Physical exercise is any bodily activity that
enhances or maintains
physical
fitness and overall
health. It is
performed for many different reasons. These include strengthening
muscles and the cardiovascular system, honing
athletic skills,
weight
loss or maintenance and for enjoyment. Frequent and regular
physical exercise boosts the immune system, and helps prevent the
"
diseases of affluence" such
as
heart disease,
cardiovascular disease,
Type 2 diabetes and
obesity. It also improves mental health, helps
prevent depression, helps to promote or maintain positive
self-esteem, and can even augment an individual's sex appeal.
Childhood obesity is a growing global concern and physical exercise
may help decrease the effects of childhood obesity in developed
countries.
Classification
Types of exercise
Exercises are generally grouped into three types depending on the
overall effect they have on the human body:
- Flexibility exercises, such as stretching, improve the range of motion of
muscles and joints.
- Aerobic exercises, such as
cycling, swimming, walking,
rowing, running, hiking or playing
tennis, focus on increasing cardiovascular endurance.
- Anaerobic exercises, such as
weight training, functional training or sprinting, increase short-term muscle
strength.
Categories of physical exercise
Sometimes the terms 'dynamic' and 'static' are used. 'Dynamic'
exercises such as steady running, tend to produce a lowering of the
diastolic blood pressure during exercise,
due to the improved blood flow. Conversely, static exercise (such
as weight-lifting) can cause the
systolic pressure to rise significantly
(during the exercise).
Benefits
Physical exercise is important for maintaining
physical fitness and can contribute
positively to maintaining a healthy weight, building and
maintaining healthy bone density, muscle strength, and joint
mobility, promoting physiological well-being, reducing surgical
risks, and strengthening the immune system.
Exercise also reduces levels of
cortisol,
thereby benefiting health. Cortisol is a stress hormone that builds
fat in the abdominal region, making weight loss difficult. Cortisol
causes many health problems, both physical and mental.
Frequent and regular aerobic exercise has been shown to help
prevent or treat serious and life-threatening chronic conditions
such as
high blood pressure,
obesity,
heart
disease,
Type 2 diabetes,
insomnia, and
depression. Endurance exercise before
meals lowers blood glucose more than the same exercise after
meals.
There is some evidence that vigorous exercise (90-95% of
VO2 Max) is more beneficial than moderate
exercise (40 to 70% of
VO2
Max).Some studies have shown that vigorous exercise executed by
healthy individuals can effectively increase
opioid peptides (a.k.a.
endorphins, naturally occurring
opioids that in conjunction with other
neurotransmitters are responsible for
exercise-induced
euphoria and
have been shown to be addictive), positively influence hormone
production (i.e., increase testosterone and growth hormone),
benefits that are not as fully realized with moderate exercise.
More recent research indicates that
anandamide may play a possibly greater role than
endorphins in "
runner's high" and
other exercise benefits.
Both aerobic and anaerobic exercise also work to increase the
mechanical efficiency of the heart by increasing cardiac volume
(aerobic exercise), or myocardial thickness (strength training).
Such changes are generally
beneficial and healthy if they occur in response to exercise.
Not everyone benefits equally from exercise. There is tremendous
variation in individual response to training: where most people
will see a moderate increase in endurance from
aerobic exercise, some individuals will as
much as double their oxygen uptake, while others will never get any
benefit at all from the exercise. Similarly, only a minority of
people will show significant muscle growth after prolonged weight
training, while a larger fraction experience improvements in
strength. This genetic variation in improvement from training is
one of the key physiological differences between elite athletes and
the larger population. Studies have shown that exercising in middle
age leads to better physical ability later in life.
Effect on the immune system
Although there have been hundreds of studies on exercise and the
immune system, there is little direct evidence on its connection to
illness.
Epidemiological evidence
suggests that moderate exercise appears to have a beneficial effect
on the human
immune system while
extreme exercise appears to impair it, an effect which is modeled
in a
J curve. Moderate exercise has been
associated with a 29% decreased incidence of
upper respiratory tract
infections (URTI), but studies of marathon runners found that
their prolonged high-intensity exercise was associated with an
increased risk of an infection, although another study did not find
the effect. Immune cell functions are impaired following acute
sessions of prolonged, high-intensity exercise, and some studies
have found that athletes are at a higher risk for infections. The
immune systems of athletes and nonathletes are generally similar.
Athletes may have slightly elevated NK cell count and cytolytic
action, but these are unlikely to be clinically significant.
Supplementation with the antioxidants vitamin C and E has been
found to decrease the release of
interleukin-6 (IL-6), which would be expected
to decrease the depression of the immune system. Further, vitamin C
supplementation has been associated with lower URTIs in marathon
runners. However, the decreased release of IL-6 limits the
anti-inflammatory effect of exercse and could limit the positive
adaptation effects of exercise.
Biomarkers of
inflammation such as
C-reactive protein, which are associated
with chronic diseases, are reduced in active individuals relative
to sedentary individuals, and the positive effects of exercise may
be due to its anti-inflammatory effects. The depression in the
immune system following acute bouts of exercise may be one of the
mechanisms for this anti-inflammatory effect.
Effects on brain function
In the long term, exercise is beneficial to the brain by:
A 2008 review of cognitive enrichment therapies (strategies to slow
or reverse cognitive decline) concluded that "physical activity,
and aerobic exercise in particular, enhances older adults’
cognitive function".
Exercise has been shown to improve cognitive functioning via
improvement of hippocampus-dependent spatial learning, and
enhancement of synaptic plasticity and neurogenesis. In addition,
physical activity has been shown to be neuroprotective in many
neurodegenerative and neuromuscular diseases. For instance, it
reduces the risk of developing
dementia.
Furthermore, anecdotal evidence suggests that frequent exercise may
reverse alcohol-induced brain damage.
Physical activity is thought to have other beneficial effects
related to cognition as it increases levels of nerve growth
factors, which support the survival and growth of a number of
neuronal cells.
Public health measures
Signs that encourage the use of stairs, as well as community
campaigns, have been shown to be effective in increasing exercise
in a population.
The city of Bogota
, Colombia
, for
example, blocks off 113 kilometers (70 miles) of roads on
Sundays and holidays to make it easier for its citizens to get
exercise. These
pedestrian
zones are part of an effort to combat chronic diseases,
including obesity.
Common misconceptions
Many myths have arisen surrounding exercise, some of which have a
basis in reality, and some which are completely false. Myths
include:
- That excessive exercise can cause immediate death. Death by
exercise has some small basis in fact. Water intoxication can result from
prolific sweating (producing electrolyte losses) combined with
consumption of large amounts of plain water and insufficient
replenishment of electrolytes,
especially salt and potassium (e.g. when running a marathon). It is also possible to die from a heart
attack or similar affliction if overly intense exercise is
performed by someone who is not at an appropriate level of fitness
for that particular activity or has an undiagnosed rare condition
like hypertrophic
cardiomyopathy. A doctor should always be consulted before any
radical changes are made to a person's current exercise routine.
Rhabdomyolysis is also a risk. Other
common dangers may occur from extreme overheating or aggravation of
a physical defect, such as a thrombosis or aneurysm.
- That weightlifting makes you short or stops growth. One highly
debated caveat is that heavy weight training in adolescents can
damage the epiphyseal plate of long
bones.
Targeted fat reduction
Spot reduction is a myth that
exercising and training a particular body part will preferentially
shed the fat on that part. For example, doing
sit-ups is not the best way to reduce
subcutaneous belly fat. One cannot
reduce fat from one area of the body to the exclusion of others.
Most of the energy derived from fat gets to the muscle through the
bloodstream and reduces stored fat in the entire body, from the
last place where fat was deposited. Sit-ups may improve the size
and shape of abdominal muscles but will not specifically target
belly fat for loss. Such exercise might help reduce overall body
fat percentage and shrink the size of fat cells.
Muscle and fat tissue
One misconception is that muscle tissue will turn into fat tissue
once a person stops exercising. This is not literally true — fat
tissue and muscle tissue are fundamentally different — but the
common expression that "muscle will turn to fat" is truthful in the
sense that
catabolism of muscle fibers
for energy can result in excess glucose being stored as fat.
Moreover, the composition of a body part can change toward less
muscle and more fat, so that a cross-section of the upper-arm for
example, will have a greater area corresponding to fat and a
smaller area corresponding to muscle. This is not muscle "turning
into fat" however — it is simply a combination of muscle atrophy
and increased fat storage in different tissues of the same body
part. Another element of increased fatty deposits is that of diet,
as most trainees will not significantly reduce their diet in order
to compensate for the lack of exercise/activity.
Excessive exercise
Exercise is a
stressor and the
stresses of exercise have a
catabolic
effect on the body - contractile proteins within muscles are
consumed for energy, carbohydrates and fats are similarly consumed
and
connective tissues are
stressed and can form micro-tears. However, given adequate
nutrition and sufficient rest to avoid
overtraining, the body's reaction to this
stimulus is to adapt and replete tissues at a higher level than
that existing before exercising. The results are all the training
effects of regular exercise: increased muscular strength,
endurance, bone density, and connective tissue toughness.
Too much exercise can be harmful. The body parts exercised need at
least a day of rest, which is why some health experts say one
should exercise every other day or 3 times a week. Without proper
rest, the chance of
stroke or other
circulation problems increases, and
muscle tissue may develop slowly. It has also been noted by the
medical field that expectant mothers should never exercise two days
consecutively.
Inappropriate exercise can do more harm than good, with the
definition of "inappropriate" varying according to the individual.
For many activities, especially
running,
there are significant injuries that occur with poorly regimented
exercise schedules. In extreme instances, over-exercising induces
serious performance loss. Unaccustomed overexertion of muscles
leads to
rhabdomyolysis (damage to
muscle) most often seen in new army recruits. Another danger is
overtraining in which the intensity or
volume of training exceeds the body's capacity to recover between
bouts.
Stopping excessive exercise suddenly can also create a change in
mood. Feelings of depression and agitation can occur when
withdrawal from the natural endorphins produced by exercise occurs.
Exercise should be controlled by each body's inherent limitations.
While one set of joints and muscles may have the tolerance to
withstand multiple
marathons, another body
may be damaged by 20 minutes of light jogging. This must be
determined for each individual.
Too much exercise can also cause a female to miss her period, a
symptom known as
amenorrhea.
Exercise trends
Worldwide there has been a large shift towards less physically
demanding work. This has been accompanied by increasing use of
mechanized transportation, a greater prevalence of labor saving
technology in the home, and less active
recreational pursuits.
Nutrition and recovery
Proper
nutrition is as important to health
as exercise. When exercising, it becomes even more important to
have a good diet to ensure that the body has the correct ratio of
macronutrients whilst
providing ample
micronutrients, in
order to aid the body with the recovery process following strenuous
exercise.
Proper rest and recovery are also as important to health as
exercise; otherwise the body exists in a permanently injured state
and will not improve or adapt adequately to the exercise. Hence, it
is important to remember to allow adequate recovery between
exercise sessions. It is necessary to refill the
glycogen
stores in the skeletal muscles and liver. After exercise, there
is a 30 minute window critical to muscle recovery. Before doing
anything else, one should drink something for recovery. Liquids are
ideal after exercise and there are several studies that show
low-fat milk and chocolate milk as being effective recovery
beverages because of its ideal 4:1 combination of carbohydrate and
protein that fuels and replenishes our muscles the best.
Branched-chain amino acids are
also recommended for exercise recovery.
The above two factors can be compromised by psychological
compulsions (
eating disorders such
as
exercise bulimia,
anorexia, and other
bulimias), misinformation, a lack of organization,
or a lack of motivation. These all lead to a decreased state of
health.
Delayed onset muscle
soreness can occur after any kind of exercise, particularly if
the body is in an unconditioned state relative to that
exercise.
History
The benefits of exercise have been known since antiquity.
Marcus Cicero, around 65 BC, stated: “It is
exercise alone that supports the spirits, and keeps the mind in
vigor.” However, the link between physical health and exercise (or
lack of it) was only discovered in 1949 and reported in 1953 by a
team led by
Jerry Morris. Dr Morris
noted that men of similar social class and occupation (bus
conductors versus bus drivers) had markedly different rates of
heart attacks, depending on the level of exercise they got: bus
drivers had a sedentary occupation and a higher incidence of heart
disease, while bus conductors were forced to move continually and
had a lower incidence heart disease. This link had not previously
been noted and was later confirmed by other researchers.
See also
References
Sources
- Hardman, A.; Stensel, D. 2009. Physical Activity and
Health: The Evidence Explained. London: Routledge ISBN
978-0-415-42198-0
Further reading
- Guidance on the promotion and creation of physical environments
that support increased levels of physical activity.
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