Exposure to high solar radiation reduces self-regulated exercise intensity in the heat outdoors

Otani, Hidenori; Kaya, Mehmet; Tamaki, Akira; Goto, Heita; Maughan, Ronald J.

doi:10.1016/j.physbeh.2018.11.029

Cited by 27 publications

(24 citation statements)

References 33 publications

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“…Epidemiological studies have identified that the risk for work-related injuries and accidents increase during periods with elevated environmental heat stress 32,33 and these incidents may be aggravated if exposure to solar radiation is superimposed 34 . The causal link for these incidents cannot be derived from such observational studies, since superimposed solar radiation may have a direct effect and influence the overall heat-load (integrated effect of air temperature, humidity, windspeed and radiation) 35,36 , which will consequently exaggerate the core temperature response for a given workload, provoke fatigue, and worsen thermal discomfort 36,37 . These high core temperature-derived consequences may be of particular relevance for sporting activities and very physically demanding occupations.…”

Section: Discussionmentioning

confidence: 99%

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Piil

Christiansen

Morris

et al. 2020

Sci Rep

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Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m 2). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects. Approximately half of the global population live in regions where environmental heat stress is an issue that annually affects the ability to live healthy and productive lives 1,2. Negative effects range from thermal discomfort and impaired physical work capacity for healthy adults 3 to increased morbidity for workers regularly experiencing hyperthermia 1 and higher mortality for vulnerable citizens during heatwaves 4,5. While these issues are well-documented and exposure likely to be worsened by global warming, the effect of environmental heat stress on performance in cognitively dominated tasks is less clear. Intriguingly, in laboratory experiments, impairments in cognitively dominated task performance emerge only with profound hyperthermia 6-10 , whereas productivity losses in occupational settings are reported at considerably lower temperatures 1,11. The ability to maintain concentration and avoid attenuation of motor-cognitive performance is certainly of relevance for work and traffic safety as well as for minimizing the risks of making mistakes during other daily tasks. However, the lack of ecological test validity 1,12-14 as well as the low sensitivity of the stereotypical test protocols used in previous clinical or mechanistic studies in controlled indoor settings may have underestimated the impact of environmental heat stress in real-life scenarios 6-10. In particular, although laboratory-controlled environmental heat-stress studies commonly investigate or control for temperature, humidity and wind speed, solar radiation is often neglected, despite contributing a substantial heat load in outdoor settings, especially in the upright position with the human head directly exposed to solar radiation 15. Human brain function is highly dependent on a stable supply of blood glucose and oxygen, but the brain is also highly vulnerable to alterations...

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Section: Discussionmentioning

confidence: 99%

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Piil

Christiansen

Morris

et al. 2020

Sci Rep

View full text Add to dashboard Cite

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“…The best- and worst-case scenario for temperature and relative humidity were 26.3 ± 0.85°C and 51.8 ± 3.4% and 34.3 ± 1.8°C and 47.4 ± 5.6%, respectively. Furthermore, no cloud cover alongside high ambient temperature and relative humidity during the hottest period of the day (see Table 1) can add considerable thermal challenges and negate performance (Otani et al, 2019). The worst-case scenario during the Olympics could be solar radiation of 855–917 W/m 2 between 12:00 and 15:00 h. The evidence to date suggests that athletes and coaches may consider preparing for the worst-case scenario; heat adaptation strategies, pre- and per-cooling, clothing, reducing time outdoors, and strategies to promote behavioral thermoregulation should be considered.…”

Section: Discussionmentioning

confidence: 99%

Ambient Conditions Prior to Tokyo 2020 Olympic and Paralympic Games: Considerations for Acclimation or Acclimatization Strategies

et al. 2019

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The Tokyo Olympics and Paralympic games in 2020 will be held in hot and humid conditions. Heat acclimation (in a climatic chamber) or heat acclimatization (natural environment) is essential to prepare the (endurance) athletes and reduce the performance loss associated with work in the heat. Based on the 1990–2018 hourly meteorological data of Tokyo and the derived wet bulb globe temperature (WBGT) (Liljegren method), Heat Index and Humidex, it is shown that the circumstances prior to the games are likely not sufficiently hot to fully adapt to the heat. For instance, the WBGT 2 weeks prior to the games at the hottest moment of the day (13:00 h) is 26.4 ± 2.9°C and 28.6 ± 2.8°C during the games. These values include correction for global warming. The daily variation in thermal strain indices during the Tokyo Olympics (WBGT varying by 4°C between the early morning and the early afternoon) implies that the time of day of the event has a considerable impact on heat strain. The Paralympics heat strain is about 1.5°C WBGT lower than the Olympics, but may still impose considerable heat strain since the Paralympic athletes often have a reduced ability to thermoregulate. It is therefore recommended to acclimate about 1 month prior to the Olympics under controlled conditions set to the worst-case Tokyo climate and re-acclimatize in Japan or surroundings just prior to the Olympics.

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“…The present study was conducted in a completely sunny condition. This means that outdoor heat stress continued to increase during the morning and decrease during the afternoon as solar elevation angle rises and falls [28]. That would result in a stable increase of indoor heat stress during AM trial and a stable decrease of indoor heat stress during PM trial in a judo training facility without air conditioning.…”

Section: Plos Onementioning

confidence: 99%

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

et al. 2020

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Purpose The time-of-day variations in environmental heat stress have been known to affect thermoregulatory responses and the risk of exertional heat-related illness during outdoor exercise in the heat. However, such effect and risk are still needed to be examined during indoor sports/exercises. The current study investigated the diurnal relationships between thermoregulatory strain and environmental heat stress during regular judo training in a judo training facility without air conditioning on a clear day in the heat of summer. Methods Eight male high school judokas completed two 2.5-h indoor judo training sessions. The sessions were commenced at 09:00 h (AM) and 16:00 h (PM) on separate days. Results During the sessions, indoor and outdoor heat stress progressively increased in AM but decreased in PM, and indoor heat stress was less in AM than PM (mean ambient temperature: AM 32.7±0.4°C; PM 34.4±1.0°C, P<0.01). Mean skin temperature was higher in AM than PM (P<0.05), despite greater dry and evaporative heat losses in AM than PM (P<0.001). Infrared tympanic temperature, heart rate and thermal sensation demonstrated a trial by time interaction (P<0.001) with no differences at any time point between trials, showing relatively higher responses in these variables in PM compared to AM during the early stages of training and in AM compared to PM during the later stages of training. There were no differences between trials in body mass loss and rating of perceived exertion. Conclusions This study indicates a greater thermoregulatory strain in the morning from 09:00 h than the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning facility on a clear day in the heat of summer. This observation is associated with a progressive increase in indoor and outdoor heat stress in the morning, despite a less indoor heat stress in the morning than the afternoon.

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Exposure to high solar radiation reduces self-regulated exercise intensity in the heat outdoors

Cited by 27 publications

References 33 publications

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Ambient Conditions Prior to Tokyo 2020 Olympic and Paralympic Games: Considerations for Acclimation or Acclimatization Strategies

Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

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