Exercise Science & Sport Studies Physiological Principles of Conditioning for Sports Dr. Moran EXS 558

Class Textbook Class Website Physiological Aspects of Sport Training and Performance J. Hoffman http://www.amazon.com/exec/obidos/ASIN/0736034242/interactiveda162-20/102-3304755-7467337 Class Website http://web.cortland.edu/moranm/EXS558/EXS558.html Download weekly readings (.PDF) Research source links EXS 558

Neuromuscular System Outline Muscle Types Skeletal Muscle Design a. Myofibrils (Actin and Myosin) Sliding Filament Theory Factors Influencing Muscle Force Production Excitation-Contraction Coupling Muscle Fiber Types a. Slow b. Fast (Oxidative-Glycolytic) c. Fast Glycolytic EXS 558

Types of Muscle Skeletal w Voluntary muscle; controlled consciously Over 600 throughout the body Cardiac w Controls itself with assistance from the nervous and endocrine systems w Only in the heart Smooth w Involuntary muscle; controlled unconsciously In the walls of blood vessels and internal organs EXS 558

Design of Skeletal Muscle Epimysium (connective tissue) surrounds whole muscle Fasicles (groups of fibers) surrounded by perimysium Myofibrils surrounded by endomysium Responsible for contraction Sarcolemma surrounds cellular contents of each muscle fiber EXS 558

Myofibrils Composed of myofilaments Consist mainly of two proteins MYOSIN (thick) Features globular heads acting as ATPase (determines rate of contraction) M-line in middle of myosin molecule, heads on each side move toward M-line (bipolar) ACTIN (thin): -two intertwined subunits (forms groove) -no ATPase (“molecular motor”) -terminated at Z-line EXS 558

Sarcomere: Z-line to Z-line M line: “naked” region – which way muscle pulls depends on which side is better anchored (ex: curl vs chin up) Level of Filament Overlap dictates Force Production EXS 558

Sliding Filament Theory (Huxley 1969) Wrapped around ACTIN is Tropomyosin Associated with tropomyosin is Troponin Troponin consists of three subunits: TnI – bound to actin TnT – bound to tropomyosin TnC – bound to calcium EXS 558

Sliding Filament Theory (con’t) When calcium is released from SR, it binds to TnC Causes conformational shift (transmitted to rest of troponin and to tropomyosin) Causes conformational shift in ACTIN ( exposes active sites) MYOSIN’s ATPase cleaves bound ATP (myosin-ADP-Pi) Myosin-ADP-Pi binds to active site (release of ADP-Pi) Actomyosin complex formed “Power stroke” occurs at myosin cross-bridge heads (shortening) Following flexion of cross-bridge, ATP binds to myosin Release myosin cross-bridge from ACTIN (relaxation) Process repeats or stops when intercellular calcium ↓ EXS 558

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ACTIN and MYOSIN do not change length! Shortening occurs asynchronously to provide continuous muscle action EXS 558

Factors Affecting Force Development # of cross-bridge formations - based upon probability - faster the movement of ACTIN, ↓ probability of cross-bridge formation EXS 558

Factors Affecting Force Development 2. Overlap of ACTIN-MYOSIN EXS 558

Motor Unit * The more delicate the movement the less fiber per motor unit as opposed to gross movements Nerve fiber + muscle it innervates = motor unit EXS 558

Excitation/Contraction Coupling - Electrical impulse conducted down axon of motor neuron - Release of Ach (acetylcholine) at nerve terminal - ACh crosses cleft and binds with AChR at endplate - Opens sodium channels and depolarizes (excites) endplate: endplate potential (EPP) - EPP causes depolarization (action potential) of entire sarcolemma surface, including T-tubules At specialized regions of T-tubule system there is a close proximity between its membrane and SR (terminal cisternae) In this region T-tubular membrane has dihydropyridine (DHP) receptors, that act as voltage sensors, sense depolarization EXS 558

Excitation/Contraction Coupling (con’t) In same region, membrane of SR has ryanodine receptors (Ca2+ channels) Depolarization causes conformational change in ryanodine receptors which causes Ca2+ influx Cascade Effect: release of Ca2+ causes additional Ca2+ channels to open Results in sharp in cystolic Ca2+ which then binds to troponin to stimulate muscle contraction EXS 558

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Overview Muscle Fiber Action (continued) w Muscle action is initiated by a nerve impulse. w The nerve releases ACh, which allows sodium to enter and depolarize the cell. If the cell is sufficiently depolarized, an action potential occurs which releases stored Ca2+ ions. w Ca2+ ions bind with troponin, which lifts the tropomyosin molecules off the active sites on the actin filament. These open sites allow the myosin heads to bind to them. (continued) EXS 558

Overview (continued) Muscle Fiber Action w Once myosin binds with actin, the myosin head tilts and pulls the actin filament so they slide across each other. w Muscle action ends when calcium is pumped out of the sarcoplasm to the sarcoplasmic reticulum for storage. w Energy for muscle action is provided when the myosin head binds to ATP. ATPase on the myosin head splits the ATP into a usable energy source. EXS 558

Slow-Twitch (Type I) Muscle Fibers w High aerobic (oxidative) capacity and fatigue resistance w Low anaerobic (glycolytic) capacity and motor unit strength w Slow contractile speed (110 ms to reach peak tension) and myosin ATPase w 10–180 fibers per motor neuron w Low sarcoplasmic reticulum development EXS 558

Fast-Twitch (Type IIa) Muscle Fibers w Moderate aerobic (oxidative) capacity and fatigue resistance w High anaerobic (glycolytic) capacity and motor unit strength w Fast contractile speed (50 ms to reach peak tension) and myosin ATPase w 300–800 fibers per motor neuron w High sarcoplasmic reticulum development EXS 558

Fast-Twitch (Type IIb) Muscle Fibers w Low aerobic (oxidative) capacity and fatigue resistance w High anaerobic (glycolytic) capacity and motor unit strength w Fast contractile speed (50 ms to reach peak tension) and myosin ATPase w 300–800 fibers per motor neuron w High sarcoplasmic reticulum development EXS 558

Muscle Biopsy w Hollow needle is inserted into muscle to take a sample. w Sample is mounted, frozen, thinly sliced, and examined under a microscope. w Allows study of muscle fibers and the effects of acute exercise and exercise training on fiber composition. EXS 558

“Eccentric exercise-induced morphological changes in the membrane systems involved in excitation-contraction coupling in rat skeletal muscle” Takehura H. et al. (2001) EXS 558