Power numbers explained

Not everyone has a power meter, mostly because they are really expensive. Fortunately mine was not, in comparison ($330 in ebay for a full wireless set-up). But because of this, not everyone if familiar with the lingo. I know I just learned it some of it this weekend, and I’ve had this thing since March. Here’s definitions straight from my manual:



Generation III iBikes have Normalized PowerTM(NP), Training Stress ScoreTM (TSS), and
Intensity FactorTM (IF) measurements. If you are a seasoned veteran of power training,
you realize how important this information can be, and how great it is that iBike can display
this information on the road.

TSS, IF, and NP were developed by well-known exercise physiologist Dr. Andrew R.
Coggan. These three measurements use the “raw” power data from your iBike,
along with sophisticated mathematical formulas, to provide more detailed
information about the intensity and quality of your workouts. If you have never
heard of these three useful factors, then keep reading to find out what they are and how
they can help you get the most out of your workouts and your fitness
improvement goals.

Getting Started: Determining Your Functional Threshold Power (FTP)
Before you can obtain TSS, IF and NP measurements you need to have a “baseline”
that characterizes your current level of fitness. This reference point is called your
“Functional Threshold Power”, or FTP.

One way to determine your FTP is to do a one hour Time Trial; your average watts
for that one hour period is your FTP. Another way to estimate your FTP is by using
the iBike’s 20 minute fitness test. The iBike 20 minute fitness test is similar to a
time trial, just shorter in time. To estimate your FTP from the iBike fitness test,
take the watts per kilogram number shown in your “FIT TEST” screen, multiply that
number by your weight (in kilograms), then multiply that number by 0.95. For
example, if your W/KG measurement is 3.02 and your weight is 81KG, then your
estimated FTP is 3.02 *81 *.95 = 233W.

Once you have determined your FTP number from either method, you must enter
that value into the iBike. Go to Setup/FTP CFG (FTP Configuration). Click the
center button, then use the arrows to enter your FTP in watts. Click the center
button to Accept.

If you’re training regularly you’ll want to check your FTP about once a month.
Normalized Power (NP)

Have you ever participated in a group ride where your watts are never steady?
Group rides can be very difficult, but afterwards looking at your average watts
might not reflect how difficult the ride was. The disparity between measured and
perceived effort is due to coasting, surging, using brakes, and soft pedaling. In fact,
your average watts will be lower than your perceived effort suggests. This is where
Normalized Power (NP) comes in.

NP takes your “raw” power data and gives you a related power measurement number
(reported in watts) that better represents the “tax” on your body for the ride, especially
when you’re varying your power output considerably from moment to moment. For
example, in a criterium, the NP number will be much higher than the average power
because the NP measurement does a better job of accounting for the effects of coasting
and large power surges. The NP number will be more representative your effort for theride.
In events such as a time trial or climbing hills where the wattage holds very steady, NP and
average power will be very close to each other because you pedal almost all the time.
Using Intensity Factor (IF) to gauge the difficulty of your Workout.

If you do cycling workouts regularly you know that some of your workouts are more
intense than others. Average power and NP alone won’t quantify the intensity of
your workout, because the intensity of a workout is not based on power output
alone but also the time length of your workout and how hard you work during each
moment of your workout.

Normalized Power (NP) and Functional Threshold Power (FTP) can be used together
to quantify the overall intensity of each of your workouts. The Intensity Factor (IF)
is very simple to calculate: divide your NP by your FTP. The number IF represents
the intensity of your workout as compared to the effort you expend in a one hour
Time Trial. So, an IF of 1.0 represents a time trial effort and in theory can only be
maintained for an hour.

One of the great things about an IF measurement is that you can manage your
training schedule to make sure you’re training hard, but not training too hard. Here
are some values for IF and the kind of rides they represent:

• Less than 0.75 – recovery rides
• 0.75-0.85 – endurance-paced training rides
• 0.85-0.95 – tempo rides, aerobic and anaerobic interval workouts (work and
rest periods combined), longer (>2.5 h) road races
• 0.95-1.05 – lactate threshold intervals (work period only), shorter (<2.5 h)
road races, criteriums, circuit races, longer (e.g., 40 km) TTs
• 1.05-1.15 – shorter (e.g., 15 km) TTs, 10 minute hill climb
• Greater than 1.15 – prologue TT, track pursuit, 5 minute hill climb

One more way to gauge your workouts: Training Stress Score
We now know the true tax on our body (NP), and how intense each workout is (IF)
compared to a reference one hour TT, but there is still one more thing to think
about. For example, what is the comparative stress on the body from riding at
50% of our FTP for two hours, compared to a 100% FTP effort for one hour? A
simple number called Training Stress Score (TSS) allows you to quantify and
compare your different workouts, even when they are considerably different in time
length and power intensity.

TSS is designed to give you a numeric value for each ride that tells you how much training
load was on your body for that day’s ride. A TSS of 100 equals an hour at an IF of 1.0. So,
if you were out for a fairly easy four hour ride, and accumulated 200 TSS points, it’s the
same training load as doing two hours at time trial pace.

Importantly, TSS also quantifies how tired you can expect to be after a workout and
how long the residual fatigue might last.

• Less than 150 – low (recovery generally complete by following day)
• 150-300 – medium (some residual fatigue may be present the next day, but
gone by 2nd day)
• 300-450 – high (some residual fatigue may be present even after 2 days)
• Greater than 450 – very high (residual fatigue lasting several days likely)


By looking at your TSS, IF and NP numbers after each ride you can track your
workouts based on data from your own personal FTP number. Furthermore, these
three metrics can be used to diagnose workouts and even prescribe rest days.
If you can normally ride two hours at an IF of .9, but today you really struggled, it
might be time for a couple of easy recovery rides (IF of under .7). Using this
information can make your iBike power data even more personalized to you, and
help you maximize the effectiveness of your training.

For more detailed explanations of NP, IF, and TSS, see the Trainingpeaks article at:

TSS™ is a trademark of Peaksware, LLC
Training Stress Score™ is a trademark of Peaksware, LLC
IF™ is a trademark of Peaksware, LLC
Intensity Factor™ is a trademark of Peaksware, LLC
NP™ is a trademark of Peaksware, LLC
Normalized Power is a trademark of Peaksware, LLC