All about Heart Rate measurements
Normal Heart Rate
The normal resting heart rate for adults ranges from 60-100 beats/min. This means that it should be measured when you are in a calm relaxed state.
Children have higher resting heart rates and well trained athletes have lower resting heart rate of between 40-60 beats/min and is perfectly normal. Our heart rate also goes up when we exercise, get stressed or excited too.
What's fast and what's slow?
For normal adults the resting rate of less than 60 beats/min can be clinically defined as bradycardia which means slow heart rate and resting heart heart rate of > 100 beats/min is defined as fast heart rate or tachycardia.
What causes heart rate to increase/decrease?
When cells in the body demand more oxygen, the message gets sent to the heart to beat faster, which delivers more oxygen to the blood for any given time. Exercise is the first reason why heart rate can be increased. The higher the intensity, the higher the rate rate.
Secondly, stress can also cause heart rate to increase. Stress activates the sympathetic drive of the body that prepares it for fight or flight. The parasympathetic drive is responsible for rest and recovery and would lower the heart rate. When we are relaxed, the parasympathetic drive kicks in and we expect heart rate to be lowered. Certain medications can also cause heart rate to increase or decrease. It is important that we are aware of such side effects so we take them into account when measuring our heart rate. Some of these medications include medication for anxiety, hypertension and depression. Certain foods can also affect heart rate. These include caffeine and alcohol and food containing tyramine such as bananas and chocolate. Certain medical conditions also affect heart rate. Our heart rates go up when we are having an infection or have conditions such as anaemia and hyperthyroidism.
How do we measure heart rate?
Manual measurements
The most common sites of measuring manual pulse rate would be the inner wrists (radial pulse) and the neck (carotid pulse). Other locations include the top of the foot (pedal pulse), above the elbow (brachial pulse).
For manual measurements, place your index and middle finger on the site of the pulse for 15 secs and multiply that by 4. This would give you your pulse rate which is the number of beats per minute.
Heart rate tracker watches
These days many smartwatches include heart rate tracking abilities. There are various brands out there to cater to different budgets. Smart watches use sensors to measure changes in blood flow with each beat and calculate beats per minute. This would be a very easy way to measure your heart rate.
Pulse oximeters
Pulse oximeters are devices that use sensors to measure oxygen saturation of the blood. They also have the ability to measure heart rate the same way heart rate tracker watches measure heart rate. It usually takes about 5 secs to obtain a reading and is commonly used in the hospitals to measure vital signs.
Automatic blood pressure machines
Blood pressure machines also have the ability to give heart rate readings. Some machines provide the reading under or after the blood pressure readings.
ECG machines
ECG machines measure heart rate by measuring the electrical impulses made by the heart and display it on the screen or on paper. This is the gold standard of measuring heart rate and is used in clinics and hospitals.
How can heart rate measure exercise intensity?
Simple calculation
We can calculate our estimated maximum heart rate by subtracting 220 by our age. Percentage of maximum heart rate can be multiplied by that number to obtain the correlation to exercise intensity.
E.g 70 % max HR of and individual 50 years of age would be
(220-50) x 0.7 = 119 bpm
Karvonen method
The Karvonen takes into account resting heart rate along with the estimated max heart rate. Taking into account this extra variable, it is a more accurate way of measuring exercise intensity. There is also some evidence showing how this method of calculation correlates to VO2max and that’s how smart watches provide VO2max estimates via measuring heart rate.
E.g 70 % max HR of and individual 50 years of age with a resting heart rate of 65 would be
Heart rate reserve = (220-50) - 65 = 105
70% RHR = 105x0.7 = 73.5
70% intensity = 65+73.5 = 138.5 bpm
Using % max heart rate, there would be an underestimation of exercise intensity versus the Karvonen method. The good news is most watches are able to measure resting heart rate and hence are able to calculate intensity using the Karvonen method.
What is heart rate variability?
Heart rate variability is the amount of fluctuations between heart beats. Generally, the higher the number, the better the body’s ability to handle stress. A lower heart rate variability would indicate that the body is not recovered enough to handle more stress. We can use this information as a guide to know how recovered we are from previous days of exercise and guide how intense the next workout should be. This is particularly useful for athletes who train frequently to prevent over training. Most sedentary people who do not exercise regularly may not require this function. If you are training regularly and need this information, ensure that the smart watch has it before purchasing.
When is it necessary to see a doctor?
When your resting heart rate (measured in a calm relaxed state) is below or above the normal range along with the following symptoms:
Palpitations
Shortness of breath
Feeling dizzy or light headed
Chest discomfort
Weakness or fatigue
Pounding in your chest
Reference
Ostchega Y, Porter KS, Hughes J, Dillon CF, Nwankwo T. Resting pulse rate reference data for children, adolescents, and adults: United States, 1999-2008. Natl Health Stat Report. 2011 Aug 24;(41):1-16. PMID: 21905522.
