1. Muscle Performance, Aging, and Pathology of the Muscular System

2. Increased use: strength training
Early gains in strength appear to be predominantly due to neural factors…optimizing recruitment patterns.
Long term gains almost solely the result of hypertrophy i.e. increased size.

3. Threshold stimulus: The minimum amount of stimulus required for a muscle contraction to occur

4. ATP
ATP or adenosine triphosphate is the form of energy that muscles and all cells of the body use. *The chemical bond between the last two phosphates has just the right amount of energy to unhook myosin heads and energize them for another contraction. Pulling of the end phosphate from ATP will release the energy. ADP and a single phosphate will be left over. New ATP can be regenerated by reconnecting the phosphate with the ADP with energy from our food.

5. Aerobic Cellular Respiration
Organisms take in oxygen (aerobic) and breakdown glucose to make ATP, Carbon dioxide, and water
Extra energy is stored in the form of glycogen in the liver and muscles
Respiration occurs in the mitochondria, where glucose is broken down into ATP

6. Creatine Creatine + ATP Creatine phosphate + ADP
Primary function of ATP is to transfer energy from one location to another rather than long term storage of energy
At rest, skeletal fibers produce more ATP than it needs. Under these conditions, ATP transfers the extra energy to creatine.
Creatine is a molecule capable of storing ATP energy. It can combine with ATP to produce creatine phosphate and ADP. The third phosphate and the energy from ATP attaches to creatine to form creatine phosphate.
Creatine + ATP
Creatine phosphate + ADP

7. Creatine Creatine + ATP Creatine phosphate + ADP
During a contraction, each myosin head breaks down ATP to make a phosphate group and ADP
The energy stored in creatine phosphate “recharges” ADP, converting it back to ATP:
Creatine + ATP
Creatine phosphate + ADP

8. Muscle Fatigue
An active muscle is fatigued when it can no longer continue to perform at the required level of activity
If ATP demands can be met through aerobic metabolism, fatigue will not occur until glycogen reserves are depleted
This fatigue affects the muscles of long distance athletes after hours of exertion

9. Muscle Fatigue
Athletes who run sprints require immediate intense bursts of energy.
Majority of ATP provided for this is done through glycolysis (converts glycogen into energy)
Energy demands are high, and oxygen cannot diffuse into muscle fiber fast enough to produce ATP

10. Recovery Period
If contraction occurs at peak levels, lactic acid is generated (anaerobic respiration)
During recovery, muscles fiber conditions return to normal levels
Recovery can last anywhere from several hours to a week, depending on the activity level

11. Oxygen Debt
During recovery, the body’s oxygen demands remain above normal resting levels
The amount of oxygen required to restore the body to its normal, pre-exertion conditions is called oxygen debt
While oxygen debt is being repaid, breathing rate and depth are increased, causing you to breathe heavily long after exercise has ceased

12. Muscle Performance Two factors affect muscle performance:
(1) types of muscle fibers in the muscle
(2) physical conditioning or training

13. Skeletal Muscle Fibers
Three main types:
(1) fast fibers
(2) slow fibers
(3) intermediate fibers

14. Fast Fibers (White Muscles)
Most skeletal muscles are fast
Called fast due to the ability of muscle to contract in 0.01 sec or less after stimulation
Large diameter, densely packed myofibrils, large glycogen reserves, few mitochondria
Produce powerful contractions, but fatigue quickly
Comparable to “white meat” in chickens; breast

15. Slow/Red Fibers
Half the diameter of fast fibers and require 3 times as long to contract
Specialized to continue contracting for extended periods
More vascular and higher energy supply as a result
Contain myoglobin – red pigment that binds oxygen molecules
Equivalent to “dark meat” – thighs in chicken

16. Performance Declines with Aging
--despite maintenance of physical activity
100 80
Performance (% of peak) 60 40
Shotput/Discus
Marathon 20
Basketball (rebounds/game) 10 20 30 40 50 60
Age (years)
D.H. Moore (1975) Nature 253:
NBA Register, Edition

17. Number of motor units declines during aging
- extensor digitorum brevis muscle of humans
AGE-ASSOCIATED
ATROPHY DUE TO BOTH…
Individual fiber atrophy
(which may be at least
partially preventable and
reversible through exercise).
Loss of fibers
(which as yet appears
irreversible).
Campbell et al., (1973) J Neurol Neurosurg Psych 36:

18. Motor unit remodeling with aging
Central
nervous
system
Muscle
Motor
neuron
loss
AGING
Fewer motor units
More fibers/motor unit

19. Muscle injury may play a role in the development of
atrophy with aging.
Muscles in old animals are more susceptible to contraction-
induced injury than those in young or adult animals.
Muscles in old animals show delayed and impaired recovery
following contraction-induced injury.
Following severe injury, muscles in old animals display
prolonged, possibly irreversible, structural and functional
deficits.

20. What is rigor mortis? Rigor Mortis
A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.
Rigor Mortis
A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place.

21. Disorders of Muscle Tissue
Muscular dystrophy – a group of inherited muscle destroying diseases
Affected muscles enlarge with fat and connective tissue
Muscles degenerate
Types of muscular dystrophy
Duchenne muscular dystrophy
Myotonic dystrophy

22. Duchenne’s Muscular Dystrophy
Predominantly affects males, because it is a sex-linked trait

23. Myasthenis Gravis
A progressive muscular paralysis that occurs due to the loss of Ach receptors. Autoimmune disorder where the body attacks its own Ach receptors. Genetic factors play a role in predisposing individuals to this condition.

25. Tetanus
Tetanus causes acetylcholinosterase to not break down the acetylcholine in the synapse.  This results in a person's muscles contracting and not relaxing.
A tetanus shot must be administered shortly after exposure to the  bacteria.
Once you develop tetanus, there is no cure.

26. Botulism
Results from the consumption of contaminated canned or smoked foods that contain a toxin. The toxin, produced by bacteria, prevents the release of Ach, leading to potentially fatal muscular paralysis.