Why at just under 3 hours you're racing near threshold almost the whole way — and why the run of all things decides your finish time.
How hard are you actually allowed to push in an Olympic distance race — is it more like a relaxed community triathlon or a hard time trial with breaks? The honest answer: much closer to the hard time trial. An observational study on well-trained age-group athletes measured a heart rate of around 90 percent of maximum across all three legs — swim 89.8%, bike 91.1%, run 90.7%. That's not an easy base pace, that's controlled sustained effort.
Even more revealing is how that load is distributed. In the swim, athletes spent 91.9% of the time in the highest intensity zone — barely any breathing room. On the bike it was 78.8% in the highest zone and 18.4% in the middle zone. The run showed a different picture: 56.0% in the highest zone but 39.9% in the middle zone — clearly more variability. So the run isn't a constant redline, it's a continuous negotiation between holding pace and losing it.
And that's exactly where the key finding sits: athletes with a finish time around 2:12 hours ran at markedly higher intensity — 94.0% of maximum heart rate — than slower finishers at 87.0%. Swim and bike barely distinguished the fast athletes from the slow ones. The run is the leg that ultimately decides your finish time, because it reveals who saved reserves for the final kilometers.
Train Smart. Play Hard. — for pacing that means: the fastest bike doesn't win the race, the strongest run afterward does. Treat swim and bike as preparation for your real opportunity.
At around 90% of zone time in the highest bracket, swimming at Olympic distance is nearly constant hard effort. Still keep your technique clean — spending effort without technique control costs more time than the pace ever gains.
78.8% of bike time in the highest zone means intensity is high here too — but the 18.4% in the middle zone shows that successful athletes deliberately build in phases with slightly less pressure. Use those phases actively to recover before the run.
The biggest difference between fast and slow athletes lies in run intensity — 94.0% versus 87.0% of maximum heart rate. Spend too much on the bike and you'll have no reserves left for that higher run intensity.
39.9% of run time in the middle rather than the highest zone shows: even strong athletes vary their running pace instead of holding it stubbornly at maximum. Small, deliberate pace shifts aren't a sign of weakness.
Practice swimming and biking near threshold in separate sessions, and practice running deliberately after a bike session to realistically simulate the interaction — more on that in the brick guide in this series.
Racing at nearly 90% of maximum heart rate almost continuously is a serious cardiovascular load. If you have pre-existing conditions or are new to training in this intensity range, build up your pacing gradually in training rather than testing it for the first time in a race.
Watch for warning signs during the race like dizziness, irregular heartbeat, or unusual shortness of breath — these are signals to reduce pace immediately, regardless of your planned pacing.
Set yourself a concrete zone number for the run instead of a pure pace target — for example "hold heart rate between 88 and 92% of maximum." That's more robust against wind, heat or fatigue than a rigid kilometer time, which rarely holds exactly under real conditions.
A trick from coaching practice: simulate the exact pacing pattern — hard, hard, fluctuating — as a "mini-race" during a training week, with real swimming, biking and running back to back. Having lived through the pattern once in your body changes how you call on it in the real race.
Very hard: well-trained athletes sit at around 90% of maximum heart rate across all three legs. That's much closer to a hard time trial than a relaxed base pace.
The run. Faster athletes ran at 94.0% of maximum heart rate, slower ones at 87.0% — swim and bike barely differed between the groups. Keeping reserves on the bike pays off on the run.
No, even though 78.8% of bike time falls in the highest intensity zone, successful athletes show deliberate phases with slightly less pressure. The goal is arriving with reserves for the decisive run.
Yes. Even strong athletes spend around 40% of their run time in a middle rather than the highest intensity zone. Small, deliberate pace changes are part of smart pacing, not a sign of weakness.
Olympic Distance: Brick Training for Race Intensity