I get that not everyone will agree with me here, but I’ve found that I just can’t do structured training outside. Some of this is based on where I live, but most of it comes down to other factors that introduce variability. Which is bad because it makes the structure, less structured, and much of the value is in the structure. While it’s possible that what limits me doesn’t limit you, but even if that is the case, I can’t see how what works for me wouldn’t work for everyone as long as they have the right equipment (i.e. you need a smart trainer, proper cooling, space, etc) and mindset (Zwift helps a lot here).

The most important thing about training is the structure, not just the way the workout is laid out, but that it’s actually followed, and is completed on the schedule. Following this structure is so much easier inside, on a trainer, than it is outside for a lot reasons (we’ll get to these below). Most of this flows from the fact that you really only have two choices when training inside: do the watts in the prescribed pattern, or quit. But, outside, there are a million excuses, many very legit, why it’s only too easy to veer off the plan…

1. Locale: I live in the suburbs of Chicago. Simply put, there are no roads within a reasonable distance from here where I can ride flat-out for any trainable length of time. Between the stop signs, stop lights, cars, pedestrians, pot holes, and random other things. It is impossible to have a structured plan, and follow that structure. Just too many variables in the mix to get it done with anywhere near the efficiency and effectiveness as on the trainer.
2. Pacing: I have a hard time with pacing, but not in the way that most people do. I find it incredibly difficult to “empty the tank” outside. Some of this may be my background in team endurance sports (soccer), where pacing for the long haul is so essential that it becomes instinctual. Inside, I don’t have this problem because the trainer doesn’t ask me. If the workout requires 12x 30 seconds @1.3xFTP / 15 seconds @0.5FTP intervals, break, repeat, I do the work. It’s either that, or I get off the bike (hasn’t happened yet, touch wood). Even if I lived somewhere I could do that outside, it would never get done because, well it hurts, but more importantly my brain steps in and tells me that I need to be able to get home after, walk after, finish the day after.
3. Rabbits: I find rabbits (riders who need passing) to be incredibly motivating, and distracting. This is absolutely a will power thing on my part. More than one SST attempt has become a VO2 max interval session because I got passed… I am weak. So here again, is where the smart trainer workout makes it much easier to follow the structure. At least in Zwift, the rabbits can see that you’re in a structured workout, which means they should know that they aren’t really passing you. You’re just in the warm up, enforced break, or cool down sections of the plan. You’ll get back to CRUSHING IT in a few minutes. It’s easy to let that go. On a training platform with less social (e.g. Trainer Road & The Sufferfest), there aren’t rabbits.
4. Solo: I don’t mind riding by myself, especially long distance, but it’s more fun with other people (your friends can be rabbits too). This is the weakest point in the list, but it’s hard to get everyone to agree to do a VO2max interval session, and antisocial to do one without their agreement.
5. Environment: There are plenty of times of day, and year, where riding a bike outside isn’t safe or fun. There is never a time when can’t inside; unless the power goes out. Because of that, excuses are harder to come by when it’s training time. Rain, not a problem. Snow, not a problem, Dark, not a problem. There’s a theme here :).
6. Time efficiency: My trainer is in the basement. It takes significantly less logistical time around the workout to get there, get started, finish, and shower than doing the same thing outside. Unless you can start your workout on the driveway, I suspect the same thing is true for you. If rushed, I can fit an hour of hard inside training into 75 minutes, including the shower. It’s at least 90, if I go outside. Which if you’re trying to sneak the workout into lunch, can be the difference between doing it, and not.
7. Time economy: Physics on the trainer are different from physics in the real world, so it’s much, much harder to take those little “cheat” breaks on the trainer. Combine that with the lackluster implementation of momentum/freewheeling (I see this as a feature, not a bug), I can do more work in less time, even on a free ride.