Properties of Biological Materials -- Skeletal Muscle 柴惠敏 台灣大學 物理治療學系

主要參考書 Nordin, M. & Frankel V.H., 2001. Basic Biomechanics of the Musculoskeletal System, 3rd ed. Philadelphia, PA, Lea & Febiger. Chapter 6.

Properties of Biological Materials -- Skeletal Muscle Basic Concepts

Classification of Muscles Striated muscles skeletal muscles: voluntary contraction cardiac muscles non-striated (smooth) muscles

Function of Skeletal Muscle To create motion by producing force To provide strength To protect joints by absorbing shock

Components of Skeletal Muscles Fascia Epimysium Fascicle perimysium muscle fiber (cell) endomysium sacrolemma myofibril: myosin and actin

Components of Muscle Fibers muscle fiber: a long cylindrical cell with hundreds of nuclei 10-100 m in diameter 1-30 cm in length myofibril: contractile component Biomechnics is a discipline of science, newly developed and in the process of becoming established. myosin crossbridge actin

Sliding Filament Mechanism AF Huxley & HE Huxley, 1964 active shortening of sacromere, resulting from the relative movement of actin and myosin filaments with retaining its original length force of contraction is developed by the crossbridges of myosin

Movement of Cross Bridges

Excitation-Contraction Coupling An action potential in the sacrolemma provides electrical signal which triggers calcium ions undergoing chemical reactions of contraction

Types of Muscle Contraction Static work isometric contraction Dynamic work concentric contraction eccentric contraction isokinetic contraction

Isokinetic Contraction joint moment Isokinetic mg M  Isotonic joint angle F

Force Production in Muscle Length-Tension relationship Load-Velocity relationship Force-Time relationship

Length-Tension Relationship The tension that a muscle generates varies with its length Obtained under isometric contractions and for maximum activation of the muscle

Length-Tension Curve of A Single Muscle Fiber sacromere length tension resting length

Length-Tension Curve total tension tension active passive tension

Mechanical Model of Skeletal Muscle Fiber parallel elastic component series elastic component contractile component

Length-Tension Curve length tension total tension active passive

Force-Velocity Curve Hill’s model contraction velocity force eccentric concentric isometric

Force-Time Curve isometric force force time

Effect of Temperature temperature  nerve conduction velocity  frequency of stimulation  muscle force  temperature  enzyme activity  efficiency of muscle contraction  temperature  elasticity of collagen  extensibility of muscle  muscle force 

Muscle Atrophy  cross-sectional area of fibers  number of muscle fibers  aerobic capacity by changing the proportion of muscle fiber types sedentary people:  # of type I fibers athletes:  fiber type affected by that sports

Muscle Hypertrophy By physical training By electric stimulation  cross-sectional area of muscle fibers  number of muscle fibers change in proportion of muscle fiber types By electric stimulation

Single Fiber Twitch 0 50 100 150 200 ms S contraction