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The rate at which your heart is beating is one of the most easily-quantifiable, yet informative, attributes of your body. Most people know that your heart rate increases as you strain yourself in some way, but the factors which impact heart rate are numerous. Sleep, activity level, temperature, mental or emotional stress, atmosphere/environment and a number of other things can all play a role in how many times your heart is beating per minute (BPM). Knowing the reasons and what your heart range is can give you valuable insight into what is going on.
Occasionally, over a number of months and in a number of different cultures and climates around the world, I tracked my heart rate. I have recordings from going for jogs in France, shivering in the Michigan cold, barely sleeping while living in a car in Ireland, working out in a gym in San Francisco, and so on. In the end, I became convinced that heart rate tells us much more than simply activity level.
Normal Heart Rate Range (“Zones”)
As we age, the range of our heart rates change. What was medium for a 20-year-old is on the high end of a 80-year-old’s heart rate range. If you’ve been to the gym recently and had a look at the cardio equipment there, you may have seen a chart like this one:
As you can see, what is 100% effort for a 70-year-old is actually only 70% effort for a 20-year-old. The implication here, for working out at least, is straightforward: different ages should aim for different target heart ranges as a goal.
Yet, there is also something more subtle going on here. Notice the suggestions of the “purpose” of each of the heart rate ranges. The easiest level is called “moderate activity” or “warm up” while the next level up is called “fat burn.” The truth is, while heart rate is only one aspect of how our bodies are functioning, it is interconnected with a number of other factors…
Just What Does Heart Rate Represent, Really?
The heart moves blood around the body. The faster the heart is beating, the more actively blood is being pumped around… or, so it would appear at first. There is also the fact that the heart is a muscle, and like any muscle it can become stronger. Trained athletes have a lower-than-average heart rate because the heart is able to pump more blood per beat. Think of it like a hose — if you turn it on higher, more water comes out.
Ultimately, though, the purpose of moving all that blood around is to get oxygen to the muscles, which they require in order to function properly. During strenuous exercise, more oxygen is required (to complete the chemical reactions that allow for contraction), so it is up to the heart to get the blood there.
The brain also needs blood to do it’s job. In fact, one of the more popular brain imaging techniques used by scientists (the fMRI) actually uses blood flow to identify neuronal activity.
It should be no surprise that the heart is powering so many of the mechanisms of the body. Yet, if we look closer at Heart Rate as an indicator of overall health, some interesting ideas begin to emerge…
Heart Rate Can Be Changed
Athletes, through training, lower their resting (“normal”) heart rate. Monks, yogis and other practitioners of yoga have been show to be capable of significantly modifying their heart rate at will quite drastically. Even the average person has some rudimentary control over how fast their heart is beating, should they choose to exercise conscious thought. Like breathing, it happens without our conscious thought – yet by applying thought, we are able to modify it.
Why is this interesting? Well, it implies that we are changing something very fundamental about how our bodies are functioning. Remember, the heart fulfills a necessary role in order to perform basic mental/physical actions. If we are changing the rate at which oxygen is delivered, we must be changing the reaction itself (a bit like slowing down a car in order to preserve gasoline, perhaps).
Think of heart rate like a barometer, which measures air pressure. Air pressure, on its own, is pretty uninteresting. It is just a number. But to the trained eye, air pressure tells an interesting story – it is one of the key bits of information used in predicting weather (eg. for detecting incoming storm fronts), can also be used for altitude measurements, and so on. The number itself is influenced by a lot of factors – so if you understand these you can make some conclusions.
First, I had a look at my baseline data. I knew that my heart rate was genetically low (my father has a very low heart rate, and when I was born the doctors were actually worried because my HR was so slow). Lying down, I found my heart rate to be about 38. Sitting at my desk brought it to the mid-40s, peaking in the mid 50s when I was working. Standing up, it rose into the mid 60s and occasionally into the 70s if I had been moving around.
Next up, I tried to get a maximum heart rate. Despite sprinting at full speed for several minutes (and a number of other activities) I had a hard time ever breaking 170, though I did manage to (just barely) once or twice.
Finally, I was able to record data from other activities. Doing a typical cardio workout (treadmill, elliptical, etc.) I saw a range of 115-145 (depending on intensity). Lifting weights, I saw a range of 85-120 (it would peak quickly during the lifting, then fall off… what was interesting was that it fell off more slowly each time… so by the end, it took several minutes to fall back under 90, where at the beginning it took only a few seconds). Biking around the city, I saw a range of 70-120. Rock climbing, I saw a range of 110-135. You get the idea.
So, what did I learn? For one, this gave me an interesting way to compare the “difficulties” of each different exercise. For example, rock climbing is interesting because the range falls somewhere between that of weight lifting and cardio… likewise, the activity feels like a mix of muscular and endurance effort. Furthermore, I learned some interesting things about what my body was doing on a day-to-day basis. Cold temperatures, failing to work out regularly, etc. all played a role.
It also led me to some interesting speculation. I played ice hockey for most of my young life, which is a sport which requires short (45-60 sec) bursts of incredibly high effort, followed by several minutes of rest. Indeed, my body seems best adapted to exert lots of effort and then recover quickly, perhaps exactly because of this training. When I try exert effort for and extended period of time, I have a difficult time breaking through “plateaus” of effort.
It would be very interesting to correlate this data to other measurements in my body (blood pressure, white blood cell count and so on and so on). Unfortunately, heart rate is one of the only factors which is easily trackable without sophisticated equipment. There’s a lot going on in the bio/health technology fields these days, though. The best cure is prevention, and many of these companies are attempting to help us track all this data so that our doctors can keep us healthy. Until then, though, it is best to understand how your body works as best you can.