Ironman WA is 13 weeks out. Here’s when you’ll actually get injured.

Triathletes in wetsuits and coloured caps swimming freestyle in open water

Ironman Western Australia is on 6 December at Busselton, with the 70.3 run on the same day. That’s 93 days from this weekend — just over 13 weeks. If you’re racing either distance, your build starts about now.

Busselton has a reputation as the place Australians go for a personal best — the bike and run courses are among the flattest on the global Ironman circuit, and people travel for exactly that reason. So the training gets taken seriously. Spreadsheets come out. Coaches get hired. And almost everyone plans around the same assumption: that the dangerous part of the build is the big weeks in late October and November, when the long ride hits five hours and the long run creeps past two — or half that, if you’re on the 70.3.

That assumption is backwards. The most likely time for this build to fall apart is the next four weeks.

What the largest running study ever run actually found

Until recently, the standard model of overuse injury was gradual accumulation. You load the tissue a bit too much, week after week, until it gives. Every training-load metric on your watch is built on that model — acute-to-chronic workload ratios, weekly ramp rates, the little coloured bar telling you whether you’re “productive” or “overreaching.”

The Garmin-RUNSAFE study went looking for evidence that this model works. It followed 5,205 runners across 87 countries for 18 months and recorded 588,071 running sessions. It’s the largest study of its kind ever run.

It didn’t find what everyone expected. The weekly and fortnightly load metrics — the ones your watch uses — showed no clear relationship with injury. What did predict injury was much simpler and much more specific: how far a single run went compared with your longest run of the previous 30 days.

The numbers are stark. Runners who went 10–30% further in one session than their longest run of the past month carried roughly 64% higher injury risk. Push further past that and the risk climbs steeply from there.

The researchers’ conclusion was that most running overuse injuries don’t creep up on you over a training block. They happen in one session — and that session is usually identifiable in advance.

Why that puts the risk at the front of your build, not the back

Here’s the part that matters for anyone starting a Busselton build this month.

The metric that predicts injury is a relative one. Not how far you ran, but how far you ran compared with what you’d recently done. And relative jumps are always biggest at the start of a build, because that’s when the baseline is lowest.

Run the numbers on a fairly typical case. Say you’ve come off a quiet winter and your longest run in the past month is 10km. Week three of your new program calls for 14km, because 14km is nothing — you ran 30km races last summer. Except in the terms that actually predict injury, that’s a 40% single-session jump, and it lands you squarely in the risk band the study describes.

Now fast-forward to November. Your longest run in the past month is 28km. The program calls for 30km. Everyone treats that as the scary week. It’s a 7% jump. Mechanically, it’s one of the safest sessions in the entire block.

The peak weeks feel harder. That’s not the same as being riskier. By the time you get there, your baseline has caught up — assuming you got there at all.

Triathlon compounds the problem three ways

If you were only running, the above would be the whole story. You’re not.

Lower limb injuries dominate triathlon — around three-quarters of them — and the running leg is consistently associated with the highest injury rates of the three disciplines. Most triathlon injuries also happen in training rather than racing, which is unsurprising given where the hours are, but worth stating plainly: the race is not the risk. The build is.

Three specific things go wrong at this point in the season.

Everyone ramps all three sports at once. The program starts, and swim, bike and run volume all step up in the same week. Each individual jump might look modest. The combined jump in total load is not, and your tendons don’t file the stress by discipline.

The swim gets the worst of it. Going from occasional off-season swims to three or four sessions a week is, proportionally, the single largest jump most triathletes make. Shoulders that were fine in August start complaining in late September, and the reflex is to blame technique. Sometimes it is technique. More often it’s arithmetic.

Old injuries get deferred. The strongest single predictor of a running injury is having had one before. The niggle you’ve been managing since autumn is not neutral background — it’s the most useful piece of information you have about what’s likely to end this build. September is a cheap month to deal with it. November is not.

What to actually do about it

Concrete, and none of it requires a coaching change.

Cap your single-session jumps against a 30-day lookback, not a weekly plan. Before any long run or long ride, ask what your longest of the past month was. Keep the increase under about 10% where you can. This one habit addresses the strongest predictor in the data and costs nothing.

Stagger your ramps. Increase one discipline meaningfully in any given week, not all three. If the run steps up, hold the bike and swim steady.

Build the swim by frequency before duration. Four short swims beats two long ones for shoulder tolerance while you’re re-establishing the habit.

Deal with the existing niggle in the next fortnight. Not because it’s dramatic now, but because the version of it that shows up in week ten is a much worse problem with far fewer options.

Get the bike position checked before the volume arrives, not after. Positions that were fine for 90-minute winter rides frequently aren’t fine for four-hour ones. A hip angle that’s marginally too closed is invisible at low volume and unmissable at high volume — usually as knee pain, sometimes as low back pain. Fixing it in September is a fit adjustment; fixing it in November is a fit adjustment plus six weeks of rehab.

When to get it looked at

The rule we’d give any athlete in a time-boxed build: if something has been there for more than about ten days and isn’t trending down, it’s not settling on its own, and you have a fixed race date that isn’t moving.

The honest reason to come in early isn’t that early treatment is magic. It’s that early treatment leaves the options open. In September you can usually modify around a problem and keep training. In November, the modification often becomes the training.

On Form Physiotherapy treats triathletes and endurance athletes at our Rockingham and Yangebup clinics. If you’re building towards Busselton and something isn’t right, book an assessment online or call us on 08 6385 8029. We also offer bike fitting — worth doing before the long rides start rather than after.

Sources

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