Exercise Physiology

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Human body contains over

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600 skeletal muscles (40-50% of total body weight)

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3 major functions of Skeletal Muscles

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Force production for locomotion and breathing, and for postural support, also heat production during cold stress.

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Flexors

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Decrease joint angle

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Extensor

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Increase joint angles

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Epimysium

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Surrounds entire muscle

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Perimysium

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Surrounds bundles of muscle fibers

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Endomysium

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Surrounds individual muscle fibers

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Satellite cells

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Play key role in muscle growth and repair

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Myonuclear domain

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Volume of cytoplasm surrounding each nucleus

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More nuclei allows

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Greater protein synthesis

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Myofibrils

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Contain contractile proteins such as actin (thin) and Mayosin (thick)

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Sarcoplasm reticulum

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Storage sites for calcium, terminal cisternae

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Sarcomere

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Includes z line, M line, h zone, A band, I band

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Transverse tubules

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Extend from sarcolema to sarcoplasmatic recticulum

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Neuromuscular Junction

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Junction between motor neuron and muscle fiber

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Motor end plate

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Pocket formed around motor neuron by sarcolemma

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Neuromuscular cleft

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Short gap between neuron and muscle fiber

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Individual muscle fibers are composed of hundreds of threadlike protein filaments called

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Myofibrils

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Importance of myonuclear domain

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single nucleus is responsible for the gene expression for its surrounding cytoplasm

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Acetylcholine is

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Neurotransmitter that stimulates the muscle fiber to depolarize, which is the signal to start the contractile processes

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Process of muscular contraction can be best explained by what model ?

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Sliding filament/ swinging cross-bridge model

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Process of muscular contraction can be best explained by what model ?

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Sliding filament/ swinging cross-bridge model

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What does Sliding filament\ swinging cross bridge model proposes?

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Muscle shortening occurs due to movement of the actin filament over the myosin filament

Front 24

Excitation-contraction coupling refers to

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Sequence of events in which nerve impulse (action potential) depolarizes the muscle fiber, leading to muscle shortening by cross-bridge cycling

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The trigger to initiate muscle contraction is

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Depolarization-induced release of calcium from the sarcoplasmic reticulum

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Muscular contractions occurs via

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The binding of the myosin cross-bridge to actin and the repeated cycling of myosin pulling on the actin molecule resulting in the shortening of the muscle fiber

Front 27

Muscular contractions occurs via

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The binding of the myosin cross-bridge to actin and the repeated cycling of myosin pulling on the actin molecule resulting in the shortening of the muscle fiber

Front 28

Muscle relaxation occurs when

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The motor neuron stops exciting the muscle fiber and calcium is pumped backed into the sarcoplasmic reticulum

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Removal of calcium from the cytosol causes a position change in tropomyosin, which blocks the

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Myosin cross-bridge binding site on the actin molecule

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Muscle fatigue

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Decline in muscle power output

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Causes of exercise-induced muscle fatigue are complex and vary depending upon what?

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Type of exercise performed

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Muscle cramps

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spasmodic and involuntary skeletal muscle contractions

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Research indicates that many cases of exercise-associated muscle cramps occur due to

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Abnormal spinal reflex activity that results in hyper active motor neurons

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Human skeletal muscle fiber types are divided into three general classes of fibers, what are them ?

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Type 1, Type IIx, Type lla

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Type 1 fibers

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Slow-twitch, slow oxidative fibers

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Type 1 fibers

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Slow-twitch, slow oxidative fibers

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Type 11a fiber

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Intermediate fibers, fast oxidative glycolytic fibers

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Type 1 fibers

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Slow-twitch, slow oxidative fibers

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Type lla fiber

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Intermediate fibers, fast oxidative glycolytic fibers

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Type IIx fibers

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Fast-twitch fibers, fast-glycolytic fibers

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Biochemical properties of muscle fiber types

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Oxidative capacity, type of myosin ATPase isoform, Abundance of contractile protein in the muscle fibers

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Biochemical properties of muscle fiber types

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Oxidative capacity, type of myosin ATPase isoform, Abundance of contractile protein in the muscle fibers

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Contractile properties of Muscle fiber types

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Maximal force production, speed of contraction (Vmax), maximal power output, muscle fiber efficiency

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Successful power athletes (sprinters, power lifters) possess what type of fibers ?

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Large percentage of fast muscle fibers, and therefore a low percentage of slow, type l fibers

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Successful power athletes (sprinters, power lifters) possess what type of fibers ?

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Large percentage of fast muscle fibers, and therefore a low percentage of slow, type l fibers

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Endurance athletes posses what type of fibers

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High percentage of slow muscle fibers and a low percentage of fast fibers

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Isometric

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Muscle exerts force without changing length

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Dynamic (isotonic)

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Concentric (muscle shortens during force production) eccentric ( muscle produces force but length increases)

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The amount of force generated during muscular contraction is depending on what factors

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1. Types and number of motor units 2. The initial muscle length 3. The nature of the motor units’ neural stimulation

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Summation

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The addition of muscle twitches

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When the frequency of neural stimulation to a motor unit is increased

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Individual contractions are fused in a sustained contraction called tetanus

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When the frequency of neural stimulation to a motor unit is increased

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Individual contractions are fused in a sustained contraction called tetanus