Biology of Exercise Intensity I. Homeostasis. During exercise. At rest. Effects of exercise on circulation. The following variables of the circulation system will be affected by exercise. Heart rate (b/min) The number of times that the heart beats per minute. Stroke volume (mL/beat)
The following variables of the circulation system will be affected by exercise
Heart rate (b/min)
The number of times that the heart beats per minute
Stroke volume (mL/beat)
The volume of blood that is ejected by the heart each beat
Cardiac output (L/min)
The volume of blood pumped by the heart per minute
Blood pressure (mmHg)
The forces that are created on a vessel wall by the blood within it
Maximum heart rate 196 beats per minute
As exercise intensity increases, heart rate increases
Increase in heart rate (b/min)
Maximum level on beep-test, level 10–6
Increase in beep-test level and therefore exercise intensity
As exercise intensity increases, stroke volume increases. In this example, stroke volume has increased from 79 mL/beat to 100 mL/beat.
Increase in stroke volume (mL/beat)
Increase in time (min:sec)
Note that as time is increasing, exercise intensity is also increasing.
A typical graph showing cardiac output against level on the beep-test
As the level on the beep-test increases, the cardiac output increases to provide a greater volume of oxygen to the active muscles.
The graph shows that as exercise intensity increases, blood pressure also increases.
Two values are provided for blood pressure – systolic blood pressure (SBP) and diastolic blood pressure (DBP), therefore the graph plots two sets of values.
Systolic blood pressure
This is the pressure that is recorded when the heart contracts to eject blood from the heart and is always the highest blood pressure value.
Diastolic blood pressure
This is the pressure that is recorded when the heart relaxes as the ventricles are being filled with blood and is always the lowest blood pressure value.
The following variables of the respiratory system will be affected by exercise
Breathing rate / respiratory rate (b/min)
The rate of breathing, recorded as the number of breaths per minute
Depth of breathing / tidal volume (mL)
The volume of air in each breath
Minute ventilation (L/min)
The volume of blood that is taken into (or out of) the lungs each minute
Depth of breathing or tidal volume
Rate of breathing or respiratory rate
At low to moderate intensity there is an increase in depth of breathing and then this decreases.
At low to moderate intensity there is a gradual increase in the rate of breathing and then it increases more rapidly.
An exponential graph
During the early stages of the beep-test changes are slow, but at higher work rates breathing increases very rapidly.
The following variables of the muscular system will be affected by exercise
Lactic acid (mMol)
A molecule in the body produced as a by-product of anaerobic energy
Metabolic rate (kJ/min)
The rate of energy turnover used in a given period of time. It is the conversion of chemical energy into mechanical and heat energy to produce ATP and to perform work.
Heat generated (kJ/min)
A by-product of energy release
The graph of lactic acid against level on the beep-test shows a non-linear graph – a slower rate of change at lower exercise intensity followed by an accelerated increase as exercise intensity increases.
A rapid increase in lactic acid at high levels of intensity
A slow rate of increase at low levels of intensity
The metabolic rate is the rate of energy used in the muscles. At a low exercise intensity, metabolic rate is low. As the exercise intensity increases the muscles work harder to produce greater force, therefore the metabolic rate increases.
A by-product of aerobic respiration is heat. Heat generated increases with exercise intensity. The face goes red and the body sweats to help to reduce an increase in body temperature.