Functional Threshold Power (FTP) is simply the maximum power your body can maintain under aerobic condition for typically one hour. Most of us do not do the one hour FTP test as it can be done doing a 20 minute time trial and your FTP being 95% being the average of that 20 minute time trial.
FTP is actually a percentage of your overall VO2 max capacity. So next time someone says triathletes don’t need to worry about their VO2 max, you can tell them to rack off.
Increasing your FTP
There is already a lot of information out there about how to improve your FTP by doing 20min sweet spot sets (sweet spot is between 84-95% of your FTP). Yes this will work but at some point, you will need to focus on increasing your VO2 max ceiling in order to give your FTP room to grow.
Start off 5-8 minute efforts @110% FTP, move towards 3 minute efforts @ 120% of FTP. Start off doing 3-4 reps and slowly build towards 9 reps.
Building FTP is more a case of building endurance at a high percentages of VO2 max. The standard interval is 2x 20 minutes at sweet spot (84-95% of FTP), as you progress, you can slowly increase this to 100% FTP then do 3x 20min @ sweet spot.
If you are looking at raising your VO2 max ceiling and FTP, I would recommend including into your weekly program a strength endurance session. Doing hill repeats or low cadence sets with cadence or around 55-65 RPM at 84-110% of FTP. Starting off doing 4min efforts and slowly building over time.
Don’t have a power meter?
Moderate: keeping it all aerobic (should be able to hold a conversation comfortably)
Medium: this will be your FTP intervals (this should be uncomfortable but manageable)
MAD: this will be your VO2 max intervals (As fast as possible without compromising your technique)
Easy: when doing these intervals, easy is EASY