The Acute and Chronic Effects of Physical Activity

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The Acute and Chronic Effects of Physical Activity
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Acute Response to Exercise

• The sudden, temporary changes in body function
  caused by exercise.
• They disappear shortly after the exercise period
  is finished.

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Chronic Adaptation to Exercise

• Persistent changes in the structure and function
  of your body following regular exercise.
• Changes that enable your body to respond more
  easily to exercise

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Physiological Responses to Acute Exercise

• Acute responses to exercise are influenced by a
  number of factors
• Level of training or fitness status
• Sufficiency of sleep
• Coffee intake
• Alcohol
• Tobacco
• General anxiety

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Increase in Heart rate

• The pre-exercise heart rate may be elevated due
  to the anticipatory response.
• During the GXT, heart rate will increase in
  direct proportion to the intensity of the
  exercise.
• HR rises in a linear fashion with increases
  workload.
• At exhaustion the rise in HR will flatten out.
  This is called the maximal heart rate.
• At this point the rise in HR becomes more
  curvilinear and will not increase further.

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Increase of Stroke Volume

• SV is the quantity of blood pumped out of the
  heart per heart beat.
• SV is regulated by
• Amount of venous return to the heart.
• The force of contraction of the heart muscle.
• Sympathetic nervous stimulation.
• The change in SV during a GXT does not follow the
  pattern of change in heart rate.
• SV increases strongly up to 40-60 of V02max.
• Beyond this intensity level, increasing workload
  brings only small increase in SV.

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Stroke Volume

• Resting SV values for sedentary people range
  between 60 and 70 ml of blood per heart beat.
• Highly trained people may have resting SV values
  as high as 100ml.
• Submaximal and maximal SV volumes are also higher
  for fit than sedentary people.
• SV for elite runners have been measured as high
  as 180ml/beat.

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Body Position Effects SV

• When you go from lying down to standing there is
  an immediate drop in your SV.
• This is because of the influence in gravity and a
  corresponding increase in your heart rate to
  maintain the flow of blood out of your heart.
• When exercise is performed in a horizontal
  position (swimming), the SV is larger and the HR
  is lower than when the same level of upright
  exercise is performed (running).
• Exercise training HRs should be adjusted
  downward by 10-15 BPM when swimming.

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Increase in Cardiac Output

• Q SV x HR ( quantity of blood pumped out of
  the heart each minute)
• At rest, Q is approximately 5 liters
• During maximal exercise it can rise to 20-40
  liters per minute, depending on individual
  fitness level and body size.
• Q rises linearly with increasing workload and
  plateaus slightly at exer. exhaustion.
• Initially the increase is due to both HR and SV
  increasing. After 40-50 of V02 max, it is due
  to increased heart rate.

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Increased Arteriovenous Oxygen Difference

• a-v02 the difference between the amount of
  oxygen carried in the arterial blood and the
  amount in the mixed venous blood.
• The a-v02 reflects the amount of oxygen extracted
  by the tissues of the body.
• At rest, the 02 content of arterial blood is
  approximately 20 ml of oxygen per 100 ml of
  blood, compared to an 02 content of 15ml/100
  blood for the mixed venous blood.
• The a-v02 difference at rest is 5 ml/100ml blood.
• During intense exercise, the venous oxygen
  content can drop to 2 to 4 ml/100ml blood.
• The a-v02 diff. can increase to 16-18ml/100ml
  blood.

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Increase in V02

• V02max the greatest rate at which oxygen can be
  consumed during exercise at sea level.
• During GXT, active muscle tissue uses more and
  more oxygen to burn CHOs and fats needed for
  energy production.
• For every liter of oxygen consumed, about 5
  calories of energy are produced.

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V02 Max

• If Q and the a-v02 difference are known, oxygen
  consumption can be calculated by using the
  formula V02 Q x a-v02.

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Oxygen Debt/Deficit

• 02 debt refers to the volume of oxygen consumed
  during the recovery period following exercise in
  excess of the volume normally consumed at rest.
• This debt pays back the deficit built up during
  the initial minutes of exercise, on account of
  the body adjusting to the exercise.
• During the first 2-3 minutes of exercise, your
  body is adjusting to the new workload. During
  recovery, you will breathe harder than during
  rest to help restore this deficit to normal.

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