I won’t overtrain if I do Zone 2 riding outdoor next to a high volume training plan? Or are the training plans designed that you do no additional outdoor riding?
See here for a discussion of a similar question.
Remember: you set the rules! These are not custom workouts designed by a coach who knows how you’re feeling today and helps you adjust the rides to get outdoors when you need the refreshment of open space. You can substitute a recovery/gentle endurance outdoor ride for its equivalent indoors. Or if you personally can handle the volume, you can add it to your program. Listen to your body. If you are feeling too fatigued, skip a workout or drop intensity. See here for an article about listening to your body.
I’m following All Purpose at the moment, last weekend there were 2 zone rides (saturday and sunday) I simply replaced those without side rides
But you should never just blindly follow a training plan, it doesn’t take into account “life”, your ability to recover and multiple other factors, there’s a very good article in the knowledge section about skipping a workout
But I also believe it goes the other way as well, if the plan has 3 hour zone 2, you feel good and fresh at the end of 3 hours, do more, if you think you can add zone 2 work in and it won’t be at the expense of the next workout, add it in (I do)
If you want more flexibility to add in extra Z2 rides (or even harder rides) then it might be worth considering moving from a high to mid or even low volume plan. Then you effectively get to add in your extra “freeride” volume alongside a lower volume structured plan rather than adding even more volume to a high-volume plan.
But really it depends on both the amount of time you have available and also what sustainable volume you can actually handle. Both those parameters are very individual.