If there is a single statistic that is most predictive of success in racing, it is FTP. The higher the number, the higher the probability of success.
Here is the data and the science: All good science and our personal experience on the subject of raising FTP is consistent. This is best accomplished by spending significant blocks of time riding just below and that at an athlete's FTP. Ten minutes of riding at or just below threshold is the minimum time for effectively raising FTP. That is the minimum. In this particular place, more is better, however, it is not as obvious or straightforward as it may seem. There are limits and parameters.
The first of those parameters is how many total minutes an athlete is riding at or just below FTP combined. A total of 30 minutes(combined time of intervals)can be effective. That is a great place to begin and that is where we will start. For most riders, sixty minutes of combined interval time is really the maximum. There are some exceptions. Elite athletes or those with very long target events may want to do more, where about 80 minutes of combined interval time is the maximum. More than that and an athlete is either riding at lower watts or getting too fatigued. Most will go backwards. There are almost unlimited variations as to how to construct the 30 to 60 minutes of combined interval time. This can be 4 x 10, or 2 x 20 or many other variations that can be effective.
The “classic FTP builder” is riding 2 times 20 minutes at your FTP. There is a reason this is a time tested, classic workout that racers have been doing for many years. Because it works. If you have not done this one, you will find that it is quite hard to ride at FTP for 20 minutes, two times. This requires a lot of focus. Doable, not easy, but the payoff is huge.
Better than just bashing a lot of 2 x 20’s however, is to do variations that start out modestly and build. This can be done by either increasing the number of combined minutes or by raising target numbers. Doing both at the same time is a mistake. We prefer a steady diet of increasing the number of minutes just below FTP first. After that period is done, then we will start raising target watts. This is where most athletes will find a pop in their FTP. There is no perfect answer for everyone. Now it is time to get to work!