AML2506 Biomechanics and Flow Simulation Day 03B The Biomechanics of Human Skeletal Muscle Session Speaker Dr. M. D. Deshpande 1
Session Objectives At the end of this session the delegate would have understood The human skeletal muscles function and how it produces coordinated dmovement of the body The effects of the force-velocity and length-tension relationships and electromechanical delay on muscle function. The concepts of strength, power, and endurance from a biomechanical i perspective 2
Session Topics 1. The basic behavioral properties of the musculotendinous unit 2. The relationships of fiber types and fiber architecture to muscle function 3. The skeletal muscles function and its relation to the movement of human body 4. The force-velocity and length-tension relationships 5. Concepts of strength, power, and endurance 3
Behavioral Properties of the Musculotendinous Unit 1) Extensibility: ability to be stretched or to increase in length 2) Elasticity: ability to return to normal resting length following a stretch 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 stretched 4
Behavioral Properties of the Musculotendinous Unit From 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). Parallel Elastic Component Contractile Component Series Elastic Component 5
Behavioral Properties of the Musculotendinous Unit What is the stretch-shortening shortening cycle? Eccentric contraction (in which the muscle is actively stretched) followed immediately by concentric contraction Irritability: ability to respond to a stimulus Ability to develop tension: the contractile component of muscle function 6
Structural Organization of Skeletal Muscle What is a muscle fiber? Single muscle cell surrounded by a membrane called the sarcolemma and containing specialized cytoplasm called sarcoplasm What 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 training What is a motor unit? Single motor neuron and all fibers it innervates Considered the functional unit of the neuromuscular system 7
Structural Organization of Skeletal Muscle FT ST Fast 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 Te ension Time 8
Skeletal Muscle Fiber Characteristics TYPE IIA Type I Fast-Twitch Type IIB Slow-Twitch Oxidative Fast-Twitch Oxidative Glycolytic Glycolytic CHARACTERISTIC (SO) (FOG) (FG) Contraction Speed slow fast fast Fatigue rate slow intermediate fast Diameter small intermediate large ATPase concentration low high high Mitochondrial i concentration highh highh low Glycolytic enzyme low concentration intermediate high 9
Structural Organization of Skeletal Muscle How are muscle fibers organized? Parallel fiber arrangement: fibers are roughly parallel to the longitudinal l axis of the muscle; examples are? Pennate fiber arrangement: short fibers attach to one or more tendons within the muscle; examples? Parallel l fiber arrangements Pennate fiber arrangements 10
Skeletal Muscle Function How 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 thresholds What terms are used to describe muscle contractions based on change in muscle length? Concentric: involving shortening Eccentric: involving lengthening Isometric: involving no change 11
Skeletal Muscle Function What 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 agonist What 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 12
Skeletal Muscle Function Active insufficiency : Failure to produce force when muscles are slack (decreased ability to form a fist with the wrist in flexion) Passive insufficiency: restriction of joint range of motion when muscles are fully stretched (decreased ROM for wrist extension with the fingers extended) 13
Factors Affecting Muscular Force Generation The force-velocity relationship for muscle tissue: When resistance (Low resistance, (force) is negligible, high contraction muscle contracts with velocity) maximal velocity. Fo orce Velocity 14
Factors Affecting Muscular Force Generation isometric maximum The force-velocity relationship for muscle tissue: As the load increases, concentric contraction velocity slows to zero at isometric maximum. For rce Velocity 15
Factors Affecting Muscular Force Generation The 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. Tension Active Tension Total Tension Passive Tension 50 100 150 Length (% of resting length) 16
Factors Affecting Muscular Force Generation What is electromechanical delay? Myoelectric activity Force Stimulus Electromechanical delay Time between arrival of a neural stimulus and tension development by the muscle 17
Muscular Strength, Power and Endurance How do we measure muscular strength? The amount of torque a muscle group can generate at a joint F t F t The component of muscle force that t produces torque (Ft) at the joint is directed perpendicular to the attached bone. 18
Muscular Strength, Power and Endurance What factors affect muscular strength? Tension-generating capability of the muscle tissue, which is in turn affected by: Muscle cross-sectional sectional area Training state of muscle 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 bone 19
Muscular Strength, Power and Endurance A B The 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 of the muscle is lessened because more and more of the force is pulling the radius toward or away from the elbow rather than contributing to forearm rotation. 20 C
Muscular Strength, Power and Endurance What 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 joint Force-Velocity Power-Velocity Force Power Velocity The general shapes of the force-velocity and power-velocity curves for skeletal muscle. 21
Muscular Strength, Power and Endurance What is muscular endurance? The ability of muscle to exert tension over a period of time The opposite of muscle fatigability What is the effect of muscle temperature (warm up)? The speeds of nerve and muscle functions increase 22
Muscular Strength, Power and Endurance With 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. Force Normal body temperature Elevated body temperature Vl Velocity 23
Common Muscle Injuries Strains Contusions Cramps Delayed onset Muscle Soreness Compartment Syndrome 24
Further Reading E-Tech: An Orthopaedics & Biomechanics Resource http://dspace.dial.pipex.com/town/square/fk1 di i / / /fk1 4/index.htm Myology Section from Gray's Anatomy www.bartleby.com/107/102.html 25
Laboratory Refer laboratories exercise 26
Review In this session the delegates are taught: The basic behavioral properties of the musculotendinous unit The relationships of fiber types and fiber architecture to muscle function The skeletal muscles function and its relation to the movement of human body The force-velocity and length-tension relationships Concepts of strength, power, and endurance 27
Thank you 28