Exercise does however explicitly require some zero days, a lesson I've learned the hard way. You need time to recover, and that involves doing nothing.

To my experience this is only true if you totally max yourself out when exercising. An alternative is to do light (ish) exercise every day. Makes getting totally ripped pretty much impossible, but it makes staying fit easy, because it's easy to build a habit around and it's easy to make fun.

I'd see it as covering for sick days, busier days etc.

Some people purposefully break their streaks and habits to make sure they give themselves mental room to have 0 days whenever needed.

(Ultimately it comes down to what's harder for you, to start or to stop. Some need strong boosters to start, others need reminders to stop)

A streak strikes me as a very different thing than a habit. Habits aren't hard to pick up after a break, streaks are. I have a hard time to figure out what it means for someone to "purposefully break a habit", except in the context of bad habits of course (eg a smoker trying to not smoke for a day). This is my whole point I guess, if you manage to make exercise a habit and not a streak (by making it fun, and feeling good, and having space for it in the daily calendar), then you can stop worrying about 0 days altogether and just do it every day except when you don't.

> by making it fun, and feeling good, and having space for it in the daily calendar

That's definitely the healthiest approach to it. I agree with you it won't matter if you stop for a while or not, as it was done for pleasure in the first place.

I disagree.

Imo this is mostly true of running and bodybuilding... where the average person is most likely to encounter "programming."

A "gotcha" with minimum dose is that you need to precisely define the goal.

"Minimum effective" to build muscle or cardio might not be sufficient to build "habits" or whatnot.

A short, daily warmup might be the minimum effective dose for habit building.

Physiologically, 20 minutes every 10th day training heavy deadlifting... will be effective.

But this will probably be below effective does for habit forming, and other psychological/behavioral changes.

Rest days are for mobility and stretching exercises.

You can certainly do that if you want, but lying on the sofa is quite viable as well.

The point I wanted to make was that if you go hard every day, that will be actively harmful to your fitness goals.

No one was suggesting to go hard every day. The suggestion was that "no zero days" is a good way to build an exercise habit.

The OP comment was pretty specific and explicit that it is not going hard every day, it is about doing some minimal something every day to maintain and reenforce the habit. You asserted that you “explicitly require some zero days” but that is not true. You can have no zero gym days by using your heavy lifting rest days to do mobility exercises and stretching.

Stretching in any relevant intensity actively impedes muscle recovery, you're just straining the muscle further while it's trying to recover.

If you're damaging the muscle while stretching… Okay, I'm gonna assume you're not letting any of you're stretches produce pain. You should feel tension, only, which should not be harmful.

In my experience and training, stretching every day is practical and effective. Skipping a day can cause noticeable tightening. Tension for the purpose of becoming more limber should be held for a minimum of 10 sec, but 30 sec. is a much better basic level. There should not be tremor or pain; either of those will be counter-productive and potentially result in injury.

What are you basing that on? Elite mobility coaches like Kelly Starter recommend daily - even hourly -mobility and stretching workouts, with the goal of being constantly mobile.

With many types of skills putting in some time every day can be very beneficial.

Keep in mind though that with things like strength your body also needs recovery time (in fact your gains happen during recovery, not during the workout).