I read a post where a member asked if others saw a decrease in their Resting Heart Rate (RHR). Here’s a short primer on how effective training affects RHR.
At any level of exertion, our body requires a given amount of blood supply, which brings fuel to our cells and carries away waste products. The amount of blood flow pumped by our heart at any moment is called Cardiac Output (CO). CO typically ranges from approximately 4 liters/minute up to ~28 liters liters/minute, depending upon the body’s demand. So, our heart can increase its output about 7 times during maximum demand. This increase demonstrates that our heart’s output is regulated by our exertion level (illness, injury, and over-training are examples of demand that may increase CO without exerting ourselves). Our heart rate can increase a maximum of about 4-5 times our resting rate, and the remainder of our maximum output is caused by increased contractility (squeeze power).
Since we’re focusing on RHR, we’ll leave the issues of exercise-level heart function for another discussion.
Cardiac output has two components: heart rate and contractility. Heart rate can be loosely compared to cycling cadence, as changing either will affect “output”. Contractility (how hard your heart squeezes) can be loosely compared to resistance, with changes affecting output as well.
Heart rate responds according to the amount of waste product in our blood. Most members have seen that their heart rate tends to fall into a given range for each Power Zone in which they ride. Any given wattage output on the bike will cause our body to produce a certain amount of waste product (lactate) which the body then works to remove (buffering). If the amount of lactate increases, our body reacts by increasing cardiac output to increase its fresh blood supply.
Our heart is affected by Power Zone training by becoming more efficient at its job. Here’s what happens:
Endurance-oriented training (Zones 2-4) cause the chambers of our heart to increase in size, allowing them to hold more blood. When the chambers (atria & ventricles) can hold more blood, they can pump more blood per heartbeat. As long as the muscular walls of the heart strengthen appropriately, this enlargement of the chambers is beneficial. (*special PZ training aha moment coming!)
Power-oriented PZ training (Zones 6 & especially 7) require our heart to squeeze harder in order to fight the increase in blood pressure which high exertion creates. Picture a weightlifter straining to get a heavy lift completed: the blood pressure in his aorta spikes and his heart must push blood against that resistance! These high-resistance efforts cause our heart muscle to become thicker and stronger, just like doing curls makes our biceps grow, etc.
So, we end up with a heart that has larger single-stroke volume capacity AND its muscle can squeeze more powerfully!
At rest, our body requires a minimal, but metabolically necessary, amount of blood flow. Since our heart is now a bit larger and stronger, we require less beats to meet the demand. (You’ll see the reduction in heart rate at other exertion levels too!). So, we adjust our “idle” speed downward accordingly. What used to take 60-70 beats/minute now takes only 50 (for example).
While it’s obvious that I glided through some details, etc., this is basically how it works!
👉Here’s why doing all the different Power Zone ride types is important:
If we only do endurance (lower-exertion) rides, our heart chambers enlarge but the muscle stretches without the corresponding strength increase provided by high-exertion work. A large, baggy heart is not a good thing.
If we only do high-exertion work, the chambers don’t enlarge so much but the muscular walls get thicker. This process acts to limit the amount of blood pumped in one beat because it’s harder to stretch that chamber to fill it with blood to pump!
So, the combination of cardiac-positive effects of the various Power Zone ride types is actually structured to create the best possible mixture of training stimulus to build our heart. Now this “secret benefit” of PZ TRAINING is revealed. This is why I try so hard to help others understand and maximize the process.
If you’re still awake after reading this, it must be due to that awesome Power Zone heart allowing you to stay awake!😂
Good luck, all!
This article is part of an ongoing series on Power Zone Training. You can find the other entries below in suggested reading order:
#1 – What is Power Zone Training?
#2 – FTP Test Strategies & Lessons
#3 – Power Zone Training – My Zones Are Too Easy!
#4 – Living with new zones & more FTP test
#5 – Post FTP-Test New Zone Struggles (Mental & Physical)
#6 – Decreases in FTP
#7 – Power Zone Training – My Zones Are Too Easy!
#8 – Age-related limitation & degradation of FTP in Power Zone Training
#9 – Resting Heart Rate: Why Power Zone Training reduces it (This Article)
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