Dr.NateNeph said:

Training does two things here and only one of them is on the scale.

Gym confidence after training weight loss: walked into a gym for the first time in 8 years yesterday. Was terrified. But you know what? Nobody stared. Nobody judged. Everyone was focused on their own workout.

Started with 20 minutes on the treadmill and some machine-based resistance exercises. Nothing fancy. But I DID IT. And I'll go back tomorrow.

To anyone too intimidated to start: the hardest rep is walking through the door. Everything after that is just movement. 💪

One thing that is still open after hyun_seoul’s answer:

How would you tell the difference between that and the alternative explanation?

Dr.PeteFamMed said:

Gym confidence after training weight loss: walked into a gym for the first time in 8 years yesterday.

There is a second half to this that has not been said yet. If two explanations both fit, the useful question is which one predicts something the other does not. That is answerable; arguing about which sounds more plausible is not.

Happy to go further on any of that.

Closing the loop on my own question.

Closing the loop. The answer turned out to depend on the detail I had left out of the opening post, which is a lesson about how to ask rather than about the subject.

sarah_TO said:

If two explanations both fit, the useful question is which one predicts something the other does not.

Agreed, and the size of the effect matters as much as its existence. Something real and small gets treated here as though it were real and decisive.