You don't get fitter during a run. You get fitter afterwards, asleep.
This is the part that is hardest to believe when you are enjoying running: the run is the stimulus, not the improvement. The improvement is what your body builds in response, and it builds it while you are doing nothing.
Skip the doing nothing and you get the damage without the repair.
Sleep is the big one
There is no supplement, stretch or gadget that comes close. Most of the repair work happens during deep sleep. If you are choosing between an extra forty minutes of running and an extra forty minutes in bed, in most weeks the bed wins.
This is worth saying out loud in a club whose main run starts at ten at night. If getting home at half past eleven wired and buzzing costs you an hour of sleep twice a week, that is a real cost. Some of us are better off on Thursday mornings, and there is no prize for the night run.
Rest days
At least one a week, doing nothing at all. Complete rest — not a recovery run, not “just a few kilometres”.
If you are new, two are better than one. Running four days a week consistently for a year will beat running six days a week for two months and then stopping, which is what usually happens.
Down weeks
Every third or fourth week, cut the distance by about a quarter. Full detail in adding distance. This is the same idea on a longer timescale.
When your body is telling you
Take an unplanned rest day if two or more of these show up together:
- Resting heart rate several beats higher than usual for a few days
- Legs still heavy three days after a hard session
- Sleeping badly despite being tired
- Losing interest in running you normally look forward to
- Getting every cold going round
None of these is a moral failing and none of them is fixed by trying harder.