Muscular-Skeletal System

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
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