The TrainingPeaks Guide to Cycling Power TerminologyAn athlete’s guide to understanding the key terms of training with power.

“It is the most effective tool you can get to go faster on a bike.” - Joe Friel

IntroductionTraining with a power meter is the most precise and detailed way to get results. But the power meter is only part of the equation, you need to know what the numbers mean and how to interpret them. There are a few key terms you need to understand to take full advantage of this amazing tool. The following slides will explain what these terms mean and how they apply to your training.

WattsSimply put, a watt is a measure of power per unit time. To be more precise, it is 1 joule per second.

Unlike heart rate, watts do not fluctuate due to outside factors. 300 watts is 300 watts no matter what speed you are going.

Watts are the most precise way to truly measure your effort.

Functional Threshold Power (FTP)Popularized by Hunter Allen and Dr. Andrew Coggan in their book, Training and Racing with a Power Meter, the term Functional Threshold Power, or FTP, refers to the maximum power you can sustain evenly for one hour.

Your FTP can be determined during a lab test, by performing a field test, or estimated from a race or hard workout in training.

Determining FTPThis test was created by Hunter Allen and is a simple way athletes can test their FTP. Perform this field test on a flat course relatively free of stop signs or traffic, and if possible one that has a steady, uphill grade of less than 5%. The uphill grade helps you to maintain a constant output, as opposed to rolling terrain where it’s difficult to keep your power up on the downhills.

Test• 15-minute endurance paced warm-up.

• 3 x 1 minute fast pedaling drills of at least 100 rpm with 1-minute recoveries in between each.

• 20-minute time trial all by yourself—no training partners, and not in a race. Your effort should be done as if it was a race for the entire 20 minutes—all out, but sustainable for the 20 minutes.

Your average power for that 20 minutes, less 5%, is an approximation of your FTP. For example, if your average power for the 20-minute test was 250 watts, then your FTP is 250 watts x .95 = 238 watts.

Determining FTP

ZonesOnce you know your FTP you should set up your power training zones. Each zone works a different physiological system. Using your power meter allows for greater precision and targeting of specific zones.

This is where the detailed data from a power meter is much more beneficial than data from a heart rate monitor.

This table created by Dr. Andrew Coggan shows the performance benefits from training in zones 1-7.

Along with your power meter, you’ll need a device to display and record the data. There are many terms and acronyms that you need to know to understand what you see on the screen and to analyze your file post-ride. The following terms are the most important metrics you need to understand in order to use your power meter to it’s fullest.

What Do the Numbers Mean?

Average PowerAverage power is simply the numerical average power you put out for a given time. Many devices come with non-zero averaging or smart recording turned on. This means the device won’t record zeros when you are not pedaling. While this will make your numbers look better it is not a true accounting of your effort and we recommend you turn that function off.

Normalized Power® (NP®)No ride is perfectly steady. Your power output varies due to factors like wind, terrain and other riders. Here’s where Normalized Power (NP) comes in. This algorithm is somewhat complicated, but it incorporates two key pieces of information:

• The physiological responses to rapid changes in exercise intensity are not instantaneous, but follow a predictable time course.

• Many critical physiological responses (e.g. glycogen utilization, lactate production, stress hormone levels) are curvilinearly, rather than linearly, related to exercise intensity.

Your NP is an estimate of the power you could have maintained for the same physiological “cost” (in terms of glycogen utilization, lactate production, stress hormone levels, and neuromuscular fatigue) for a given effort or ride if your power output had been perfectly constant (e.g., as on a trainer) rather than variable. As such, NP is always higher than average power.

NP is a better indicator than average power of how metabolically challenging your workout was. It emphasizes power surges which require a lot of glycogen (carbs) and therefore contribute to an increase in fatigue.

Normalized Power® (NP®)

An example is if you pedal at 200 watts for 1 hour, you will have an AP and NP of 200. If you pedal at 100 watts for 20’, 200 watts for 20’ and 300 watts for 20’ you will still have an AP of 200 watts but your NP will be 239 watts.

Normalized Power® (NP®)

Variability Index (VI)Variability Index is a way to measure how smooth or “variable” your power output was during the ride. It is calculated by dividing your Normalized Power by your Average Power. A steady and even output, like during a triathlon, should have a VI of 1.05 or less. During a criterium race, where there would be more coasting and surging, the VI may be as high as 1.2 or more.

Intensity Factor® (IF®)Intensity Factor provides a valid and convenient way of comparing the relative intensity of a training session or race either within or between riders, taking into account changes or differences in threshold power.

The IF of a ride is the ratio of your Normalized Power to your FTP. For example, if your Normalized Power for a long training ride done early in the year is 210 W and your FTP at the time was 280 W, then the IF for that workout would be 0.75. However, if you did that same exact ride later in the year after your FTP had risen to 300 W, then the IF would be only 0.70.

Watts Per Kilogram (w/kg)Using Watts per Kilogram is the best way to compare two different riders. Usually expressed as watts per kilogram of body weight (w/kg), the higher the watts, or lower the weight, the faster the rider will go.

A power to weight ratio of 4 to 4.5 w/kg is equivalent to a competitive Category 2 racer. A power to weight ratio of 5 to 6 w/kg would put you in the range of a Category 1 elite professional according to Dr. Andrew Coggan’s Power Profile Chart.

MatchesThis term seeks to show those points in a race or ride where you exceeded your abilities and burned energy at a high rate.

A match can loosely be defined as an effort in which you go over your threshold power by a certain percentage and hold it there for a period of time. The table below is a guide for what may constitute burning a match. Every rider has a certain number of matches they can burn. If your burn too many matches it will be a long ride home.

Training Stress Score® (TSS®)Based off of the duration and intensity of your session, Training Stress Score is a single, numerical value for the effective load of your training session. You earn 100 TSS for an all out, 100%, 60-minute workout. Since your FTP value is the wattage you can hold for 1 hour, holding that value for 1 hour equates to 100 TSS points. Of course most workouts are not completed at 100%, so most workouts will accumulate less than 100 TSS per hour.

For example, if your FTP is 250 and you hold 200 watts for 1 hour you would have a TSS score of 80. You can earn more than 100 TSS within a single workout (as long as it is longer than an hour), but never more than 100 TSS per hour. If you find that you are accumulating more than 100 TSS points per hour you have either bad data readings or your FTP needs to be raised. TSS values are critical to using the Performance Management Chart to track long term data trends.

Combining detailed data with an understanding of a few key terms allows you to analyze each ride and prescribe more exact workouts in the future. You’ll be able to quantify the true load of your training- for each ride and over time. Don’t just look at your numbers and wonder, use them to become a faster rider.

Putting it All Together