Just getting in from a 350km solo training checkup (enroute to my goal of completing a 1200km this Fall). So here's my 2 cents.

I am in the "just go ride" and not worry about doing intervals camp. (By the way, I HATE intervals like the plague.) Since starting my quest to completing a 1200 this past January with basically zero base miles, I have worked thru riding 200 and 300km distances by simply adding miles each ride, absolutely no high intensity interval work - some would argue that's base building. Shrug - for me it was just what is my style. I've concentrated primarily on getting my cadence to a consistent low-90s rpm and being able to hold it for an hour at a time, then two..and so on. The secondary concentration area has been figuring out hydration and nutrition - lucky for me, I have a reasonably "cast-iron" stomach and I digest most things fairly easily, but real meals mean I'm digesting real food while pedaling in the low-mid-80s - so, I do lose some speed for about 30 minute periods every 4-5 hours or so (yeah, I DO eat real meals while riding).

Lastly, the thing that has been "beneficial if not pleasurable" is having ridden a fair bit in undesirable weather - wind, rain, high humidity(70%+) and heat(90-95F) - the last two are impossible to avoid where I live. By themselves, the environmental factors have each strained on my body/"the physical engine" in ways that I didn't anticipate but will hopefully be beneficial when I ride in the more pleasant conditions I hope to face on the 1200.

To sum up, I started with no miles to speak of, riding only 10 miles each on 3 days a week and worked my way up to 5 days a week riding at least 50-75 miles on 2or3 of those days at a target heart rate and cadence pace that I found work for me at any distance so far. I've completed 3 unofficial, solo 400km and 1-600km training rides not to mention a number of 200 and 300km rides all within "official" time limits. A few posters here have said this schedule is "over-training" considering the time period they've been completed in AND over-concentrating on endurance while ignoring "power". Shrug. I'm doing all of this solo - planning the routes, ride scheduling, and keeping track of what's working for me or not. (There's no one dumb enough to ride with me at this "pace" so...) I'm doing what *I* feel feels right at the time and that seems to be working for me.

The 400's are tougher on me than the 300's mainly because I get mentally bored around 275-325km and I can drift and lose focus during that period. Once I get over that, I'm okay. On the 300's by the time I'm bored, I'm already seeing the finish so it's easier.

By the way, I'm in my 60s, haven't lost an ounce of weight since January and my resting heart rate has stayed the same despite all this "cardio". Oh, and I ride a recumbent which means I get off the bike at the end of the ride and the only thing that is routinely sore now are my buttocks (none of this sore neck or back stuff for me).

Obviously, YMMV.