Effect of exercise on rate of cardiac cycle

An average heartbeat is approximately 60 beats per minute

The heart unlike other muscles does not need any external nerve input to contract, the stimulus that drives it beat originates in the muscle itself, because of this we say that the human heart is myogenic.

A single heartbeat starts with an electrical signal from a region of specialised tissue called the sino-atrial node, on the wall of the right atrium. This is the heart beat regulator. The electrical signal spreads out over the walls of the atria, causing them to contract. From there, the signal does not pass directly to the ventricles. If it did, the ventricles would contract before they had filled with blood. Instead the impulse is delayed slightly. A second node, the atrio-ventricular node picks up the signal and channels it down the middle of the ventricular septum through the bundle of His. From here the signal spreads throughout the wall of the ventricles, though the Purkinje fibres and the ventricles then contact and are by this time filled with blood.

So the heart is capable of beating on its own, however the cycle speed can be increased or decreased by using the sino-atrial node of atrio-ventricular node if necessary.

Method

i. Select 5 volunteers who are willing to exercise

ii. The volunteers must then rest for 60 seconds and then take their pulse rate, (record this as this is the control)

iii. Then make the volunteers jog a set distance of 50 metres at the same pace, so all the volunteers should finish at the same time

iv. Then record the volunteers pulse rate

v. Allow the volunteers pulse rate to return to normal by allowing them to rest for approximately 60 seconds.

vi. Repeat from step three using the following distances, 75, 100, 150, 175, 200 and 250 meters.

Principle

This method works on the principle that as the rate of activity increases; specific muscles in the body will be respiring faster due to the fact that they will require more energy. With this increased rate of respiration more oxygen will be required and there will be increased levels of Carbon dioxide being produced. With these altering levels of CO2 the body will require to alter the rate of blood flow as to get more oxygen into the blood quicker, and expel carbon dioxide out of the blood quicker. This means that the speed of blood flow will either have to increase or decrease, this of course being controlled by the heart.

Steven Spencer