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Cardiac output: Stroke volume & Heart rate – What is it all?
Blood pressure and cardiac output are two essential health functions and measurements of the cardiovascular system. All fitness professionals need to understand these measurements to design and deliver effective and safe exercises to all clients.
Cardiac Output
Also known as ‘Q,’ cardiac output is the measure of how much blood a person’s heart pumps out in a minute. It specifically measures the blood pumped out of the left ventricle as that is the ventricle responsible for pumping blood away from the heart to the organs and muscles across the body.
You can calculate cardiac output using stroke volume and heart rate, and you can calculate it in millilitres or litres per minute.
Cardiac output = stroke volume x heart rate (CO= SV X HR)
An increase in heart rate, stroke volume, or both will increase the cardiac output, which mainly happens during exercises.
Heart Rate (HR)
This is the number of times a person’s heart beats per minute. You can measure this using a heart rate monitor or taking someone’s pulse, for example, at the radial artery in the insides of the wrist or elbows.
You can also feel the pulse at the top of the feet or sides of the neck. Count the number of beats for 10 seconds, then multiply the number by 6.
An increase in the intensity of activity increases a person’s heart rate. That is because there is a demand for energy by all the working muscles, which causes the heart to beast faster to ensure an adequate supply of oxygen and nutrient the muscles need to generate the needed energy.
Depending on the intensity of the activities, it can take between 30 and 45 seconds for the cardiopulmonary system to adapt and meet the new muscle demands.
The ability of somebody’s body to meet the current exercise demand is called attaining steady-rate, mostly referred to as attaining the ‘second-wind.’
Other factors affecting heart rate include weather, body size, emotions, body position like standing up or lying down, medications, caffeine, and nicotine.
Healthy adults’ normal resting heart rate ranges between 60 and 100 beats per minute. If the heat rate is below 60bpm, it is referred to as bradycardia, and if it’s above 100bpm, it’s called tachycardia.
Both can indicate possible cardiovascular problems, and if you see any of them in your client, advise them to see the doctor immediately. However, bradycardia can be present in fit individuals like triathlons and international level multisport individuals.
A client’s heart rate should not go past their maximal heart rate, no matter how intense their exercises are. Maximal heart rate is the highest a person’s pulse can get, and it is mainly determined by genetics.
To roughly estimate, you can take the client’s age and subtract that from 220, a formula known as Fox and Haskell model. However, this formula has a margin of error of around 12bpm (one standard deviation).
This means that 68% of people can get the true maximal heart rate with a 12bpm margin of error, 95% could have a doubled margin of error, and 99% would have a margin of error of around 36 bpm. Another limitation of this formula is that it often overestimates the maximal heart rate in younger people and under-estimates in older people.
Another formula you can use with a lower margin of error is the Tanaka formula.
Tanaka = 208 – (0.7 x age)
When doing moderate-intensity workouts, the target heart rate of your client should be range from 64-76% of their maximum heart rate. For vigorous activities, the target heart rate should be range from 77-93% of their maximal heart rate. While these formulas may imply that people of the same age group have the same maximal heart rate, it is usually individualized and influenced by things like:
Fitness levels: All humans experience lower maximal heartbeat with age, but it does not happen linearly or uniformly in everyone. Fit people will maintain the same maximal heart rate over a long period. Unfit people, however, will witness a faster decrease in their maximal heart rate. Also, unfit individuals could have a lower maximal heart rate than healthy fit older people.
Conditioning level: The more people train, the more their cardiopulmonary system adapts to the training. This increases stroke volume, which maximizes cardiac output, increasing the maximal heart rate.
Stress, recovery status, stimulants, and blood volume- These all affect a person’s exercising and resting maximal heart rate. A person’s maximal heart rate will increase or reduce depending on how these factors change daily.
Stroke Volume (SV)
This refers to the amount of blood the heart pumps out of the left ventricle with each beat, and you can measure it either in litres or ml per minute. Measuring the exact stroke volume is not easy. Therefore, people estimate the volume based on the formula used to calculate heart rate and measurable factors that stroke volume estimates, like blood pressure.
While stroke volume and heart rate can influence cardiac output, stroke volume does not change too much, with only small fluctuations even during exercises. On the other hand, heart rate changes dramatically, which makes it the greatest influencer of someone’s cardiac output.
Changes in people’s cardiac output are vital as they determine how well the bear will meet the increasing energy demands of the exercising muscles. As a personal trainer, you might never have to measure your client’s cardiac output, but it’s important because it affects blood pressure.
Blood Pressure
Blood pressure refers to the force that blood exerts on arterial walls as it is being pumped from the heart. You can easily measure a client’s blood pressure using a sphygmomanometer and stethoscope on the upper arm.
Cardiac output is one of the main factors that affect blood pressure because an increase in cardiac output increases the pressure and volume of blood passing through the arteries.
Before designing a workout plan for your client, ensure that you know their blood pressure to know how much exercises are safe for them and how intense the workout should be. You should also check any medications or health conditions that could affect the client’s heart rate, stroke volume, or blood pressure.
If you have any questions on the above or would like some advice on how we could help you with your fitness goal, don’t hesitate to contact us or head over to the gym to have a chat with one of our coaches.