Intensity Factor* (IF) is an indication of how hard or difficult a ride was in relation to your overall fitness. IF values are calculated by taking your Normalized Power (NP) and dividing it by your Functional Threshold Power (FTP).
Typical IF values can range from 0.75 to 1.15 with 0.75 being the easiest and 1.15 being the hardest.
The IF system compares the energy exerted from one training session to another and lets you check for changes in your FTP. A ride of 1.0 would be equal to your FTP. An IF value more than 1.05 for a one hour race typically means that a rider's FTP is now higher. Therefore, changes in FTP can be revealed without the need of frequent formal testing.
Here is an example of how this entire system could be used:
Your NP is 300 W. Your FTP is 310 W. The IF for that ride would be 0.97.
If the same ride is performed later in the year and your FTP had risen to 320 W, your IF would be 0.93. This would mean the same workout required you to exert less energy.
The IF will show on the Edge 810, 800, 510, 500 and the Forerunner 910XT. If it does not appear as an optional data field, update the software.
You will find NP in Garmin Connect on the activity's Details page. There will be a Power section within the Details box.
*In order to receive an accurate IF calculation, you will need to set your accurate FTP in Garmin Connect's power zones. For further details on IF/FTP, view the Training Peaks web site.
Update software - http://connect.garmin.com/firmware