Download 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
Requires antagonist or gravity force
Elasticity: return to resting length
Dept. of Biomedical, Industrial, & Human Factors Engineering
1
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
Dept. of Biomedical, Industrial, & Human Factors Engineering
2
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
1.5
% max tension
100
1
50
0.5
0
60
0
-0.5
1002
180
4
6
8
% resting length
-1
-1.5
Dept. of Biomedical, Industrial, & Human Factors Engineering
3
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
Dept. of Biomedical, Industrial, & Human Factors Engineering
4
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
Dept. of Biomedical, Industrial, & Human Factors Engineering
5
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
Dept. of Biomedical, Industrial, & Human Factors Engineering
6
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.
Dept. of Biomedical, Industrial, & Human Factors Engineering
7
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
Dept. of Biomedical, Industrial, & Human Factors Engineering
8