Thursday, January 4, 2018

Overtraining and Heart Rate Variability (HRV)- Part I

I'm pretty sure most of you know what overtraining is?  Maybe you've experienced it.  Maybe not.  If not, here are the symptoms:

  • Persistent muscle soreness
  • Elevated resting heart rate
  • Increased susceptibility to infections
  • Increased incidence of injuries
  • Irritability
  • Depression
  • Loss of motivation
  • Insomnia
  • Decreased appetite
  • Weight loss
As an engineer, I wanted a more scientific way of measuring or diagnosing overtraining.  They (the experts) say when you overtrain, your resting heart rate increases (or is elevated).  I'm sure that's true.  The problem with measuring resting heart rate is that there are too many variables that can affect it from day-to-day such as: diet, amount of sleep, stress, time of day, position (sitting, lying, etc) you're in when taking resting heart rate, the monitoring device (heart rate monitor), etc. What I found is a better indicator of overtraining is Heart Rate Variability (HRV).  

Heart Rate Variability (HRV) is the variation in time between successive heart beats over a given period of time.  The time between beats is called R-R intervals measured in milliseconds.  The time between intervals, unbeknownst to me, is not constant.  That is, if your resting heart rate is 50bpm your heart doesn't beat 50 times in a minute at exactly 1 second intervals each time.  I thought it did. Sometimes it beats less than a second apart and sometimes it beats more than a second apart..just like the diagram above (0.97s between beats and 1.1s between beats).   But, the average over a minute period of time is one second between intervals. Why is that?  It's due to your Autonomic Nervous System (ANS).  Your ANS controls your nerves, muscles, glands, etc.  The ANS touches every process within your body.  It affects blood sugar, adrenaline, digestion, pupil dialation, heart rate and much more.  The ANS has two systems or branches: the Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS).  The PNS is your "rest and digest" branch and is responsible for muscle repair, decreased heart rate and lowering blood pressure.  The SNS branch is your "fight or flight" branch and is responsible for increased heart rate, increasing blood pressure, dilating pupils, making you sweat, etc.  Obviously, you want your ANS leaning towards the PNS branch..otherwise you'd be like a cat in a room full of rocking chairs- a nervous Nelly.  However, when it's time to perform, you want your SNS branch to kick in and take over and dominate.  So, the two branches are competing to keep you alive.  Thus, the changes in heart rate and Heart Rate Variability (HRV).  These changes are the ones we want to measure to help us determine if we're overtraining or not.

How do we measure HRV?  You can measure it with a good Heart Rate Monitor, such as the Polar H7 or H10 Bluetooth HRM and an App for your smartphone called "Elite HRV" which I highly recommend.  You can get the Polar H7 HRM online for $50 or the H10 for $85.  The Elite HRV App is FREE.

See Part II (coming soon) for a description of the Polar H7 HRM and the Elite HRV App.  Until then, Power ON!  Coach Rob

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