This is just a quick comment in regards to the post I did a few days ago on measuring aerobic endurance progress. In that post I suggested that for experienced and generally fit athletes that training a lot in zone 3 would improve aerobic endurance and that this improvement could be determined by doing a CP30 test for cycling functional threshold power (FTPo) or running functional threshold pace (FTPa). I've seen such training boost FTP significantly in a few weeks. Here's a real-world example of that, but a unique one due to the training response time.
One of the road cyclists I coach has been traveling a lot and his training has been rather spotty as a result. But on April 3 things finally settled down for him and he was able to devote a couple of hours daily to riding. On April 9 he did a CP30 test. Before this test he was rested with a day off the bike and one short, low intensity ride. The result indicated that his FTPo was 241w. Over the next 12 days he trained 24 hours and 42 minutes (including testing on both ends). Here is a power distribution chart which shows how much time he got in each zone during this time (click to enlarge).
Today (April 21) he retested after 2 days off due to travel and a recovery ride. We found his FTPo to be 257w, his highest in the two years I've been coaching him. That's a 7% increase with a bit more than 24 hours of training and just over 60% of it in aerobically active zones (z2, z3, z4).
The focus during this time was primarily on z3 intervals of 15-20 minute durations with 5-minute recoveries. But we included just a bit of z4 shorter-interval work also. Not much as you can see from the chart. When not doing an interval he was to recover in z2. There was a z1 ride every other day for recovery. These typically included a bit of z2 and z3 due to hills and traffic.
This is the quickest response of FTP I have ever seen. I wish everyone I coach responded so quickly to training, but this is seldom the case. In the late Base period in a 4-week period I'll often see a 2-3% increase - and I consider that good. A 7% gain is off the charts.
Now the focus is on bumping it up just a bit higher before his first road race in late May. The emphasis will now shift to FTP (z4) training intensity while we maintain the aerobic gains with some z3 training around the edges. In another couple of weeks we'll introduce anaerobic endurance training in zones 5 and 6. He won't be fully race ready by late May (it's B-priority race) but he'll be strong, meaning good muscular endurance. This will give us a good platform on which to prepare him for his A races in the summer.