© 2007 McGraw-Hill Higher Education. All rights reserved. 2-1 Chapter 2 Neuromuscular Fundamentals.

© 2007 McGraw-Hill Higher Education. All © 2007 McGraw-Hill Higher Education. All rights reserved.rights reserved. 2-2-11

Chapter 2 Chapter 2 Neuromuscular Neuromuscular FundamentalsFundamentals


QuestionsQuestions

• What dictates the amount of muscle What dictates the amount of muscle force created?force created?

• Which requires more motor units; gross Which requires more motor units; gross movements or precision units?movements or precision units?

• How far would you bend your knees to How far would you bend your knees to do a max test for Vertical Jump?do a max test for Vertical Jump?

• What occurs when NM system is What occurs when NM system is diseased? Write down some diseases diseased? Write down some diseases that impact the NM system.that impact the NM system.


Skeletal MusclesSkeletal Muscles

• Responsible for movement of body and Responsible for movement of body and all of its jointsall of its joints

• Muscle contraction produces force that Muscle contraction produces force that causes joint movementcauses joint movement

• Muscles also provide Muscles also provide – protectionprotection– posture and support posture and support – produce a major portion of total body heatproduce a major portion of total body heat


Shape of Muscles & Fiber Shape of Muscles & Fiber ArrangementArrangement

• Muscles have different shapes & fiber Muscles have different shapes & fiber arrangementarrangement

• Shape & fiber arrangement affectsShape & fiber arrangement affects– muscle’s ability to exert forcemuscle’s ability to exert force– range through which it can effectively exert range through which it can effectively exert

force onto the bonesforce onto the bones



• Cross section diameterCross section diameter – factor in muscle’s ability to exert forcefactor in muscle’s ability to exert force– greater cross section diameter = greater greater cross section diameter = greater

force exertionforce exertion

• Muscle’s ability to shortenMuscle’s ability to shorten– longer muscles can shorten through a longer muscles can shorten through a

greater range greater range – more effective in moving joints through more effective in moving joints through

large ranges of motionlarge ranges of motion



• 2 major types of fiber arrangements2 major types of fiber arrangements– parallel & pennateparallel & pennate– each is further subdivided according to each is further subdivided according to

shapeshape

• Parallel musclesParallel muscles– fibers arranged parallel to length of musclefibers arranged parallel to length of muscle– produce a greater range of movement than produce a greater range of movement than

similar sized muscles with pennate similar sized muscles with pennate arrangementarrangement


Fiber Arrangement - ParallelFiber Arrangement - Parallel

• Categorized into following shapesCategorized into following shapes– FlatFlat– FusiformFusiform– StrapStrap– RadiateRadiate– Sphincter or circularSphincter or circular

Modified from Van De Graaff KM: Human anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.


Fiber Arrangement - PennateFiber Arrangement - Pennate

• Categorized based upon the exact Categorized based upon the exact arrangement between fibers & tendonarrangement between fibers & tendon– UnipennateUnipennate– BipennateBipennate– MultipennateMultipennate

Modified from Van De Graaff KM: Human anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.


Muscle Tissue PropertiesMuscle Tissue Properties

• Skeletal muscle tissue has 4 properties Skeletal muscle tissue has 4 properties related to its ability to produce force & related to its ability to produce force & movement about jointsmovement about joints– Irritability or excitability Irritability or excitability – ContractilityContractility– ExtensibilityExtensibility– ElasticityElasticity



• IrritabilityIrritability or or Excitability Excitability - property of - property of muscle being sensitive or responsive to muscle being sensitive or responsive to chemical, electrical, or mechanical chemical, electrical, or mechanical stimulistimuli

• ContractilityContractility - ability of muscle to - ability of muscle to contract & develop tension or internal contract & develop tension or internal force against resistance when force against resistance when stimulatedstimulated



• ExtensibilityExtensibility - ability of muscle to be - ability of muscle to be passively stretched beyond it normal passively stretched beyond it normal resting lengthresting length

• ElasticityElasticity - ability of muscle to return to - ability of muscle to return to its original length following stretchingits original length following stretching


Muscle TerminologyMuscle Terminology

• IntrinsicIntrinsic - pertaining usually - pertaining usually to muscles within or to muscles within or belonging solely to body part belonging solely to body part upon which they actupon which they act– Ex. small intrinsic muscles Ex. small intrinsic muscles

found entirely within the hand found entirely within the hand or feetor feet



• ExtrinsicExtrinsic - pertaining usually to - pertaining usually to muscles that arise or originate muscles that arise or originate outside of (proximal to) body part outside of (proximal to) body part upon which they actupon which they act– Ex. forearm muscles that attach Ex. forearm muscles that attach

proximally on distal humerus and proximally on distal humerus and insert on fingersinsert on fingers



• ActionAction - - specific movement of joint specific movement of joint resulting from a concentric contraction resulting from a concentric contraction of a muscle which crosses jointof a muscle which crosses joint– Ex. biceps brachii has the action of flexion Ex. biceps brachii has the action of flexion

at elbowat elbow

• Actions are usually caused by a group Actions are usually caused by a group of muscles working togetherof muscles working together



• InnervationInnervation - - segment of nervous segment of nervous system defined as being responsible for system defined as being responsible for providing a stimulus to muscle fibers providing a stimulus to muscle fibers within a specific muscle or portion of a within a specific muscle or portion of a musclemuscle– A muscle may be innervated by more than A muscle may be innervated by more than

one nerve & a particular nerve may one nerve & a particular nerve may innervate more than one muscle or portion innervate more than one muscle or portion of a muscleof a muscle



• Amplitude - Amplitude - range of muscle fiber length range of muscle fiber length between maximal & minimal between maximal & minimal lengtheninglengthening

• Gaster (belly or body)Gaster (belly or body)– central, fleshy portion of the muscle that central, fleshy portion of the muscle that

generally increases in diameter as the generally increases in diameter as the muscle contractsmuscle contracts

– the contractile portion of musclethe contractile portion of muscle



• Tendon - Tendon - Fibrous connective tissue, often Fibrous connective tissue, often cordlike in appearance, that connects cordlike in appearance, that connects muscles to bones and other structuresmuscles to bones and other structures– Two muscles may share a common tendonTwo muscles may share a common tendon

• Ex. Achilles tendon of gastrocnemius & soleus Ex. Achilles tendon of gastrocnemius & soleus musclesmuscles

– A muscle may have multiple tendons connecting it A muscle may have multiple tendons connecting it to one or more bonesto one or more bones• Ex. three proximal attachments of triceps Ex. three proximal attachments of triceps

brachiibrachii



• OriginOrigin– Structurally, the proximal attachment of a Structurally, the proximal attachment of a

muscle or the part that attaches closest to muscle or the part that attaches closest to the midline or center of the bodythe midline or center of the body

– Functionally & historically, the least Functionally & historically, the least movable part or attachment of the musclemovable part or attachment of the muscle



• InsertionInsertion– Structurally, the distal attachment or the Structurally, the distal attachment or the

part that attaches farthest from the midline part that attaches farthest from the midline or center of the bodyor center of the body

– Functionally & historically, the most Functionally & historically, the most movable part is generally considered the movable part is generally considered the insertioninsertion



• When a particular muscle contractsWhen a particular muscle contracts– it tends to pull both ends toward the it tends to pull both ends toward the gastergaster– if neither of the bones to which a muscle is if neither of the bones to which a muscle is

attached are stabilized then both bones attached are stabilized then both bones move toward each other upon contractionmove toward each other upon contraction

– more commonly one bone is more more commonly one bone is more stabilized by a variety of factors and the stabilized by a variety of factors and the less stabilized bone usually moves toward less stabilized bone usually moves toward the more stabilized bone upon contraction the more stabilized bone upon contraction


Types of muscle contractionTypes of muscle contraction

• Contraction - when tension is developed Contraction - when tension is developed in a muscle as a result of a stimulusin a muscle as a result of a stimulus

• Muscle “contraction”Muscle “contraction” term may be term may be confusing, because in some contractions confusing, because in some contractions the muscle does not shorten in lengththe muscle does not shorten in length

• As a result, it has become increasingly As a result, it has become increasingly common to refer to the various types of common to refer to the various types of muscle contractions as muscle contractions as muscle actionsmuscle actions instead instead



• Muscle contractions can be used to Muscle contractions can be used to causecause, , controlcontrol, or , or preventprevent joint movement joint movement oror– to initiate or accelerate movement of a body to initiate or accelerate movement of a body

segmentsegment– to slow down or decelerate movement of a to slow down or decelerate movement of a

body segmentbody segment– to prevent movement of a body segment by to prevent movement of a body segment by

external forcesexternal forces• All muscle contractions are either All muscle contractions are either

isometric or isotonicisometric or isotonic



• Isometric contractionIsometric contraction– tension is developed within muscle tension is developed within muscle

but joint angles remain constantbut joint angles remain constant– static contractionsstatic contractions– significant amount of tension may be significant amount of tension may be

developed in muscle to maintain developed in muscle to maintain joint angle in relatively static or joint angle in relatively static or stable positionstable position

– may be used to prevent a body may be used to prevent a body segment from being moved by segment from being moved by external forcesexternal forces



Muscle ContractionMuscle Contraction(under tension)(under tension)

IsometricIsometric IsotonicIsotonic

EccentricEccentricConcentricConcentric



• Isotonic contractions involve muscle Isotonic contractions involve muscle developing tension to either cause or developing tension to either cause or control joint movementcontrol joint movement– dynamic contractionsdynamic contractions– the varying degrees of tension in muscles the varying degrees of tension in muscles

result in joint angles changingresult in joint angles changing

• Isotonic contractions are either Isotonic contractions are either concentric or eccentric on basis of concentric or eccentric on basis of whether shortening or lengthening whether shortening or lengthening occursoccurs



• Movement may occur at any given joint Movement may occur at any given joint without any muscle contraction without any muscle contraction whatsoeverwhatsoever– referred to as passive referred to as passive – solely due to external forces such as those solely due to external forces such as those

applied by another person, object, or applied by another person, object, or resistance or the force of gravity in the resistance or the force of gravity in the presence of muscle relaxationpresence of muscle relaxation



• Concentric contractions Concentric contractions involve muscle developing involve muscle developing tension as it shortenstension as it shortens

• Eccentric contractions involve Eccentric contractions involve the muscle lengthening under the muscle lengthening under tensiontension

Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill



• IsokineticsIsokinetics - a type of dynamic exercise - a type of dynamic exercise using concentric and/or eccentric muscle using concentric and/or eccentric muscle contractionscontractions– speed (or velocity) of movement is constantspeed (or velocity) of movement is constant– muscular contraction (ideally maximum muscular contraction (ideally maximum

contraction) occurs throughout movementcontraction) occurs throughout movement– not another type of contraction, as some not another type of contraction, as some

have describedhave described– Ex. Biodex, Cybex, LidoEx. Biodex, Cybex, Lido


Proprioception & KinesthesisProprioception & Kinesthesis

• Taken for granted are sensations Taken for granted are sensations associated with neuromuscular activity associated with neuromuscular activity through proprioceptionthrough proprioception

• Proprioceptors - internal receptors Proprioceptors - internal receptors located in skin, joints, muscles, & located in skin, joints, muscles, & tendons which provide feedback relative tendons which provide feedback relative to tension, length, & contraction state of to tension, length, & contraction state of muscle, position of body & limbs, and muscle, position of body & limbs, and movements of jointsmovements of joints



• Proprioceptors work in combination with Proprioceptors work in combination with other sense organs to accomplish other sense organs to accomplish kinesthesiskinesthesis

• Kinesthesis – conscious awareness of Kinesthesis – conscious awareness of position & movement of the body in position & movement of the body in spacespace

• Proprioceptors specific to musclesProprioceptors specific to muscles– Muscles spindlesMuscles spindles– Golgi tendon organs (GTO)Golgi tendon organs (GTO)



• ProprioceptionProprioception– Subconscious mechanism by which body is Subconscious mechanism by which body is

able posture & movement by responding to able posture & movement by responding to stimuli originating in proprioceptors of the stimuli originating in proprioceptors of the joints, tendons, muscles, & inner earjoints, tendons, muscles, & inner ear


Proprioception & KinesthesisProprioception & Kinesthesis• Muscle spindlesMuscle spindles

– concentrated primarily in muscle belly concentrated primarily in muscle belly between the fibersbetween the fibers

– sensitive to stretch & rate of stretchsensitive to stretch & rate of stretch– Insert into connective tissue within muscle & Insert into connective tissue within muscle &

run parallel with muscle fibersrun parallel with muscle fibers– Spindle number varies depending upon level Spindle number varies depending upon level

of control neededof control needed• Ex. Greater concentration in hands than thighEx. Greater concentration in hands than thigh



• Muscle spindles & myotatic Muscle spindles & myotatic or stretch reflexor stretch reflex1.1. Rapid muscle stretch occursRapid muscle stretch occurs

2.2. Impulse is sent to the CNSImpulse is sent to the CNS

3.3. CNS activates motor neurons CNS activates motor neurons of muscle and causes it to of muscle and causes it to contractcontract

Modified from Shier D, Butler J, Lewis R: Hole’s human anatomy & physiology, ed 9, Dubuque, IA, 2002, McGraw-Hill.



• Ex. Knee jerk or patella tendon reflexEx. Knee jerk or patella tendon reflex– Reflex hammer strikes patella tendonReflex hammer strikes patella tendon– Causes a quick stretch to musculotendinis Causes a quick stretch to musculotendinis

unit of quadricepsunit of quadriceps– In response quadriceps fires & the knee In response quadriceps fires & the knee

extendsextends

• More sudden the tap, the more significant More sudden the tap, the more significant the reflexive contractionthe reflexive contraction



• Stretch reflex may be utilized to facilitate Stretch reflex may be utilized to facilitate a greater responsea greater response– Ex. Quick short squat before attempting a Ex. Quick short squat before attempting a

jumpjump– Quick stretch placed on muscles in the squat Quick stretch placed on muscles in the squat

enables the same muscles to generate more enables the same muscles to generate more force in subsequently jumping off the floorforce in subsequently jumping off the floor


All or None PrincipleAll or None Principle

• All or None PrincipleAll or None Principle - regardless of - regardless of number, individual muscle fibers within number, individual muscle fibers within a given motor unit will either fire & a given motor unit will either fire & contract maximally or not at allcontract maximally or not at all



• When muscle contracts, contraction When muscle contracts, contraction occurs at the muscle fiber level within a occurs at the muscle fiber level within a particular motor unitparticular motor unit

• Motor unitMotor unit– Single motor neuron & all muscle fibers it Single motor neuron & all muscle fibers it

innervatesinnervates– Function as a single unitFunction as a single unit



• Typical muscle contractionTypical muscle contraction– The number of motor units responding (and The number of motor units responding (and

number of muscle fibers contracting) within number of muscle fibers contracting) within the muscle may vary significantly from the muscle may vary significantly from relatively few to virtually allrelatively few to virtually all

– depending on the number of muscle fibers depending on the number of muscle fibers within each activated motor unit & the within each activated motor unit & the number of motor units activatednumber of motor units activated


Factors affecting muscle tension Factors affecting muscle tension developmentdevelopment

• Difference between lifting a minimal vs. Difference between lifting a minimal vs. maximal resistance is the number of muscle maximal resistance is the number of muscle fibers recruitedfibers recruited

• The number of muscle fibers recruited may The number of muscle fibers recruited may be increased bybe increased by– activating those motor units containing a greater activating those motor units containing a greater

number of muscle fibersnumber of muscle fibers– activating more motor unitsactivating more motor units– increasing the frequency of motor unit activationincreasing the frequency of motor unit activation



• Number of muscle fibers per motor unit Number of muscle fibers per motor unit varies significantlyvaries significantly– From less than 10 in muscles requiring From less than 10 in muscles requiring

precise and detailed such as muscles of precise and detailed such as muscles of the eyethe eye

– To as many as a few thousand in large To as many as a few thousand in large muscles that perform less complex muscles that perform less complex activities such as the quadriceps activities such as the quadriceps



• Motor unit must first receive a stimulus Motor unit must first receive a stimulus via electrical signal known as an via electrical signal known as an action action potentialpotential for the muscle fibers in the unit for the muscle fibers in the unit to contractto contract

• Subthreshold stimulusSubthreshold stimulus– not strong enough to cause an action not strong enough to cause an action

potentialpotential– does not result in a contraction does not result in a contraction



• Threshold stimulusThreshold stimulus– stimulus becomes strong enough to stimulus becomes strong enough to

produce an action potential in a single produce an action potential in a single motor unit axonmotor unit axon

– all of the muscle fibers in the motor unit all of the muscle fibers in the motor unit contractcontract



• Submaximal stimuliSubmaximal stimuli– Stimuli that are strong enough to produce Stimuli that are strong enough to produce

action potentials in additional motor unitsaction potentials in additional motor units

• Maximal stimuliMaximal stimuli– Stimuli that are strong enough to produce Stimuli that are strong enough to produce

action potentials in all motor units of a action potentials in all motor units of a particular muscleparticular muscle


Muscle Length - Tension Muscle Length - Tension RelationshipRelationship

• Maximal ability of a muscle to develop Maximal ability of a muscle to develop tension & exert force varies depending tension & exert force varies depending upon the length of the muscle during upon the length of the muscle during contractioncontraction



• Generally, depending upon muscle Generally, depending upon muscle involvedinvolved– Greatest amount of tension can be Greatest amount of tension can be

developed when a muscle is stretched developed when a muscle is stretched between 100% to 130% of its resting lengthbetween 100% to 130% of its resting length

– Stretch beyond 100% to 130% of resting Stretch beyond 100% to 130% of resting length significantly decreases the amount length significantly decreases the amount of force muscle can exertof force muscle can exert



• Generally, depending upon muscle Generally, depending upon muscle involvedinvolved– A proportional decrease in ability to A proportional decrease in ability to

develop tension occurs as a muscle is develop tension occurs as a muscle is shortenedshortened

– When shortened to around 50% to 60% of When shortened to around 50% to 60% of resting length ability to develop contractile resting length ability to develop contractile tension is essentially reduced to zerotension is essentially reduced to zero



• Ex. 1 Increasing ability to exert Ex. 1 Increasing ability to exert forceforce– squat slightly to stretch the calf, squat slightly to stretch the calf,

hamstrings, & quadriceps before hamstrings, & quadriceps before contracting same muscles contracting same muscles concentrically to jumpconcentrically to jump

• Ex. 2. Reducing ability to exert Ex. 2. Reducing ability to exert forceforce– isolate the gluteus maximus by isolate the gluteus maximus by

maximally shortening the hamstrings maximally shortening the hamstrings with knee flexionwith knee flexion


Muscle Force – Velocity Muscle Force – Velocity RelationshipRelationship

• When muscle is contracting (concentrically or When muscle is contracting (concentrically or eccentrically) the rate of length change is eccentrically) the rate of length change is significantly related to the amount of force significantly related to the amount of force potentialpotential

• When contracting concentrically against a When contracting concentrically against a light resistance muscle is able to contract at a light resistance muscle is able to contract at a high velocityhigh velocity



• As resistance increases, the maximal velocity As resistance increases, the maximal velocity at which muscle is able to contract decreasesat which muscle is able to contract decreases

• Eventually, as load increases, the velocity Eventually, as load increases, the velocity decreases to zero resulting in an isometric decreases to zero resulting in an isometric contractioncontraction

• As load increases beyond muscle’s ability to As load increases beyond muscle’s ability to maintain an isometric contraction, the muscle maintain an isometric contraction, the muscle begins to lengthen resulting in an eccentric begins to lengthen resulting in an eccentric contractioncontraction



• Slight increases in load results in relatively Slight increases in load results in relatively low velocity of lengtheninglow velocity of lengthening

• As load increases further the velocity of As load increases further the velocity of lengthening will increase as welllengthening will increase as well

• Eventually, load may increase to point where Eventually, load may increase to point where muscle can no longer resist, resulting in muscle can no longer resist, resulting in uncontrollable lengthening or dropping of loaduncontrollable lengthening or dropping of load

• Inverse relationship between concentric Inverse relationship between concentric velocity & force productionvelocity & force production



• As force needed to cause movement of an As force needed to cause movement of an object increases the velocity of concentric object increases the velocity of concentric contraction decreasescontraction decreases

• Somewhat proportional relationship between Somewhat proportional relationship between eccentric velocity & force productioneccentric velocity & force production

• As force needed to control an object’s As force needed to control an object’s movement increases, the velocity of eccentric movement increases, the velocity of eccentric lengthening increases, at least until when lengthening increases, at least until when control is lostcontrol is lost


Angle of pullAngle of pull

• Angle between the line of pull of the muscle & Angle between the line of pull of the muscle & the bone on which it inserts (angle toward the the bone on which it inserts (angle toward the joint)joint)

• With every degree of joint motion, the angle With every degree of joint motion, the angle of pull changesof pull changes

• Joint movements & insertion angles involve Joint movements & insertion angles involve mostly small angles of pullmostly small angles of pull



• Angle of pull decreases as bone moves away Angle of pull decreases as bone moves away from its anatomical position through local from its anatomical position through local muscle group’s contractionmuscle group’s contraction

• Range of movement depends on type of joint Range of movement depends on type of joint & bony structure& bony structure

• Most muscles work at angles of pull less than Most muscles work at angles of pull less than 50 degrees50 degrees

• Amount of muscular force needed to cause Amount of muscular force needed to cause joint movement is affected by angle of pulljoint movement is affected by angle of pull



• Rotary component (Rotary component (vertical component) - vertical component) - component of muscular force that acts component of muscular force that acts perpendicular to long axis of bone (lever)perpendicular to long axis of bone (lever)– When the line of muscular force is at 90 When the line of muscular force is at 90

degrees to bone on which it attaches, all of degrees to bone on which it attaches, all of the muscular force is rotary force (100% of the muscular force is rotary force (100% of force is contributing to movement) force is contributing to movement)

– All of force is being used to rotate the lever All of force is being used to rotate the lever about its axisabout its axis

– The closer the angle of pull to 90 degrees, The closer the angle of pull to 90 degrees, the greater the rotary componentthe greater the rotary component

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.



• At all other degrees of the angle of pull, one At all other degrees of the angle of pull, one of the other two components of force are of the other two components of force are operating in addition to rotary componentoperating in addition to rotary component– Rotary component continues with less force, to Rotary component continues with less force, to

rotate the lever about its axisrotate the lever about its axis– Second force component is the horizontal, or Second force component is the horizontal, or

nonrotary componentnonrotary component and is either a and is either a stabilizing stabilizing componentcomponent or a or a dislocating componentdislocating component, depending , depending on whether the angle of pull is less than or greater on whether the angle of pull is less than or greater than 90 degreesthan 90 degrees



• If angle is less than 90 If angle is less than 90 degrees, the force is a degrees, the force is a stabilizingstabilizing force because its force because its pull directs the bone toward the pull directs the bone toward the joint axisjoint axis

• If angle is greater than 90 If angle is greater than 90 degrees, the force is degrees, the force is dislocatingdislocating due to its pull due to its pull directing the bone away from directing the bone away from the joint axisthe joint axis

Modified from Hall SJ: Basic biomechanics, New York, 2003, McGraw-Hill.



• Sometimes desirable to begin with the Sometimes desirable to begin with the angle of pull is at 90 degreesangle of pull is at 90 degrees– chin-up (pull-up)chin-up (pull-up)– angle makes the chin-up easier because of angle makes the chin-up easier because of

more advantageous angle of pullmore advantageous angle of pull– compensate for lack of sufficient strengthcompensate for lack of sufficient strength


Uniarticular, biarticular, and Uniarticular, biarticular, and multiarticular musclesmultiarticular muscles

• Uniarticular musclesUniarticular muscles– Cross & act directly only on the joint that Cross & act directly only on the joint that

they crossthey cross– Ex. BrachialisEx. Brachialis

• Can only pull humerus & ulna closer Can only pull humerus & ulna closer togethertogether



• Biarticular muscles – cross & act on two Biarticular muscles – cross & act on two different jointsdifferent joints– Depending, biarticular muscles may Depending, biarticular muscles may

contract & cause motion at either one or contract & cause motion at either one or both of its jointsboth of its joints

– Two advantages over uniarticular musclesTwo advantages over uniarticular muscles• can cause and/or control motion at more than can cause and/or control motion at more than

one jointone joint• are able to maintain a relatively constant length are able to maintain a relatively constant length

due to "shortening" at one joint and due to "shortening" at one joint and "lengthening" at another joint"lengthening" at another joint



• Muscle does not actually shorten at one Muscle does not actually shorten at one joint & lengthen at otherjoint & lengthen at other– The concentric shortening of the muscle to The concentric shortening of the muscle to

move one joint is offset by motion of the move one joint is offset by motion of the other joint which moves its attachment of other joint which moves its attachment of muscle farther awaymuscle farther away

– This maintenance of a relatively constant This maintenance of a relatively constant length results in the muscle being able to length results in the muscle being able to continue its exertion of forcecontinue its exertion of force



• Ex.1 Hip & knee biarticular muscles Ex.1 Hip & knee biarticular muscles – ConcurrentConcurrent movement pattern occurs when movement pattern occurs when

both the knee & hip extend at the same both the knee & hip extend at the same timetime

– If only knee extension occurs, rectus If only knee extension occurs, rectus femoris shortens & loses tension as do femoris shortens & loses tension as do other quadriceps muscles, but its relative other quadriceps muscles, but its relative length & subsequent tension may be length & subsequent tension may be maintained due to its relative lengthening maintained due to its relative lengthening at the hip joint during extensionat the hip joint during extension



• Ex. 2 Hip & knee biarticular musclesEx. 2 Hip & knee biarticular muscles– CountercurrentCountercurrent movement pattern occurs movement pattern occurs

in kickingin kicking– During the lower extremity forward During the lower extremity forward

movement phase the rectus femoris movement phase the rectus femoris concentrically contracts to flex the hip & concentrically contracts to flex the hip & extend the kneeextend the knee

– These two movements, when combined, These two movements, when combined, increase the tension or stretch on the increase the tension or stretch on the hamstring muscles both at the knee & hiphamstring muscles both at the knee & hip



• Multiarticular muscles act on three or Multiarticular muscles act on three or more joints due to the line of pull more joints due to the line of pull between their origin & insertion crossing between their origin & insertion crossing multiple jointsmultiple joints

• Principles relative to biarticular muscles Principles relative to biarticular muscles apply similarly to multiarticular musclesapply similarly to multiarticular muscles


Reciprocal Inhibition or Reciprocal Inhibition or InnervationInnervation

• Antagonist muscles groups must relax & Antagonist muscles groups must relax & lengthen when the agonist muscle group lengthen when the agonist muscle group contractscontracts– This reciprocal innervation effect occurs through This reciprocal innervation effect occurs through

reciprocal inhibition of the antagonistsreciprocal inhibition of the antagonists– Activation of the motor units of the agonists Activation of the motor units of the agonists

causes a reciprocal neural inhibition of the motor causes a reciprocal neural inhibition of the motor units of the antagonistsunits of the antagonists

– This reduction in neural activity of the antagonists This reduction in neural activity of the antagonists allows them to subsequently lengthen under less allows them to subsequently lengthen under less tensiontension


Reciprocal Inhibition or Reciprocal Inhibition or InnervationInnervation

• Ex. Compare the ease ofEx. Compare the ease of– stretching hamstrings when simultaneously stretching hamstrings when simultaneously

contracting the quadriceps contracting the quadriceps

vs.vs.– stretching hamstrings without contracting stretching hamstrings without contracting

quadricepsquadriceps


Active & Passive Active & Passive InsufficiencyInsufficiency

• As muscle shortens its ability to exert As muscle shortens its ability to exert force diminishesforce diminishes– Active insufficiencyActive insufficiency is reached when the is reached when the

muscle becomes shortened to the point muscle becomes shortened to the point that it can not generate or maintain active that it can not generate or maintain active tensiontension

– Passively insufficiencyPassively insufficiency is reached when is reached when the opposing muscle becomes stretched to the opposing muscle becomes stretched to the point where it can no longer lengthen & the point where it can no longer lengthen & allow movementallow movement



• Easily observed in either biarticular Easily observed in either biarticular or multiarticular muscles when full or multiarticular muscles when full range of motion is attempted in all range of motion is attempted in all joints crossed by the musclejoints crossed by the muscle– Ex. Rectus femoris contracts Ex. Rectus femoris contracts

concentrically to both flex the hip & concentrically to both flex the hip & extend the kneeextend the knee

– Can completely perform either action Can completely perform either action one at a time but actively insufficient to one at a time but actively insufficient to obtain full range at both joints obtain full range at both joints simultaneouslysimultaneously



– Similarly, hamstrings can not usually Similarly, hamstrings can not usually stretch enough to allow both maximal hip stretch enough to allow both maximal hip flexion & maximal knee extension due flexion & maximal knee extension due passive insufficiencypassive insufficiency

• As a result, it is virtually impossible to As a result, it is virtually impossible to actively extend the knee fully when actively extend the knee fully when beginning with the hip fully flexed or beginning with the hip fully flexed or vice versavice versa

© 2007 McGraw-Hill Higher Education. All rights reserved. 2-1 Chapter 2 Neuromuscular Fundamentals.

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Transcript of © 2007 McGraw-Hill Higher Education. All rights reserved. 2-1 Chapter 2 Neuromuscular Fundamentals.