Understanding And Using Strava's Relative Effort Score
"Relative Effort" score, which is available to those of us dorky
enough to subscribe to their premium membership, is an interesting piece of
data to think about.
While the exact
formula for calculating Relative Effort is one of Strava's proprietary secrets,
they readily acknowledge that it is based on the athlete's heart rate during
exercise. When you click on your Relative Effort score for a particular
activity (from the browser-based user portal), you are taken to an analysis of
heart rate. Specifically, you're given a bar graph, by Heart Rate Zone, of
percentage of time spent in each Zone. You're given extra points for time spent
"in the red," which any time you spend in Heart Rate Zones 4 or 5.
(This is all based on a 5-zone approach.)
Those of you
familiar with the fitness industry will recognize this principle immediately.
It's the "theory" behind Orange Theory
Fitness, ie., you'll get a more worthwhile workout if you spend time in the
"orange" zone, which is usually designated Heart Rate Zone 4. (Zone 5
is usually shown in "red," and constitutes the athlete's maximum
Needless to say (I
hope), neither Strava nor Orange Theory Fitness innovated this approach to
working out. Targeting Heart Rate Zone 4 a few times per week has been a
regular part of heart rate zone training for as long as people have been
grouping their heart rates into "zones."
A year ago, as I
built up my aerobic capacity, I noticed that over time workouts that covered
the same distance and speed were getting "easier" from the standpoint
that my average heart rate was getting lower. I might have run 5 miles at
6:45/mile pace every day for a month, but at the beginning of the month I'd
spend 10 minutes, say, in Zone 4, whereas at the end of the month I might have
only spent 1 or 2 minutes in that zone. This signifies an increase in my
aerobic fitness level, but not the fitness of my legs. More on that in a bit.
In order to get at
that information last year, I had to watch my Heart Rate Zone diagrams on my
Garmin Connect app. Every day, I'd check the bar graph and visually confirm
where my average heart rate was going. It was imprecise, but close enough for
rock and roll. To improve on that, I may have graphed maximum heart rate during
exercise over time, grouping by similar distances, and checked for a
downward-sloping trend line. That's not impossible, of course, but it is a
Effort score works much better. Charting that one number over time gives you
insight into how your training is progressing. Indeed, this is the graph that
Strava calls your "Fitness" graph. Remember, Relative Effort involves
the total amount of time you spend in each Heart Rate Zone, so even if you only
spend all your time in Zone 1, 10 minutes is worth more than 5 minutes. So it
combines both aerobic effort and total time spent training, which also
functions as a proxy for weekly mileage.
Thus, if your
aerobic fitness improves, but you do not increase your weekly mileage, then you
could plausibly see your Fitness level drop,
since you'll either spend less time in higher Heart Rate Zones, or less total
time exercising (since you'd be running the same number of miles faster). The only way to increase your Fitness
level (that's capital-F Fitness, ie. Strava's "Fitness" number) is to
run more miles or run the same number of miles in higher Heart Rate Zones (or
isn't good at explaining this at all! They give you general information about
Relative Effort, heart rate zones, and "Power" (for cyclists), but
they don't have any explanation that brings it all together so that you can use
your personal Fitness chart. If I hadn't have figured it out, I likely would
have cancelled my premium Strava subscription, since without a good
explanation, the data is essentially useless. Chalk another one up to the
uselessness of the way our data is served back to us by the tech industry.
No, that's not quite
fair. Relative Effort is a really good number -- for once, we've been given
something that is actually highly useful. Unfortunately, it's just not
presented in a way that is readily usable to anyone except people like myself,
data geeks who are already quite accustomed to probing the data deeply.
Hopefully the above
explanation helps you more than Strava's online materials.