Friday, October 15, 2010

Heart Rate Variability: The New New Training Tool?

A couple of weeks ago I downloaded a new app on my phone that I am using as another tool in my tool belt for training.   In fact, I changed phones from a Palm to an iPhone just for this app.  It’s called ithlete, and it measures Heart Rate Variability.   It cost me a little under $70 for the app, and ithlete then sent me a device that plugs into the headphone jack of my iphone.   Every morning right after I get out of bed, I strap on a heart rate monitor and try as best as I can to stand and breathe deeply to measure my Heart Rate Variability (HRV). 

HR monitor and ithlete plug in

Heart Rate Variability is not your resting Heart Rate, nor is it a measurement of your blood pressure.  Heart Rate Variability (HRV) has been around since the sixties.  Basically it is a measurement of the time interval in between heart beats.  The key to this tool is that it gives you an indicator of the state of your nervous system, which will show signs of overtraining or readiness before it registers in your resting heart rate. 
Screen shot from iphone ithlete app
Read out from ithlete

Top athletes have been using HRV but the commercial products are really outside the reach of most everyday athletes, costing between $1,000 to more than $20,000.  Under $70 seemed like quite a bargain.  

According to an article published in 1996 by the American Heart Association, HRV became a relevant measurement in a clinical setting when doctors discovered that the time increments in between heart beats for a fetus were a precursor to fetal distress before any change in heart rate. 

HRV was then used in the seventies as a bedside tests for diabetics.  In the eighties, HRV became a measurement tool post heart attack to predict whether or not a patient was going to recover.  In each of these clinical settings, the less variability in the time increments between heart beats, the greater the chance of sudden death. 

It seems counter intuitive that the less variability in time intervals between beats, the closer one is to mortality.    Why is this?    An understanding of the function of the nervous system helps to explain this phenomenon.  The heart rate and the rhythm of the heart are among some of the body functions controlled by the nervous system.  The nervous system is broken down into two functions: sympathetic and parasympathetic. The sympathetic and parasympathetic division of the nervous system works in “opposition” to one another, but in a complimentary way.    The sympathetic increases the heart’s action and the parasympathetic work more like a brake by slowing the action of the heart.  Together they moderate the heart rate.    The higher the “variability” of the time in between heartbeats is an indication that the sympathetic and parasympathetic actions of the nervous system are working well.    The lower the variability of time in between heart beats means that the nervous system is working hard to manage heart rate, and it is an indicator of fatigue, and taken to an extreme, mortality.

Therefore, HRV is an indicator of how well rested your nervous system is…and monitoring HRV can give you a warning before you notice changes in your resting heart rate.

How does this apply to athletes?

As runners, we aren’t really thinking about mortality, in fact, we are often thinking we belong squarely in the opposite category.   But we are also thinking about how hard we can push our bodies in training.  How much is too much and when do we know we should back off training?    We all go through phases where it seems like our bodies are able to absorb the training we are handing it, and other times we feel like we somehow stepped off a cliff into a giant abyss with really no warning sign. 

Before I knew about HRV, if I ever suspected I was teetering on the edge of the abyss in training, I would take my resting Heart Rate (HR) before I got out of bed in the morning.  I know many athletes and coaches use this simple test as an indicator of whether or not your body is prepared to go hard.  A rule of thumb is that if your resting HR in the morning is 10% above your normal resting HR, then take a day off.  Multiple days at an elevated HR along with fatigue and trouble sleeping are a sign that the body is not recovered from training and that the athlete could be on the bring of overtraining.   But sometimes once the HR has elevated, it's too late to take corrective action.  Enter Heart Rate Variability (HRV).  

What can impact HRV?

In well-trained athletes, over the course of a training cycle (hard work, recovery) there will be a reflection of that training in the HRV.  After a hard workout, HRV is going to decrease.  But after the appropriate rest period, HRV should go back up indicating the body has recovered from the stress of the previous workout.  Too many hard workouts in a row without the proper recovery will lead to a chronically low HRV, which indicates the nervous system is not properly adjusting to the stress, and left unchecked, the athlete will then experience overtraining. 

Same as an interval workout?
Other things that can negatively impact your HRV are  physical and emotional stresses such as not getting enough sleep, alcohol, smoking, even day-to-day tasks like raising children.  All of these can have a negative impact on HRV, and depending on the level of stress, the nervous system can treat these stresses the same as a hard workout.    

But, having a dip in HRV reflecting stress on the system is not a bad thing.  What is bad is not taking the appropriate recovery to allow your body to adapt to the higher level of stress.  Without recovery, we can not become stronger.  Leaps in fitness come during recovery from training stress.  

HRV in practice

I’ve been experimenting with ithlete's HRV tool for the past 12 days.  Granted, it takes a couple of weeks of data to really build a baseline, but I’ve gleaned some really valuable information already.   

At one point, I needed help interpreting the results because I received some conflicting HRV readings after the Portland Marathon.    So I sent an e-mail to ithlete.   In less than a day, I received an e-mail back from the founder himself, Simon Wegerif.    He wrote a very thorough response and provided me with multiple documents backing up his conclusion.   Many of his insights come from hundreds of research papers he has poured through as well as many of the athletes with whom he has worked.  You can learn more about HRV here on the ithlete FAQ page.

You can also request the full User's Guide, which is packed with information not only about HRV, but also about training and the symptoms of over training. 

I paid for ithlete; I am not in anyway sponsored by them. I’m definitely a fan of the tool.  While there is no silver bullet out there for becoming a better athlete, I believe information is key, and having ithlete in the tool belt definitely provides specific, actionable feedback on a daily basis.