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Athletic development specialists dedicated to the art and science of excellence in movement

Heart Rate vs. Heart Rate Variability: Endurance Sport Application, Part I

Why are you telling me to track heart rate variability?  I thought heart rate was unreliable??  


It is correct that heart rate (HR), though potentially valuable, has several pitfalls as a resting state measurement.  It also has pitfalls as a working measurement, but does become valuable when tracked with other variables such as velocity, power output, and time.  When tracked consistently over a long period (months, years) HR gains more reliability, but still is vulnerable to false positives and false negatives in the short term.   HEART RATE VARIABILITY (HRV) does not replace heart rate as a working measurement but does have distinct advantages for resting state conditions.   

First, a brief description of the differences...

HRV measures variation in timing between heart beats.  The science behind the measurement is quite complex but for now its important to just understand what HRV represents, which is the state of the autonomic nervous system ("fight or flight").  There’s nothing magic in the variability itself, but high variability has been long established in the cardiac literature as a sign of nervous system health.  Think of someone on TV lying on their death bed in the emergency room...the beeping line is typically low variability.  However, in a healthy system there is greater variability between each beat.  A body that's in a chronic state of stress ("fight") when at rest is less prepared to train than a system that can modulate between tension and relaxation.

Many believe the Russians and eastern European regimes of the 60s/70s were the first to use HRV in athletic settings, but like much of the work from that time, the western countries shunned their methods due to the specter of drug abuse.  It was not until modern coaches dusted off the books that HRV began to reemerge in sports, although it had consistently been studied in labs.  

HR is indicative how hard the cardiovascular system is working, with a lower heart rate generally indicating a more efficient system.  Resting heart rate is often recommended as a way to assess physical readiness, but is often susceptible to false positives and false negatives.  Current hydration status, feeding status, and temperature are among variables potentially yielding false positives and false negatives.  The key point is that heart rate can fluctuate wildly even without any change in exercise output.   

Here’s where heart rate variability enters the picture....  Endurance sport world has a fetish for measuring anything and everything (which is fine) but rarely measures from a PRESENT DAY baseline.  And by baseline, I’m not talking pre-season time trial for output, but instead, “What is the athlete bringing to the workout TODAY?”  Maybe your anaerobic threshold pace is “X” but is your body in the same state as it was when the test was performed?  

The effect of the workout does not only depend on the extrinsic load, which you might measure by duration, intensity, sets, repetitions, and terrain.  It also depends on the athlete’s intrinsic state.  If you’re tired, you are going to respond and adapt (or fail to adpat) differently than if in a rested state.  HRV is simply an evidence based audit that indicates whether we’re in the right spot for training on that particular day.  It’s certainly not perfect, and is more reliable when paired with methods like blood testing, saliva testing, and sensory measurements (vision, reaction).  

But it does remove some emotion from the daily calculus and, in effect, call out coaches and athletes who habitually treat fatigue as some biblical test of character to be conquered each day.  Instead, fatigue is often a protective mechanism from the body and is often difficult to interpret.  HRV is simply a way to refine our understanding of stress and recovery to allow our body’s protective mechanisms to work for us, rather than make careless decisions and potentially have those mechanisms work against us.  

In Part II, we'll cover the research specific to the endurance sport world and discuss practical applications within real-world settings. 

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