How to Pace a 70.3 or Ironman Triathlon

One of the most common questions in long-course triathlon is how to pace a 70.3 or full-distance Ironman. While training and fitness establish what is possible, execution, particularly pacing and effort distribution, determines how well you perform relative to your potential.

Pacing is therefore foundational, yet often difficult to conceptualize in events that are both long and multi-disciplinary.

This article outlines key principles to help you dial in this critical aspect of racing.

First, Context Matters: Why These Targets Are Only a Starting Point

Before getting into specific guidance, a brief but important caveat: the pacing targets and effort ranges outlined here are evidence-informed, but necessarily generalized. Like training or fueling strategies, they provide a strong starting point, but require individual refinement based on your physiology and experience.

For those interested in the physiology behind this (and if not, feel free to skip ahead), the limitation lies in how we define fitness.

Metrics such as critical swim speed (CSS), functional threshold power (FTP), and threshold run pace are useful benchmarks, but they do not capture metabolic individuality. Two athletes with identical numbers can have different underlying physiological profiles, and therefore different capacities to sustain those outputs over time.

For example, two athletes with the same FTP may arrive there through different mechanisms. One may rely more heavily on anaerobic contribution, making that power less sustainable over long durations. Another may have a more aerobically developed “diesel engine,” supporting greater durability at the same output.

This distinction becomes even more relevant when considering durability – a concept increasingly studied by researchers such as Dr. Dan Plews – which reflects how physiological thresholds decline over prolonged efforts. In practical terms, an FTP of 200 watts at the start of an Ironman bike leg is unlikely to represent the same physiological cost late in a 180km ride. The external output may remain constant, but the internal load increases.

Despite these limitations, threshold-based estimates remain highly useful. For first-time athletes, they provide a critical anchor for pacing. For more experienced athletes, deviations from these guidelines can be informative, often pointing to underlying metabolic strengths or limiters. In those cases, working with a coach or pursuing lab testing can offer valuable insight into how to train and race more effectively. (Identifying limiters is not a drawback; it is a pathway to improvement!)

With this context in mind, the following sections outline general, evidence-informed pacing ranges that are broadly achievable across the 70.3 and Ironman distances. These are intentionally presented as ranges, reflecting the reality that athletes at the front of the field are racing a shorter, more intense version of the event than those focused on reaching the finish line – both of which represent meaningful performances in their own right.

Pacing the 70.3: Pushing Without Overreaching

A 70.3 is raced closer to threshold, with less margin for error but greater tolerance for sustained intensity. Athletes are typically operating in upper aerobic to sub-threshold zones, where small pacing errors can cascade quickly on the run.

Typical finish times range from under 5 hours to 8 hours or more, with intensity sitting largely in upper Zone 3 and, for some professionals, on the edge of threshold (Zone 4).

SWIM

• Pace Guidance: 1-3 seconds slower per 100m than CSS, 6-7.5/10 RPE
• Key Intent: Start controlled, not aggressive. The goal is to exit the water composed and physiologically settled, not chasing marginal gains at the cost of elevated heart rate and early fatigue.

BIKE

• Pace Guidance: 77-85% FTP, 4.5-7/10 RPE
• Key Intent: Ride steady and disciplined. Most pacing errors occur here – overbiking early can compound significantly on the run.

RUN

• Pace Guidance: 86-91% of threshold run pace, start moderate and build to max RPE by the finish line
• Key Intent: Build into the effort, and get your legs used to the feel of the transition through regular brick work. If the run deteriorates early, the issue almost always traces back to the bike.

Pacing the Ironman: Where Restraint (Often) Wins the Race

Successful Ironman pacing, especially in age-group racing, tends to be defined by restraint. The event sits firmly in the aerobic domain, where durability, fueling, and discipline matter more than absolute output. The goal is not to maximize early performance, but to preserve the ability to run.

For most athletes, this means operating at the upper end of Zone 2 to the lower end of Zone 3 across a race duration typically ranging from 8 to 13 hours or more.

SWIM

• Pace Guidance: 2-6 seconds slower per 100m than CSS, 5-7/10 RPE
• Key Intent: Stay relaxed and economical. The swim sets the tone for the entire day; exiting with a controlled heart rate and minimal energy cost is far more valuable than marginal time gains.

BIKE

• Pace Guidance: 70-80% FTP, 3.5-6/10 RPE
• Key Intent: The bike is where the race is set up, not won. Effort should remain steady, preserving energy for the run.

RUN

• Pace Guidance: 73-88% of threshold run pace, start moderate and build to max RPE by the finish line
• Key Intent: Maintain control deep into the race. The first half of the marathon should feel sustainable. Success in Ironman is less about speed and more about durability – holding pace while others fade.

Bringing It All Together

Pacing is one of the most decisive (and most trainable) skills in long-course triathlon. While fitness determines your ceiling, execution determines how much of that fitness you are able to realize on race day.

The most successful athletes are those who understand their limits, respect them, and build their race with intention. Whether you are stepping up to the distance for the first time or refining your approach after years in the sport, the objective remains the same: distribute your effort in a way that allows you to perform when it matters most – late in the race.

Because in long-course triathlon, it is not the fastest start that defines your day, but often the strength of your finish.