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In depth: Strava’s “Best Efforts Power Curve” feature.

Monday, April 28, 2014 by  
Filed under Daily Blog


Some of you may recall an article I wrote late last year, “Don’t care about Strava segments? There is more to Strava than you think“. In that article I discussed some of the many useful, yet underutilized, training features that can be found on Strava. If you’d like to dig a little deeper than Strava’s most obvious feature–segments–it’s worth a read. For future reference, that article, along with many more, can always be found in the Articles section of this site.

A couple of the features discussed in my article are only useful to cyclists who use power meters (and those power meter-related features are only available Strava users with a Premium membership). In the time since I wrote that article I purchased a Stages Cycling power meter, and so a couple of the features mentioned in my article have become highly relevant to me as training and data analysis tools.

This morning I’d like to take a renewed look at one of those features: specifically, the “Best Efforts Power Curve” (also known as the “Critical Power Curve”).

If you are not familiar with power curves, they are used to display the maximal power a cyclist has sustained for various time intervals; the time intervals are displayed along the horizontal-axis, while the power output is displayed along the vertical axis.

Strava gives you the ability to compare power curves using fully customizable time periods. Overlaying your current power curve against various historical power curves will provide you with extremely useful data; specifically, are you getting stronger on the bike, or weaker?

Strava not only gives you the ability to customize the time frames of your power curves, it also allows you to chose between “Watts”, or the more useful (IMO), “Watts/KG”.

In cycling, an athlete’s power-to-weight ratio (Watts/KG) is extremely important. Assuming two cyclists with identical wattage outputs, bikes and bike handling skills, the lighter cyclist will always be faster. This difference is especially apparent when climbing or accelerating.

Even though I only started using a power meter five weeks ago, I do have power data from 2013. The 2013 power data comes from TrainerRoad’s “VirtualPower”, and that means the power data from my indoor stationary trainer rides were used to create the 2013 curve (I’ll touch on the ramifications of that below the chart).

Click to enlarge:

My Watts/KG power curve: last 5 weeks vs. 2013 best efforts.

My Watts/KG power curve: last 5 weeks vs. 2013 best efforts.


As you can see, my Watts/KG over the past five weeks is consistently and significantly higher than it was during all of 2013 (best efforts are represented). This is especially true considering that in my tests I found that TrainerRoad’s VirtualPower measured 12% higher than the Stages Cycling power meter (you can check out my tests and full analysis here: Part I and Part II). In other words, the 2013 line is artificially higher than it should be.

Looking at the image, you’ll see that I’ve selected one data point as an example: my 8-minute Watts/KG. My best 8 minute Watts/KG this year is 4.52, while my best effort during 2013 was 3.86 Watts/KG. Again, last year’s 3.86 Watts/KG was measured using TrainerRoad’s VirtualPower, so that means it’s about 12% higher than it would have been if I’d been using a power meter. In other words, 3.40 Watts/KG is probably the correct number for an apples-to-apples comparison.

I think that 8-minute sample from my curve is a pretty good indication of the improvements I’ve made as a cyclist since last year. A jump from 3.40 Watts/KG to 4.52 Watts/KG is pretty definitive proof that I’m a much stronger cyclist now than I ever was last year.

So, using Strava’s Watts/KG power curve tool I’m able to quickly determine that my weight loss has not affected my power. In fact, I can easily switch over to the “Watts” view and see that I’ve actually increased my power as I’ve lost weight. When I weighed 83 kilograms (183 pounds) late last year, my 8-minute wattage output was 290 watts (VirtualPower data adjusted -12% to match the Stages power meter); This year my 8-minute wattage output is 326 watts, and I’m much lighter (72.58 KG/160 pounds). Getting lighter while increasing wattage output is what every cyclist strives for.

Strava’s various data analysis tools allows athletes to quickly gain valuable insight into the effectiveness of their training programs. This is especially true for Premium members with power meters, however there’s still a wealth of information available to more casual cyclists who are interested in analyzing their rides. If you’re not familiar with those features, take a few minutes to read my original article and do some exploring of your own.

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