CARDIORESPIRATORY ADAPTATIONS TO TRAINING
During a single bout of exercise, the human machine is quite adept at
adjusting its cardiovascular and respiratory functioning to adequately meet
the heightened demands of active muscles. When these systems are faced
with these demands repeatedly, such as on a daily basis when training, they
adapt in ways that allow the body to improve its performance of endurance
activity. For example, the miler can run a faster mile. The physiological and
metabolic processes that bring oxygen into the body, distribute it, and allow it
to be used by active tissues become and remain highly efficient at these
tasks. In this chapter, we will examine adaptations in cardiorespiratory
function in response to training, and how such adaptations affect an athlete’s
endurance capacity and performance.
Cardiorespiratory endurance is probably the least understood component of a
total training program. The training programs for many nonendurance athletes
completely ignore the endurance factor. This is understandable, because for
maximum improvement in performance, training should be higbly specific to
the particular sport or activity in which the athlete participates, and endurance
is frequently not recognized as important to nonendurance activities. The
reasoning then is "Why waste valuable training time if the result is not
improved perfonnance?"
The problem with this reasoning is that often, although it might not be obvious,
a nonendurance sport does indeed have an endurance, or aerobic,
component. For example, if you play football, you and your coach might fail to
recognize the importance of cardiorespira~ tory endurance as part of your total
training program. From all outward appearances, football is an anaerobic or
burst-type activity, consisting of repeated bouts of high-intensity work of short
duration. Seldom does a run exceed 40 to 60 yd (37 to 55 m), and even this is
followed by a substantial rest interval. The need for endurance is not readily
apparent.
What you and your coach might fail to consider is that this burst-type activity
must be repeated many times during the game. With a high endurance level,
the quality of your burst activity could be maintained throughout the game, and
you would still be relatively fresh during the fourth quarter.
'
Sport scientists are beginning to realize the importance of endurance training
for almost all types of sports or activities:
. Burst-type, such as football,basketball and some parts in dance
. Moderate-intensity and skilled, such as baseball ,golf and dance
. Endurance-type, such as running. cycling and swimming
Many authorities now believe football teams that fall apart in the final quarter have
ignored the endurance component in their training programs, A similar case can be
made for athletes in most sports. But before we look specifically at how endurance
can improve performance, we must understand what endurance is.
Endurance
Endurance is a term that describes two separate but related concepts: muscular
endurance and cardiorespiratory endurance. Each makes a unique contribution to
athletic performance, so each differs in importance to different athletes.
For sprinters, endurance is the quality that allows them to sustain a high
speed over the full distance of, for example, the 100- or 200-m race. This quality is
muscular endurance-젳the ability of a single muscle or muscle group to sustain
high-intensity, repetitive, or static exercise. This type of endurance is also
exemplified by the weight lifter, boxer, and wrestler. The exercise or activity can be
rhythmical and repetitive in nature, such as the bench-press for the weight lifter and
jabbing for the boxer. Or the activity can be more static, such as a sustained muscle
action when a wrestler attempts to pin an opponent to the mat. In either case, the
resulting fatigue is confined to a specific muscle group and the activity's duration is
usually no more than I or 2 min. Your muscular endurance is highly related to your
muscular strength and anaerobic development.
Whereas muscular endurance refers to the ability of individual muscles,
cardiorespiratory endurance relates to the body as a whole. Specifically, it refers
to your body's ability to sustain prolonged, rhythmical exercise. This type of
endurance is typified by the cyclist, distance runner, or endurance swimmer who
can complete long distances at a fairly fast pace. Your cardiorespiratory endurance
is highly related to the development of your cardiovascular and respiratory systems,
and thus your aerobic development.
KEYPOINT
CARDIOVASCULAR ENDURANCE IS THE ABILITY OF THE BODY TO
SUSTAIN PROLONGED EXERCISE
EVALUATING AEROBIC POWER
To study training effetcs on endurance, we need a means for evaluating an
individual’s endurance capacity which we can easily use to mintor her or his
improvement during the training program.
VO2 MAX: AEROBIC POWER
VO2 max is defined as the highest rate of oxygen consumption attainable
during maximal or exhaustive exercise. If you increase your exercise intensity
beyond the point at which you reach VO2 max, your oxygen consumption will either
plateau or decrease slightly.
Reaching the plateau means that you can’t deliver oxygen as quickly as is needed
to meet your muscles’ demands You can continue exercising for a brief period after
reaching VO2 max by calling on your aerobic resreves, but these also have a finite
capacity.
With endurance training , more oxygen can be delivered and consumed than in
untrained state. Previously untrained subjects show average VO2 max increases of
20% or more after a 6 month training program. These improvements allow you to
perform endurance activities at a higher work rate or faster pace, improving your
performance potential.
OXYGEN TRANSPORT SYSTEM
Oxygen transportation and delivery are major functions shared by both your
car diovascular and respiratory systems, All components of these two systems
that are related to the transportation of oxygen are collectively referred to as
the oxygen transport system.
The functioning of the oxygen transport system is defined by the interaction of
the arterial venous oxygen difference (a—vo2: diff). Cardiac output 琴volume x
heart rate) tells us (stroke how much oxygen-carrying blood leaves the heart in
1 min. The arterial venous difference, which is the difference between the
oxygen content of the arterial blood and the oxygen content of the venous
blood, tells us how much oxygen is extracted by the tissues. The product of
these values tells us the rate at which oxygen is being consumed by the body
tissues.
CARDIOVASCULAR ADAPTATIONS TO TRAINING
Numerous cardiovascular adaptations occur in response to training:
-
Heart size
Stroke volume
Heart rate
Cardiac output
Blood flow
Blood pressure
Blood volume
SYNTHESIZING
1.
Cardiovascular endurance refers to your body’s ability to sustain
prolonged, rhythmical exercise. It is highly related to your aerobic
development
2.
Most sport scientists regard VO2 max- the highest rate of oxygen
consumption, obtainable during maximal or exhaustive exercise- to be the
best indicator of cardiovascular endurance
3.
Cardiac output tells how much blood leaves the heart each
minute, whereas “a VO2 max diff.” Indicates how much oxygen is
extracted from the blood by the tissues. The product of these tells us the
rate of oxygen consumption:
VO2max- SV x HR x a VO2 maxdiff
4.
The left ventricle undergoes the most change in response to
endurance training
1. The internal dimensions of the left ventricle increase, mostly in
response to an increase in ventricular filling
KEYPOINT
A stronger heart and the availability of a greater blood volume appear
to account for the increases in resting, submaximal, and maximal
stroke volumes following an endurance training program.
Studies in which the oxygen consumption of the heart has been directly monitored
have shown that the heart rate, both at rest and during exercise, is a good index of
how the heart is working. Because active muscle requires more oxygen than resting
muscle, it is not surprising that the heart’s oxygen consumption, and thus the amount
of work it performs, are directly related to the heart’s consrtaction rate.
RESTING HEART RATE
The heart at rest decreases markedly as a result of endurance training. If you are a
sedentary individual with an initial resting heart rate of 80 beats /minute, your heart
rate will decrease by approximately 1 beat/minute each week for the first few weeks
of training.
Highly conditioned endurance athletes often have resting heart rates lower than 40
beats/minute, and some have values lower than 30 beats/minute!
Bradycardia is a clinical term indicating a heart rate of less than 60 beats/minute. In
untrained individuals, bradycardia is usually the result of abnormal cardiac function or
a diseased heart. Therefore, it is necessary to differentiate between training-induced
bradycardia, which is a natural response to endurance training, and pathological
bradycardia, which can be a serious cause for concern.
HEART RATE RECOVERY
During exercise your heart rate must increase to meet the demands of your active
muscles. When the exercise bout is finished, your heart rate does not instantly return
to its resting level. Instead, it remains elevated for a while, slowly returning to its
resting rate. The time it takes for your heart rate to return to its resting rate is called
the heart rate recovery period.
RESISTANCE TRAINING AND HEART RATE
The reductions in heart rate that have been reported in resistance training are much
less than the typical reductions obtained in endurance training.These changes
appear to be dependent on the following characteristics of the resistance training
program:
- training volume
- training intensity
- training duration
- length of rest periods bewteen stes
- amount of muscle mass used
SYNTHESIZING
1.
Resting heart rate decreases considerably as a result of
endurance training. In a sedentary person the decrease is
typically about 1 beat/minute per week during initial training.
Highly trained endurance athletes often have rest rates of 40
beats/minute or less.
2.
Heart rate during submaximal exercise also decreases, often
by 20 to 40 beats/minute following 6 months of moderate training
A person’s maximal heart’s rate decreases proportionally with the
amount of traing completed.
3.
Maximal heart either remains unchanged or decreases
slightly with training. When a decrease occurs , it is probably to
allow maximum stroke volume to maximize cardiac output.
4.
The heart rate recovery period decreases wit瑨 increased
endurance , making this value well suited to tracking an
individual’s progress with training.
5.
Resistance training can also lead to reduced heart rates,
however these decreases are not as reliable or as large as those
seen with endurance training.
MAXIMUM BREATHING CAPACITY TEST
To better understand the concept of optimizing the heart rate- stroke volume
relationship
ce the greatest ventilation
vol
to provide the greatest cardiac output.
BLOOD FLOW
We know that active muscles need much more oxygen and nutrients. To meet
these needs, more blood must be brought into these muscles during exercise. As
the muscles become better trained, the cardiovascular system adapts to increase
blood flow to them. Three factors account for this enhanced blood supply following
training:
1. Increased capillarisation of trained muscles
2. Greater opening of existing capillaries in trained muscle൳
3. More effective blood redistribution.
To permit increased blood flow, new capillaries develop in trained muscles. The
allows the blood to more fully perfuse the tissues.This increase in capillaries is
usually expressed as an increase in the number of capillaries per muscle fiber.
The existing capillaries in trained muscles can open up more, which increases
blood flow through the capillaries and into the muscles. Because endurance
training also blood because more blood is present in the system to begin with, so
shifting more into capillaries will not severely compromise venous return.
Blood flow to the active muscles can also be increased by a more effective
blood redistribution of the cardiac output. Blood flow is directed to the active
musculature and shunted away from areas that don’t need high flow. Venous
compliance can also be decreased with endurance training as a result of
increased because more blood is present in the system to begin with, so
shifting more into capillaries will not severely compromise venous return.
Blood flow to the active muscles can also be increased by a more effective
blood redistribution of the cardiac output. Blood flow is directed to the active
musculature and shunted away from areas that don’t need high flow. Venous
compliance can also be decreased with endurance training as a result of
increased venous tone. That means that the veins are not as easily distended
by the blood, so less blood pools in the venous system, thereby increasing
the amount of arterial blood available for working muscles.
BLOOD VOLUME
Endurance increases blood volume. This effect is greater with more intense
levels of training. This increased blood volume iactually results from an
increase in blood plasma volume. This is thought to be primarily caused by
two mechanisms. First, exercise increases the release of antidiuretic
hormone( ADH)
and aldosterone.These cause the kidneys to retain water which increases
blood plasma.Second, exercise increases the amount of plasma,particularly
albumin. The plasma proteins are the major basis for the blood’s osmotic
pressure. The result is that more fluid is retained in the blood. Thus both
mechanisms work together to increase the fluid portion of the blood- the blood
plasma.
RESPIRATORY ADAPTATIONS TO TRAINING
No matter how efficient the cardiovascular system is at supplying adequate
amounts of blood to tissues, endurance would be hindered if the respiratory
system didn’t bring in enough oxygen to meet oxygen demands.Respiratory
system functioning usually does not limit performance because ventilation can
be increased to a greater extent than cardiovascular function. But, as with the
cardiovascular system, the respiratory system undergoes specific adaptations
to endurance training to maximize its efficiency.
LACTATE THRESHOLD
Endurance training increases lactate threshold . In other
words,, after
training you can perform at a higher rate of work and at a higher absolute rate
of oxygen consumption without raising your blood lactate above resting
levels.The lactate threshold occurs at a higher percentager of VO2 max after
training.
This increase in the lactate threshold appears to be due to several factors:
-
a greater ability to clear lactate produced in the muscle
an increase in muscle enzymes
The net result is less lactate production for the same work rate.
Synthesizing
1. Lactate threshold increases with endurance training, which
allows you to perform at higher rates of work and levels of
oxygen consumption without increasing your blood lactate
above resting levels. Maximal blood lactate levels can be
increased slightly.
2. The respiratory exchnage ratio decreases at submaximal
work rates, indicating a greater utilization of free fatty
acids, but increases at maximal effort
3. Oxygen consumption can be increased slightly at rest and
decreased slightly or decreased or unaltered during
submaximal exercise
4. VO2 max increases substantially following training, but the
amount of increase possible is limited in each
individual.The major limiting factor appears to be oxygen
delivery to the active muscles.
FACTORS AFFECTING THE RESPONSE TO AEROBIC TRAINING
We must always remember that we are talking about adaptations in
individuals, so not everyone will respond in the same manner.several factors
must be considered that can affect individual response to aerobic training:
-
Heredity
Age
Gender
Even with identical programs, not everyone will respond the same. Genetics
accounts for much of this variation in response.
SPECIFICITY OF TRAINING
Physiological adaptations in response to physical training are highly specific
to the nature of the training activity. The program must be closely mathched to
the indivual needs to maximize the physiological adaptations to training,
thereby optimizing the athlete’s performance.
CARDIOVASCULAR ENDURANCE AND PERFORMANCE
Cardiorespiratory endurance is regarded by many people as the most
important component of physical fitness. It is an athlete’s major defense
against fatigue, even in the more sedentary sports or activities. For any
athlete, regardless of the sport or activity, fatigue represents a major deterrent
to optimal performance. Even minor fatigue can have a detrimental effect on
the athlete’s total performance:
-
Muscular strength is decreased
Reaction and movement times are prolonged
Agility and neuromuscular coordination are reduced
Whole-body movement is slowed
Concentration and alertness are reduced
The decline in concentration and alertness associated with fatigue is
particularly important. The athlete can become careless and prone to injury.
IN REVIEW
1. Although VO2 max has an upper limit, endurance performance can
continue to improve for years with continued training
2. An individual’s genetic makeup predetermines a range for his or her
VO2max, accounting for 25 to 50% of the variance in VO2 max values.
Heredity also largely explains individual variations in response to identical
training programs.
3 Age- related decreases in aerobic capacity might partly result from
decreased activity
4 Highly conditioned female endurance athletes have VO2 max values only
about 10% lower than those of highly conditioned male endurance
athletes.
5 To maximize the cardiorespiratory gains from training, the training should
be specific to the type of activity that the athlete performs.
Resistance training in combination with endurance training does not appear to
restrict improvement in aerobic capacity and may increase short-term
endurance