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

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

Before moving to Part II of this series (evidence of HRV applications in endurance athletes), I think it’s worth brief detour… 

(See Part I HERE)

Remember that variability is healthy.  That’s probably a good rule for many things, but particularly with performance.  High HRV generally indicates a relaxed body, while low HRV indicates more chronic stress.  If you’re body’s working hard just to keep you alive at rest, there’s very little in reserve for when you really need it.  Controlled relaxation is underrated, yet crucial.  Consider these words by Dr. Stuart McGill:

“Breaking the board by the martial artist requires the skill of compliance (relaxation) to build speed but with rapid super stiffness just at impact. The professional golfer who has a relaxed backswing but rapidly obtains super stiffness at ball impact (followed by an astounding relaxation rate) is the one who achieves the long ball. The one who tries to swing too hard too soon actually decreases speed of movement with inappropriate stiffness. We have measured the creation of "pulses" of muscle force in athletes used to create "shockwaves". Precise timing, the rate of relaxation, joint buttressing together with all of the principles of Superstiffness are optimized.”

As Prof McGill describes, chronic tension may impair maximal tension ability.  HRV is simply one way to measure the “yin and yang” of tension vs. relaxation on a broader nervous system level.  Studies on military special operators are instructive on this point…

Paulus (2010) compared active duty Navy SEALs with healthy volunteers in an experiment in which subjects were shown two types of faces: threat related faces, and non-threatening faces.  Authors found that the SEALs demonstrated greater brain processing activity in response to the threatening faces, and less brain processing activity in response to non-threatening faces.   In conclusion, “rather than expending more effort in general, elite warfighters show more focused neural and performance tuning. In other words, greater neural processing resources are directed toward threat stimuli and processing resources are conserved when facing a nonthreat stimulus situation.”

That last line is EXACTLY what we’re looking for via the autonomic nervous system, as measured by HRV. By extension, we plan our training to exploit the times when the body is ready, and back off when it needs rest. 

On the flip side, we don’t want chronic relaxation.  Some people misinterpret HRV to mean that high is always good and low is always bad.  Instead, we DO want to be stressed at times…but at the right times.  Stress is what keeps us alive and able to summon our greatest faculties when most needed.  Conversely, if the body is not aroused during crisis, there could be serious consequences (think evolution…if you can’t heighten your awareness when being chased by a bear, you’re probably going to get eaten…those who did get eaten were not around to pass the optimal arousal/survival strategy onto future generations).   

Morgan (2002) examined students in combat diver school and found those who suffered burnout and failed the course actually had higher HRV than those who passed.  Though high HRV often indicates readiness to train, this is not always true.  In other words, failed students couldn’t get themselves “up” to perform due to burnout.  Tension and relaxation must be properly timed.

What does this mean for exercise?  Most people chronically in a middle zone: never fully relaxed, but never capable of maximum tension.  In the RKC we address this by mixing grinds (heavy weights, slower movements, longer tension) and ballistics (faster movements alternating tension with relaxation). 

As Pavel writes, “Our slow strength lifts or “grinds” are performed like the Sanchin kata – with dynamic tension.  Then tenser your muscles are, the more strength you display and build….At the same time we practice our relaxation skills.  Mastery of relaxation is a hallmark of an elite athlete.  Prof. Leonid Matveyev observed that the higher the higher the athlete’s level, the quicker he can relax his muscles.”

The concept applies to rehab too.  When we’re hurt, we often default to a chronically guarded state with muscle tightness and hypersensitivity to touch or movement.  Pain is typically a response to threat.  Sometimes the threat is removed, yet we still feel pain.  The relationship between pain and HRV is still undetermined, but it’s clear that feeling pain without a threat is not good…  At the least it means our muscles respond suboptimally during training, but at the worst chronic pain can be debilitating (fibromyalgia and other similar conditions).


We started with endurance sports, discussed elite military forces, and ended with chronic pain.  Ultimately, it’s all the same nervous system.  HRV is simply one evidence based way to ensure our body is ready to train.  In the next installment (I promise) we’ll discuss endurance sport application and evidence. 

Gee, kinda cool how all this stuff relates, isn’t it...


Paulus MP, Simmons AN, Fitzpatrick SN, Potterat EG, Van Orden KF, Bauman J, Swain JL.  Differential brain activation to angry faces by elite warfighters: neural processing evidence for enhanced threat detection.  PLoS One. 2010 Apr 14;5(4):e10096.

McGill, S.M., Ultimate back fitness and performance, Third Edition, 2006

Morgan CA 3rd, Cho T, Hazlett G, Coric V, Morgan J.  The impact of burnout on human physiology and on operational performance: a prospective study of soldiers enrolled in the combat diver qualification course.  Yale J Biol Med. 2002 Jul-Aug;75(4):199-205.


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