Exercise

When the heart contracts, the surge of blood distends the arteries, which contain elastic tissue. The stretch and recoil of the arteries travels as a wave along them and can be felt as your pulse. The pulse rate is identical to the heart rate and at rest can be used to give an indication of fitness.

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People who are physically fit often have a low resting pulse rate and their pulse rate returns to normal quickly after exercise. This is because they have a large stroke volume (their heart can pump a lot of blood each time) and so a small increase in pulse rate results in a big increase in output (cardiac output = stroke volume x heart rate).

The maximum arterial pressure caused by contraction of the left ventricle of the heart is called the systolic pressure and is the pressure at which blood leaves the heart. The minimum pressure in the arteries is called the diastolic pressure. It reflects how much resistance the blood meets in the small arteries and capillaries and so how hard the heart must work.

A reading of Copyright S-cool would mean that your systolic blood pressure is 140 mm Hg and your diastolic blood pressure is 90 mm Hg.

Systolic pressure will rise during exercise but diastolic pressure rarely changes in healthy people. If both are high at rest, this suggests that somebody is suffering from hypertension. In the long term, this condition can lead to heart failure, heart attacks or strokes. The condition has been linked to high alcohol intake, smoking, obesity, too much salt in the diet and genetic factors.

This is any exercise, which is powered by aerobic respiration in the muscles and so requires them to be supplied with oxygen. This means that the lungs, heart and blood vessels are working efficiently and so with training they improve their ability at oxygenating and pumping the blood around the body.

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Prior to exercise, your body anticipates an increase in demand and adrenaline is released. This causes the constriction of the arterioles in the gut and skin, diverting blood to the skeletal muscles. The blood supply always remains stable to the vital organs, the brain, kidneys and heart.

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The glycogen stores are broken down releasing glucose and the fat stores release fatty acids. Both of these can be used to increase respiration rate and produce more ATP, which is what powers the muscle cells.

At the same time, the bronchioles dilate in the lungs, in response to adrenaline and more oxygen can get into the blood. The output from the heart rises and maximises aerobic respiration. As more oxygen is used up, the more the oxyhaemoglobin dissociates and this rate of dissociation is also increased by an increase in carbon dioxide levels in the blood, a temperature rise or a pH fall.

Often during strenuous exercise, there is not enough oxygen for complete aerobic respiration and anaerobic respiration starts. This produces lactate and carbon dioxide, which causes the further dilation of the arterioles supplying the muscles and so the blood flow to them.

Lactate is dangerous because it reduces the pH in cells and decreases the efficiency of the enzymes working inside them. It also causes fatigue and pain (stitch), so it is taken to the liver and converted back to glucose because it is too rich a source of energy to be excreted.

The oxygen debt

Whenever lactate is produced by anaerobic respiration, an oxygen debt is being built up. This debt is paid back at the end of the exercise by breathing more deeply than you would normally need to at rest.

This oxygen is used to convert the lactate to glucose, the haemoglobin to oxyhaemoglobin, oxygenate the myoglobin and supply the higher metabolic rate caused by many organs working harder than usual.

For lengthier exercise, oxygen supply must equal oxygen demand and so an athlete will be more successful the more the muscles are supplied with oxygen.

To increase fitness, you need to train at about 70% of your hearts maximum heart rate for twenty minutes, three times a week. A more intense approach would get quicker results but four or five times a week is the maximum recommended frequency.

The benefits of exercise

These are far reaching and include:

  • A decrease in resting heart rate and an increase in stroke volume due to an increase in heart size. This reduces blood pressure.

  • The tidal volume and vital capacity of the lungs increase so oxygen can be taken up more quickly.

  • The muscles will increase in size and have a greater density of capillaries, more mitochondria, more glycogen and myoglobin.

  • Exercise increases the use of fat and so helps to reduce weight, cholesterol and atherosclerosis. It increases your resistance to infection and decreases the chance of a stroke, coronary heart disease or osteoporosis.

  • Your balance, strength, co-ordination and flexibility will all improve as your ligaments and tendons strengthen and you are less likely to suffer from lower back pain.

  • Finally, exercise improves your mood and decreases stress.

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