How Often Should I Reassess My FTP?
Typically, FTP tests are standardized throughout training plans every six weeks.
If you aren't using one of TrainerRoad's structured training plans, if you're using your own plan, or if the plan you're using doesn't include regular FTP assessments, you should still schedule your FTP assessments about every six weeks or so.
It takes the body about this long to absorb training stress, i.e. adapt physiologically to consistent stress, therefore six weeks seems to be the best amount of time between tests.
Any more often than this and you might not see any sort of measurable change; any less often and you might be under-challenging yourself with power levels that don't match your improved fitness.
When Should I Raise My FTP?
That's a good question and the answer is: it depends.
Our cyclocross training plans will increase the demands of each week's workouts so that you don't have to increase your FTP, but will instead increase the duration of your intervals and then use the monthly time trials to less-formally measure improvement in FTP.
Most plans, however, assume that you're routinely assessing FTP so that each subsequent 6-8 weeks of training is based on your most recent FTP. Accordingly, assessment workouts are scheduled throughout these plans as that day's workout.
At TrainerRoad, one way to generate your FTP is to reassess every 6-8 weeks. The nice thing about repeating a structured assessment protocol is that it's repeatable and you can control the variables. It's not only easy to see a bump in average power over your 20 minute or 8 minute test but our software will automatically calculate and update your FTP.
Personally, I like to raise my FTP based on the power I can routinely sustain in my longer interval workouts.
For example, if I do a 2x20-minute workout at FTP it should feel pretty hard, but if I get through the workout without digging too deeply then I'll consider raising my FTP by 5 watts after the workout. Then, over the course of the next workout I see how I feel make small adjustments from there, if necessary.
I prefer this method because I'm constantly pushing my FTP and making the workouts more demanding and more productive.
On the other side of this coin, if I find I can't complete my more intense workouts with this recently increased FTP then I might drop those 5 watts off again.
The idea is to keep pushing and challenging myself while still completing the workouts.
Combine the Two
Ideally, you'll utilize some combination of the two above techniques as this is probably the most thorough way to measure progress. With both, you'll constantly be pushing yourself in addition to having repeatable, measurable tests to get some hard numbers.