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TrainerRoad VirtualPower compared to Stages Power Meter: Round 2!

Monday, March 31, 2014 by  
Filed under Daily Blog

March
31
2014

This is a follow-up article to my examination of TrainerRoad’s VirtualPower, and how it compares to a Stages power meter (see “TrainerRoad VirtualPower compared to Stages Power Meter“).

For this test, I wanted to do an intense 1-hour workout. I decided to ride Sufferfest’s “Angels” workout. In order to obtain a complete set of data, I had to perform this workout twice…

The first time I rode the workout was on Thursday, March 27th. For that workout I used my Stages power meter as the primary power source, and so all wattage targets were hit based on my power output according to the Stages.

The second time I rode the workout was on Saturday, March 29th. For that workout I used TrainerRoad’s VirtualPower as the primary power source, and so all wattage targets were hit based on my power output according to VirtualPower. I also recorded my Stages power data at the same time for later comparison.

Before I get to the test results, here are a few words about VirtualPower, the equipment I used for my tests and my testing methodology.

What is TrainerRoad’s “VirtualPower”?
For cyclists who wish to improve their speed and fitness, nothing is more effective than power-based training (for more information on training with power, please see my article “Coggan’s Power-Based Training“). Unfortunately power meters are not inexpensive items (although that is slowly changing), and are outside the budget of many cyclists. This is where TrainerRoad’s “VirtualPower” comes in.

Simply put, “VirtualPower” works by converting the cyclist’s speed into power using known power curves for indoor trainers that are supported by TrainerRoad (most are). VirtualPower is an inexpensive, yet accurate, alternative to expensive power meters.

 

All tests were performed in my Bike Torture Chamber.

All tests were performed in my Bike Torture Chamber.

Equipment Used
Here’s a list of the equipment I used for my tests. For more detailed information and photos of my Bike Torture Chamber (BTT), please see this article.

 

Testing Methodology
All tests were performed using the following procedures and settings:

  • Rear tire inflated to 120 PSI
  • Kurt Kinetic Road Machine rear roller set to 3.5 turns
  • Stages power meter zeroed out/calibrated immediately preceding each test
  •  

    TEST #3: 65 minutes, Sufferfest’s “Angels” workout

    This is a very tough workout–far more intense than anything I did in the previous two tests. Nearly 30 minutes of the ~hour long workout is spent riding in the Threshold, VO2Max or Anaerobic power zones. Here are the test results (click any image to enlarge):

     

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest's Angels workout – Data Chart

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest’s Angels workout – Data Chart

     

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest's Angels workout – Data Summary

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest’s Angels workout – Data Summary

     

    The previous two tests I performed demonstrated that TrainerRoad’s VirtualPower (using a Kurt Kinetic Road Machine) tracks extremely well with a real power meter; this test was no different. As you can see (and as previously observed), the only real difference between the VirtualPower data and the Stages data is that the VirtualPower is consistently higher after a few minutes of riding. Perhaps due to the intensity of this workout (and–I’m speculating here–the rear tire becoming hotter than in the previous two tests), this time the average power difference was 27 watts (189 watts for the Stages vs. 216 watts for VirtualPower). The previous 60 minute test I performed was at a considerably lower overall intensity, and on that test the difference was 21 watts.

    So what does that 27 watts translate to in terms of effort? Quite a bit, actually. Check out my heart rate graph from both workouts (click to enlarge):

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest's Angels workout – Heart Rate

    TrainerRoad’s VirtualPower (Purple) compared to Stages Power Meter (Red): Sufferfest’s Angels workout – Heart Rate

     

    That’s a 16 BPM average heart rate difference, and that’s pretty huge. When I rode this workout using the Stages as my power source I had to bury myself to hit the wattage targets. When I used VirtualPower to do the same workout, I found the workout somewhat challenging, but considerably more manageable.

    The takeaway is simply this: FTP is just a number and, for the most part, meaningless when compared to other FTP numbers measured using different methods. What’s vitally important is consistency in your equipment and equipment setup from one workout to the next. In other words, if you perform your FTP test with a Stages power meter (or, presumably, any other accurate power meter), and then use TrainerRoad’s VirtualPower to do subsequent workouts, you’re doing yourself quite a disservice (the workouts will be too easy). Conversely, if you perform your FTP test using TrainerRoad’s VirtualPower and then use a power meter to do your training, the workouts will be scaled to a difficulty level well beyond your FTP (roughly ~12% higher, based on my testing).

    So, TrainerRoad’s virtual power is an awesome and inexpensive way to train using power. The only caveat is to recognize that the power numbers are only useful when compared to rides using the exact same equipment and setup. Any change in equipment (especially a change in your power source) will require a new FTP test.

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John Stone Fitness Comments

One Response to “TrainerRoad VirtualPower compared to Stages Power Meter: Round 2!”
  1. joec4242 says:

    Sounds like you’re on the right mindset about this (i.e. precision vs. accuracy)

    These numbers are way more meaningful in measuring how for one has developed. It kinda reminds me about what you say/said about the amount of weight you work out with. How much you bench only is only useful to you…

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