Heart rate and exercise

For most adults, a resting heart rate between 60 and 100 beats per minute is normal.

Finding your pulse

Your heart rate is the number of times your heart beats in one minute, and the easiest way to measure it is to count your pulse. The American Heart Association describes a simple method. Place the tips of your first two fingers, not your thumb, lightly on the inside of your wrist on the thumb side. Count the beats for 30 seconds and multiply by 2. A good time to check your resting heart rate is in the morning after a good night's sleep, before you get out of bed.

What is normal at rest

For most adults a resting heart rate between 60 and 100 beats per minute is normal. Many things change it: stress, anxiety, hormones, medicines and how physically active you are. A very active person or an athlete may have a resting rate as low as 40 beats per minute. A trained heart muscle can move enough blood with fewer, stronger beats, so it does not have to work as hard to keep a steady rhythm.

Who turns the rate up and down

The sinoatrial node sets a basic rhythm by itself, but the brain adjusts it to match what the body needs. A control centre in the lower part of the brain, the medulla oblongata, has two sets of nerve connections to the heart. One set speeds the heart up and the other slows it down. Emotions, the levels of certain salts in the blood and body temperature also affect heart rate, usually acting through this control centre. That is why your heart races when you are startled and slows when you relax.

Exercise and target zones

When you exercise, your muscles need more oxygen, so the heart beats faster. A rough estimate of your maximum heart rate is 220 minus your age. The American Heart Association gives target zones as a share of that maximum: about 50 to 70 percent during moderate activity and about 70 to 85 percent during vigorous activity. For a 20 year old, the estimated maximum is 220 − 20 = 200 beats per minute, so moderate activity would be about 100 to 140 and vigorous activity about 140 to 170.

These figures are averages and work only as a general guide. Real maximum rates vary from person to person, and some medicines change heart rate. These are averages for teaching, not a guide to how hard any one person should exercise.

More beats, more blood

The amount of blood the heart pumps each minute is called the cardiac output. The body adjusts it to its changing needs, mainly by changing the heart rate. At rest, about 5 liters a minute is enough. During exercise the working muscles need much more oxygen, and the heart answers by beating faster. In the model, move the slider from 60 to 150 and watch how much shorter each cycle becomes: at 60 beats a minute one cycle lasts 1 second, at 150 only 0.4 second.

What about the resting rate over the long term? The American Heart Association notes that, for resting heart rate, lower usually means the heart muscle is in better condition, and that studies have linked a higher resting heart rate with lower physical fitness, higher blood pressure and higher body weight. A single reading says little, though. Rates change with sleep, caffeine, stress and many other things, so one reading on its own says little.