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Acute Responses to Exercise

VCE PE Unit 3 AOS 2

Tim Hodge

on 8 March 2012

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Transcript of Acute Responses to Exercise

Acute Responses to Exercise
When exercise commences, there is a need to make a number of physiological changes to accomodate the energy requirements of the activity
There is an increased demand for oxygen and energy substrates and the cadiovascular, respiratory and muscular systems respond to meet these needs.
the level of response is
dependant on both the and the of exercise being undertaken

Tidal Volume
Respiratory Rate
How much air is inspired per Breath
the number of breaths taken in one minute
How much air is breathed in or out in one minute
(Liters per min)
(Breaths per minute)
Summary of Acute responses of ventilation to exercise
V, TV & RR all increase
@ submax intensity
V increses rapidly at the start & reaches a plateau around 4-5mins
RR & TV are increase proportionally
@ max intensity
V increses rapidly and continues to increase until exercise stops
TV plateaus & further increase in V comes from RR
When V no longer increases @ a linear rate is know at the Ventlatory Threshold
@ rest V can equal btw 4-15 litres depending on body size and gender
During exercise, can become 15-30 times greater than @ rest
The movement of molecules from an area of higher concentration to lower concentration
Gas exchange occurs in the lungs at the alveolar-capillary interface and in the muscles at the tissue-capillary interface through diffusion.
In the lungs
Oxygen concentration is high, so oxygen difusses from the alveoli into the bloodstream

Carbon Dioxide levels in the blood are high, so CO2 moves from the blood into the alveoli via a diffusion path
At the muscles
Opposite occurs as blood oxygen levels are high and muscle oxygen levels are low

Carbon Dioxide levels in the muscle is high, so CO2 moves from the muscle into the bloodstream
The amount of blood pumped out of the heart in one minute
Cardiac Output
Stroke Volume
Heart Rate
The amount of blood ejected by the left ventricle per beat
the number of times the heart beats in one minute
(Liters per min)
(Litres per beat)
(Beats per minute)
During exercise, the cardiovascular system needs to deliver greater amounts of oxygen and energy substrates to the working muscles, in order to meet the increasing energy demands of the activity.
The focus is on getting more blood to the working muscles to meet this need and to speed up the removal of carbon dioxide and other waste products. The cardiovascular system undergoes a number of changes to do this.
Summary of Acute responses of Cardiac Output to exercise
Trained Vs Untrained athlete
Q is the same with higher SV and lower HR
@ rest, SV is about 40-50% of blood in the Left Ventricle
SV increases to 100% during submax exercise. Further rise in Q come from increased HR.
@submax, HR will increase & Plateau once O2 demand is met (Steady State)
With increased workload, HR will increase to max
If the exercise duration continues past 30 minutes, HR will continue to increase but SV will decrease.
Changes in HR and SV are equal in size but opposite in direction.
Therefore Q stays the same.
Systolic Blood Pressure
Diastolic Blood Pressure
Blood Pressure
increased Q causes an increase in BP
Exercise involving large muscle groups
Increased Systolic
Diastolic stays relatively constant
Strengthening exercises
greater change in both Sys & Dias BP but Q is less
pressure in the arteries following contraction of ventricles as blood is pumped out of the heart
pressure in the arteries when the heart relaxes and ventricles fill with blood
Venous Return
increases during exercise via 3 mechanisms

mechanical pumping action of the muscle contractions
one-way valves prevent back flow

diaphragm increases abdominal pressure during inspiration
when venous return needs to increase, RR will also increase

a reflex control by the CNS
redecues the capacity of the veins, forcing blood to be pushed out
2. Respiratory pump
1. Muscle Pump
3. Venoconstriction
During exercise blood volume decreases
plasma volume deceases rapidly in the first 5 mins and the stabilises
the size of decrease depends on
exercise intensity
environmental factors (eg. temperature)
level of hydration
Blood Volume
Redistribution of
blood flow
during exercise, blood flow is redirected away from the spleen, kidneys, gastrointestinal tract and inactive muscles to the working muscles.
Vasoconstriction occurs in the arterioles supplying the inactive areas of the body
Vasodilation occurs in the arterioles supplying the working muscles
Brain=BF maintained, Heart=BF increased
BF to skin is increased to assist thermoregulation
Oxygen consumption
Arteriovenous oxygen difference (a-vO2 diff)
volume of oxygen that can be taken up and used by the body.
as intensity of exercise increases, so does oxygen consumption
direct result of
an increase in Cardiac Output (Q)
an increase in aVO2 diff
difference in oxygen concentration in the arterioles compared with the venuoles
@ rest, as little as 25% of O2 given to the tissues.
During exercise, the working muscles extract greater amounts of oxygen from the blood, increasing the a-vO2 difference
O2 extraction approaches 100%
Increased blood flow
During exercise, skeletal capillaries open up and serve three main purposes
allow for increases in total muscle blood flow
deliver large blood volume with minimal increase in blood flow velocity
increase the surface area to increase diffusion rates
This results in an increase in blood flow to the working muscles, allowing for greater delivery
of oxygen to meet the metabolic demands of the exercise.
Recruitment and activation of muscle fibres
CNS uses Motor units to 'talk' to the muscle
Depending on required strength and speed of the contraction, the
of motor units recruited, and the
at which they are recruited, can be adjusted
All-or-nothing principle in a motor unit unit
Motor unit recruitment follows a set pattern
smaller slow twitch fibres (ST)
fast oxidative glycolytic fibres (FTA)
Larger fast glycolytic fibres (FTB)
Whilst ST fibres are activated during all contractions, depending on intensity, duration and fatigue, FTA & FTB may also be recruited
Energy Substrates
ATP is the immediate source of energy but only available in short supply.
once used up, must rely on other substrates
Decrease in fuel level/concentration in the muscles
ATP, PC, glycogen & intramuscular triglyceride
High intensity Vs endurance activities
which would have a greater depletion
As exercise starts, large amounts of lactate are released from the muscle due to anaerobic production of ATP through the anaerobic glycolysis system.
@ submax exercise, sharp increase in lactate – until O2 consumption meets energy demands & lactate is delivered to sites for removal
as exercise intensity increases, as will removal & production, until the point where lactate production goes above the rate at which it can be removed. This point is known as the Lactate Inflection Point (LIP)
Body temperature
When exercise commences, there is an increase in the rate of metabolism required to produce ATP in the muscle

Heat is the by-product of the process of converting chemical energy (fuel) to mechanical energy (movement).
Body temperature

Increased rate of reactions
Increased heat production
in turn
Increased body temperature
Body temperature
The body accommodates these changes by:
stimulating the sweat glands in the skin to produce sweat.
This combines with increased blood flow to the skin
The acute responses to exercise contribute to increasing the availability of oxygen to the working muscles
Summary of Acute responses to exercise
Refers to the moment when the body can just prevent the accumulation of H+ in the working muscles
Beyond the LIP, lactic acid is produced faster than it can be oxidised or broken down & lactate will accumulate in the bloodstream.
This is reflected as a steep rise on a graph.
LIP will vary amongst individuals depending on their level of training and will occur later in endurance-trained athletes.
LIP is usually triggered at 85% max HR
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