{"id":386,"date":"2026-08-05T14:47:33","date_gmt":"2026-08-05T13:47:33","guid":{"rendered":"https:\/\/blogs.ncl.ac.uk\/extremeenvironments\/?page_id=386"},"modified":"2026-08-05T14:55:30","modified_gmt":"2026-08-05T13:55:30","slug":"consultancy-fifa-world-cup-2026-heat-preparation-with-english-professional-football-referee-michael-oliver","status":"publish","type":"page","link":"https:\/\/blogs.ncl.ac.uk\/extremeenvironments\/consultancy-fifa-world-cup-2026-heat-preparation-with-english-professional-football-referee-michael-oliver\/","title":{"rendered":"Consultancy: FIFA World Cup 2026 heat preparation with English professional football referee Michael Oliver"},"content":{"rendered":"\n
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Michael returned to the environmental chamber again this year after a successful heat preparation last season prior to the Club World Cup, to prepare for the 2026 FIFA World Cup held across Canada, Mexico and the United States.<\/p>\n\n\n

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We used a similar exercise protocol to the previous year with 5x high intensity running intervals at a fixed speed close to Michael’s HR threshold interspersed with 2min at 7km\/h (equivalent to a moderate walk). On the graphs you can see the intervals represented by the vertical coloured bars in figure 1 and corresponding oscillations in heart rate relating to intensity. We found in hot dry conditions this exercise protocol would generally push body core temperature to reach the target 38.5 o<\/sup>C within around 30-35min, thereafter Michael would enter a maintenance phase at a steady walking pace. We discussed his struggles in the humidity of Florida at the Club World Cup in 2025, where he was based between games, and during the game he refereed (Bayern Munich v Flamengo) in Miami. Therefore we used a fairly aggressive heat strain protocol introducing more humidity to the preparation protocol and pre\/post tests to see how he would cope with it. For pre\/post testing we set conditions to 40 o<\/sup>C and 50%RH (equating to a WBGT of 30.9 o<\/sup>C ). <\/p>\n\n\n\n

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Wet Bulb Globe Temperature (WBGT)<\/strong> is a composite index of environmental heat stress that integrates the effects of air temperature, humidity, radiant heat, and air movement to estimate the thermal strain experienced by humans. A WBGT of 28\u00b0C is widely recognised as a critical threshold above which the risk of heat-related illness increases substantially, particularly during prolonged or strenuous physical activity, hence recommendations for activity modification or additional heat mitigation strategies are often implemented at or beyond this threshold. <\/p>\n\n\n\n

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Figure 1.<\/strong> Pre-test (red) Post-test (green) for (A) Body core temperature (o<\/sup>C) and (B) Cardiovascular strain \u2013 heart rate (bpm) in WBGT 30.9 o<\/sup>C. Red vertical boxes in represent high intensity running intervals with low intensity between bouts. Note the green vertical box represents an incomplete interval in the Pre-test where Michael could not finish the 4th running interval. Dashed line in A represents the internal body core temperature target.<\/p>\n\n\n\n

As typical with successful heat acclimation protocols we can observe a small lowering in resting body core temperature at the beginning of the post session (figure 1A). Whilst the heat stress imposed a comparable load on the body over the first 30minute induction phase, thereafter body core temperature increased at a much higher rate in the pre test (red line, Figure 1A) despite him not being able to complete the 4th or 5th run interval due to the very high thermal perceptive discomfort he experienced. By the post trial Michael was able to complete the predetermined 5 running intervals and body core temperature was lower in the final 30 minutes. Heart rate, a measure of cardiovascular strain, was also lower in the post session, suggesting that Michael was not “working” as hard to maintain the same exercise demands. Again note the green bar, in the pre test Michael could not complete the full 4th interval and did not attempt the 5th interval – hence HR did not spike. <\/p>\n\n\n\n

Typically we would also expect to see an increase in sweat production as a key measure of heat adaptation, however sweat volume was similar between pre\/post tests at ~1.1L, this may reflect the reduced workload in the pre test. <\/p>\n\n\n\n

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Figure 2.<\/strong> Pre-test (red) Post-test (green) for (C) Thermal sensation.<\/p>\n\n\n\n

A cognitive measure of thermal sensation can often be very informative when understanding how individuals cope with imposed heat. Thermal sensation is a person’s subjective perception of their body temperature\u2014that is, how hot, warm, neutral, cool, or cold they feel and we ask participants to rate how they feel based on the integration of these metrics. It reflects the brain’s interpretation of signals from temperature receptors in the skin and body, rather than the actual body temperature itself and can be very informative particularly in the early stages of heat exposure. We can see that Michael really struggled in the pre session. Within the first 15 minutes he felt “Hot” and within 25 minutes he was clearly very uncomfortable reporting being “Very Hot” – the highest ranking on the ashrae scale. This was maintained until he could not complete running interval 4 and walked for the remainder of the 1 hour session. The noted reduction in thermal sensation in the post test suggests that Michael was able to cope better despite the high temperature and high humidity imposed on him during the exercise protocol. <\/p>\n\n\n\n

Altogether these physiological and perceptual changes support his reported greater comfort in the hot\/humid environments in Florida noted below. <\/p>\n\n\n\n

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Figure 3.<\/strong> Heart rate, Pace and power data, calculated from a polar wrist worn watch provided by MO when refereeing the only outdoor game in Boston (France v Norway) where WBGT was 27 o<\/sup>C.<\/p>\n\n\n\n

Data provided by Michael shows the intensity in the only outdoor game he refereed in Boston (France v Norway) where WBGT was 27 o<\/sup>C. Heart rate during the game reached a relative steady state almost immediately following the start of the game and was, for the majority, in zone 4 (threshold zone). His heart rate indeed aligns with the highest values observed during the shorter running intervals in testing. Pace was made up of a composite of walking 58% (note this includes the warmup 45min period prior to the match) moderate jogging ~32% and higher intensity running ~10% as typically reported (see Krustrup et al., 2009) highlighting the dynamic nature of professional football refereeing. We know from last year (see here<\/a>) that in the hot humid conditions of Miami, his heart rate responses were similar suggesting that both game imposed significant heat stress, yet Michael reported “not struggling as much” this year. <\/p>\n\n\n\n

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After the Word Cup I asked him several questions about his experience of the heat:<\/p>\n\n\n\n

1. Were there any specific heat-related strategies that were newly introduced for referees in this WC? <\/strong><\/p>\n\n\n\n

Nothing specific from their side. Access to electrolytes and carb gels, along with water but nothing different to last year. The approach from their side was pretty similar to be honest. HR and GPS monitoring, training every morning as per last year. Lactate tested every 7-10 days.<\/em><\/p>\n\n\n\n

2. You refereed 4 games across the competition, how did they go, did you feel the heat? <\/strong><\/p>\n\n\n\n

Well, great for me, 3 of my 4 games were played inside. The 2 in Houston and 1 in LA were air conditioned to around to 22 o<\/sup>C. The game in Boston (WBGT was 27 o<\/sup>C) was ok. I know the lads who went to NY, Kansas and generally the lunchtime kick offs were difficult.<\/em><\/p>\n\n\n\n

3. Any cramping or struggles in the heat?<\/strong><\/p>\n\n\n\n

Thankfully I never felt like I got close to cramping up that much.<\/em><\/p>\n\n\n\n

4. At the Club World Cup last year in the United States you said you struggled in the humidity. We adapted the heat preparation programme this year to include high humidity, so how did you find the more humid climates of Florida (the holding camp) where WBGT regularly exceeded 32 o<\/sup>C?<\/strong><\/p>\n\n\n\n

I definitely feel that I found the humidity easier this time, but I can’t compare exactly as our outdoor game wasn’t in Miami. It was in the Miami game that I struggled last year, but certainly felt that training was easier this year in Miami.<\/em> It looks like I did a bit more distance this year, but HR and average pace, calories etc all down this year which I presume is a good thing if I am doing more but not ‘struggling’ as much.<\/em><\/p>\n\n\n\n

5. Did the staff instruct you to train during the hot parts of the day to maintain the thermal impulse and you heat adaptation?<\/strong><\/p>\n\n\n\n

Training always at 9:30am. At the start, lasting around 2-2.5 hours but down to around 1 hour maximum by the end of the tournament. So we didn’t seek out the hottest parts of the day. <\/em><\/p>\n\n\n\n

6. Did you hear about any other heat preparation work people had done or any other strategies to cope with the heat?<\/strong><\/p>\n\n\n\n

From what I understand it was only the English who did any prep work! Which is amazing to me. The staff were good and helpful in training when you had particularly hot and humid days, but you can hide a little bit in training when compared to the games.<\/em><\/p>\n\n\n\n

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