Bài giảng Basic Biomechanics - Chapter 6 The Biomechanics of Human Skeletal Muscle

Chapter 6The Biomechanics of Human Skeletal MuscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.© 2012 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/IrwinBehavioral Properties of the Musculotendinous Unit1) extensibility: ability to be stretched or to increase in length2) elasticity: ability to return to normal resting length following a stretchBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Behavioral Properties of the Musculotendinous Unit Components of elasticity: parallel elastic component - passive elasticity derived from muscle membranes series elastic component - passive elasticity derived from tendons when a tensed muscle is stretchedBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Behavioral Properties of the Musculotendinous UnitParallel Elastic ComponentSeries Elastic ComponentContractile ComponentFrom a mechanical perspective, the musculotendinous unit behaves as a contractile component (muscle fibers) in parallel with one elastic component (muscle membranes) and in series with another elastic component (tendons).Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.What is the stretch-shortening cycle? eccentric contraction (in which the muscle is actively stretched) followed immediately by concentric contraction Can you think of examples? Behavioral Properties of the Musculotendinous UnitBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Behavioral Properties of the Musculotendinous Unit3) irritability: ability to respond to a stimulus4) ability to develop tension: the contractile component of muscle functionBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleWhat is a muscle fiber?(single muscle cell surrounded by a membrane called the sarcolemma and containing specialized cytoplasm called sarcoplasm)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.SarcolemmaStructural Organization of Skeletal MuscleWhat do we know about muscle fibers? some fibers run the entire length of a muscle; others are shorter skeletal muscle fibers grow in both length and diameter from birth through adulthood fiber diameter can be increased through resistance trainingBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.SarcomereThe sarcomere is the basic structural unit of the muscle fiber. The alternating dark and light bands give muscle its striated appearance. The A bands contain thick, rough myosin filaments surrounded by six thin, smooth actin filaments. The I bands contain only thin actin filaments.Structural Organization of Skeletal MuscleWhat is a motor unit? single motor neuron and all fibers it innervates considered the functional unit of the neuromuscular systemBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleFast twitch (FT) fibers both reach peak tension and relax more quickly than slow twitch (ST) fibers. (Peak tension is typically greater for FT than for ST fibers.)Twitch TensionTimeFT STBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle Fiber Characteristics TYPE IIAType I Fast-Twitch Type IIB Slow-Twitch Oxidative Fast-Twitch Oxidative Glycolytic GlycolyticCHARACTERISTIC(SO) (FOG) (FG)Contraction Speed slow fast fastFatigue rate slow intermediate fastDiameter small intermediate largeATPase concentration low high highMitochondrial high high lowconcentrationGlycolytic enzyme low intermediate highconcentrationBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleHow are muscle fibers organized? parallel fiber arrangement: fibers are roughly parallel to the longitudinal axis of the muscle; examples are? pennate fiber arrangement: short fibers attach to one or more tendons within the muscle; examples?Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Structural Organization of Skeletal MuscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Parallel fiber arrangementsPennate fiber arrangementsStructural Organization of Skeletal MuscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.RelaxedWith tension developmentThe angle of pennation increases as tension progressively increases in the muscle fibers.Skeletal Muscle FunctionHow are motor units (MUs) recruited? slow twitch (ST) fibers are easier to activate than fast twitch (FT) fibers ST fibers are always recruited first increasing speed, force, or duration of movement involves progressive recruitment of MUs with higher and higher activation thresholdsBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle FunctionWhat terms are used to describe muscle contractions based on change in muscle length? concentric: involving shortening eccentric: involving lengthening isometric: involving no changeBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle FunctionWhat roles are assumed by muscles? agonist: acts to cause a movement antagonist: acts to slow or stop a movement stabilizer: acts to stabilize a body part against some other force neutralizer: acts to eliminate an unwanted action produced by an agonistBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle FunctionWhat are disadvantages associated with muscles that cross more than one joint? active insufficiency: failure to produce force when slack passive insufficiency: restriction of joint range of motion when fully stretched Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle Function active insufficiency: failure to produce force when muscles are slack (decreased ability to form a fist with the wrist in flexion)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle Function passive insufficiency: restriction of joint range of motion when muscles are fully stretched (decreased ROM for wrist extension with the fingers extended)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Factors Affecting Muscular Force GenerationThe force-velocity relationship for muscle tissue: When resistance (force) is negligible, muscle contracts with maximal velocity.VelocityForce(Low resistance, high contraction velocity)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Factors Affecting Muscular Force GenerationThe force-velocity relationship for muscle tissue: As the load increases, concentric contraction velocity slows to zero at isometric maximum.VelocityForceisometric maximumBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Factors Affecting Muscular Force GenerationThe length-tension relationship: Tension present in a stretched muscle is the sum of the active tension provided by the muscle fibers and the passive tension provided by the tendons and membranes.TensionLength (% of resting length)50 100 150Active TensionPassive TensionTotal TensionBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Factors Affecting Muscular Force GenerationWhat is electromechanical delay?(time between arrival of a neural stimulus and tension development by the muscle)Myoelectric activityForceElectromechanical delayStimulusBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceHow do we measure muscular strength?(the amount of torque a muscle group can generate at a joint)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceHow do we measure muscular strength? The component of muscle force that produces torque (Ft) at the joint is directed perpendicular to the attached bone.FtFtBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWhat factors affect muscular strength? tension-generating capability of the muscle tissue, which is in turn affected by: muscle cross-sectional area training state of muscleBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWhat factors affect muscular strength? moment arms of the muscles crossing the joint (mechanical advantage), in turn affected by: distance between muscle attachment to bone and joint center angle of the muscle’s attachment to boneBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Skeletal Muscle FunctionBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Torque produced by a muscle (Tm) at the joint center of rotation is the product of muscle force (Fm) and muscle moment arm (d ). Muscular Strength, Power and EnduranceThe mechanical advantage of the biceps bracchi is maximum when the elbow is at approximately 90 degrees (A), because 100% of muscle force is acting to rotate the radius. As the joint angle increases (B)or decreases (C) from 90 degrees, the mechanical advantage ofthe muscle is lessened because more and more of the force is pullingthe radius toward or away from the elbow rather than contributing to forearm rotation.CABBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWhat is muscular power? the product of muscular force and the velocity of muscle shortening the rate of torque production at a joint the product of net torque and angular velocity at a jointBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceThe general shapes of the force-velocity and power-velocity curves for skeletal muscle.ForceVelocityPowerPower-VelocityForce-VelocityBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWhat is muscular endurance? the ability of muscle to exert tension over a period of time the opposite of muscle fatigabilityBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWhat is the effect of muscle temperature on (warm up) ?(the speeds of nerve and muscle functions increase)Basic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.Muscular Strength, Power and EnduranceWith warm-up, there is a shift to the right in the force-velocity curve, with higher maximum isometric tension and higher maximum velocity of shortening possible at a given load.VelocityForceNormal body temperatureElevated body temperatureBasic Biomechanics, 6th editionBy Susan J. Hall, Ph.D.