Thanks for the interesting post! This is one of my favorite forum threads as well and I review it often. That being said I think your project is interesting in a different way... How to create training sets that are slightly more specific to the principals TI is teaching. Your project is a perfect example.
I have a few questions for you.
do you have a 400m baseline time that you can use to evaluate imrpovement?
What are your target times/SPLs for the 400 (zone 2) for each round?
While I don't disagree that combining speed and endurance work in the same practice keeps things itneresting, I don't think that the physiology of hte first set is exactly what Gerry thinks it is... I don't think you can sustain VO2 max effort for the +/- 20 sec 25 yard swims for a 10 minute set with 10 seconds of rest inbetween. The duration of the set is too long and the recovery too short to allow for VO2 max levels to be maintained.
I have a protocol to help determine your VO2 max swim pace or you could simply swim all out for 5-6 minutes and use that pace as your target 25 pace, while being aware of your SPL. Try that pace plus 10 seconds rest...I'll be pleased if you can hold that pace and do it 20 times in a row. Maybe it's possible, but I admit I'm a bit skeptical.
When I'm in better CV condition and a bit more durable I'll try it myself.
My next thought is that in your interpretation of the set, I'd suggest that you SIT OUT a repeat if you miss on the SPL, rather than simply acknowledging and continuing on. While it's better than no awareness, the USRPT side of the inspiration would suggest you sit out the next round, and if it happens 3 times in teh set you simply stop for the day. There are a few more "rules" to that as well. But I don't see the value in contininuing once you know you're over your set target, with the exception of possibly ONE additional repeat to see if you can reign it back in. But if #2 is over, then rest Otherwise you've only partially "TI-ified" the set, adn turned it into a physiologic set where you hope you improve by pushing through.
That being said, I like the way you have set up some parameters where you won't continue to progress your practices utnil you are "successful" at yoru 20x25 holding your SPL where you've chosen.
I'm curious if you have a similar set of parameters for the easy 400, or if you are using it as a "swim down" between the sets of 20 x 25?
Looking forward to hearing more PLUS I'd encourage you to start a new thread, reposting your post above as the first post. If you do, I'll copy my post below it as well.