What is your resting heart rate?

Blog entry posted by SI barefoot, Jul 22, 2014.

Hi, I’m new to this forum but I have a background in health care, specifically cardiac care, and thought it would be fun to occasionally write blogs on health related topics. I figure a forum dedicated to the betterment of ones lifestyle is the perfect venue to get a little preachy.

First, a little on me. I’m a registered nurse who has worked on a cardiac step down unit for the past 14 years. Our unit has grown to include neurologic services, so I have learned quite a bit about those topics, too. Our hospital it kind of neat because it is medium sized and offers “big city” hospital services. We are also the premiere facility in my region. So, we stay busy and get some really interesting cases. I see pathologies from virtually every body system because, though our focus is on heart and neuro, most of our patients have multiple problems which include, but aren’t limited to, heart issues or neurologic dysfunction. A big part of my job is to assess and treat diseased states and to educate, educate, educate. I work in a facility where we don’t want you to come back, lol, so we try to educate folks so they can take better care of themselves and stay out. Our docs are great and greatly appreciate the care we provide and the patient data we collect. Ok, enough on me, and my credentials. On to the good stuff.

While at work the other day I decided to pop on a pulse ox (a small device that measures the percentage of hemoglobin with oxygen bound to it, and pulse) and measure my pulse. I’ve tried to live my life healthy and have always put value into being physical and eating well. I’ve done a pretty good job so far, I think, but have lived with my fair share of aches and pains. I have since learned that aches and pains can be dealt with by using good body mechanics and living barefoot! In the past my resting heart rate has been in the upper 50s to lower 60s, pretty good! When I popped that little pulse ox on I found my heart rate to be 50-55! An improvement! Why is this important? What does heart rate have to do with fitness and health?

Anatomy and function. . .

The human heart has 4 chambers. 2 small ones on top (atrium) and two larger ones on the bottom (ventricles). Each chamber has a door (valve) leading from either one chamber to the next or from one chamber to the lungs or from one chamber to the rest of the body. The atriums’ role isn’t all that important to this discussion so just know they mostly get a decent volume of blood into each ventricle when the ventricle needs it. The ventricle on the right (a couple inches to the right of your left nipple) has the very very important job of pushing blood into blood vessels innervating the lungs so that blood can pick up oxygen (O2). It requires some work to push the volume of blood around those vessels, but not too much. The real workhorse of the heart is the left ventricle (down an inch and over to the left an inch of your left nipple). The left ventricle’s job is to push the blood around the vessels of the whole body! A much bigger job in terms of work. Heart doctors can measure how effectively your left ventricle is doing that job and if it below a certain pumping level then you are slapped with the nasty diagnosis, heart failure. It must be understood that when the ventricles contract they don’t push out every last drop of blood they are storing. Also, each chamber fills with blood as the muscle making up the walls of that chamber relax and the valve between it and the smaller chamber before it (in terms of the sequence of the circulation) opens. A healthy left ventricle (LV), which is the ventricle I am now going to focus on, should squirt out 55-65% of its contents each beat. If that percentage drops to 40%, or less, then guess what, heart failure. As an example, lets say my LV has 100 ml of blood in it when it is completely relaxed and full. When it is at maximum contraction it will push out about 55 – 65 ml. The other 35-45 mls will stay in that ventricle and wait for new blood, stored in the atrium before it (in terms of the sequence of circulation), to fill it as that ventricle relaxes and the space inside expands (a vacuum force is created as the ventricle’s chamber expands, which helps to pull the new blood in, too). The total volume your LV can hold when completely relaxed is a key point to this discussion and will be covered later.

Workload, the need for increased O2. . .

Every movement we make can be considered work. The human body needs O2 to do that work. More work = more O2 needs. As we work harder and the need for O2 increases our body raises the heart rate, which, in turn, pumps more O2 rich blood to the body and allows us to sustain the given amount of work. Turning your head will increase your heart rate. Talking will increase your heart rate. Chopping wood increases your heart rate and running marathons increases your heart rate. Your metabolism does very well with an accelerated heart rate, to a point. Beyond that point things start to falter and your system becomes overtaxed, a state we adapted to sustain for some duration of time, but not for too long. The goal of fitness is to do massive amounts of work in at that optimal accelerated heart rate for long periods of time, and not end up in that overtaxed bracket. The heart has a cool adaptive way of accommodating this. Every task at a specific effort requires a certain amount of O2 (see example below). For those who are unfit the heart handles this by going faster and faster to get the O2 where it needs to go. As we exercise properly and build our muscles, our heart isn’t left out. It physically gets larger and stronger. The heart is hollow so as it gets larger the volume of the hollow spaces (each of the 4 chambers) inside get bigger. Expanding on the example above, as I become more fit my LV goes from holding 100ml of blood a full relaxation to 120ml of blood at full relaxation. It will still contract to push out 55-65% of its contents, and this is the key to having a slower heart rate, because, instead of pushing out 55-65mls per beat it will push out 66-78mls per beat. The blood doesn’t have any extra O2 in it but it is a larger volume of blood squirting out per beat. Now each more O2 rich blood per beat is being delivered to the muscles that need it for the given demand of whatever task you are doing. The heart can effectively slow down while still delivering the same VOLUME of O2 rich blood to the muscle. Pretty slick, huh?
As an example to try and put it all together and to illustrate that it is all about O2 and O2 delivery, here goes. Lets pretend each ml of blood holds 30 O2 molecules (its actually more like trillions, or higher, but I’ll stick with smaller, made up numbers to illustrate), and the unfit LV can hold 100 ml of blood. This means, when totally relaxed and full, the LV has 3000 molecules of O2. By contrast, the fit heart can hold 120ml of blood, which means 3600 molecules of O2. Lets pretend your LV reliably squirts out 60% of the blood into the body each contraction, 60 for the unfit heart and 72 mls for the fit heart. This means the unfit heart squirts out 1800 molecules of O2 each beat and the fit heart squirts 2160 O2 molecules each beat. Now, lets pretend it costs exactly 1 million molecules of O2 to walk 1 mile at 3 mph. It takes a total of 555.5 beats for the unfit heart to complete the work whereas it only takes the fit heart 462.9. Even though these numbers are bogus the example shows the lesson to be learned – a fit heart is more efficient for an equal task.
Other minor physiologic changes do occur in a fit heart compared to an unfit heart, but having a slow heart rate due to being fit is a good measurement that you are doing something right. If you have a slow heart rate and are a couch potato, then you may have a real problem. I’d say my drop of 5 beats per minute shows I’m on the right path and I think some of that can be credited to moving better, being barefooted, and not being dragged down by aches and pain. Now I plan to work on my running economy as outlined by Dr Mark Cucuzzella. He has done a phenomena job putting together, what I think are, the true nuts and bolts of attaining truly healthy fitness. I hope you found this interesting, and fell free to ask questions, leave comments or offer suggestions.
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SI barefoot

About the Author

Come and learn a little about what the slow heart rate found in truly fit people means.