Resting heart rate, overtraining, and recovery: an experiment

Update (Oct 2019): This article has become rather outdated. With today’s wide variety of health monitoring devices (FitBit, Apple Watch, etc.), things have become a lot easier and better.

For over a year, I’ve been measuring my resting heart rate at the same time every morning. I’m using a simple pulse oximeter for that purpose because it’s fast and reliable. It’s also a great gadget to have if you are racing at higher elevations and want to keep an eye on your SpO2 (blood oxygen saturation level) to determine if you are acclimatized properly.

Recent research tells us (see also bibliography below) that the average weekly resting heart rate can be an indicator for overreaching and overtraining. The key is not to rely on punctual measures, but to average the daily measures for an entire week. There is simply too much noise in the data otherwise. This method is described in [1]. See also [2] for a more accessible description: “The key finding (echoing some earlier HRV studies) is that day-to-day measurements are simply too variable to extract reliable information from – but weekly averages can reliably show significant trends that reveal how your body is responding to the training load.” [4] states that “[t]he research suggests that by itself, your resting heart rate is likely not all that useful of a measurement.” However, the author only cites old and possibly outdated studies that did not use the method described in [1].

So I was curious to find out if this heart rate business may work for me and started an experiment in Jan 2014.

The plot below shows my weekly mileage (blue bars) and the average weekly resting heart rate (solid red line). I’ve deliberately left out the y-axis labels because they do not add to the story. As one can see, after big races and training weeks, the average weekly resting heart rate increases, then goes back to the average value within 1-2 weeks because of recovery and resting. Also, one can see that before big races, the average weekly resting heart rate decreases below average due to tapering. That tells me that my tapering is effective, with one exception: the last 100mi race on this plot was likely too close to the 120mi race. It does not look like I was fully recovered by then. That’s an important lesson for my future race planning.

Another interesting conclusion from this data is that despite a gradually increasing weekly mileage (indicated by the dashed blue line), my average weekly resting heart rate was slowly decreasing (dotted red line). I take this as a sign that my body successfully adapts and copes with the additional stress of increasing mileage. How far can I still push the envelope? We shall see.

For statistics freaks: the relationship between the weekly mileage and the average weekly heart rate shows a significant negative correlation, r(41) = 0.38, p = 0.005. Note that this is not a solid statistical analysis. There are several artefacts that would need to be controlled for in a thorough analysis of these time series.

In summary: collecting that data and watching the trends carefully has been a very valuable tool for a beginner like me to spot early signs of short- and long-term overtraining and to determine if I’m properly recovered for the next epic shit. The data simply allows me to back off if I see worrisome trends. Of course I realize that heart rate does not tell the entire story and that there are many other factors to consider in the way one trains and races.

As a next step, I am interested to find out how the data correlates with (1) the heart rate data during actual runs and (2) with the perceived effort (which is different from the actual effort). As you can tell, I love data and numbers…

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