Many of us have smart watches that tell us our heart rate, but what is a normal heart rate? What causes the rhythm of our heart, and how does this change with different activities?
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Our heart rate is the speed of the contractions of the heart's muscle. These muscle contractions (of the ventricles of the heart) are what pumps blood around our body.
Our heart rate and muscle contractions are under the control of a group of pacemaker cells in the top of the heart (in the right atrium) that have spontaneous electrical activity.
These cells start an electrical impulse that then spreads between cells along electrical pathways in the heart. When each heart muscle cell receives this electrical impulse, this causes the muscle cell to contract.
The combination of all the muscle cells of the heart contracting squeezes blood out of our heart into our arteries. Each contraction that pumps blood out of the heart is essentially our heart rate.
The natural rate of the pacemaker cells of the heart fire is about 100 beats per minute (bpm). This is the tempo of the Backstreet Boys hit I Want It That Way. However, this is quite fast, so nerves to the heart slow this rate down as it passes through the heart, to about 70bpm. This is the tempo of Queen's Bohemian Rhapsody.
A normal heart rate is considered anything from 60 to 100bpm. A heart rate slower than 60bpm is referred to as bradycardia while a heart rate faster than 100bpm is called tachycardia.
Relaxation lowers the heart rate, and our heart rate is naturally slower while we sleep, at around 50-60bpm, the tempo of Andrew Strong's Mustang Sally. Stress, as well as increased temperature and exercise, all increase our heart rate.
The maximum speed that our heart can get to is estimated using the equation of "220 minus a person's age". So, the maximum heart rate for a 20-year-old person is 200bpm (Guns N Roses' Paradise City) and for a 70-year-old person is 150bpm [Bruce Springsteen's Dancing in the Dark].
Interestingly, even though exercise itself results in a higher heart rate, athletes often have a lower resting heart rate. Cardio training helps the heart to operate more efficiently: the heart can pump more blood with each beat, so it can beat slower, i.e. have a lower heart rate.
Athletes can have a heart rate around 40bpm, the tempo of Peter, Paul and Mary's Blowin in the Wind).
- Dr Theresa Larkin is an associate professor in medical sciences at the University of Wollongong's Graduate School of Medicine.
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