REF-833 · Laursen & Rhodes, 2001 · Sports Medicine, Vol. · Paper · PubMed

Factors Affecting Performance in an Ultraendurance Triathlon

C+thin evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

VO2max, the anaerobic threshold (AT), economy and fractional utilisation of VO2 predict endurance performance well, but beyond events of more than 4 hours ("ultraendurance") performance is harder to predict. For the ultraendurance triathlon (3.8 km swim, 180 km cycle, 42.2 km run) it had been hypothesised that triathletes ride at about the ventilatory threshold.

Yet laboratory time to exhaustion when cycling at AT peaks at 255 minutes, which the authors read as AT being too high an intensity to hold through the race.

They name fuel and fluid provision (limited by finite gastric emptying rates, with changes in substrate use) and fluid and electrolyte imbalance as other limiting factors, and propose defining an optimal "ultraendurance threshold" relative to AT.

Participants

Not applicable — narrative review. Number of studies not given in the abstract.

Protocol

Narrative synthesis of physiological predictors of endurance performance and of ultraendurance triathlon research.
No systematic search method or pooled analysis is described in the abstract.

Key Results

Classic predictors — VO2max, anaerobic threshold, economy of motion and fractional utilisation of VO2 — correlate highly with endurance performance, but performance in events of more than 4 hours is harder to predict.
Race format reviewed: 3.8 km swim, 180 km cycle, 42.2 km marathon run.
Hypothesis in the literature: triathletes ride the bike leg at approximately their ventilatory threshold (Tvent).
Laboratory cycling time to exhaustion at a subject's AT peaks at 255 minutes — the authors' reading: AT is too great an intensity to maintain during an ultraendurance triathlon.
Other limiting factors named: provision of fuels and fluids given finite gastric emptying rates (with changes in substrate utilisation), and fluid and electrolyte imbalances.
Proposal: an optimal ultraendurance intensity, relative to AT, is needed for intensity guidelines — the "ultraendurance threshold".

Practical Application

Can I ride the Ironman bike at my threshold? This review says no: cycling time to exhaustion at the anaerobic threshold peaks at 255 minutes in the lab, so the authors conclude that the anaerobic threshold is too great an intensity to hold through an ultraendurance triathlon, and they add fuel, fluid and electrolyte limits to the cost. Set the Ironman bike intensity clearly below threshold and plan the fuelling as part of the pacing, not after it.
Inference, not tested here: 255 minutes is less than many age-groupers' Ironman bike split alone, before the marathon, which makes the authors' point stronger for slower athletes.
The review names the intensity problem but does not give a tested number for the "ultraendurance threshold"; treat any percentage of threshold for Ironman pacing as practice, not as this paper's finding.
Fuel and fluid are not an afterthought in this view: gastric emptying limits how much can be absorbed, so an intensity that looks sustainable on a fresh lab test may not be once intake cannot keep up.
Not from this paper; the base's own practice: well-trained Ironman riders on power meters still faded lap by lap (REF-786) and the athletes who fuelled more finished faster (REF-787); hold back early and fuel from the start.
Inference, not tested here: "threshold" in this review means the anaerobic (lactate/ventilatory) threshold of the time; a rider's FTP or CP is a related but different number (REF-747, REF-750).

Limitations

Older narrative review proposing a concept; the "ultraendurance threshold" is not defined numerically or tested in the abstract.
The 255-minute figure is a laboratory time to exhaustion at AT, not a race measurement, and the population behind it is not described in the abstract.
Threshold methods of the time differ from today's FTP/CP testing; the numbers are not interchangeable.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

narrative review; the central idea is a hypothesis, not a tested result