Blood pressure is a measure of the force that blood applies to the walls of the arteries as it flows through them. Blood pressure is measured in millimetres of mercury (mmHg) using a sphygmomanometer and is expressed using two numerical readings.
The optimal blood pressure reading is 120/80 mmHg (‘one hundred and twenty over eighty’). These two numbers represent the systolic and diastolic pressure readings respectively.
Systolic blood pressure (SBP) is the pressure exerted on the artery walls during the contraction phase of the heartbeat. This is always the higher of the two pressures and is usually noted first. It is caused by the increased volume of blood flowing through the arteries with each beat, therefore increasing the pressure within the arteries.
Diastolic blood pressure (DBP) is the pressure exerted on the artery walls during the relaxation phase of the heartbeat. The heart goes through this period of relaxation (or diastole) to allow the chambers of the heart to fill with blood prior to contraction. The diastolic blood pressure is always the smaller of the two readings. Blood pressure is an expression of arterial blood flow and the peripheral resistance the blood encounters as it flows round the body. It can therefore be expressed in the following equation.
BLOOD PRESSURE = CARDIAC OUTPUT X TOTAL PERIPHERAL RESISTANCE
Cardiac output is the volume of blood pumped out by the heart in one minute (ml/min). The greater the cardiac output, the higher the blood pressure.
Total peripheral resistance is the resistance the blood vessels offer to blood flow; the greater the resistance, the higher the blood pressure. Peripheral resistance is increased by constriction or decreased by dilation of the blood vessels (arterioles).
It’s normal for blood pressure to temporarily increase during exertion or when feeling anxious or stressed. Hypertension (high blood pressure) is the term used to describe blood pressure that is consistently higher than the healthy level when at rest. A high SBP provides an indication of the strain on the blood vessels when the heart is attempting to pump out blood. If the DBP is high, it indicates that the blood vessels have little chance to relax between heartbeats. Consequently, measuring blood pressure provides an indication of the health of the vascular system and an overall gauge of a person’s health.
Hypertension increases the risk of ischaemic heart disease and cerebrovascular disease – two of the three biggest killers in the developed world.
Ischaemic heart disease covers a variety of heart conditions including valve disease and more acute problems such as myocardial infarction (heart attack).
Cerebrovascular disease includes acute problems such as haemorrhagic and ischaemic strokes and chronically degenerative conditions like vascular dementia and Alzheimer’s disease.
Hypertension also places stress on the small vessels to the retina, which can cause blindness, as well as the small vessels of the kidneys, which can lead to renal failure. The average resting blood pressure is defined as 120/80 mmHg. A blood pressure of 140/90 mmHg is considered to be high. Individuals with measures above 140/90 mmHg are encouraged to see their doctor before commencing physical activity programmes. Readings above 180 systolic and 110 diastolic are a contraindication for exercise.
People with low blood pressure readings may also require medical referral.
CATEGORY SYSTOLIC (mmHg) DIASTOLIC (mmHg)
Low < 100 < 60
Optimal < 120 < 80
Normal < 130 < 85
High normal – Pre-hypertension 130-139 85-89
Stage 1 Hypertension 140-159 90-99
Stage 2 Hypertension 160-179 100-109
Stage 3 Hypertension > 180 > 110
There are currently about 12 million people in the UK who have hypertension (blood pressure ≥140/90mmHg), and more than half of those are over the age of 60. Around 5.7 million people have undiagnosed hypertension. (UK Blood Pressure Association, 2012)
Short Term Effect of Exercise
A short-term effect of exercise will show a linear increase in systolic blood pressure (SBP) with increasing levels of exertion. In contrast, diastolic blood pressure (DBP) may decrease slightly during exertion due to vasodilation, or it will remain unchanged. Individuals with hypertension may experience a rise in DBP as a result of an impaired vasodilatory response. Heavy weight training and isometric exercise will significantly increase both systolic and diastolic blood pressure. It is important for an individual not to hold their breath when performing these exercises to avoid the Valsalva effect.
The Valsalva Effect
The Valsalva effect is a manoeuvre, which involves holding your breath while straining or a forced exhalation against a closed airway (glottis). This action increases pressure within the thoracic cavity and thereby impedes venous return of blood to the heart. During the manoeuvre, the mouth and nose are closed while the air is ‘pushed’ against the closed airway without breathing out. It’s similar to the pressure created when passing a bowel movement. The Valsalva effect can drastically increase blood pressure and heighten the risk of a cardiovascular event such as a heart attack or stroke. To avoid excessive increases in blood pressure while resistance training (as a consequence of the Valsalva effect), inhale as you’re bringing the resistance back to its resting position and exhale as you’re working hardest against the resistance.
Long Term Effect of Exercise
Aerobic exercise using large muscle groups in rhythmical activity is very useful for reducing blood pressure over time. Endurance training can elicit an average decrease of 10 mmHg in both systolic and diastolic blood pressure in mild and moderate hypertensives. With the exception of circuit weight training, chronic strength or resistive training has not consistently been shown to lower resting blood pressure.
Resistance training can have many benefits for hypertensives, but it is not recommended as a means of decreasing blood pressure on its own.
For certain clients, the risks associated with exercise need to be weighed up against the benefits before they engage in any physical activity – especially if it’s high-intensity. Physical activity can carry risks for people with high blood pressure, but for most people, the benefits far outweigh the dangers. Exercise is therefore associated with a number of cardiovascular risks including: Increased risk of stroke during and immediately after exercise. Increased risk of heart attack (myocardial infarction) during and immediately after exercise.
Cardiovascular benefits of endurance training
Physical activity has both short- and long-term effects on the cardiovascular system. The short-term changes are natural physiological responses to physical activity, such as an increase in heart rate, stroke volume (the amount of blood pumped out with each beat of the heart), blood pressure and cardiac output (the volume of blood pumped around the body per minute). These changes represent the body’s attempts to deliver more blood around the system to cope with the physiological demands of physical exertion.
Resting cardiac output in the heart of a well trained athlete will be about the same as in a healthy untrained athlete. This is because while stroke volume is increased, the heart rate is decreased. The long-term changes to cardiovascular function are the positive effects of physical activity and can be seen in lasting adaptations to the cardiovascular system.
For example, with regular aerobic training there will be improvements in the efficiency of the heart as a pump and the ability of the vascular system to deliver blood to the working body parts. This will be reflected during activity by a lower heart rate, a greater stroke volume and an increase in maximal cardiac output. When we are in a rested state, the body’s adaptation to regular aerobic activity will also be shown by a lower resting heart rate, lower blood pressure and a greater stroke volume.
Aerobic or endurance-based training has been shown to have particularly important benefits for the cardiovascular system.
• A greater stroke volume, i.e. more blood pumped per beat.
• A lower relative exercise heart rate, which allows for greater performance potential.
• Stronger, more elastic arteries.
• Lower levels of bad cholesterol (LDL) and higher levels of good cholesterol (HDL).
• An improved blood supply to the body’s tissues.
• Higher levels of haemoglobin in the blood, which increases its oxygencarrying capacity.
• Improved aerobic capacity (VO2 max).
• Lower blood pressure in the long term.
We hope you found this article helpful but if you have any questions, please do get in touch.
The Fitness Focus Team
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