Using heart rate zones in ultramarathon training

Ultra distance is decided in the slow ones. The long training runs, the easy weekday sessions, the hours spent on Yarra Ranges bushland while a watch quietly records a steady 138 beats per minute. Heart rate zones give those quiet miles a language. They turn subjective effort into something measurable, so the easy days stay easy and the hard days actually push the right system.

For trail runners targeting races such as Ultra-Trail Australia in the Blue Mountains or the Six Foot Track south of Sydney, the value of zone-based training is less about chasing numbers and more about managing fatigue across weeks of high volume. A 100-kilometre effort is not won in the final climb alone. It is built from hundreds of low-intensity sessions that respect the aerobic system, sprinkled with shorter, sharper blocks that lift the ceiling.

Australia's endurance scene has matured quickly. Local coaches in Melbourne, Brisbane and Perth now prescribe zone work with the same rigour seen in cycling, and the gear market has caught up. Chest straps and optical sensors pair reliably with watches over multi-hour runs. What used to feel like laboratory work has become a regular feature of any sensible 50k to 5km-plus build.

This piece looks at how to apply heart rate zones through a full training block, from base-building months to the taper week. The aim is practical: enough theory to trust the method, enough real-world framing to use it on the kind of rocky, root-strewn singletrack that defines Australian ultras.

Understanding the five-zone model

Most coaches use a five-zone framework borrowed from sport science. Zone 1 is true recovery, zone 2 is conversational aerobic work, zone 3 is the moderate band that feels productive but often is not, zone 4 sits just below threshold, and zone 5 is short, hard interval effort. The numbers depend on a runner's maximum heart rate and, more usefully, on lactate threshold testing.

For ultras, the zones that matter most are 1, 2 and 4. Zone 2 builds mitochondrial density and trains fat oxidation, both of which delay the bonk on a long climb. Zone 4 raises lactate threshold so that climbing Mount Portal in the Blue Mountains at kilometre 60 still feels like a tempo rather than a sprint. Zone 1 protects recovery on double-up days, particularly when the Australian summer turns training trails into furnaces.

The mistake many runners make is treating zone 3 as the default. It is comfortable enough to talk through, hard enough to feel like training, and slow enough to skip the real adaptations. Replacing some of those sessions with genuine zone 2 or genuine threshold work produces stronger race outcomes, even when weekly volume stays the same.

Building a true aerobic base

A solid base block runs roughly ten to sixteen weeks. Most of it sits in zone 2, capped with one short zone 4 session per week and a long run that drifts upward in duration. The point is not to crush the long run. The point is to finish it within a sensible heart rate ceiling, even when legs grow heavy.

In practical terms, a Sydney runner logging an easy Sunday loop through the Lane Cove bushland should aim for a ceiling around 140 to 150 beats per minute, depending on threshold. If the trail is technical and the watch keeps bouncing off lock, effort feel is the fallback. A nose-breathing pace, where conversation remains easy, is usually a fair proxy for zone 2.

Base work has a built-in cardiac drift test. Run the same loop at the same pace a few weeks apart. If heart rate climbs higher for the same output, fitness is improving. If heart rate rises sharply without an obvious cause such as heat or poor sleep, the body is asking for more recovery, not more mileage.

Threshold sessions that transfer to the trail

Lactate threshold sits a few beats below maximum heart rate and roughly matches the pace a runner can hold for about an hour. For ultras, the goal is not to raise it dramatically but to keep it stable under fatigue. Sessions such as four by ten minutes at threshold, with float recoveries, do this well.

A simple threshold session on a hilly route near Brisbane's Mt Coot-tha might look like four reps up the summit road, each taking around twelve minutes, with a slow jog back down as recovery. Heart rate should rise into the zone 4 band by the end of each rep. If it climbs into zone 5, the effort is too hard. If it never leaves zone 3, the session is too easy.

These sessions should sit no more than once or twice per week, ideally after an easy day, with another easy day following. During the Australian summer, the same session moves indoors or to shaded trails before sunrise, both for heat management and because elevated heart rate from warmth can blur the actual training signal.

Race day: pacing by feel and heart rate

Race day rarely goes to plan. Heat rises, gels under-fuel, and an unexpected climb at kilometre 45 reshapes the day. Heart rate gives runners a flexible anchor in that chaos. Start near the top of zone 2, drift into zone 3 on climbs, and bring it back to zone 2 on descents and flats. Avoid sustained zone 4 until the final stretch, when whatever remains in the legs is going to the cause anyway.

Aid stations become the heart-rate checkpoint. Pause for thirty seconds, check the watch, drink, eat, reset. Ultra-Trail Australia and several other Australian events now mandate GPS tracking, which broadcasts heart rate to followers at home. That transparency helps runners stick to a plan, because the temptation to chase a competitor up the first big climb is harder to give in to when the data is right there on the strap.

The late-race protocol matters. Cardiac drift pushes heart rate higher for the same pace in the back half. Compensate by slowing down rather than pushing harder. Cooler mornings in Tasmania's Overland Track or Adelaide's trails make drift less severe. Hot stretches along the Great North Walk corridors in New South Wales turn drift into a constant companion.

Adapting to Australian conditions

Local realities shape how zones get used. Summer temperatures in Melbourne, Adelaide and inland New South Wales regularly push past thirty-five degrees, inflating heart rate by ten to twenty beats at any given pace. Adjust the ceiling for the season rather than abandoning the framework. Train in the pre-dawn window before the city's heat kicks in, and accept that some sessions will run hotter than the watch's pre-set bands suggest.

Bushfire smoke is another reality. On poor air-quality days, swap road intervals for an indoor treadmill or a pool run, both of which spare the lungs without abandoning the training block. Runners in affected postcodes should check state health guidance before heading out.

Finally, factor in the long Australian working week. Sydney and Melbourne commutes chew through training windows, so weekday zone 2 often happens in the dark before sunrise or on a treadmill at the gym. The watch still records the data, the adaptations still happen, and the trail will be there on the weekend. The zones do not care about the scenery.

A simple starting point: spend the next four weeks running every easy session at a true zone 2, defined as a pace where full sentences can be spoken out loud. Log heart rate, perceived exertion and the route, then re-run the same loop four weeks later at the same pace. A lower heart rate for the same output is the clearest signal that the aerobic engine is growing, and the trail work to come will reward the patience.