Why does systolic pressure increase during exercise

This page looks at how blood flow, acidity and pressure respond to different types and intensities of exercise. Read this page to understand the critical implications for your clients safety.

Blood flow responses to exercise

Over 60% of blood flow at rest is directed to the liver, kidneys and brain.  This is illustrated on the adjacent graph.   

Blood flow to the lungs also increases due to the increased activity of the right ventricle which pumps blood to the lungs. 

Up to 87% of circulating blood can go to working muscles during prolonged vigorous exercise!

Blood pressure responses to exercise

Systolic blood pressure increases linearly with increases in exercise intensity.   As a greater quantity of blood gets pumped from the heart the pressure rises in the blood vessels that transport the blood with each heart beat.

In a healthy person with a ‘normal’ systolic pressure of 120 mmHg, vigorous aerobic fitness training can increase systolic pressure to 180 mmHg and take 10-20 minutes to return to resting levels.

With most types of training there is minimal change in diastolic blood pressure.  Blood pressure changes with incremental exercise are shown on the following diagram.

The higher the intensity of exercise, the greater the rise in heart rate will be, and consequently the larger the increase in systolic blood pressure. 

This is an important factor when considering the best type of training for beginners or those with cardiovascular risk factors. 

Low intensity aerobic fitness training tends to have the lowest increases in systolic pressure, and is therefore the safest training for new exercisers or those with cardiovascular risk factors. 

Muscular strength and hypertrophy training with heavy loads are two types of training that can however have dramatic effects on raising blood pressure.

This occurs because the skeletal muscles under strain from the heavy load increase the intra-muscular pressure, as a result the heart has to work harder to push blood into the tightly contracted muscles and it can take 20-40 minutes to return to resting levels.

We see this in the following graph where a person with a ‘normal’ resting blood pressure of approximately 120/80mmHg can have their blood pressure increased to approximately 240/160mmHg with heavy strength training for the muscles of the arm and 280/180mmHg with heavy strength training for the large muscles of the lower body.

While this does not pose much of a danger to an otherwise healthy individual, it does pose a significant risk for those with raised blood pressure.  This doesn’t mean weight training should be avoided, rather approached with caution and care. 

As the increase in systolic pressure is proportional to the load being lifted then sticking to lighter loads with higher repetitions with a focus on muscular endurance, correct technique and breathing (vital to remind people to continue breathing and not hold their breath) helps to mitigate the risks for beginner exercisers or those with blood pressure concerns.

Blood acidity responses to exercise

At rest our blood has a PH of 7 which is classed as neutral.  With training of moderate to high intensity and longer duration (≥ 1 minute), lactate levels increase in the blood.

At the point known as the anaerobic or lactate threshold, lactate is produced more quickly than it can be removed or metabolised. 

This results in a build up of hydrogen ions within the muscle, causing the muscle(s) to become increasingly acidic. 

Once the intensity of exercise exceeds the anaerobic threshold the exercise becomes ‘unsustainable’ because of the excessive build up of hydrogen ions.

This is shown in the graph adjacent, as the exercise gets harder (shown as increase in power/watts) the heart rate increases steadily (the lightly shaded line). 

As the intensity exceeds 180 watts (in this example – not standard for all people) lactate is produced increasingly by working muscles in order to buffer the increase in hydrogen ions (shown as the darkly shaded line). 

Anaerobic threshold in this example occurs at approximately 270 watts where there is a sharp increase in lactate production. 

At this point more lactate is being produced than can be removed from the muscle, the build up of hydrogen ions now increases without control, the muscle starts to burn, becomes acidic and fatigue is very close.

Being able to determine when anaerobic ‘lactate’ threshold occurs in clients is a very useful measure for trainers – it enables intensities to be set for maximum effect and prevent intensities from becoming excessive. 

Lactate threshold has been consistently shown to occur between 5-7 on the RPE scale where clients would describe exercise to be between ‘somewhat hard – hard’.

Another reliable method is the use of talk tests with clients.  If a client (while exercising) can easily explain to you what they did in the weekend (for example) then they are below lactate threshold.  If they can explain but with difficulty they will be at lactate threshold, and if they cannot explain at all then they will be above threshold.

Anaerobic fitness and muscular endurance training are the two types of exercise that will most often cause an unsustainable build up of lactate. 

For the accumulated lactate to be removed exercise either needs to stop completely or the intensity needs to be reduced.  If exercise continues at a low intensity lactate is removed approximately twice as quickly as it would if exercise stopped completely.

This is illustrated in the adjacent graph, and is known as active recovery – where exercise continues at a low intensity.  It also highlights a benefit of a well structured cool down after an intense anaerobic fitness workout as a way to help clear lactate more quickly.

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