Ask most people with AS how many flares they had last year and the answer is a shrug. Ask how long the last one lasted and the answer is "a while". Flares are vivid at the time and blurry afterwards, which is why recording them as they happen is so useful.
What counts as a flare
There is no single agreed definition that every clinic uses, and for a personal record you do not need one. The NHS describes AS symptoms as coming and going, with periods where they get worse (NHS); for your own diary, a flare is a stretch that is clearly worse than your usual baseline and lasts more than a day or two. The point of the record is to be consistent with yourself, so decide what "clearly worse" means for you and stick to it.
What to record
At the start of a flare
- The date it started — or your best estimate, marked as an estimate.
- What is worse: stiffness, spinal pain, another joint, fatigue, something else.
- A quick severity: your usual 0–10 for pain and stiffness, so the flare sits on the same scale as ordinary days.
- Anything you can think of from the preceding few days — without deciding it was the cause.
During the flare
- Keep the daily check-in going. The whole value of the flare record is seeing it against the ordinary days on either side.
- Note what you changed: training scaled down or stopped, extra rest, any medication taken as agreed with your team.
- Note sleep. Poor sleep and flares often sit together, and it is worth knowing which came first in your own record.
When it settles
- The date you would call it over.
- One line on what the recovery looked like: gradual, sudden, back to baseline or not quite.
Reading a year of flares
Once you have several flares recorded, a few questions become answerable that were guesswork before:
- How many, and how long on average? "Four flares, typically ten days" is information a rheumatologist can use; "quite a few" is not.
- Is the frequency or duration changing over time?
- What was true in the week before each one? Look at sleep, training load, stress and medication timing across all of them, not just the most recent.
- How quickly did you return to baseline, and did you fully return?
Be cautious with the third question. If poor sleep preceded three of four flares, that is an association in your own record and worth mentioning at your next review. It does not mean poor sleep causes your flares, and it does not mean better sleep will prevent them. HAVYT’s pattern detection is framed the same way — as something worth paying attention to, never as a cause or a prediction.
Exercise and flares
What to do about training during a flare is a question for you and your physiotherapist or rheumatology team; NASS’s guidance is that there are good and bad days where you can do a bit more or need to do a little less, and that many people prefer to avoid high-impact sport during a flare (NASS, Safely exercising). The exercise during an AS flare guide covers what that can look like in practice, and how to record it so the flare and the training decisions sit side by side.