Duathlon pacing
Run, bike, run: three legs, two transitions and a single finish time. PeakPacing plans them together, not one at a time.
Duathlon is one of the race types in the PeakPacing planner, with its three legs in the run → bike → run order. Each leg has its own GPX track: the two runs get a target pace corrected segment by segment for gradient, the bike leg gets target watts computed with a physics model that accounts for gradient, drag area, rolling resistance, air density at the altitude of the course, and the wind component taken from the GPS bearing of every piece of road.
The two transitions are entered in minutes and land in the finish time along with the three legs, and the fuelling plan — fluid, sodium and carbohydrate per hour — is computed over the whole race duration, transitions included. The plan can then be rehearsed on a smart trainer in ERG mode before race day.
Why a duathlon is not a triathlon minus the swim
In a triathlon the bike leg comes after a swim, which costs the legs little. In a duathlon it comes after a run, and before another one: the watts you spend on the bike are a decision you pay for, or bank, in the final leg. That is why planning the three legs separately, with three different tools, does not help — what you need is a single finish time that immediately shows what raising or lowering one of the three intensities does to it.
The best-known pacing tools grew around the bike leg of a triathlon. PeakPacing treats duathlon as a first-class race, with its three legs and its two transitions inside the same plan.
The two run legs
Target pace starts from the athlete's run threshold pace and an adjustable intensity factor — the default for the run is 88% of threshold. From there every kilometre is corrected for the real gradient of the road, with an uphill penalty larger than the downhill credit. The correction is applied piece of road by piece of road, not on the average gradient of the kilometre, because a kilometre made of 500 m at +8% and 500 m at -8% does not cost what a flat kilometre costs.
The two runs share the same intensity factor: it can be lowered for a more conservative plan on both, but the two runs cannot be set apart from each other. What does differ between them is the course, and therefore the elevation profile the pace is corrected against.
The bike leg
Target watts start from FTP times an adjustable intensity factor — the default for the bike is 75% of FTP — and from there the engine computes the speed and the time of every segment by solving the power-speed equation on each piece of road in the GPX track. What goes into it:
- the gradient of the piece of road, taken from the GPX points rather than from the average of the kilometre;
- drag area (CdA), with two presets — TT/aero position and road position — because between the two there are minutes, not seconds;
- rolling resistance (Crr) and drivetrain loss;
- air density at the altitude of the course and at the forecast temperature: a leg at 1,800 m meets roughly 19% less aerodynamic resistance than one at sea level;
- the wind component, computed by comparing the forecast wind direction with the GPS bearing of each piece of road, so out and back along the same straight get different times;
- a descent model, because nobody holds race watts at 80 km/h.
The transitions
T1 and T2 are entered in minutes and added to the three legs in the finish time. They are not an estimate hidden inside the plan: they are a number the athlete sets and can change, because a sprint duathlon transition and a long-course one with a shoe change are not the same thing.
The fuelling plan
Alongside the power and pace plan comes the fuelling plan: fluid, sodium and carbohydrate per hour. Fluid and sodium rise with the forecast temperature and humidity; carbohydrate sits at 60 g/h on shorter races and goes to 90 g/h beyond two and a half hours of estimated duration, with the option to force your own figure. The duration the calculation runs on is the whole race, transitions included.
Rehearsing it first
A duathlon plan is judged on one question: are those watts, sandwiched between two runs, sustainable? PeakPacing answers it by letting you ride them on a smart trainer in ERG mode, where resistance holds the target for you. What a rehearsal involves, and what it tells you, is covered on the race rehearsal page.
What you need
- The GPX track of each of the three legs (or a course already saved for that race).
- Your thresholds: FTP for the bike and threshold pace for the run, entered by hand or imported from Intervals.icu.
- A Google account to sign in.
- To rehearse the plan: a Bluetooth FTMS smart trainer and a browser with Web Bluetooth (Chrome, Edge or Opera on desktop and Android), or the native iOS/Android build.
Frequently asked questions about duathlon pacing
Does PeakPacing plan duathlons?
Yes. Duathlon is one of the race types in the PeakPacing planner, with the three legs in the run, bike, run order. Each leg has its own GPX track and its own plan: target pace corrected for gradient on the runs, target watts computed with a physics model on the bike leg.
How is the pace of the two runs in a duathlon calculated?
Target pace starts from the athlete's run threshold pace times an adjustable intensity factor, 88% of threshold by default, and is then corrected for the real gradient of every piece of road in the GPX track, with an uphill penalty larger than the downhill credit. The two runs share the same intensity factor.
How are the watts for the bike leg of a duathlon calculated?
Target watts start from FTP times an adjustable intensity factor, 75% of FTP by default. The time of each segment is then computed by solving the power-speed equation on every piece of the GPX track, accounting for gradient, drag area (CdA), rolling resistance, drivetrain loss, air density at the altitude of the course, and the wind component taken from the GPS bearing of that piece of road.
Are the T1 and T2 transitions included in the finish time?
Yes. The two transitions of a duathlon are entered in minutes and added to the three legs in the estimated finish time. They are a value the athlete sets, not an estimate hidden inside the plan.
Does the fuelling plan account for all three legs?
Yes. Fluid, sodium and carbohydrate per hour are computed over the whole race duration, transitions included. Fluid and sodium rise with the forecast temperature and humidity; carbohydrate sits at 60 g/h on shorter races and goes to 90 g/h beyond two and a half hours of estimated duration.