1. Characteristics of Muscle  Irritability Ability to respond to stimulation  Contractility Ability to shorten when it receives sufficient stimulation Unique to muscle tissue  Extensibility Ability to stretch/lengthen beyond resting length Protective mechanism  Elasticity Ability to return to resting length after being stretched Protective mechanism

2. Groups of Muscles  Muscles typically act in unison – not individually  Fascia Sheet of fibrous tissue Compartmentalizes groups of muscles

3. Individual Muscle Organization  Belly Thick central portion  Epimysium Outside covering of a muscle  Fascicles Bundles of muscle fibers  Perimysium Dense connective sheath covering a fascicle  Fibers Cells of a skeletal muscle

4. Individual Muscle Organization (cont.)  Endomysium Very fine sheath covering individual fibers  Sarcolemma Thin plasma membrane branching into muscle  Myofibrils Rod-like strands of contractile filaments Many sarcomeres in series  Sarcoplasma Cytoplasm of muscle cell  Sarcoplasmic reticulum Specialized endoplasmic reticulum of muscle cells

5. Individual Muscle Organization (cont.)  T-tubules Extension of sarcolemma that protrudes into muscle cell Also called, transverse tubule  Myosin Thick, dark filament  Actin Thin, light filament  Sarcomere Unit of myosin and actin Contractile unit of muscle

6. Fiber Organization  Fusiform Parallel fibers and fascicles High speed of contract, force production ACS = PCS Anatomical Cross-Section (ACS) Physiological Cross-Section (PCS) Sartorius, biceps brachii, brachialis

7. Fiber Organization  Penniform 3 Types Unipennate  Off one side of tendon  Semimembranosus Bipennate  Off both sides of tendon  Gastrocnemius Multipennate  Both varieties  Deltoid PCS > ACS

8. Fiber Type  Type I Slow twitch, oxidative Red (because of high myoglobin content) Endurance athletes  Type IIa Intermediate fast-twitch, oxidative-glycolytic  Type IIb Fast twitch, glycolytic White Sprinters, jumpers

9. Muscle Attachment  3 ways muscle attaches to bone Directly Via a tendon Via an aponeurosis  Tendon Inelastic bundle of collagen fibers  Aponeurosis Sheath of fibrous tissue  Origin More proximal attachment  Insertion More distal attachment

10. Characteristics of a Tendon  Transmits muscle force to associated bone  Can withstand high tensile loads  Viscoelastic stress-strain response  Myotendinous junction Where tendon and muscle join

11. Functions of Muscle  Produce movement  Maintain postures and positions  Stabilize joints  Other functions Support and protect visceral organs Alter and control cavity pressure Maintain body temperature Control entrances/exits to the body

12. Role of Muscle  Prime mover Muscle(s) primarily responsible for a given movement  Assistant mover Other muscles contributing to movement  Agonist Muscles creating same joint movement  Antagonist Muscles opposing joint movement  Stabilizer Holds one segment still so a specific movement in an adjacent segment can occur  Neutralizer Muscle working to eliminate undesired joint movement of another muscle

13. Muscle Actions  Isometric Tension produced without visible change in joint angle Holding arms out to sides  Concentric Muscle visibly shortens while producing tension Up phase of a sit-up  Eccentric Muscle visibly lengthens while producing tension Lowering phase of squat

14. Stretch-Shortening Cycle  Pre-stretch Quick lengthening of a muscle before contraction Generates greater force than contraction alone Utilizes elastic component of muscle  Prestretch & Fiber Type Type I Slower pre-stretch best because of slow cross- bridging Type II Faster pre-stretch best because of fast cross- bridging

15. Plyometrics  Conditioning protocol that utilizes pre-stretching Single-leg bounds, depth jumps, stair hopping

16. One- and Two-Jointed Muscles  Muscles can cross one or two joints  One-Jointed Muscles Brachialis, pectoralis major  Two-Jointed Muscles (biarticulate) Save energy Gastrocnemius, hamstrings, biceps brachii

17. Two-Jointed Muscles RF: Better leg extensor, H: better hip extensor

18. Motor Unit  Group of muscles innervated by the same motor neuron  From 4 to 2000 muscle fibers per motor unit  Action potential Signal to contract from motor neuron  Neuromuscular junction Also called end plate Where action potential from neuron meets muscle fiber  Conduction velocity Velocity at which action potential is propagated along membrane

19. Muscle Contraction  Resting potential Voltage across the plasma membrane in a resting state  Excitation-Contraction Coupling Transmission of action potential along sarcolemma  Twitch Rise and fall reaction from a single action potential  Tetanus Sustained muscle contraction from high-frequency stimulation

20. Muscle Contraction (cont.)  Depolarization Loss of polarity  Repolarization Movement to the initial resting (polarized) state  Hyperpolarization State before repolarization

21. Sliding Filament Theory  A.F. Huxley  Seeks to explain production of tension in muscle  Myosin & actin Create cross-bridges Slide past one another Cause the sarcomere to contract

22. Mechanical Model of Muscle  A.V. Hill  3 Component Model Contractile (CC) Converts stimulation into force Parallel elastic (PEC) Allows the muscle to be stretched Associated with fascia surrounding muscle Series elastic (SEC) Transfers muscle force to bone

23. Factors Influencing Muscle Force  Angle of attachment  Force-time characteristics Force increases non-linearly due to elastic components  Length-tension relationship  Force-velocity relationship

24. Electromyography  Correct placement of electrodes is critical  Electrodes oriented parallel to muscle fiber  Prepare skin by… Shaving Abrading Cleaning with alcohol  Signal must be amplified  Sample rate ≥ 1000 Hz required

25. Electromyography (cont.)  Rectification Taking the absolute value of raw signal  Linear envelope  Time domain  Frequency domain  Electromechanical delay (EMD) Temporal delay between onset of EMG signal & development of muscle tension

26. Muscle Fatigue  Fatigue results from… Peripheral (muscular) mechanisms Central (nervous) mechanisms  When motor unit fatigues… Change in frequency content Change in amplitude of EMG signal  Sufficient rest restores initial signal content and amplitude

27. Clinical Gait Analysis  EMG used to investigate which muscle group is used in a certain phase of gait  Determine activation order  Raw or rectified EMG signal is used

28. Ergonomics  Ergonomics  EMG used to investigate effects of… Sitting posture Carrying loads

29. Principles of Training  Genetic predisposition  Training specificity  Intensity  Rest  Volume

30. Strength Training and the Nonathlete  ACSM 2 days per week 8–12 exercises per day  Counteracts atrophy of muscle and bone  Elderly  Children High-intensity not recommended Epiphyseal plates susceptible to injury under high loads

31. Training Modalities  Isometric No visible movement Rehabilitation  Isotonic Same weight throughout range of motion (ROM)  Isokinetic Same velocity, varied resistance  Close-linked Isotonic, in which one segment is fixed in place  Variable resistive Supposedly overloads muscle throughout ROM

32. Injury to Skeletal Muscle  At risk Two-jointed muscles at greatest risk of strain Eccentrically contracted to slow limb movement Hamstrings, rotator cuffs Fatigued or weak muscles When performing unique task for first time Already injured  Prevention Warm-up Build up when starting new program Recognize signs of fatigue Give body adequate rest

33. Summary  Characteristics of muscle tissue Irritability, contractility, extensibility, elasticity  Often act in compartmentalized groups  Fiber organization Fusiform, penniform  Fiber types Type I, IIa, IIb  Functions of muscle Produce movement, maintain postures, stabilize joints, and others