Start at roughly half of what you think you can do, and use walk-run intervals for the first two to three weeks. Your heart and lungs come back within weeks; tendons and joints need longer, and that gap is where comeback injuries happen.

Aerobic fitness declines measurably within a few weeks of stopping, and your body has also lost some running-specific efficiency. The effort feels disproportionate because your expectations are still set to your old fitness.

Much less time than it took to build. Many returning runners feel close to their old easy pace within six to eight weeks of consistent, gentle sessions, as long as they don't restart at their old training load.

Start over from the beginning of the effort, not the beginning of your identity. Your technique and experience are still there; only the conditioning needs rebuilding.