For obesity treatment, exercise has been established as an effective
option.
Primarily, the research focuses on two strategies:
(1)
Exercise for weight reduction, with the premise that lower body weight can
lead to better health.
(2) Exercise for health and fitness, with the philosophy that correct
exercise can lead to better health, no matter what the resulting weight
change.
In all circumstances of exercise intervention, consultation with a physician
should be done first to rule out any contraindications to exercise.
Exercise for Weight
Loss
In order to loose weight an energy deficit must be met.
Essentially, this means that throughout the day and individual must burn
(expend) more calories than they consume (absorb) from food. Many attempt to
loose weight by dietary modification alone. This, when done appropriately can
garner positive results However, many individuals that modify their diet do
so inappropriately by either not getting enough calories or choosing diets
that lack proper nutrients and balance. The term, yo-yo dieting, is often
used to describe the up-and-down weight fluctuations that can occur with
drastic dietary plans. Some studies have implied that weight fluctuations may
be more harmful than remaining overweight.
Diet alone is seldom recommended by doctors for weight reduction One
reason for this is that diet without exercise does not improve cardio
respiratory fitness
If the goal is to loose weight, the combination of energy intake
reductions and energy expenditure increases through structured exercise and
other forms of physical activity are recommended as a weight loss
intervention.
Exercise can be a key component for inducing an energy deficit.
When an individual exercises, they expend more calories then when sedentary.
Research has demonstrated that structured exercise interventions alone can
produce weight loss as well as changes in body composition.
The American College of Sports Medicine (ACSM) recommendations for
weight loss programs as follows:
- A cardiovascular exercise
program of a minimum of 3 days per week, 20 - 30 minutes per session.
Ideally, a 5 day per week 30 minute per session (or 150 minutes of
cumulative exercise per week) should be performed. Additionally, there
may be additional benefits in progressively increasing exercise to 200 -
300 (3.3 - 5 h) per week. The program should be at a minimum of 60%
HRmax in otherwise healthy individuals.
- Additionally, strength
training may provide benefit through the development of lean muscle
mass.
- A diet that provides a
minimum of 1200 calories per day for normal adults to meet nutritional
requirements.
- The diet should include
food that is acceptable to the individual in terms of nutritional needs,
sociocultural background, taste, cost, and ease of acquisition and
preparation.
- The difference between
energy intake and expenditure should provide a negative caloric balance
that does not exceed 500 - 1000 calories per day and results in gradual
weight loss without metabolic abnormalities. Weight loss should not
exceed 2.2 lb per week.
- Behavior modification
should be instigated in order to identify and eliminate dieting habits
that contribute to improper nutrition.
- New eating and physical
habits should be reasonable, manageable, and appropriate. This is
important if such habits are expected to be continued for life.
Exercise for Health
and Fitness
Recent research has explored the effects of cardiorespiratory fitness on
men of various BMI's and body compositions. What such studies have found is
that the health benefits of being lean are limited to those who are physically
fit.
Recent research has come to following conclusion.
- Unfit lean men have double
the mortality risk of fit lean men.
- Unfit lean men have a
higher risk mortality and cardiovascular disease than men who are fit
and obese.
- Unfit men have a higher risk
of mortality and cardiovascular disease than fit men in all categories
of fat and fat-free mass.
- Unfit men with low waist
girths have a higher risk of mortality than fit men with high waist
girths.
- Being obese does not appear
to increase mortality risk in fit men.
Such findings indicate that obese men should be encouraged to increase
their cardiorespiratory fitness through regular, moderate intensity physical
activity.
Benefits should be achieved even if they remain overweight.
The
American
College
of Sports
Medicine (ACSM): Specific recommendations for Exercise Program :
Cardiorespiratory Fitness and Body Composition Guidelines
- Frequency of training
sessions: 3 - 5 days per week. This does not mean one cannot or should
not choose some form of physical activity on non-training session days.
Examples: gardening and yard work, walking the dog, etc.
- Intensity of training: 65 -
90% of maximum heart rate (HRmax) or 55 - 64% HRmax for those that are
especially unfit.
- Duration of training: 20 -
60 minutes of continuous or intermittent (minimum of 10-min bouts
accumulated throughout the day) aerobic activity. Duration is dependent
on intensity, therefore, lower intensity activities should be conducted
over longer time periods (? 30 minutes) and higher levels of activity
should be maintained for 20 minutes or longer. Moderate intensity over
longer duration is recommended for adults not training for athletic
competition.
- Mode of activity:
activities that use large muscle groups and can be maintained continuously.
Such modes of activity should be rhythmical and aerobic in nature.
Examples: walking, hiking, running/jogging, cycling, cross-country
skiing, aerobic dance/group exercise.
Muscular Strength and Endurance, Body Composition, and Flexibility
Guidelines.
- Resistance training
sessions:
Frequency of training: 2 - 3 days per week
Sets and Repetitions: Multiple-set regimens may provide greater benefit
if time allows. Most people should complete 8 - 12 repetitions of each
exercise. It may be appropriate for frail individuals to complete 10 -
15 repetitions at a lower relative weight.
Resistance training should be progressive, individualized, and provide
stimulus to all major muscle groups.
- Flexibility training
sessions: Flexibility exercises should stretch the major muscle groups
and be performed a minimum of 2 - 3 days per week and should incorporate
appropriate static (held 10 - 30 sec) and/or dynamic techniques. The
rational behind flexibility training is to develop and maintain range of
motion (ROM).
Type of Exercise based on oxygen consumption:
Depending of the oxygen consumption, exercise is can be classified as
aerobic or anaerobic. The terms "aerobic" and
"anaerobic" refer to the presence and absence of oxygen,
respectively.
Most cells of our body prefer to get the energy they need by using oxygen
to fuel metabolism. During exercise with adequate fuel and oxygen ( i.e.,
aerobic), muscle cells can contract repeatedly without fatigue.
During anaerobic or non-oxygen conditions (higher intensity exercise), muscle
cells must rely on other reactions that do not require oxygen to fuel muscle
contraction.
This anaerobic cell metabolism produces waste molecules that can impair
repeated muscle contractions. We call this deterioration in performance as
fatigue.
While at rest, we rely totally on aerobic metabolism to fuel almost all
our body's needs for energy. As we start to exercise, such as progressing
from sitting to a slow walk, the increased energy needs of muscle contraction
require that we increase our breathing and oxygen intake.
So long as we increase our exercise intensity slowly, we can maintain our
muscle's dependence on aerobic metabolism, and we don't experience symptoms
of fatigue.
However, as exercise intensity increases, the need for energy release
eventually exceeds that which can be supplied by aerobic metabolism.
Our muscles simply need more reactions to support the energy demand.
Therefore, anaerobic contribution to metabolism increases.
When this happens, we refer to this change in metabolism as a metabolic
threshold.
This metabolic threshold represents the exercise intensity where we start to
produce those waste products of anaerobic metabolism that can eventually lead
to fatigue.
Aerobic exercise conditions enable you to exercise for long periods of
time, potentially benefiting from the sustained energy expenditure (i.e.,
calories burned). Aerobic exercise tends to be less stressful to muscles,
joints, and your heart, which may be important for individuals with
arthritis, heart disease, or high blood pressure. However, to more rapidly
improve your exercise capacities, tolerance, and performance, some anaerobic
exercise training is a necessity.
Therefore, performing anaerobic exercise is typically more suitable for
competitive athletes and less so for weight reduction programs.
Metabolic equivalent
A unit of metabolic equivalent, or MET, is defined as the number of
calories consumed by an organism per minute in an activity relative to the
Basal metabolic rate (BMR/RMR, see below). A single unit (1 MET) is the
caloric consumption of that organism, or individual, while at complete rest.
For example, one might consider the restful state following a quiet night's
sleep as a good example of a single MET. This is a base-line unit for that
one individual, and since each individual has a varying BMR, a MET is,
therefore, variable from one person to the next. One might consider a single
unit the energy required to just stay alive without doing anything more.
The unit is commonly used in the context of aerobic exercise to gauge the
intensity of the workout. A workout of 2-4 METs is considered light, while
intensive running (8 minutes/mile, or 12 km/h) or climbing can yield workouts
of 12 or more METs.
Since METs are variable units, they can only be used in calculating
relative energy expenditures in "context;" meaning within the
parameters per individual, unlike caloric expenditures which are unitary
standards not variable from one person to another. While exercising at 6
METs, a 200-pound (90 kg) man would burn considerably more calories than his
120-pound (55 kg) son doing the same exercise.
METs are particularly relevant to those who intend to lose weight, because
they are a simple approximation of the rate at which exercise causes calories
to be burned. Many modern exercise machines can indicate METs, although the
numbers given are estimates since, as mentioned above, the rate at which
calories are burned while at rest (the Basal Metabolic Rate or, more
strictly, the Resting metabolic rate: RMR) varies from person to person.
The Types of Exercise based on
muscle contraction.
One type of classification of exercise is based on type of muscle
contractions.
There are four different types of muscle contraction.
1. Isotonic
2. Eccentric
3. Isometric
4. Isokinetic
Isotonic
All lifting exercises require Isotonic contractions. This happens when the
muscle shortens as it contracts. Typical examples are lifting objects above
the head - front shoulder (anterior deltoid) shortens, doing a sit up,
throwing a ball
In fact Isotonic contractions are the most common, many exercises and
activities we routinely do involve this type of contraction.
Eccentric
Eccentric contraction is the opposite of isotonic, the muscle lengthens as
it gains tension. These are much less common and not as beneficial as the
common Isotonic. An example is when someone manages to pull your arm straight
while at the same time you are try to keep the arm locked in one position. In
other words, the load is too great!
Other examples are...
running downhill
walking downstairs
landing on the ground from a jump
This type of contraction is not recommended!
Isometric
An Isometric contraction happens when there is tension on the muscle but
no movement is made causing the length of the muscle to remain the same. This
type of contraction is also referred to as a static contraction. Typical
example include attempting to lift an immoveable object, or some wrestling
movements.
These type of exercises are generally not suitable for weight reduction
programs.
Isokinetic
Similar to the Isotonic contraction, the Isokinetic contraction causes the
muscle to shorten as it gains tension. The difference is Isokinetic requires
a constant speed over the entire range of motion, therefore this type of
contraction require special equipment to exercise properly. An example is an
arm stroke when swimming, the even resistance from the water offers a
constant speed.
As far as weight reduction goal is concerned isotonic and isokinetic
exercises gives similar benefits.
While exercising our muscles burn both fat and glucose (carbohydrates in
the blood) in different proportions. Depending on how an individual exercises
muscle can burn fat in a larger proportion to glucose.
When activity is light and easy we tend to burn a much higher percentage
of fat. Fat is a slow burning fuel that requires oxygen so if oxygen is
delivered to muscle cells in sufficient quantities the cells can easily burn
fat for most of its energy requirement. A potential problem for weight loss
is lighter exercise burns fewer total calories.
If an individual increases their effort by performing a more intense
exercise they will burn more calories however, because oxygen cannot always
be delivered to the hard-working cells in sufficient quantities, cells are
forced to burn more carbohydrates in order to keep up with increasing demand.
If the level of exertion continues to increase then glucose eventually
becomes the predominant energy source for muscles as this quick-burning fuel
does not require oxygen. It means to burn fat directly we should exercise at
a lower level of effort and for longer duration.
The best way to exercise will depend on whether you want fat burning,
fitness or muscle toning. The way we choose to exercise determines the
results and which fuel the working cells use, for example, a more aggressive
way of exercising will result in the use of carbohydrates as the main source
of energy and will even stress the muscles enough to cause the toning or
building up of muscle. A more gentle way of exercising means the cells can
best use the slow-burning fuel - fat!
Time may also come into the equation, the best way to exercise for
effective fat burning is at a low intensity for at least 30 minutes. However,
for increased fitness it requires a moderate level of effort but performed
for 15 minutes.
As can be seen there are different ways to exercise in order to gain
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