A Heart rate data primer
This is part 1 of a series on training data
When it comes to my own training, I’m a data nerd. After workouts, I’m glancing at my splits, my cadence and other form stats like vertical oscillation, and my heart rate stats to see if they match up with how I was feeling. (Side note: I'm talking about actual honest-to-God measurements here, not Strava’s fitness score or Garmin’s VO2 Max estimate, etc. Those are fun to look at, but you should really never make training decisions based on those numbers, nor should you ascribe much meaning to them one way or another). But while deep-diving into the data can be fun, there are diminishing returns when you get too far into the weeds. So I think we should talk about heart rate data: when it's useful, when it's not, and how I’d encourage athletes to think about it in their training day to day.
At the simplest, dividing your heart rate into zones is a way to standardize effort across individuals. Sounds simple enough: theoretically, an olympian is working just as hard as a recreational runner in any given zone. While there are several models, the most common is to divide your heart rate range into five zones. This is what you’ll see with Garmin and Strava. Typically they’re laid out like this:
Zone 1: Very easy (warm-up and recovery)
Zone 2: Easy to moderate (bread-and-butter easy runs)
Zone 3: Moderately hard (uptempo but could sustain for a while)
Zone 4: Quite hard (Tempo/Threshold pace—max pace for 40-60 mins)
Zone 5: Very difficult (maximum aerobic capacity/VO2 Max)
Looking at efforts through this lens is really helpful for coaches and runners as a shortcut. For example, even without knowing what paces I was running, you can get a solid idea of what was going on during these runs:
A standard easy run
A very challenging workout including significant time near my VO2 max (maximum aerobic capacity)
A 5K race
As a basic sketch of difficulty or output, heart rate is probably the most useful of the many measurements at your disposal. On the one hand, it’s a helpful single number that tracks very closely with aerobic effort. The broad strokes are transferrable from person to person: for any given runner, if your HR is 110? You’re chilling. 192? You’re sucking wind.
However, the diminishing returns I mentioned earlier are always lurking right around the corner. There are a million ways to calculate heart rate zones even with a 5-zone model, not to mention models which use 3, 6, or even 7 zones. Additionally, accurate measurement is an issue, as many folks using a running watch in the winter have discovered. And finally, everyone and their uncle on the internet has a conflicting opinion on the optimal way to actually use HR zones in training (guilty as charged).
You should maintain a healthy skepticism of anything you see online that claims to be the definitive way to use heart rate data in your training. The answer to the vast majority of coaching and training questions is “it depends.” My hope in writing this blog and others like it is to try to help equip you to answer the “it depends” questions for yourself, and to help you formulate better and better questions along the way.
So stay tuned for these forthcoming deeper dives I’ve got in the works related to heart rate training:
- Different ways to calculate and actually use HR zones in your day-to-day training
- Zone 2 training and low-heart rate training
- Tempo vs Threshold vs VO2 Max
- The good, bad, and ugly about composite fitness scores from Garmin, Strava, etc that use proprietary formulas
- 80/20 (or polarized) training