• heat
• IOC
• olympics
• elite performance
• exercise physiology

The Tokyo 2020(1) Olympics are expected to be the hottest in modern history,1 resulting in much conjecture within the literature.2–5 Long-term (~10 to 14 days) heat acclimation/acclimatisation (HA) is the gold-standard strategy to protect against heat-mediated performance decrements and exertional heat illnesses (EHI).6 Short-term heat reacclimation (~5 days), proximal to competition, can also be incorporated within athlete training and taper programmes, complimenting the earlier long-term HA. This approach allows the balance of training/load and HA agendas within the often time poor and logistically challenging elite sport environment.5 7 8

With the assumption that athletes arrive robustly heat acclimated/acclimatised to Tokyo 2020(1), practitioners have a variety of precooling, during(mid) and postcooling event interventions to consider on competition day – that are complimentarily to – rather than instead of HA.8 In brief, these can include various combinations of: (i) internal (ice slurry ingestion, cold water ingestion, etc) and external (any cold fluid, medium or air source the body is immersed or exposed to) body cooling interventions to reduce body tissue temperatures [eg, core (Tc), muscle (Tmu) and skin (Tsk) temperature (see figure 1 for summary)]8–10; (ii) interventions to evoke local cooling sensations (eg, menthol mouth rinse) which could be favourably interpreted (ie, their perception) by higher brain centres without altering Tc11 and (iii) titration of competition warm-up procedures and/or alterations in pacing, tactics and/or strategy. At the recent 2019 IAAF World Athletics Championships (Doha, Qatar), LT and TS were ‘trackside’ in either research or practitioner roles, respectfully, for the race-walks and marathons in extreme environmental conditions (WBGT 30°C+, relative humidity 90%+, virtually zero wind speed), despite races starting after 23:30 hours. There they observed (some ill advised), or implemented, an array of these cooling approaches. Ultimately, the battery of cooling related interventions agreed between athlete and practitioner should be thoroughly piloted in training first, followed by ‘minor’ competitions (particularly to gauge practice/rule compatibility and gain athlete trust), to negate the risk of adverse performance and/or medical outcomes (eg, excessive ice slurry ingestion causing gastrointestinal cramps, delay to the sweat onset response, non-desired Tc vs Tmu responses relative to initial physical performance demands).

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Figure 1

Real-world application of rule-compatible cooling interventions for a 50 km race-walk event (left to right in orange) and Rugby Seven’s match (right to left in blue). The middle panel highlights practical considerations to integrate cooling interventions within varied sporting events. The bottom panel depicts the cooling interventions used during the 50 km race-walk and Rugby Seven’s examples above, while also providing some directions for use. Please see editorial ‘Cooling at Tokyo 2020(1): The why and how for endurance and team sport athletes’ by LT, SC and TS for the full reference list.

As practitioners, clinicians and athletes we strive to be evidence-informed regarding our practice. A meta-analytical review12 demonstrated a 2%–6% performance benefit in the hottest conditions (26°C) from precooling during endurance events. More recent meta-analytical review9 revealed: (i) sprint performance is impaired by precooling (mean and weighted Cohen’s d: d=−0.26), whereas (ii) intermittent (d=0.47) and prolonged exercise (time to exhaustion d=2.88; time trial d=1.06; combined d=1.91) are improved by precooling. The performance effects of precooling are delivered through the creation of a body tissue heat sink (eg, Tc decreased ~0.3°C compared with baseline3 8 9; N.B. notable individual and cooling intervention-specific variability in Tc dose response) and favourable perception of body temperature by higher brain centres.11 Ideally, precooling will not evoke a shivering response or compromise the desired physical and/or technical outcomes of an appropriate warm-up [eg, a reduction in Tmu compromising initial physical performance (ie, a maximal sprint)].3 Cooling during exercise (also termed mid-cooling or per-cooling) can have a positive effect on performance and capacity (d=0.76).9 Mid-cooling performance effects can, although with notable discipline, individual and cooling intervention-specific variability, derive through any combination of: (i) decreasing Tsk; (ii) favourable thermal sensation/comfort responses through cutaneous (particularly head and face) and/or oral pharyngeal thermoreceptors and (iii) a potential slowing of the rise in Tc.11 Together these mid-cooling (i-iii) mechanisms can, in some circumstances, augment performance in the heat without a reduction in Tc.11

Despite obvious appeal to elite athletes and practitioners, an important caveat regarding the data9–12 interpretation and translation into practice is required. This9–12 and subsequent data predominately (although not exclusively3 13) occurs within the laboratory and/or utilises recreationally trained males. Indeed, there is a paucity of relevant precooling and mid-cooling data from real-world elite athletes, including their effects on subsequent competition performances and particularly in female populations.2 Additionally, effective precooling and/or mid-cooling from a Tc and Tsk perspective will distort peripheral (afferent; eg, thermoreceptors) feedback to higher central brain centres11; their integration [eg, rating of perceived exertion (RPE)] are integral to effective pacing strategy.11 14 Thus, an athletes ability to successfully execute an RPE (ie, perception/’feel’) guided race plan can be compromised (particularly at the start and early stages of competition given the transiently variable precooling mediated psychophysiological effects), without suitable piloting of precooling and mid-cooling interventions and an ability to pace oneself by their ‘watch’ (ie, time splits) rather than informed by RPE.

Postexercise cooling within an Olympic context will be used for two predominant purposes: (i) medical emergency (eg, EHI) with complicit hyperthermia (eg, 40.5°C) and central nervous system dysfunction15 and (ii) in an (albeit evidence-poor) attempt to accelerate athletic recovery, such as delayed onset muscle soreness (DOMS), between heats, games or events. Regarding (i), aggressive postexercise whole body cooling is the consensus recommendation until rectally determined Tc is 39°C, whereupon cooling ceases and hospital transportation is initiated15 and (ii) typically cold water immersion (CWI) of 10–15 min at 10°C–15°C (although many sports would benefit from an individually prescribed CWI dose, eg, based on playing minutes in rugby sevens2) has the best, although low-quality evidence, regarding alleviating DOMS symptomology.16

Practitioners at Tokyo 2020(1) may have several athletes to design effective race-day or match-day cooling interventions for, within a variety of environments, across the 339 events, 33 sports and 50 disciplines. As such a broad and nuanced spectrum of athletic requirements between events will be seen, with events at either end of the aerobic endurance (eg, 50 km race-walk) and repeated/intermittent performance (eg, Rugby Sevens) spectrum. This editorial will close by outlining integrated and rule-compatible real-world elite Olympic cooling interventions in the 50 km race-walk and a Rugby Sevens match day (see figure 1).