I don't think I am disagreeing with you. My main point was that the intervals as outlined in that blog entry (similar to the program Kensho outlined above) are really equivalent (at least stress-wise) to a gentle tempo/fartlek type workout, more along the lines of a "brisk" run rather than a tear-my-hammy-run-so-hard-I-dry-heave type of track workout you're thinking of. And that type of workout (the "gentle" intervals one), if we define "base" as metabolic fitness, is perfectly fine to do year round, assuming you're not starting from scratch every January after a 2-month layoff. My second point was also in line with what you are saying: that just doing some easy runs and some "brisk" runs offers a lot of age groupers plenty of intensity. Probably the vast majority can get by with only that, if you're correct in how the average age grouper trains. Just so we're not talking past one another, let me put it in more concrete terms: say my peak heart rate for running is 180, and my resting heart rate is 50, I would want to build to as much time as I was willing to devote with work in the 135-145 bpm range. Then I could start doing some of the intervals like Kensho outlined, and then even later, I would add in some steady tempo runs in the 155-165 bpm range.