In the separate phases of the cardiac cycle the diastolic phase takes around 0.5 seconds and the systolic phase takes about 0.3 seconds, however it is interesting that when studies have been done on trained athletes, they tend to have a longer diastolic phase of the cardiac cycle. This enables a more complete filling of the heart with blood; this means the trained athlete can increase venous return and therefore stroke volume during resting periods. This accounts for the decrease in resting heart rate or bradycardia which if often known to professional athletes. For example if you exercise daily and to a high tempo then your heart will be bigger as it is a muscle, therefore it can contain more blood and pump more out around the body supplying the muscles with more oxygen so you can last longer in that exercise.
Class notes
Electrocardiogram –
You are able to place electrodes on the skin of the chest to measure the electrical activity of the heart’s conduction system; this information is recorded in the form of a trace like the diagram below. The trace is known as an electrocardiogram or an ECG. On the diagram you can see a P, this wave occurs just before the atria contract, QRS wave complex occur just before the ventricles contract. The T wave corresponds to repolarisation of the ventricles before ventricular diastole. You can see this by looking at the diagram below. To measure this electrical conduction during exercise you can place the electrodes in the same place and put the person on a treadmill, this will record the results of the hearts conduction system while taking part in exercise and gives you a reading of how well the heart is able to pump blood to the working muscles.
Blood pressure is the force exerted by blood against the walls of the blood vessels, it is vital to maintain blood flow through the circulatory system and it is determined by two main factors, they are:-
Cardiac Output – the volume of blood flowing into the system from the left ventricle.
Resistance to flow – the opposition offered by the blood vessels to the blood flow. This is dependent upon many factors including blood viscosity, blood vessel length and blood vessel radius.
This means that blood pressure will increase when either cardiac output or resistance increases. Blood pressure in the arteries also increases and decreases in a pattern which corresponds to the cardiac cycle during ventricular systole, this is higher when blood is pumped into the aorta and lowest during ventricular diastole.
Blood pressure is normally measured at the brachial artery using a sphygmomanometer, which is recorded in millimetres of mercury – mmHg of systolic pressure over diastolic pressure. Systolic pressure is when the heart pumps blood into the system and diastolic pressure is recorded when the heart is relaxing with blood while relaxing. The average reading for a male adult at rest would be:-
120 mmHg = Systolic
80 mmHg Diastolic
When exercising the blood pressure changes and it is dependant upon the type and intensity of the exercise being performed.
During steady aerobic exercise involving large muscle groups, the systolic pressure increases as a result of an increased cardiac output, while diastolic pressure remains constant, although in well trained athletes this may even drop as blood feeds into the working muscle due to increased arteriole dilation. The increased systolic pressure associated with exercise is largely the result of increased cardiac output associated with an increased intensity. This ensures that adequate blood is supplied to the working muscle quickly.
During high intensity isometric and anaerobic exercise, both systolic and diastolic pressure rise significantly due to increased resistance of the blood vessels. This is a result of muscles squeezing the veins, which increases peripheral resistance and an increase in intra-thoracic pressure due to the contraction of the abdominals. For example, weightlifters will hold their breath during exertion and this causes a significant increase in both systolic and diastolic pressure.
It is important that blood pressure is regulated and where possible at rest maintained within a normal range. High blood pressure can cause serious complications to the heart, brain and kidneys, low pressure can result in insufficient oxygen and other nutrients being supplied to the muscle cells.
Class notes
The rates of blood flow determine on the amount of exercise you are performing, at rest a blood cell will take about a minute to be carried around the circulatory system, although the velocity of the blood flow is far from constant as it passes from one vessel to another. The velocity of a vessel is affected by the cross-sectional area of the blood vessels. Blood travels through the aorta at approximately 40 cm/s. As the blood travels through the smaller arteries and arterioles, the total cross-sectional area of these vessels increases, thus decreasing the velocity of the blood. The greatest total cross-sectional area is found in the capillary network as there are so many capillaries, in the capillary network the velocity of the blood is only 0.1 cm/s, slow enough to allow exchange of gases, nutrients and waste products. The blood will then flow back through the venules and veins, where the total cross-sectional area decreases which results in an increase in velocity. So during exercise the blood flow will increase or decrease at different stages. The more exercise you perform then the rate of our blood flow will increase as the heart is able to pump more blood to the working muscle at a faster rate.
Class Notes
The transport of respiratory gases, there are three main gases in the respiratory system and they are oxygen, carbon dioxide and haemoglobin. They all have their separate jobs in supplying the body with what it needs.
Oxygen diffuses into the capillaries, this is where 3% dissolves into plasma and about 97% combines with haemoglobin, when fully saturated haemoglobin can carry four oxygen molecules which can easily occur at sea level. This is because the pressure between the alveoli and the blood is high. At the tissues the oxygen dissociates from the haemoglobin because of the relatively low pressure of oxygen in the tissues. The more oxygen that can be supplied to the working muscles the better, this is because the more we train the bigger the heart muscle gets, so the more blood can be carried around the body. The oxygen is carried in that blood to the working muscles during exercise resulting in the muscles working for longer durations of time. Carbon dioxide is transported in one of three ways, around 7% dissolves in plasma and 23% combines with haemoglobin. The remaining 70% of carbon dioxide dissolves in water to form carbonic acid, when in the plasma this dissociates into hydrogen ions and biocarbonate ions. This hydrogen’s create a more acidic environment so the body needs to regulate the acid-base balance by neutralising or buffering its effects. This is achieved by combining the hydrogen ions with haemoglobin, because haemoglobin acts as a major buffer within the blood.
CO2 + H2O > H2CO3 > H+ + HCO-3
The relationship between haemoglobin and oxygen is referred to oxyhaemoglobin dissociation curves; the level of saturation of oxygen to the haemoglobin is affected by several factors. The partial of oxygen influences the saturation of haemoglobin with oxygen. The partial pressure of oxygen at sea level is always high enough for full saturation of haemoglobin in the lungs. When the blood arrives at the tissues the partial pressure of oxygen drops, causing the oxygen to dissociate from the haemoglobin and diffuse into the cell. At high altitudes the change in barometric pressure causes the partial pressure of oxygen to drop. This means that the haemoglobin is not fully saturated at the lungs and the oxygen carrying capacity of the blood is decreases. This can cause an athlete working at altitude problems. As the body temperature increases the oxygen dissociates more easily from the haemoglobin, so as the partial pressure of carbon dioxide increases the dissociation of oxygen from haemoglobin increases. During exercise the amount of carbon dioxide produced by the cells increases, this helps to increase the diffusion of much needed oxygen into the cell. A change in pH will occur as more carbon dioxide is produced so the concentration of hydrogen ions in the blood will increase, thus lowering the pH, this drop in pH will cause the oxygen to dissociate more easily which can also be known as the Bohr effect.
Class Notes
Through a combination of these factors means that as we start to exercise, the rate of diffusion of oxygen into the cells accelerates and helps to maintain a good supply of oxygen to the working muscles.
Class notes
