Coming back after time off

An injury, the flu, three weeks travelling, a whole winter. Everyone stops at some point, and almost everyone makes the same mistake coming back: resuming the plan at the week they left it.

How much you actually lose

Less than your head tells you. For the first ten days almost nothing measurable changes. After that it does start to fall: in two or three weeks aerobic capacity drops by around five to ten per cent, and much of that is blood volume, not muscle. That’s why the first thing you notice is your heart rate spiking at your usual pace.

The fitter you were, the faster it falls at first — there was more to lose — and the faster it comes back afterwards. Someone who’s only been running a short while loses less in absolute terms.

Why picking up where you left off injures you

Because heart and lungs come back faster than tendons and bone. Two weeks in you feel able to do what you did before, and you genuinely can: aerobically you’re there. What hasn’t returned yet is the tissue that absorbs the impact, and that runs on a slower calendar.

That mismatch — legs that can, tissue that can’t yet — is exactly the window in which returning runners get hurt.

How to come back

• Under a week off: carry on where you were.
• One to three weeks: step back one or two weeks in the plan.
• More than a month: go back to the walk-run phase even if it feels ridiculous. You’ll pass through it in three weeks instead of eight.
• If the break was an injury, start below what you can do, not at what you can do.

And a useful fact for next time: keeping two sessions a week, even short ones, preserves nearly all the adaptation. When you know a bad stretch is coming, don’t drop it entirely: drop to two.