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Low Heart Rate Training

January 13, 2020

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From CJ

Dear Janet, I have been doing low-heart rate training for the past 4 months. Over time my pace has picked up even though I keep my heart rate in the same low easy zone (zone 2 out of 5 zones). I have two questions: 1) what happens when summer arrives? Will my fitness "gains" disappear? What I mean is will my pace slow to what it was before I tried low heart rate training. 2) Is it possible for my max heart rate to increase as I become more fit? I am in my early 60's, and have maintained fitness by running, biking, or swimming pretty consistently for the past 12 years. Best, CJ    

Response - Coach Janet

This form of training is really useful.  As your cardiovascular fitness improves, a given heart rate will support a faster pace - here's why:   The amount of blood flowing at any given point is known as your cardiac output - this is the product of the stroke volume (how much blood was ejected each time your heart beats) times the heart rate (number of beats per minute).  SO - cardiac output has two different ways of being increased - you can beat faster, or you can beat "stronger" and eject more blood each time your heart contracts.  The heart is a muscle, so each time it contracts, it requires energy to do so - and so a more efficient heart will eject a greater volume of blood and be able to produce the given cardiac output with fewer beats per minute.   Maximum heart rate usually doesn't increase for most people and in the cases where it does, it's only  minor.  So - as you become more fit - you'll find that you are able to sustain a faster pace at a given HR because you accomplished the needed cardiac output through the more efficient method (beating stronger rather than faster). 

Now, when summer arrives, there's a dual demand for the blood - you need enough to cool the core and enough to fuel the exercising muscles.  Blood that flows toward the skin surface to cool the core is not fueling the exercising muscles. So initially you're not acclimated to the heat, and your heart has to beat faster to accomplish the need for more cardiac output to satisfy the competing demands for blood.  Eventually though, your body realizes it needs more blood to satisfy both demands and you'll actually make more blood.  Cool trick eh? Your body will also adapt by adjusting your sweat rate, and activating more sweat glands so that the rate of sweat loss through any one duct can be slowed (because more sweat glands are participating in the process).  This is handy because if the sweat slows it's journey from duct to skin surface, there's extra time for you to salvage vital electrolytes and retain them.  This is why in the early summer your sweat is highly concentrated and you'll see salt streaks on your skin but after you've acclimated, your sweat is more dilute and the salt streaks are less apparent.   You'll also find that you start to sweat a little sooner - which means that your core temperature won't climb as high as quickly as it did before you acclimated to the heat.  Initially in the summer (before acclimation) you'll see your HR will be higher than you are used to for a given pace, but after a few weeks of heat training you'll see it settle back into a more normal range.  

Hope this answers the question!  Best regards, Janet Hamilton, MA, RCEP, CSCS, USATF-level 1 and RRCA-Certified running coach.