Page 112 - 84 human physiolofy part-1

Chapter 6

respiration. The drawback to this method is that lactic acid accumulates and causes the muscles to
fatigue. They will eventually stop contracting until the breakdown of lactic acid is sufficient to allow
for movement once again. People experience this most noticeably when they repeatedly lift heavy
things such as weights or sprint for a long distance. Muscle soreness sometimes occurs after vigorous
activity, and is often misunderstood by the general public to be the result of lactic acid buildup. This is
a misconception because the muscle does fatigue from lactic acid buildup, but it does not stay in the
muscle tissue long enough to cause tissue breakdown or soreness. During heavy breathing, following
exercise, the cells are converting the lactic acid either back into glucose or converting it to pyruvate and
sending it through the additional steps of aerobic respiration. By the time a person is breathing
normally again the lactic acid has been removed. The soreness is actually from small tears in the fibers
themselves. After the fibers heal they will increase in size. The number of mitochondria will also
increase if there is continued demand for additional ATP. Hence, through exercise the muscles can
increase in both strength and endurance.

Another misconception is that as the muscle increases in size it also gains more fibers. This is not
true. The fibers themselves increase in size rather than in quantity. The same holds true for adipose
tissue--fat cells do not increase in number, but rather the amount of lipids (oil) in the cells increase.

Muscle fibers are also genetically programmed to reach a certain size and stop growing from there,
so after awhile even the hardest working weightlifter will only reach a certain level of strength and
endurance. Some people will get around this by taking steroids. The artificial steroids cause all sorts of
trouble for the person. They can cause the adrenal glands to stop producing corticosteroids and
glucosteroids. This leads to the atrophy of the gland's medulla and causes permanent loss of the
production of these hormones. The testicles may also atrophy in response to steroids. Eventually the
testes will stop making testosterone and sperm, rendering the male infertile.

One of the more serious problems associated with abnormal gain of muscle mass is heart failure.
While for most people gaining muscle and losing fat is desirable, a body builder is at risk of producing
more muscle mass than the heart can handle. One pound of fat contains about 3.5 miles of blood
vessels, but one pound of muscle has about 6.5 miles. Hence, additional muscle causes the heart to
pump more blood. Some people that have too much muscle will be very strong but will not have a
healthy aerobic endurance, in part because of the difficulty of providing oxygenated blood to so much
tissue.

Sliding filament theory
This link shows the animation of the sliding filament theory.
explanation and image of sliding filament theory
this link gives a better demonstration of the theory with the explanation.

Involuntary Muscle Movement

Spasms
When Smooth and skeletal muscles go through multiple spasms it is referred either as seizure or
convulsion.

Cramps
Strenuous activities can cause painful spasms that are long, this is referred to as cramps.

112 | Human Physiology