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Study note

Core temperature and hydration status during an Ironman triathlon.

PMID 16556786 (2006): hydration, sodium — Time to exhaustion, Performance in heat, Cramp risk, Time-trial performance, Recovery speed (study note for endurance athletes).

Updated Jul 23, 2026

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Study note • PMID 16556786

Core temperature and hydration status during an Ironman triathlon.

British journal of sports medicine • 2006 • DOI 10.1136/bjsm.2005.022426
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How to use this page

This note summarizes one study record. Check the participants, methods, results, and limitations before applying it to training.

  • • Design signal: controlled study.
  • • Population relevance: athlete/trained context.
  • • Consistency: single-study evidence.
  • • Practical recommendation depends on tolerance, context, and whether it protects training consistency.

ELI5

In plain language

To measure core temperature (Tcore) in triathletes during a 226 km Ironman triathlon, and to compare Tcore with markers of hydration status after the event. (controlled study; well-trained triathletes).

The abstract doesn’t indicate a clear change in Performance in heat, Time-trial performance, Recovery speed under the tested conditions. Treat this as a signal, not a guarantee; confirm methods and context in the full paper.

Takeaways

What the abstract suggests

  • • Study question: To measure core temperature (Tcore) in triathletes during a 226 km Ironman triathlon, and to compare Tcore with markers of hydration status after the event.
  • • The abstract doesn’t indicate a clear change in Performance in heat, Time-trial performance, Recovery speed under the tested conditions.
  • • Population: well-trained triathletes.
  • • Protocol cues (title/abstract): 226 km.

Protocol

Protocol (as reported)

  • • Intervention/exposure: hydration, sodium.
  • • Dose/time/duration cues in abstract/title: 226 km.
  • • Outcomes: Time to exhaustion, Performance in heat, Cramp risk, Time-trial performance, Recovery speed.
  • • Replication note: abstracts often omit adherence and timing; confirm details before changing training or supplementation.

Fit

Who it may help, and who should be cautious

Who it helps

  • • Athletes similar to the study population (well-trained triathletes) working on hydration.
  • • Athletes who can measure Time to exhaustion, Performance in heat, Cramp risk, Time-trial performance, Recovery speed with a repeatable workout or time-trial effort.

Who should be cautious

  • • If you have symptoms or conditions that make the intervention risky, get professional guidance.
  • • If you’re near race day and can’t safely test, defer the experiment.

Methods

What the study actually did

  • • Design: controlled study.
  • • Population: well-trained triathletes.
  • • Outcomes measured: Time to exhaustion, Performance in heat, Cramp risk, Time-trial performance, Recovery speed.
  • • Protocol cues mentioned: 226 km.
  • • Source: PubMed PMID 16556786 (2006) — British journal of sports medicine.

Results excerpt

What the abstract reports

“Mean (SD) performance time in the Ironman triathlon was 611 (49) minutes; heart rate was 143 (9) beats/min (83 (6)% of maximum) and Tcore was 38.1 (0.3) degrees C.”

Note: excerpts are short; for full context, read the paper.

Limits

Limitations and bias

  • • Abstract-only summaries can miss critical details (population, protocol, adherence, and context).
  • • Single studies often don’t generalize to your event, history, and training load; treat results as a starting point.
  • • If your context differs (elite vs recreational; cycling vs running), adjust expectations and be conservative.
  • • This is performance information, not medical advice.

Do not turn one field study into a universal hydration target

Ten well-trained athletes were measured during a warm Ironman. Average body mass fell by about 3%, while plasma electrolytes did not materially change and finishing core temperature was not related to the change in body mass. In this small field sample, that level of loss was tolerated without observed thermoregulatory failure.

The result argues against forcing fluid solely to prevent any body-mass loss. It does not prescribe a 3% target or show that dehydration is harmless. Build a race plan from practiced drinking, course access, heat, duration and symptoms; avoid both rigid over-drinking and an untested low-fluid strategy.

The athletes were well trained, the conditions were specific and the sample was small. Individual medical risk and extreme weather can change the decision. Read the full design in the PubMed record.

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Sources