Effects of exercise

From the SNAB course book. Effects of too much exercise on the joints

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Over Doing It
In the last few years athletes have had more targeted training and better nutrition and
clothing. But are some athletes attempting to do more than their body can physically
tolerate? This is known as `overtraining'. `Burnour' symptoms due to overtraining can persist
for weeks/months. Symptoms include immune suppression leading to more frequent
infections, and increased wear and tear on joints, which may need surgical repair.
Sore throats and flu-like symptoms are more common. Some scientists have suggested a
U-shape relationship between risk of infection and amount of exercise.
For example in a study of runners in Los Angeles marathon 1984, 13% of runners reported
upper respiratory tract infections in the week after the race where as the control group of
runners with comparable fitness who hadn't taken part in the race had a infection rate of
only 2% in the week after the race.
There are 2 main factors that have been suggested to contribute to higher infection rates:
increased exposure to pathogens, and suppressed immunity with hard exercise.
Effects of exercise on immunity
Moderate exercise
Increases the number and activity of a type of lymphocyte called natural killer cells which are
found in the blood and lymph. They do not use specific antigen recognition ­ provide
non-specific immunity against viruses and cancerous cells.
They are activated by cytokines and interferons (exact mechanism not known but seem to
target cells that are not displaying `self' markers).
Killer cells release perforin which makes pores in the target cell membrane which allows
other molecules (proteases) to enter and cause apoptosis (programed cell death).
Vigorous exercise
The number and activity of falls after vigorous exercise.
Natural killer cells
B cells
T helper cells
The specific immune system is depressed as a consequence of these changes.
Cytokine release also falls which cannot activate lymphocytes, which in turn reduces the
amount of antibodies.

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The inflammatory response occurs in muscles due to damage to muscle fibres caused by
heavy exercise; this may reduce the available non-specific immune response against upper
respiratory tract infections.
Both physical exercise and psychological stress cause secretion of hormones such as
adrenaline and cortisol (secreted by the adrenal glands) ­ known to supress the immune
How are joints damaged by exercise
Repeated force on the joints can lead to wear and tear.…read more


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