I did a whole ton of base work from February through May this year. Typical week was 2x120 minute and 1 x 90 minute SS sessions from the HV plans, supplemented with a lot of outdoor riding in zones 2-3, including a weekly long group ride that includes a fair bit of easy spinning but does get up to 5 hours and 100 miles in the saddle. Quite a few weeks over 15 hours and 300 miles.
Got a small bump in FTP as tested (320 to 329 to 336), but much more noticeable was ability to hold sustained power and also how quickly I was recovering from intervals. Those long SS sessions were getting very comfortable plus I did some 40km TTs and long mountain climbs where average power over ~1 hour was right around FTP without tapering or being particularly fresh.
Now 2 weeks into General Build, haven’t tested yet but will do week after next, initial signs are good that the bigger base is going to be a great foundation for the higher intensity work. The hard sessions are already feeling significantly easier than they were only a couple of weeks ago, and my performance in group rides has surged, I’ve gone from being the guy who can hang with the surges and breaks to being the guy who is initiating them and putting everybody else in the red. Don’t know whether this will translate to much of a boost in FTP, but it is absolutely translating to performance on the road which is what counts!
Background for context - years of training at a consistently fairly high level, 25+ years of minimum of 200 training hours a year across all sports, and more like 4-500 hours in good years. I tend to be fairly consistent throughout the year though without a lot of periodisation, so have a tendency to plateau at a good level of fitness without ever really hitting the heights. Started using power 3 years ago, first FTP test was 298W, has rarely dropped below 300 since then, but also rarely gets above 320. So this year was a conscious decision to try and make a breakthrough with increased aerobic base and volume to get to a higher level.