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2 - Cardiorespiratory Fitness
Cardiorespiratory (CR) fitness, sometimes
called CR endurance, aerobic fitness, or aerobic capacity, is one of the five
basic components of physical fitness. CR fitness is a condition in which the body’s
cardiovascular (circulatory) and respiratory systems function together, especially
during exercise or work, to ensure that adequate oxygen is supplied to the working
muscles to produce energy. CR fitness is needed for prolonged, rhythmic use of
the body’s large muscle groups. A high level of CR fitness permits continuous
physical activity without a decline in performance and allows for rapid recovery
following fatiguing physical activity.
Activities such as running, road marching,
bicycling, swimming, cross-country skiing, rowing, stair climbing, and jumping
rope place an extra demand on the cardiovascular and respiratory systems. During
exercise, these systems attempt to supply oxygen to the working muscles. Most
of this oxygen is used to produce energy for muscular contraction. Any activity
that continuously uses large muscle groups for 20 minutes or longer taxes these
systems. Because of this, a wide variety of training methods is used to improve
cardiorespiratory endurance. Physiology
of Aerobic Training
Aerobic exercise uses oxygen to produce most of the
body’s energy needs. It also brings into play a fairly complex set of physiological
events.
To provide enough energy-producing oxygen to the muscles, the following
events occur:
• Greater movement of air through the lungs.
• Increased
movement of oxygen from the lungs into the blood stream.
• Increased delivery
of oxygen-laden blood to the working muscles by the heart's accelerated pumping
action.
• Regulation of the blood vessel's size to distribute blood away from
inactive tissue to working muscle.
• Greater movement t of oxygen from the
blood into the muscle tissue.
• Accelerated return of veinous blood to the
heart.
Correctly performed aerobic exercise, over time, causes positive changes
in the body's CR system. These changes allow the heart and vascular systems to
deliver more oxygen-rich blood to the working muscles during exercise. Also, those
muscles regularly used during aerobic exercise undergo positive changes. By using
more oxygen, these changes let the muscles make and use more energy during exercise
and, as a result, the muscles can work longer and harder.
During maximum aerobic
exercise, the trained person has an increased maximum oxygen consumption (VO2max).
He is better able to process oxygen and fuel and can therefore provide more energy
to the working muscles.
VO2max, also called aerobic capacity,
is the most widely accepted single indicator of one's CR fitness level.
The
best way to determine aerobic capacity is to measure it in the laboratory. It
is much easier, however, to estimate maximum oxygen uptake by using other methods.
It is possible to determine a soldier’s CR fitness level and get an accurate estimate
of his aerobic capacity by using his APFT 2-mile-run time. (Appendix F explains
how to do this.) Other tests - the bicycle, walk, and step tests - may also be
used to estimate one’s aerobic capacity and evaluate one’s CR fitness level.
In the presence of oxygen, muscle cells produce energy by breaking down carbohydrates
and fats. In fact, fats are only used as an energy source when
oxygen is present.
Hence, aerobic exercise is the best type of activity for attaining and maintaining
a low percentage of body fat.
A person’s maximum aerobic capacity can be modified
through physical training. To reach very high levels of aerobic fitness, one must
train hard. The best way to improve CR fitness is to participate regularly in
a demanding aerobic exercise program.
Many factors can negatively affect one's
ability to perform well aerobically. These include the following:
• Age.
• Anemia.
• Carbon monoxide from tobacco smoke or pollution.
• High altitude
(reduced oxygen pressure).
• Illness (heart disease).
• Obesity.
•
Sedentary life-style.
Any condition that reduces the body’s ability to bring
in, transport, or use oxygen reduces a person’s ability to perform aerobically.
Inactivity causes much of the decrease in physical fitness that occurs with increasing
age. Some of this decrease in aerobic fitness can be slowed by taking part in
a regular exercise program.
Certain medical conditions also impair the transport
of oxygen. They include diseases of the lungs, which interfere with breathing,
and disabling heart conditions. Another is severe blocking of the arteries which
inhibits blood flow to the heart and skeletal muscles.
Smoking can lead to
any or all of the above problems and can, in the long and short term, adversely
affect one’s ability to do aerobic exercise.
FITT Factors
As mentioned in Chapter 1, a person must integrate several factors into any successful
fitness training program to improve his fitness level. These factors are summarized
by the following words which form the acronym FITT. Frequency, Intensity, Time,
and Type. They are described below as they pertain to cardiorespiratory fitness.
A warm-up and cool-down should also be part of each workout. Information on warming
up and cooling down is given in Chapters 1 and 4. FREQUENCY
Frequency refers to how often one exercises. It is related to the intensity and
duration of the exercise session. Conditioning the CR system can best be accomplished
by three adequately intense workouts per week. Soldiers should do these on alternate
days. By building up gradually, soldiers can get even greater benefits from working
out five times a week. However, leaders should recognize the need for recovery
between hard exercise periods and should adjust the training intensity accordingly.
They must also be aware of the danger of overtraining and recognize that the risk
of injury increases as the intensity and duration of training increases. INTENSITY
Intensity is related to how hard one exercises. It represents the degree of effort
with which one trains and is probably the single most important factor for improving
performance. Unfortunately, it is the factor many units ignore.
Changes in
CR fitness are directly related to how hard an aerobic exercise is performed.
The more energy expended per unit of time, the greater the intensity of the exercise.
Significant changes in CR fitness are brought about by sustaining training heart
rates in the range of 60 to 90 percent of the heart rate reserve (HRR). Intensities
of less than 60 percent HRR are generally inadequate to produce a training effect,
and those that exceed 90 percent HRR can be dangerous.
Soldiers should gauge
the intensity of their workouts for CR fitness by determining and exercising at
their raining heart rate (THR). Using the THR method lets them find and prescribe
the correct level of intensity during CR exercise. By determining one’s maximum
heart rate, resting heart rate, and relative conditioning level, an appropriate
THR or intensity can be prescribed.
One’s ability to monitor the heart rate
is the key to success in CR training. (Note: Ability-group running is better than
unit running because unit running does not accommodate the individual soldier’s
THR. For example, some soldiers in a formation may be training at 50 percent HRR
and others at 95 percent HRR. As a result, the unit run will be too intense for
some and not intense enough for others.)
The heart rate during work or exercise
is an excellent indicator of how much effort a person is exerting. Keeping track
of the heart rate lets one gauge the intensity of the CR exercise being done.
With this information, one can be sure that the intensity is enough to improve
his CR fitness level.
Following are two methods for determining training heart
rate (THR). The first method, percent maximum heart rate (% MHR), is simpler to
use, while the second method, percent heart rate reserve (% HRR), is more accurate.
Percent HRR is the recommended technique for determining THR. Percent
MHR Method
With this method, the THR is figured using the estimated maximal
heart rate. A soldier determines his estimated maximum heart rate by subtracting
his age from 220. Thus, a 20-year-old would have an estimated maximum heart rate
(MHR) of 200 beats per minute (220 -20 = 200).
To figure a THR that is 80
percent of the estimated MHR for a 20-year-old soldier in good physical condition,
multiply 0.80 times the MHR of 200 beats per minute (BPM). This example is shown
below.
FORMULA
% x MHR = THR
CALCULATION
0.80
x 200 BPM = 160 BPM
When using the MHR method, one must compensate for
its built-in weakness. A person using this method may exercise at an intensity
which is not high enough to cause a training effect. To compensate for this, a
person who is in poor shape should exercise at 70 percent of his MHR; if he is
in relatively good shape, at 80 percent MHR; and, if he is in excellent shape,
at 90 percent MHR.
Continue to
Percentage HRR Method
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