The best part is that you won't have to go outside in the cold, rain, or wind. Instead, you can stay warm and snug in your living room.
Really? That's a good thing?
First, I disagree with the basic premise that this kind of training is sufficient for the type of riding that I do. I am an endurance cyclist. which means that I ride stupid long distance. Now, an hour of hard intervals and tempo work on a trainer may help me build more muscle in my legs and give me a little more spring on a county-line sprint, but if I count on that kind of saddle time to prepare me for a 200K in late February I will be sorely -- and I do mean sorely -- disappointed.
When I first got interested in ultra-cycling, Bill Glass (who knows more about randonneuring than just about anyone) told me that the key to training was to start doing at least one day of century length of greater mileage, every week, beginning in January. I laughed. I really thought that he was kidding. You don't do centuries in January, for crying out loud! You build up to that distance so that you can maybe do one in mid-April, when the weather gets nice.
Nope, Bill said, January. Otherwise, you won't have the miles in your legs for the April 400Ks, and the May 600Ks.
I didn't follow that advice that year. In April, I survived the 400K ... but it was close. In May, I DNF'd on the 600K after 250 miles.
Now, one option is the "indoor century," where you spend at least five hours on the trainer. There may be times this winter -- like when the roads are frozen all weekend -- when I am forced to do this. It will require one fan, 10 towels, three good movies, two ounces of Lantiseptic, and most of my sanity. Since our trainer is kind of noisy (imagine an annoying whirring buzz at D# below middle C -- basically, the sound that a huge dentist's drill would make if it was boring out a cavity in Godzilla's mouth, and Godzilla's novocain was wearing off -- that permeates the entire house), it will probably also require that RandoGirl be out for the day.
Which brings me to the other problem with indoor training: It's not outdoors.
Sure, the air can be so cold that it hurts your lungs. Yes, the wind can beat you to death. Of course, the spray can form ice on your shoes and turn your toes into little cold lumps of pain. Meanwhile, salt seeps into your bottom bracket and chews up the last vestiges of grease, then proceeds to grind the ball bearings into dodecahedrons of decay.
But you're moving out there. You're going around corners -- even if you do slip on icy patches and find that yellow lines can be really slick. But you learn just how slick they are, and how fast you can go over that patch without having the bike slide out from under you, or how to recover when it starts to slide, or how to crash in ways that do minimal damage to you and your bike.
You climb long hills, and the cold air hurts as you suck it down, but the burn in your legs spreads outward to thaw -- however briefly -- the little frozen parts of your wool-encased body. Then you tuck in to zip down the far side, probably going a little more cautiously in the curves but still exercising that part of your brain that picks out the right line on a 40+ mph descent.
You learn how to ride in slush and stay drier. You try different mixtures of clothing layers, figuring out how to keep just warm enough without overheating, and how to avoid carrying five pounds of dead-weight clothing that you never use. You experiment with wheels, tires, tubes, fenders, bags, lights, pedals, shoes, drive trains, and lubricants, so you know what's going to work for you if something goes wrong or the weather turns weird on a 1200K that summer.
On the trainer, you work your legs. On the bike -- on the road -- you work legs, back, shoulders, hips ... everything that you're going to need during the season. Most importantly, unlike the mind-numbing trainer, you work your brain.
Now, to be fair, trainer workouts are better than nothing, and they're great for doing the kind of prescribed workouts that will make you fast. If I can't get out to the track on Tuesday nights for tempos or intervals, I will probably lug the Bianchi upstairs and do that kind of workout there. There are also a few of us here that regularly get together Thursday nights in Bill Glass's barn for a "spin-in movie." You have to bring your own trainer/rollers, and somebody brings a different DVD every week, so it's basically a social work-out. It beats sitting solo on the vomitron.
But I will not depend on these to get ready for the spring brevets. The only thing that will do that is lots and lots of road time.