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Muscular-Skeletal System

Muscular-Skeletal System. Physiological Characteristics Irritability (excitability): react to stimuli (electrical stimulation) Chemical reaction creates muscle contraction Contractility: increase tension Shorter and thicker Extensibility: stretched beyond resting length

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Muscular-Skeletal System

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  1. Muscular-Skeletal System • Physiological Characteristics • Irritability (excitability): react to stimuli (electrical stimulation) • Chemical reaction creates muscle contraction • Contractility: increase tension • Shorter and thicker • Extensibility: stretched beyond resting length • Requires antagonist or gravity force • Elasticity: return to resting length

  2. Muscular-Skeletal System • Classification of muscle contraction • Isometric: no change in muscle length • No physical work performed • Tension usually constant • Concentric: decreasing muscle length • Positive work • Acceleration of limb during movement • Tension decreases • Eccentric: increasing muscle length • Negative work • Deceleration of limb • Tension increases • Isotonic: applied force is constant • Rare in practice

  3. 100 50 % max tension 60 100 180 % resting length Muscular Tension • Length of muscle • Maximum tension occurs at resting length (or slightly longer) • All active myosin sites lined up with actin attachment sites • Joint angle changes length

  4. Muscles • Velocity of Contraction • Maximum velocity at zero tension • Maximum force at zero velocity • Cross-Sectional Area • Max force (0.3-0.4 N/mm2) • Only gender difference is cross-sectional area • Women narrower muscle • Women 2/3 force of men • Electrical Process of Muscle • Resting potential of muscle fiber • 90 mV with inside negatively charge relative to exterior • Due to imbalance of ions • Action Potential is reversal of resting potential • Positive charge applied (depolarization) • Lasts 2-4 msec, speed 5 m/s • Refractory period is where muscle has decreased ion permeability • 1-3 msec after action potential

  5. Physiological Strain-Basic Concepts • Force – a unit of force is a newton (N) = 1 kg-m/s2 • 1 N = 0.225 lbf (pounds force) • Work or Energy – Work is done or energy is consumed when a force is applied over a distance • Measures: • 1 N x 1 m = 1 J (joule) • Kilocalorie (kcal) = amount of heat required to raise the temperature of 1 kg of water from 15 degrees Celsius to 16 degrees Celsius • The Calorie which is used for energy content of food is actually a kilocalorie • 1 kcal = 1000 cal = 1 Cal (food) • 1 kJ = 1000 J • 1 kcal = 4.1868 kJ • 1 kcal = 3087.4 ft lbs • Power = Work per unit time • Measures • Watt (W) = 1 J/s • Horsepower (hp) = 736 W

  6. Muscular Activity • Metabolism • Supplies the energy needed to slide the actin filaments over the myosin filaments. It is a chemical process of converting food into mechanical work and heat. • Some mechanical work is consumed by the body while other is consumed by physical activity • Basic source of energy for contraction of the muscle is glycogen or glucose which is abundant in the blood • Sources of Energy

  7. Energy • Metabolism - Sources of energy (see Figure 8-2 Sanders & McCormick (7th ed) • First 3-5 secs • adenosine triphosphate (ATP)-a high energy phosphate compound is mobilized. It breaks down to adenosine diphosphate (ADP) which releases energy. • ATP  ADP + P (phosphate radical) + free energy • ATP Regenerated • To continue muscular activity, ATP must be regenerated • creatine phosphate + ADP  creatine + ATP • creatine phosphate is high energy existing in small amounts in muscles • Depletion of creatine phosphate occurs in about 15 sec • Blood glucose or glycogen is mobilized. Glucose is a blood sugar which is converted by various stages first into pyruvic acid.

  8. Energy • Metabolism – further breakdown may be • Anaerobic work – if O2 is not supplied to the muscle, pyruvic acid is converted into lactic acid while ATP is regenerated. Lactic acid accumulation causes muscle fatigue and pain glucose + 2 phosphate + 2 ADP  2 lactate + 2 ATP • Aerobic work – if O2 is supplied, pyruvic acid is broken down into water and carbon dioxide, releasing large amounts of ATP glucose + 38 phosphate + 38 ADP + 6 O2 6 CO2 + 44 H2O + 38 ATP • Oxidation of pyruvic acid in aerobic work involves enzymes, co-enzymes, and fatty acids (Krebs cycle, figure 3.4 – Pulat) • O2 is key to efficient work. Its supply requires more blood be pumped to muscle per unit time as well as heavier breathing to oxygenate blood • Kilocalorie (kcal) – most common measure of energy requirement for physical activity • Resting energy  0.3 kcal per minute for man of about 154 lbs • Resting male (laying down and no digestive activity)  1700 kcal/day • Resting female (laying down and no digestive activity)  1400 kcal/day

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