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Chapter 2 The Structure and Function of the Musculoskeletal System.

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1 Chapter 2 The Structure and Function of the Musculoskeletal System

2 Introduction OccBio ==> performance & injuryOccBio ==> performance & injury requires knowledge of the basic structure and function of the musculoskeletal system.requires knowledge of the basic structure and function of the musculoskeletal system. Main mechanical functions of MS system:Main mechanical functions of MS system: 1) support1) support 2) protection2) protection 3) allow for motion.3) allow for motion.

3 The six major substructures of the musculoskeletal system are: 1. Tendons 2. Ligaments 3. Fascia 4. Cartilage 5. Bone 6. Muscle

4 The six major substructures of the musculoskeletal system are: 1. Tendons 2. Ligaments 3. Fascia 4. Cartilage 5. Bone 6. Muscle Soft Tissues

5 The six major substructures of the musculoskeletal system are: 1. Tendons 2. Ligaments 3. Fascia 4. Cartilage 5. Bone 6. Muscle Connective Tissues

6 The six major substructures of the musculoskeletal system are: 1. Tendons 2. Ligaments 3. Fascia 4. Cartilage 5. Bone 6. Muscle Force generating unit

7 Connective Tissue 1. Tendons 2. Ligaments 3. Fascia 4. Cartilage 5. Bone 6. Muscle provide supportprovide support transmit forcestransmit forces maintain structural integritymaintain structural integrity

8 Connective Tissue consists of cells: produce extracellular matrixcells: produce extracellular matrix extracellular matrix: consistency determines CT physical propertiesextracellular matrix: consistency determines CT physical properties ground substance (viscous fluid)ground substance (viscous fluid) fibersfibers collagencollagen elasticelastic

9 Specialized Connective Tissue cells Fibroblasts : cells produce matrix of loose connective tissue (skin, tendons & ligaments)Fibroblasts : cells produce matrix of loose connective tissue (skin, tendons & ligaments) Chondroblasts: cells produce matrix of cartilage (transform to chondrocytes)Chondroblasts: cells produce matrix of cartilage (transform to chondrocytes) Osteoblasts: cells produce matrix of bone (transform to osteocytes)Osteoblasts: cells produce matrix of bone (transform to osteocytes)

10 Fibers in matrix affect mechanical characteristics of CT Elastin fibersElastin fibers branched and wavybranched and wavy contain protein elastincontain protein elastin low tensile strength (stretch a lot) but return to original lengthlow tensile strength (stretch a lot) but return to original length Collagen fibers: most numerousCollagen fibers: most numerous long, slightly wavy and unbranchedlong, slightly wavy and unbranched bundle of protein collagenbundle of protein collagen provides high tensile strength (resists stretch)provides high tensile strength (resists stretch)

11 Fibers in matrix affect mechanical characteristics of CT Thick: collagen Thin: elastin Present in different proportions in different structures: Why?

12 Fibers in matrix affect mechanical characteristics of CT Present in different orientations in different structures: Why?

13 Tendons: connect muscle to bone transmit muscle forcetransmit muscle force

14 Tendons: connect muscle to bone transmit muscle forcetransmit muscle force Parallel collagen arrangement, minimal elastinParallel collagen arrangement, minimal elastin Surrounded by fibrous tissue sheathsSurrounded by fibrous tissue sheaths reduce friction (bony prominence, tunnels) BICreduce friction (bony prominence, tunnels) BIC sheath inner lining: synovium => synovial fluidsheath inner lining: synovium => synovial fluid

15 Tendons: connect muscle to bone transmit muscle forcetransmit muscle force Parallel collagen arrangement, minimal elastinParallel collagen arrangement, minimal elastin Surrounded by fibrous tissue sheathsSurrounded by fibrous tissue sheaths reduce friction (bony prominence, tunnels)reduce friction (bony prominence, tunnels) sheath inner lining: synovium => synovial fluidsheath inner lining: synovium => synovial fluid Damage:Damage: torntorn tendonitistendonitis tensynovitistensynovitis

16 Trigger Finger

17 Ligament: connects bone to bone provides stability to jointsprovides stability to joints

18 Ligament: connects bone to bone provides stability to jointsprovides stability to joints non-parallel collagen arrangement, aligned in direction of imposed stressnon-parallel collagen arrangement, aligned in direction of imposed stress

19 Ligament: connects bone to bone provides stability to jointsprovides stability to joints non-parallel collagen arrangement, aligned in direction of imposed stressnon-parallel collagen arrangement, aligned in direction of imposed stress Special functions:Special functions: Transverse ligament (retinaculum)Transverse ligament (retinaculum) pulley for tendonpulley for tendon change direction of force change direction of force

20 Ligament: connects bone to bone provides stability to jointsprovides stability to joints non-parallel collagen arrangement, aligned in direction of imposed stressnon-parallel collagen arrangement, aligned in direction of imposed stress Special functions:Special functions: Annular ligamentAnnular ligament

21 Ligament: connects bone to bone provides stability to jointsprovides stability to joints non-parallel collagen arrangement, aligned in direction of imposed stressnon-parallel collagen arrangement, aligned in direction of imposed stress Special functions:Special functions: Damage: sprainDamage: sprain First, second, third degree sprainFirst, second, third degree sprain

22 Fascia: separates muscles and organs contains more elastin fiberscontains more elastin fibers

23 Fascia: separates muscles and organs contains more elastin fiberscontains more elastin fibers Damage: irritation & swellingDamage: irritation & swelling plantar fasciitisplantar fasciitis

24 Fascia: separates muscles and organs contains more elastin fiberscontains more elastin fibers Damage: irritation & swellingDamage: irritation & swelling plantar fasciitisplantar fasciitis shin splintsshin splints iliotibial band syndromeiliotibial band syndrome

25 Fascia: separates muscles and organs contains more elastic fiberscontains more elastic fibers Damage: irritation & swellingDamage: irritation & swelling plantar fasciitisplantar fasciitis shin splintsshin splints iliotibial band syndromeiliotibial band syndrome

26 Cartilage: covers bone at joints hyaline cartilagehyaline cartilage bony surfaces at movable articulationbony surfaces at movable articulation reduces friction within the jointreduces friction within the joint

27 Cartilage: covers bone at joints fibrocartilage: dense collagen fibersfibrocartilage: dense collagen fibers intervertebral disks, menisciintervertebral disks, menisci

28 Cartilage: covers bone at joints fibrocartilage:fibrocartilage: distributes load at the jointdistributes load at the joint absorbs shock (?x?)absorbs shock (?x?)

29 Cartilage Unique aspect: devoid of nerves and blood vessels.Unique aspect: devoid of nerves and blood vessels. nourished by diffusionnourished by diffusion limits thicknesslimits thickness Influences healingInfluences healing

30 Cartilage Unique aspect: devoid of nerves and blood vessels.Unique aspect: devoid of nerves and blood vessels. nourished by diffusionnourished by diffusion limits thicknesslimits thickness influences healinginfluences healing DamageDamage osteoarthritisosteoarthritis “torn” cartilage“torn” cartilage

31 Cartilage Unique aspect: devoid of nerves and blood vessels.Unique aspect: devoid of nerves and blood vessels. nourished by diffusionnourished by diffusion limits thicknesslimits thickness influences healinginfluences healing DamageDamage osteoarthritisosteoarthritis “torn” cartilage“torn” cartilage

32 Cartilage Unique aspect: devoid of nerves and blood vessels.Unique aspect: devoid of nerves and blood vessels. nourished by diffusionnourished by diffusion limits thicknesslimits thickness influences healinginfluences healing DamageDamage osteoarthritisosteoarthritis “torn” cartilage“torn” cartilage

33 Stress-strain relationships Stress: applied loadStress: applied load Strain: deformationStrain: deformation Plastic region: permanent disruptionPlastic region: permanent disruption Ultimate strength: complete tearUltimate strength: complete tear

34

35

36 Bone Axial bonesAxial bones skull, vertebrae, sternum, ribs, pelvisskull, vertebrae, sternum, ribs, pelvis Appendicular bonesAppendicular bones limbslimbs

37 Functions of bone Provide supportProvide support Allow movementAllow movement ProtectionProtection Mineral storageMineral storage 99% of body Ca in bone99% of body Ca in bone Blood cell formationBlood cell formation

38 Bones Long bonesLong bones shaft (diaphysis)shaft (diaphysis) two expanded ends (epiphyses)two expanded ends (epiphyses) cortical (compact)cortical (compact) provide cortex or lining of boneprovide cortex or lining of bone cancellous (spongy, trabecular)cancellous (spongy, trabecular)

39 Fractures Bone loaded to failureBone loaded to failure tensile & compressive loadtensile & compressive load stronger compression than tensionstronger compression than tension

40 Fractures Bone loaded to failureBone loaded to failure tensile & compressive loadtensile & compressive load stronger compression than tensionstronger compression than tension Traumatic fracture: single loadTraumatic fracture: single loadTraumatic fractureTraumatic fracture Stress fracture: repetitive loadingStress fracture: repetitive loadingStress fractureStress fracture

41 Traumatic fracture: single load

42 Fracture: effect of loading type

43 Stress fracture: “hot spot”

44 Remodelling Throughout lifeThroughout life youth: length and circumferenceyouth: length and circumference

45 Remodelling Throughout lifeThroughout life adult: circumferenceadult: circumference

46 Bone Remodelling Osteocytes: hard bone cellOsteocytes: hard bone cell Osteoblasts form bone ==> osteocytesOsteoblasts form bone ==> osteocytes Osteoclast resorbs boneOsteoclast resorbs bone

47 Wolff’s Law (1892) bone is deposited where needed and resorbed where not neededbone is deposited where needed and resorbed where not needed bone remodels in response to applied stressbone remodels in response to applied stress Bone hypertrophy occurs in areas where stress and strain are increased.Bone hypertrophy occurs in areas where stress and strain are increased. Bone atrophy occurs in areas where stress and strain are decreased.Bone atrophy occurs in areas where stress and strain are decreased.

48 Remodelling Factors affecting remodeling

49 Remodeling: lifestyle success ??success ?? available nutrientavailable nutrient hormonal levels (estrogen)hormonal levels (estrogen) mechanical stressmechanical stress activity vs inactivityactivity vs inactivity

50 Osteoporosis Characteristics decrease in bone mineral content.decrease in bone mineral content. reduction in cortical bone thicknessreduction in cortical bone thickness reduction in trabecular integrityreduction in trabecular integrity Significantly reduces bone strengthSignificantly reduces bone strength reduces bone strength reduces bone strength Very prevalent in elderly femalesVery prevalent in elderly females Spontaneous compression fracturesSpontaneous compression fracturesSpontaneous compression fracturesSpontaneous compression fractures

51 Bone strength and aging

52 Spontaneous compressive fractures

53 Skeletal Muscle about 400 muscles in the bodyabout 400 muscles in the body ~ 50% of TBW~ 50% of TBW ~ 50% of body’s metabolism~ 50% of body’s metabolism Controlled by voluntary nervous systemControlled by voluntary nervous system somatic nervous systemsomatic nervous system

54 Triceps torque Biceps torque Skeletal Muscle Functions generate force (tension) across jointsgenerate force (tension) across joints moment of force or torquemoment of force or torque

55 Skeletal Muscle Functions: generate force (tension) across jointsgenerate force (tension) across joints moment of force or torquemoment of force or torque muscle pumpmuscle pump aid in venous returnaid in venous return

56 Muscle Structure muscle cellsmuscle cells muscle fibersmuscle fibers tension producertension producer connective tissueconnective tissue energy storageenergy storage transfer of energytransfer of energy nervenerve motor & sensorymotor & sensory communicationcommunication

57 Gross Muscle Anatomy

58 Skeletal Muscle Fiber MyofibrilsMyofibrils longitudinal subunits of fiberlongitudinal subunits of fiber true contractile elements (tension)true contractile elements (tension) contain myofilamentscontain myofilaments protein filaments actin and myosinprotein filaments actin and myosinprotein filaments protein filaments overlapping filaments give the muscle its striated appearance.overlapping filaments give the muscle its striated appearance.

59 Actin & Myosin

60 Electron Microscope image of Sarcomere 1 sarcomere

61 3D Structure & Cross Bridges

62 Ethier & Simmons (2007) Introductory Biomechanics From cells to Organisms

63 Skeletal Muscle Innervation Nerve cell carries electrical signal Neuron transmits impulseNeuron transmits impulse CNS to muscleCNS to muscle Motor nervesMotor nerves efferentefferent Sensory receptors to CNSSensory receptors to CNS Sensory nervesSensory nerves afferentafferent

64 Motor neuron (efferent) One nerve and all the muscle fibers it innervatesOne nerve and all the muscle fibers it innervates CollateralsCollaterals Neuromuscular junctionNeuromuscular junction motor endplatemotor endplate synapsesynapse Single muscle ==> many MUsSingle muscle ==> many MUs MotorUnit

65 In vivo motor neuron

66 Skeletal Muscle Innervation Nerve cell carries electrical signal Neuron transmits impulseNeuron transmits impulse CNS to muscleCNS to muscle Motor nervesMotor nerves efferentefferent Sensory receptors to CNSSensory receptors to CNS Sensory nervesSensory nerves afferentafferent

67 Sensory nerve (afferent) Golgi tendon organsGolgi tendon organs sensitive to amount of tension producedsensitive to amount of tension produced inhibits tension productioninhibits tension production

68 Sensory nerve (afferent) Golgi tendon organsGolgi tendon organs sensitive to amount of tension producedsensitive to amount of tension produced inhibits tension productioninhibits tension production In vivo

69 Sensory nerve (afferent) Muscle SpindlesMuscle Spindles sensitive to length of muscle (rate of lengthening)sensitive to length of muscle (rate of lengthening) enhances tension productionenhances tension production

70 Sensory nerve (afferent) Muscle SpindlesMuscle Spindles sensitive to length of muscle (rate of lengthening)sensitive to length of muscle (rate of lengthening) enhances tension productionenhances tension production

71 Skeletal Muscle Innervation

72 Principles of Activation All-or-none principleAll-or-none principle if & when a motor unit is activated, all the fibers in the motor unit produce tensionif & when a motor unit is activated, all the fibers in the motor unit produce tension

73 Excitation - Contraction Coupling Process of converting an electrical signal (action potential) into the mechanical process of sarcomere contraction and force production

74 Sliding Filament Theory Describes the physiological - biomechanical process of sarcomere shortening and force production Proposed in 1953 by Hugh E. Huxley and Jean Hanson, published in Nature, Focus of extensive research ever since.

75 Molecular basis of muscle contraction Acetylcholine released at NMJAcetylcholine released at NMJ Muscle membrane is depolarized.Muscle membrane is depolarized. Calcium is released.Calcium is released. Troponin combines with Ca exposing actin active sitesTroponin combines with Ca exposing actin active sites Cross-bridge attachment.Cross-bridge attachment. Myosin crossbridges swivel and rotatesMyosin crossbridges swivel and rotates Pulls actin over myosin  Sarcomere shortensPulls actin over myosin  Sarcomere shortens Crossbridge breaks, myosin returns to original shapeCrossbridge breaks, myosin returns to original shape Cross Bridge Cycling

76 Cross Bridges from Myosin Molecule

77 Cross Bridges Produce Power Stroke

78 Energy metabolism of muscle Contraction consumes chemical energyContraction consumes chemical energy ATP (adenosine triphosphate)ATP (adenosine triphosphate) Source of ATP: CHO, fat, (protein)Source of ATP: CHO, fat, (protein) aerobic metabolism (with oxygen)aerobic metabolism (with oxygen) byproducts CO 2 and H 2 0byproducts CO 2 and H 2 0 anaerobic metabolism (without oxygen)anaerobic metabolism (without oxygen) byproduct lactate (lactic acid)byproduct lactate (lactic acid)

79 Energy metabolism of muscle Contraction consumes chemical energyContraction consumes chemical energy Source of ATP: CHO, fat, (protein)Source of ATP: CHO, fat, (protein) FatigueFatigue lactic acid, depletion of ATP, neural, psychologicallactic acid, depletion of ATP, neural, psychological

80 Skeletal Muscle Muscle fibers terminate at the tendonMuscle fibers terminate at the tendon the myotendinous junctionthe myotendinous junction ***mysiums ==> tendon***mysiums ==> tendon weakest part of the muscle?weakest part of the muscle?

81 Connective tissue of muscle Provides pathway (blood, nerve)Provides pathway (blood, nerve) Affects mechanical characteristicsAffects mechanical characteristics Three componentsThree componentsThree componentsThree components Epimysium - outside covering (fascia).Epimysium - outside covering (fascia). Perimysium - septa separating bundles of fibers (fasciculi) internally.Perimysium - septa separating bundles of fibers (fasciculi) internally. Endomysium - surround individual fibers.Endomysium - surround individual fibers.

82 Muscle x-section

83 Gross Muscle Anatomy

84 Muscle Actions (contractions) Muscle only pullsMuscle only pulls Concentric - shortening of the muscle (causes movement)Concentric - shortening of the muscle (causes movement) Eccentric - lengthening of the muscle (slows or controls movement)Eccentric - lengthening of the muscle (slows or controls movement) Isometric - muscle tension without movement (prevents movement) 10.13Isometric - muscle tension without movement (prevents movement) 10.13

85 ConcentricEccentricIsometric Positive accelerationNegative accelerationNo. accel. Increase velocityDecrease velocityMaintain v. Jumping upLanding from jumpStanding Throwing (start toThrowing (after ballHolding ball release)release – stop arm) WeakestStrongestMiddle Comparing Types of Contractions

86 Important roles of muscle Concentric muscle activity distributes and reduces the stress within bone by generating mechanical energyConcentric muscle activity distributes and reduces the stress within bone by generating mechanical energy Eccentric muscle activity distributes and reduces the stress within bone by absorbing mechanical energyEccentric muscle activity distributes and reduces the stress within bone by absorbing mechanical energy Continuous strenuous activity can cause abnormally high stress on bone/muscle as muscle fatiguesContinuous strenuous activity can cause abnormally high stress on bone/muscle as muscle fatigues Absorbing?

87 Three Component Muscle Model (explains mechanical behavior of muscle) Schematic diagram of muscle “Muscle” represented with SEE, CE, & PEE (SEC, CC, PEC) Tendon is another component of SEE (Zajac, 1992)

88 Three Component Muscle Model Muscles with fibers in series shorten more and have faster shortening velocities Muscles with fibers in parallel produce more force

89 Shorten Sarcomeres to Stretch Springs Muscle model with Sarcomere activated and sarcomere and SEE shortened to keep (SEE) (tendon)tendon stretched (McMahon, 1987) (Roberts, 1997)

90 Mechanical Muscle-Tendon Model Mechanical model explains: Contractile and elastic components – Contractile component exerts force on SEE and SEE exerts force on bone Electromechanical Delay – delay between contractile activation and bone moving Actin & myosin, slack in SEE, overcome inertia Eccentric force greater than concentric force Definitions of concentric and eccentric contractions

91 Electromechanical Delay Explain the term, wrt 3 component model of muscle.

92 Functional Properties of Muscle Muscles contract and produce force. Force production comes from contractile and elastic elements which have entirely different force producing characteristics. Total muscle force production is a complex interaction between the force producing components and is affected by several functional characteristics. Basically, the quantity and quality of x-bridges.

93 Factors affecting force produced: Length-tension relationshipLength-tension relationship Total Tension reflectsTotal Tension reflects amount of overlap between actin & myosinamount of overlap between actin & myosin utilization of elastic componentutilization of elastic component Stretch-Shorten Cycle (SSC)Stretch-Shorten Cycle (SSC)

94 Length – Tension Relationship Force development in the sarcomeres depends on the length (overlap) of the sarcomere. Sarcomere produces maximum force at mid- length (resting length) Sarcomere Length – Tension Relationship

95 Length Tension in Sarcomeres Mid or resting length optimizes the arrangement of actin and myosin filaments. More crossbridge sites available – more cross bridges formed – more force.

96 Length Tension in Sarcomeres Shorter sarcomere lengths reduce available crossbridge sites – actin filaments overlaps and cover some sites

97 Length Tension in Sarcomeres Longer sarcomere lengths reduce available crossbridge sites – actin filaments stretched past binding sites on myosin filaments. Few or no crossbridges formed.

98 Length Tension in Elastic Elements Force development in the elastic elements depends on the length of the element according to Hooke’s Law. (F=-k  x) Elastic element maximum force at longest lengths and no force at resting or shorter lengths.

99 Length Tension in Elastic Elements Elastic element length-tension for different muscles Depends on tissue stiffness which depends on size and molecular composition

100 Length Tension in Elastic Elements Force development in the elastic elements also depends on the velocity of the stretch – modified Hooke’s Law to include rate of stretch: F= k  x + Vel. Elastic element has more force with longer and faster stretch.

101 Length – Tension Relationship Total muscle force depends on individual component contributions. At mid lengths – sarcomere dominates At long lengths – elastic elements dominate Combined Length–Tension Relationship

102 Length - Tension & Stretch - Shorten Stretch – shortening cycle employs the length tension relationship of muscle. This effect includes maximizing the amount and rate of muscle stretch. How is stretch-shortening cycle used in throwing, batting, running, and darts? How about lifting, hammering, pushing, sweeping?

103 Factors affecting force produced: Force-velocity relationshipForce-velocity relationship concentric: decrease force with increase velocityconcentric: decrease force with increase velocity inefficient coupling of actin & myosininefficient coupling of actin & myosin eccentric: increase (?) force with increase velocityeccentric: increase (?) force with increase velocity viscosity of muscle fluidsviscosity of muscle fluids effective coupling of actin & myosineffective coupling of actin & myosin

104 Functional Properties of Muscle Muscles contract and produce force. Muscle forces are produced in many different situations some of which involve slower contractions and some of which involve faster contractions. Contraction velocity (rate of shortening or lengthening of muscle fibers and elastic tissue) affects force production. Contraction velocity interacts with type of contraction – velocity effect is different for concentric and eccentric contractions.

105 Force – Velocity Relationship Concentric: Force production decreases as contraction velocity increases. Higher forces can be produced during slower contractions. Why? (sliding filaments and cross bridge formation, elastic components: quality) Contraction Type Eccentric Concentric

106 Force – Velocity Relationship Eccentric: Force production increases as contraction velocity increases. Higher forces can be produced during faster contractions. Contraction Type Eccentric Concentric

107 Force – Velocity Relationship Eccentric: Increased force production due to faster stretch of elastic tissues: F= -k  x + Vel. Stretch-shortening cycle – faster pre-stretch enhances muscle force production. Contraction Type Eccentric Concentric

108 Force – Velocity Relationship Isometric: (No velocity, constant length) Force Hierarchy: Eccentric strongest. Isometric in between. Concentric weakest. Contraction Type Eccentric Concentric

109 Force – Velocity Relationship Force Hierarchy: Eccentric – stretch utilizes elastic component and contractile works at optimum length Isometric – both elastic and contractile components can contribute but one or both will not be at optimum length Concentric – contractile and elastic components shortening & moving away from optimum length Contraction Type Eccentric Concentric

110 Force – Velocity Relationship Concentric: Knee joint velocity and muscle torque during the stance phase of running. Torque (and muscle force) are highest in midstance when the joint stops moving (zero velocity). Muscle shortening velocity is low at this time.

111 Force–Velocity Relationship Weight lifting ability limited by concentric strength. Eccentric capability not trained as effectively.

112 Length – Tension Relationship Sticking region or sticking point is the weak point in weightlifting, the phase when the lift may fail. The region is defined as the period during the early lift when less force than the weight of the bar is being applied to the bar. Sticking Region in Lifting

113 Concentric Force–Velocity Relationship F – V has identical form in males & females Training raises F – V but maintains basic form F –V has basic form in all muscles but force output at each velocity varies across muscles

114 Concentric Force–Velocity Relationship F – V has identical form in slow and fast twitch fibers but fast twitch have higher force at each velocity

115 Concentric Force–Velocity Relationship F – V has identical form in different muscles, some muscles have larger force at each velocity.

116 Functional Properties of Muscle Muscles contract and produce force and this force is applied to a bone in the skeletal system. Sometimes the muscle force causes the bone to move the force does work Work – result of a force applied with movement Work = Force * displacement or Work = Torque * angular displ.

117 Functional Properties of Muscle Power represents the rate at which work is being done. P = Work / time P= Work / time = Force * displ. / time = Torque * ang. displ./ time = Force * velocity = Torque * angular velocity measured in Watts (W) Powerful people are Strong and Fast

118 Functional Properties of Muscle Powerful people are Strong and Fast

119 0.20 m 40 N Work = Force * displacement = 0.20 m (40N) = 8 Nm = 8 J Lift in 0.5 s: P = Work/time = 16 W Lift in 1.0 s: P = Work / time = 8 W Lift in 2.0 s: P = Work / time = 4 W Work was performed from a concentric contraction. Power During Lifting

120 Power – Velocity Relationship Concentric: Power is maximized at about 1/3 maximum shortening velocity. Muscle force is still moderately high and velocity is moderately fast.

121 Power – Velocity Relationship Concentric: Power is higher in fast vs. slow twitch muscle fibers at all velocities.

122 Power – Velocity Relationship Concentric: Power – velocity form identical for different muscles but some muscles are more powerful than other muscles.

123 Knee power, torque, and angular velocity during stance phase of running. Peak torque at zero velocity – at maximum knee flexion, maximum quadriceps stretch – muscle force maximized early in movement. Peak power at mid levels of torque and velocity – both torque and velocity contribute to power – muscle work maximized in middle of movements. Joint Power Produced By Joint Torques

124 Functional Properties of Muscle Combined understanding of L-T, F-V, and P-V relations 1)Stretch-shortening cycle provides pre-stretch (eccentric contraction) prior to the desired concentric contraction 2) Stretched muscle provides high force at the start of concentric contraction due to favorable L-T and F-V characteristics 3) Muscle power and work maximized about 1/3 into movement – muscle contribution to movement (force & displacement) maximized at this time

125 What can strength training do? Muscle force affected by active generation of tension, enhancement from muscle spindle, and inhibition from Golgi Tendon Organ

126

127 Explains the effectiveness of plyometric training

128 Joints Fibrous jointsFibrous joints fibrous tissue bridges the joint (ie skull).fibrous tissue bridges the joint (ie skull). Cartilaginous jointsCartilaginous joints cartilage bridges the joint (e.g., intervertebral joints, sacrum).cartilage bridges the joint (e.g., intervertebral joints, sacrum). Synovial jointsSynovial joints no tissue between the articular surfacesno tissue between the articular surfaces

129 Synovial joints StructureStructure bone endsbone ends articular cartilage (hyaline cartilage)articular cartilage (hyaline cartilage) joint capsule (ligaments)joint capsule (ligaments) synovial membranesynovial membrane synovial fluidsynovial fluid Lubrication: fluid & hyalineLubrication: fluid & hyaline

130 Osteoarthritis aka Degenerative joint disease.aka Degenerative joint disease. Cartilage does not repair because.....Cartilage does not repair because..... CharacteristicsCharacteristics wearing away of cartilagewearing away of cartilage bony deformation (osteophytes)bony deformation (osteophytes) pain with usepain with use CauseCause genetics, mechanical wear (injury)genetics, mechanical wear (injury)

131 Intervertebral discs Intervertebral discs The Jelly Donut of our backThe Jelly Donut of our back Donut: annulus fibrosus.Donut: annulus fibrosus. Jelly: nucleus pulposusJelly: nucleus pulposus

132 Intervertebral discs Intervertebral discs The Jelly Donut of our backThe Jelly Donut of our back Donut: annulus fibrosus.Donut: annulus fibrosus. Jelly: nucleus pulposusJelly: nucleus pulposus Relationship to spinal nervesRelationship to spinal nerves

133 Back pain 'starts in school By Roger Highfield Around half of all children are at risk of suffering a lifetime of back problems because of awkward postures during lessons and using computers, furniture and other equipment designed for adults. Forty per cent of schoolchildren suffer health problems considered in adults to be "work related” that could affect them for the rest of their lives, said Prof Peter Buckle, of the University of Surrey's Robens Centre for Health Ergonomics in Guildford. He said a Danish study showed that 51 per cent of children aged 13 to 16 reported low back pain in the previous year, and 24 per cent of 11- to14-year-olds in the north-west of England reported having back pain in the month prior to completing a questionnaire. "Under European laws the health of workers is protected," he said. "But when we start to look at young adults and children the picture is far less clear. "Worryingly, evidence is starting to show that, for some health problems, we may be leaving it too late before we start helping." A study found that those reporting low back pain in school were more likely to report low back pain as adults. (Filed: 10/09/2002) © Copyright of Telegraph Group Limited 2002.

134 Intervertebral discs Intervertebral discs The Jelly Donut of our backThe Jelly Donut of our back Donut: annulus fibrosus.Donut: annulus fibrosus. Jelly: nucleus pulposusJelly: nucleus pulposus Relationship to spinal nervesRelationship to spinal nerves Herniation (low back pain)Herniation (low back pain) nucleus causes annulus to bulge at weak area nucleus causes annulus to bulge at weak area

135 Back loads Affected by: Load lifted HAT inertia & posture Muscle Activity

136 Back muscle modeling McGill, 2001


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