xPower redefines maximum sustainable output

A primary benefit of a power meter is measuring how much work you can sustain over a given duration. Since there are always fluctuations in your output when riding outside, it can be tricky to capture a true representation.

Average power is a good metric, but any periods of coasting will introduce zeros into the formula and thus lower the total number. Normalized Power is a common formula used by many cycling computers and analytics platforms that weights spikes into the formula, resulting in a higher number than just average power. However, this metric can deliver numbers that are higher than what a rider can actually sustain.

So how can one accurately measure the true highest sustainable power over a given time period? Enter xPower...

FasCat's new xPower metric is an advanced average of your power output that considers shorter higher-powered efforts for a true physiological representation of your power output. While Normalized Power often overestimates what a rider can do, xPower analyzes highly variable power output to give the true physiological effort.

xPower is useful in measuring improvement when average power does not.

xPower chart

How xPower works

Our exact formula is proprietary, but xPower measures the true physiological demands placed on an athlete from an effort, segment or hard portion of a group ride or race. xPower is the advanced average from a highly variable segment of power that the athlete could have maintained for a steady effort like a threshold field test.

For these reasons, we can compare xPower from hard group rides or races to steady threshold field tests to track threshold improvement. Criteriums are great use cases for xPower. Criteriums have lots of zero power sections for corners and energy conservation as well as many many high powered jumps out of corners or attacks and chases. Average power does not represent how hard the athlete was going whereas xPower does by considering all the peak accelerations and attacks.

Non-steady time trials with undulations and downhills are perfect for xPower because often time average power is slightly lower than the true physiological effort from the athlete.

xPower uses exponentially weighted moving averages of power samples instead of simple rolling averages for a more physiologically depiction of how power is changing. xPower doesn't upweight massive, short power spikes nearly as much as Normalized Power. xPower recognizes that big power spikes have a disproportionately large physiological impact, compared to averaging raw power values. 

xPower chart 2

Why xPower is better than Normalized Power

Using xPower prevents "NP Buster" style workouts (e.g. 30 seconds on, 30 seconds off at Zone 6 with huge amounts of rest) from potentially not reflecting what the body is physiologically doing. 

xPower uses an exponentially weighted moving average, which means that a recent surge of power has an impact on shifting the xPower value into the next 3 to 5 samples of data, but that effect diminishes very quickly.

Normalized Power uses a raw 30-second moving average and a big surge for a second will have an impact on the value of NP for the next 30 seconds, and that won't diminish until that 30 seconds is over. This is why data with repeated 10- and 20-second surges (like a criterium or 10- to 20-second intervals) often overestimates and is call an “NP Buster.”

xPower gives credit for big surges of power but returns a more "aerobically accurate" profile of the true effort than Normalized Power. 

You can view your 20-minute xPower in your post-workout Optimize screen.

Stay tuned for more updates and enhancements using xPower to help you Ride Faster and Train Smarter.


Download and join Optimize where Coaching is included, the training plans are unlimited and there's a 14 day trial to see for yourself!  

About Frank Overton

Frank founded FasCat Coaching in 2002 and has been a full time cycling coach since 2004. His educational background includes a Masters degree in Physiology from North Carolina State University, pre-med from Hampden-Sydney College. Frank raced at a professional level on the road and mountain bike and currently competes as a "masters" level gravel and cyclocrosser. Professionally Frank comes from medical school spinal cord research and molecular biotechnology. However, to this day it is a dream come true for Frank to be able to help cyclists as a coach.

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