The targets
For the bike leg of a 70.3, aim for an intensity factor between 0.75 and 0.80, ridden at a variability index of 1.05 or lower. Those are the numbers The Debrief judges a half-distance ride against, and they are narrower than most athletes expect.
Above 0.82 the ride is an overbike, and the cost is collected on the run rather than the bike. Below 0.72 you have left time on the course that your run was never going to give back.
The band is narrow for a reason. Between 0.72 and 0.82 sits roughly ten percent of your sustainable power, and that is the whole difference between a run you execute and a run you survive.
Why your FTP is the weakest number in this calculation
Every intensity factor is a fraction with your FTP on the bottom. If that figure is stale, estimated from a ramp test that flattered you, or simply never tested properly, then every target derived from it is wrong by exactly the same margin — and you will ride to it with complete confidence.
This is the single most common reason a carefully planned power target still produces a ruined run. The athlete did not misjudge the percentage. They misjudged the number the percentage was a percentage of.
So the more reliable anchor is power you have actually held in training or in a previous race for something like the duration you are about to ride. If you have a long hard session at 230 W, plan from 230 W. A 0.78 IF against a tested, recent FTP is a target; a 0.78 IF against a number from last winter is a guess wearing a decimal point.
The opener is the decision that matters
The Debrief checks the first 30 minutes against the ride's overall normalised power, and flags an opener more than 5% hot. That check exists because the opening half hour is where almost every bad half-distance bike leg is decided.
The reasons are mechanical. You come out of the swim with your heart rate already high, so effort feels cheaper than it is. The road is crowded and everyone around you is riding above their plan. You feel good, because at twenty minutes into a five-hour day you are supposed to. None of that is information about what you can sustain for 90 km.
A ride that opens 5% hot does not usually look dramatic in the file. It looks like a slightly elevated first segment followed by a slow, grinding concession for the next three hours — and then a run that starts on pace and decays from about the fifth kilometre.
Smoothness, and what your course is allowed to cost you
Variability index is normalised power divided by average power: how much harder the ride was than its average suggests. At or under 1.05 is a well-ridden bike. Between 1.05 and 1.08 the surging is starting to cost you. Above that, the pacing itself is a problem independent of how hard you went.
But VI has to be read against the road. The Debrief classifies 122 race courses into three profiles by elevation gain per kilometre: flat up to 8 m/km, rolling up to 15 m/km, and hilly beyond that. Of those, 42 are flat, 44 rolling and 36 hilly — so the odds are better than even that your race is not the flat time-trial a 1.02 VI assumes.
- On a flat course — Warsaw, Venice-Jesolo, Florida, Copenhagen — a high VI is self-inflicted. There is nothing out there forcing you to surge.
- On a rolling course, some variability is the terrain talking. The thing to control is the descents: coasting at zero watts and then over-pushing the next rise is what moves VI, not the climbs themselves.
- On a hilly course — Nice, Lanzarote, Mont-Tremblant, Kraichgau — judge the climbs by their ceiling rather than the ride by its average. A VI of 1.08 at Lanzarote is a different sentence from a VI of 1.08 at Florida.
Heart rate is the check on everything above
Power tells you what you did; heart rate tells you what it cost. Early in the ride the two move together. When heart rate drifts upward while power stays flat or falls, you are paying more for the same output — drift over 5% is the point at which that stops being noise.
This matters mid-race, not just afterwards. If you are an hour in, on target power, and your heart rate is already climbing away from it, the target was wrong for today. Heat, a bad night, an illness you have not noticed yet: the plan was built last week and your body is reporting from this morning. Riding to a number that your heart rate is actively disputing is how a good plan produces a bad race.
What this looks like as a plan
- Set the target from power you have genuinely sustained, not from a stored FTP you have not retested.
- Ride the first 30 minutes under target. Not at it — under it.
- Hold 0.75-0.80 IF through the middle, letting terrain move the power and not your mood.
- Keep VI at or under 1.05 on flat roads; on hills, cap the climbs instead of chasing the average.
- If heart-rate drift passes 5% with hours to go, lower the target rather than defend it.
Then check whether you actually did it
A plan is a hypothesis, and the race file is the result. Upload it and The Debrief reads the bike and the run together: what you held against what you have demonstrably sustained, where the opener sat, how smooth it was against that course, and whether the run decayed in the pattern that follows a bike that was too hard. Here is a full sample on a real race file.