Short-term Effects of Exercise

When we begin to exercise the body has to respond to the change in activity level in order to maintain a constant internal environment (homeostasis). Here are the changes which must take place:

Circulatory System

The release of adrenaline (often before exercise even begins) causes the heart rate to rise
This increases Cardiac Output
Venous return increases due to the higher Cardiac Output and the skeletal muscle pump and respiratory pump
Increases in Lactic Acid (produced during the early anaerobic phase of exercise), Carbon Dioxide (due to increased rates of energy production) and temperature all act as stimuli to the cardiac control centre which responds by further increasing the heart rate
Oxygen levels within the blood decrease which causes increased diffusion at the lungs
Blood pressure increases, thus increasing flow rate and the speed of delivery of O2 and nutrients to the working muscles
Vasodilation and vasoconstriction ensure blood is directed to areas that need it (muscles, lungs, heart) and away from inactive organs

Respiratory System

Changes in the concentration of CO2 and O2 in the blood are detected by the respiratory centre which increases the rate of breathing
The intercostal muscles, diaphragm and other muscle which aid the expansion of the thoracic cavity work harder to further increase the expansion during inhalation, to draw in more air.

Muscles

The higher rate of muscle contraction depletes energy stores and so stimulates a higher rate of energy metabolim.
The bodys energy stores are slowly depleted
Myoglobin releases its stored Oxygen to use in aerobic respiration. O2 can now be diffused into the muscle from the capillaries more quickly due to the decreased O2 concentration in the muscle.

Next - Long term effects of exercise >>

The heart