HighHigh

BasketballBasketball LowLow HighHigh

Distance cyclingDistance cycling HighHigh LowLow

ProprioceptionProprioception

ProprioceptorsProprioceptors – specialized sensory receptors located within joints, – specialized sensory receptors located within joints, muscles, and tendons; sensitive to pressure and tension; relay info muscles, and tendons; sensitive to pressure and tension; relay info regarding muscle dynamics to the central nervous systemregarding muscle dynamics to the central nervous system• Provide the nervous system with info to allow for performance of Provide the nervous system with info to allow for performance of

complex coordinated movements; maintains muscle tonecomplex coordinated movements; maintains muscle tone

Kinesthetic SenseKinesthetic Sense – spatial awareness; conscious appreciation of the – spatial awareness; conscious appreciation of the body in 3 dimensions; once learned, most proprioception is sub-body in 3 dimensions; once learned, most proprioception is sub-consciously controlledconsciously controlled

Two most common proprioceptors are the Two most common proprioceptors are the Muscle SpindleMuscle Spindle and the and the Golgi Tendon OrganGolgi Tendon Organ

Muscle SpindleMuscle Spindle

Muscle SpindleMuscle Spindle – (intrafusal fiber) – (intrafusal fiber)• Specialized muscle fibers that run Specialized muscle fibers that run

parallel to normal muscle fibers parallel to normal muscle fibers (extrafusal fiber) within a fasiculus; (extrafusal fiber) within a fasiculus; provide info regarding muscle length and provide info regarding muscle length and rate of length changerate of length change

• Muscle stretch activates the spindle Muscle stretch activates the spindle which sends a signal to the spinal cord which sends a signal to the spinal cord via an afferent (sensory) neuron; at the via an afferent (sensory) neuron; at the cord the afferent transfers the signal to cord the afferent transfers the signal to an efferent (motor) neuron, which sends an efferent (motor) neuron, which sends an action potential to the muscle, an action potential to the muscle, causing contraction (if AP is great causing contraction (if AP is great enough) of the muscle fibersenough) of the muscle fibers

• Spindles indicate the degree to which the Spindles indicate the degree to which the muscle must be activated to overcome muscle must be activated to overcome the given resistancethe given resistance

• Precision muscles have a greater Precision muscles have a greater concentration of muscle spindles than concentration of muscle spindles than larger muscleslarger muscles

Golgi Tendon OrganGolgi Tendon Organ

Golgi Tendon OrgansGolgi Tendon Organs – (GTO) – (GTO) proprioceptors located within the proprioceptors located within the tendon of a muscle and in contact with tendon of a muscle and in contact with extrafusal muscle fibers; activated by extrafusal muscle fibers; activated by stretch of tendon stretch of tendon • Stretch activation of the GTO Stretch activation of the GTO

results in the same type of results in the same type of neuronal pathway activation as neuronal pathway activation as muscle spindle activation, however muscle spindle activation, however the neurons activated are the neurons activated are inhibitory, that is, they inhibit inhibitory, that is, they inhibit muscular contraction, reducing muscular contraction, reducing tension within the muscletension within the muscle

• GTO’s provide protection from GTO’s provide protection from excess loadsexcess loads

Major Adaptations to Resistance Major Adaptations to Resistance vs. Aerobic Endurance Trainingvs. Aerobic Endurance Training

VariableVariable Resistance TrainingResistance Training Aerobic Endurance Aerobic Endurance TrainingTraining

Size of muscle fibersSize of muscle fibers IncreaseIncrease No changeNo change

Number of muscle fibersNumber of muscle fibers No changeNo change No changeNo change

Movement speedMovement speed IncreaseIncrease No changeNo change

StrengthStrength IncreaseIncrease No changeNo change

Aerobic capacityAerobic capacity No changeNo change IncreaseIncrease

Anaerobic capacityAnaerobic capacity IncreaseIncrease No changeNo change