Firstbeat EPOC

Heart rate monitors are a nearly universal tool in endurance athletics. I’ve owned more of them than I can recall, and have been all over the spectrum of adherence, from religiously following training zones, to ditching the monitor for years at a time. On balance I’ve come down on the side of training by feel, and using the monitor to maintain a certain level of calibration in the system. As a coach I’ve worked hard to help athletes build an understanding of qualitative effort and recovery demands. I talk a lot about “energy management”, and take a holistic approach to balancing life and athletics. Heart rate data, alone, never gave me tools to address these concerns. Until recently.

Kris, reviewing his HR file after biking (112 miles) from his house to our house.

Kris, reviewing his HR file after biking (112 miles) from his house to our house.

Last winter I started to pay more attention to what Jim Galanes was saying about the Firstbeat system, and this spring I started working with the system. My primary motivation was to add some tools to the arsenal to help support Kris Freeman and Tad Elliott as they work to overcome some hurdles. Kris has found it increasingly difficult to balance type-1 diabetes management and race fitness, while Tad has struggled with some deep-seated overtraining effect and a mono infection. I’ll write more about those guys as the training season progresses.

Firstbeat is a Finnish company, established in 2002, that grew out of research lead by Heikki Rusko at the University of Jyväskylä. Rusko is one of the most respected physiologists in the world, and a name I’ve heard frequently from Uncle John who thinks highly of his work. Firstbeat makes extensive use of heart rate variability as a tool for quantifying concepts that previously were difficult to measure.

About Heart Rate Variability
Heart function is governed by the autonomic nervous system; along with all other “automatic” systems in the body. But the ANS has different regulatory systems, and heart function is controlled by a combination of two of them. The parasympathetic nervous system governs body functions at rest, while the sympathetic nervous system governs the “fight or flight” response to stress. These two systems work in complementary opposition to maintain a state of balance in the physical systems that they govern. The parasympathetic influence lowers the heart rate and increases the variability between beats, while the sympathetic influence raises the heart rate and increases the regularity of the inter-beat interval. So a measurement of heart rate variability amounts to a fairly direct measurement of nervous system function.

Firstbeat has a number of proprietary algorithms that they’ve developed to quantify recovery and stress responses, and to predict VO2 and other measurable physical parameters. The more I work with the system the more I believe that the recovery metrics are where the most long-term value lies. But I want to talk about the very first effect that I felt, myself, with using the system.

EPOC = Disruptive Load
One of the predicted values that Firstbeat calculates is EPOC, or “excess post-exercise oxygen consumption.” In normal parlance we call it “oxygen debt”, and it refers to the measurable phenomenon of elevated oxygen consumption for a period of time after a training session. Actually measuring these oxygen-debt values requires sampling a lot of gas in a laboratory setting, and is impractical for any kind of regular use. The Firstbeat algorithm for predicting EPOC is based on post-analysis of a lot of labratory testing, and it creates a very robust and valuable metric for quantifying training disruption. As we all know from physiology 101, disruption of homeostasis – your physiological baseline – is the stimulus for training adaptation.

The cool thing about the EPOC score is that it is cumulative. We know this intuitively about training – the effect accumulates according to how hard you go, and how long you stay at that level. There is a rapid initial effect, and then it tapers off a bit, depending on your intensity. At low levels of output it should plateau quickly, while at moderate levels it will accumulate to higher levels slowly, and at intensity levels around and above “threshold” it will accumulate more quickly. And, of course, as intensity goes down, EPOC can also reduce on the fly.

All of this is very logical and intuitive. If you go harder for longer with less recovery, you get a heavier training effect – a more disruptive response in your system. If you keep the output moderate and build-in recovery, you can keep the accumulated load at a lower level. An athlete with better fitness and economy will recover more on downhills than an athlete with lower fitness and economy, and will therefor accumulate less EPOC load, even if their peak efforts are the same.

During our first ski picking trip to Europe, Amy and I went on a whole bunch of easy runs together. Amy doesn’t run a lot because she has a bad knee, so I’m quite a bit more adept at running than her, and it was alarming to see the difference in EPOC accumulation during what both of us would have called a “level-1” run by any heart rate based training level designation. It’s a stark reminder of how different a given “easy” session may be for different athletes on the same team.

The top file is my first-ever Firstbeat file - a typical run for me, finishing going downhill. The bottom file is a run in Ramsau, a couple of weeks later - after some time working with Firstbeat.

The top file is my first-ever Firstbeat file – a typical run for me, finishing going downhill. The bottom file is a run in Ramsau, a couple of weeks later – after some time working with Firstbeat.

Amy has always accused me of going too hard in my basic training. I don’t think I’m as bad about it now as I was in my twenties when I was trying hard and failing to make any notable impact on the ski racing scene. And here’s the thing – I know all the reasons to incorporate easy training, and to keep the levels under control. I preach this stuff. But I suck at following my own advice.

During our trip to Europe we rented an Audi A1 TDI – an awesome little car that I wish they brought into the US market. This thing barely burned any fuel for the week that we drove it around Austria, and I realized on our return trip to the Munich airport that we would be close to making it all the way back to rental car return on only one tank of fuel. The car had a real-time fuel economy display as well as a KM-to-empty calculation. Between that and the GPS I had all the information I needed to keep the economy optimized so that I didn’t need to stop for fuel twice. That meant driving 115 KPH on the Autobahn instead of 160 to 180 (c’mon, it’s the autobahn). The most important thing is that having access to the information provided me all the motivation I needed to exercise some moderation. That’s what having EPOC information is like – it gives me a motivational target built around moderation.

So, what’s the effect of all this moderation? Well, I can run every day without soreness. I wish I could say I had gotten a lot faster, but in truth, I don’t even have a test for that. Firstbeat tells me that my running economy has improved based on its predicted VO2max score. But the incredible thing is to see resting heart rate values in the low 30s. The entire time I was trying to train well, using heart rate monitors to record both training and recovery, I never saw anything below 42 beats per minute. And two weeks after starting to train regularly with some useful EPOC information, I was seeing overnight values in the mid and low 30s.

So what about other people? As it turns out, guys like Kris and Tad seem to have a pretty good handle on their training load. Kris can ride a bike for a hundred miles at 20 miles per hour with an EPOC score below my average workday. Tad, even coming off months of inactivity due to illness, can likewise maintain very low EPOC values when he goes out to go easy. For these guys we’re starting to use the EPOC score as a way to set training targets for harder endurance training. Especially for Tad, it’s been a good way to gauge and govern the pace of a cautious return to training. And we’re really starting to see the effects of training load in recovery metrics. But that’s fodder for another article, focusing on another Firstbeat calculation.

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