Download Response to Exercise Handout

Stroke Volume Response to Exercise
SV (ml/beats)
SV Response to Exercise
160
140
120
100
80
60
40
20
0
Series1
1
2
3
4
5
6
7
8
9
Treadmill Speed (miles/hour)
SV increases linearly as their speed /intensity increases, but only up to
40 – 60% of their maximal running speed.
After this they reach a plateau – thus Maximal SV values are reached
during sub maximal exercise (40- 60%)
Why SV increases:
SV is determined by the hearts ability to fill and empty each beat.
The hearts ability to fill is dependant upon:
1. Increase in Venous Return (blood returning to the heart.)
2. The ventricles are able to stretch further and enlarge.
Together, these increase the filling capacity of the heart and hence the
EDV.
The hearts ability to empty is dependant upon:
1. A greater EDV provides a greater stretch on the heart walls.
2. A greater stretch increases the force of ventricular systole.
Together, this increases ventricular contractility which almost empties
the blood from the ventricles.
Heart Rate
Increase before exercise – anticipatory rise – result in an early of
adrenalin which stimulates the SA node to increase the HR.
Increase as exercise intensity increases but slows down just prior to
maximal HR values.
Decrease a exercise intensity decreases.
Reach a plateau during sub maximal exercise –optimal steady state HR for
meeting the demand for oxygen at that specific intensity of work.
Decreases rapidly immediately after exercise stops due to a decrease in
the demand for oxygen for working muscles.
Gradually and more slowly decrease, but still remain elevated, towards
resting values to allow the body to recover – Oxygen Debt.
HR Response to exercise
200
HR (bpm)
150
Sub-maximal
100
Maximal
50
0
1
3
5
7
9
Time of exercise
11
Cardiac Output
Q is increased by an increase in both HR and SV. When the intensity of
the exercise exceeds 40-60% of an athlete’s maximal exercise intensity,
SV begins to plateau and any further increase in Q is a result of an
increase in HR.
Cardiac Output
Q is increased by an increase in both HR and SV. When the intensity of
the exercise exceeds 40-60% of an athlete’s maximal exercise intensity,
SV begins to plateau and any further increase in Q is a result of an
increase in HR.
THE REGULATION
OF HEART RATE
Cardiac Control Centre (CCC)
The CCC is in the medulla oblongata (brain) and is responsible for
regulation of the heart.
The CCC is controlled by the Autonomic Nervous System (ANS) – thus it
is under involuntary control and consists of sensory and motor nerves
from either the sympathetic (increase HR) or parasympathetic (decrease
HR) nervous system.
The CCC initiates the sympathetic and parasympathetic nervous systems
to stimulate the SA node to either increase of decrease the HR.
Sympathetic nervous system
* Increases heart rate by releasing adrenaline, and noradrenaline from
the adrenal medulla.
*Adrenaline increases the strength of ventricular contraction and
therefore stroke volume.
*Noradrenaline aids the spread of the impulse throughout the heart,
therefore increases the heart rate.
Parasympathetic nervous system
*Releases acetylcholine which slows the spread of impulses, therefore
reduces heart rate. Returning it to the normal resting level.
•
At rest the parasympathetic system overrides the sympathetic
system keeping the heart rate down.
•
When exercise starts the sympathetic system increases in activity,
the parasympathetic system decreases allowing heart rate to rise.
1. Neural Control
Proprio-receptors in the muscles, tendons and joints inform the CCC that
motor activity has increased.
Chemoreceptors are sensitive to chemical changes, in muscles, aorta and
carotid arteries, inform the CCC that lactic acid and CO2 levels have
increase and oxygen and pH levels have decreased.
Baroreceptors are sensitive to stretch within blood vessel walls, in aorta
and carotid arteries inform the CCC that blood pressure has increased.
CCC responds to the neural information by stimulating the SA node, via
the sympathetic cardiac accelerator nerve to increase HR and SV.
When exercise stops they are gradually reversed – the CCC increases
stimulation via the parasympathetic vagus nerve for the SA node to
decrease HR.
2. Hormonal Control
Before and during exercise, adrenalin is released within the blood stream.
Adrenaline stimulates the SA node to increase both HR and the strength
of ventricular contraction which therefore increases SV.
3. Intrinsic Control
During and after exercise there are a number of intrinsic/internal
factors that affect HR control.
During exercise:
Temperature increases: Increases the speed of nerve impulses, which in
turn increases HR
Venous Return increases HR which directly increases EDV and therefore
SV. (Starling’s Law)
After Exercise
Temperature decreases and HR decreases
Venous return decreases, which in turn decreases SV (Starling’s Law)