Comparison of the effects of high and low levels of solar radiations on exercise capacity in hot outdoor environments.

BACKGROUND: High solar radiation from the sun in the heat outdoor may be impaired exercise capacity. This study aimed to compare the effects of different levels of solar radiation on exercise capacity and evaluate skin temperature responses in the heat. METHODS: Seven male participants performed cycling exercise at 60% of their maximal oxygen uptake until volitional exhaustion in hot outdoor environments (approximately 33-35°C, 40-50% relative humidity) under both clear sky (high solar radiation trial: 1062±50 W/m2) and under thick clouds (low solar radiation trial: 438±52 W/m2). RESULTS: The time to exhaustion of the participants was shorter in the high solar radiation trial (32.0±12.4 min) than in the low solar radiation trial (39.2±18.0 min: P=0.045). Mean skin temperature was significantly higher in the high solar radiation trial than that in the low solar radiation trial (P<0.05); however, the rectal temperature did not differ significantly between the two trials. The high solar radiation trial had narrower core-to-skin temperature gradient, greater the body heat gain from the sun, and higher rating of perceived exertion than the low solar radiation trial. CONCLUSIONS: These results indicate that high solar radiation during outdoor exercise in the heat causes a greater increase in skin temperature and body heat gain from the sun than low solar radiation and consequently impairs exercise capacity.

Case Report: Countermeasures Against Heat and Coronavirus for Japanese Athletes at the Tokyo 2020 Olympics and Paralympic Games.

The Tokyo 2020 Olympics and Paralympic Games were held in the hottest environment in the history of the games. Additionally, the worldwide coronavirus disease 2019 (COVID-19) pandemic necessitated daily polymerase chain reaction (PCR) testing during the games, wearing a mask became mandatory publicly, and it was an unheard and unique Olympic with no spectators. Heat acclimation, hydration, and body cooling are essential for safe and high-performance activities in hot environments. In 2015, the Japan Institute of Sports Sciences launched the "Heat Countermeasure Project" to conduct experiments and practical research on heat countermeasures and investigate issues related to heat countermeasures in each athletic event. The results obtained were proposed to various Japan national sports teams, and support for heat countermeasures for the Tokyo 2020 games was promoted in consultation with national federations. Furthermore, due to the COVID-19 pandemic, infectious disease countermeasures for the Tokyo 2020 Games during support were a must. Moreover, athletes, coaches, and team staff could not avoid implementing heat countermeasures while adopting measures against infectious diseases. This study aimed to clarify the issues faced with heat countermeasures and report on heat acclimation training and cooling support efforts, considering measures against infectious diseases.

Cooling during short-term heat acclimation enhances aerobic capacity but not sweat capacity.

To characterize the adaptive responses to short-term heat acclimation (HA) training with repeated-sprint exercises and to determine the effects of ice slurry ingestion during HA on aerobic capacity and adaptations. Seven physically active males completed two 5 consecutive day interventions in a randomized cross-over design. Participants performed approximately 80-min intermittent repeated-sprints using a cycling ergometer including break-time and half time in 36.5°C and 50%RH. Participants ingested either 1.25 g·kg body mass-1 of ice slurry (ICE: -1°C) or room temperature beverage (NOC: 36.5°C) throughout each break and 7.5 g·kg body mass-1 of the same drink during half time. Maximum oxygen uptake (V˙O2max) test in hot conditions was completed before and after HA training. Ice slurry ingestion during short-term HA training induced significantly higher both V˙O2max and watt at V˙O2max following HA training. Total work done was significantly higher in HA with ICE than for the NOC trial on both day 1 and day 5. Sweating Na+ concentration in NOC trial at day 5 were significantly lower than those in the NOC trial day 1, but was not observed in ICE trial. Cooling during HA training may be an effective strategy for enhancement of aerobic capacity via the adaptations gained from a higher quantity of exercise caused by cooling, but does not improve heat loss capacity.HighlightsThere is the potential dilemma whether cooling during short-term training in the heat might negatively impacts the process of helping athletes adapt to hot environments.Cooling during short-term heat training may be an effective strategy to enhancement of aerobic capacity via the adaptations gained from a higher quantity of exercise caused by cooling, but does not improve heat loss capacity.The study suggests the importance to selecting cooling during the heat acclimation phase of consecutive field training according to the individual's training plan.

In-play optimal cooling for outdoor match-play tennis in the heat.

The purpose of this study was to compare the efficacy of four cooling interventions used for reducing physiological and perceptual strain and improving exercise performance during outdoor match-play tennis in the heat. Eight competitive tennis players played four counter-balanced simulated outdoor matches in the heat (WBGT: 28.4-32.5°C) at 24- or 48-h intervals. Each match comprised 3 sets for which the "no-ad" rule was applied to limit duration variability. Players underwent the following cooling interventions: ad libitum fluid ingestion (CON), ad libitum fluid ingestion and ice vest (VEST), total ingestion of approximately 1000 g ice slurry and ice vest (Combined: BINE), or total ingestion of approximately 400 g ice slurry and ice vest (Low-combined: L-BINE). Gastrointestinal temperature was lower in the BINE and the L-BINE trials than in the CON trial at the set-break of set 1, and these differences in gastrointestinal temperature persisted throughout the remainder of the match (p < 0.05). The ratio of moderate-high intensity activity (≥10 km/h) in set 3 was significantly higher in the L-BINE trial than that in the BINE trial (p < 0.05). In the CON and BINE trials, high intensity activity was significantly lower in set 3 compared with set 1 and 2, respectively. Cooling by optimal ice slurry ingestion and ice vest may be a more effective strategy in mitigating the development of heat strain during outdoor match-play tennis in the heat.Highlights Cooling by optimal ice slurry ingestion and ice vest may be a more effective strategy in mitigating the development of heat strain during outdoor match-play tennis in the heat.Ingesting of large amounts ice slurry may be caused the bloating and stomach discomfort, in turn declined in the ratio of moderate-high intensity activity in the second half of match-play tennis in hot outdoor environments.Future studies should not only utilize match characteristics, but also measure on-court tennis specific performance.

Effect of a cooling strategy combining forearm water immersion and a low dose of ice slurry ingestion on physiological response and subsequent exercise performance in the heat.

Although numerous studies have shown the benefits of cooling strategies for reducing thermal strain and subsequent exercise performance in the heat, few studies have focused on a combination of external and internal cooling. Therefore, the purpose of the present study was to examine the impact of a cooling strategy combining forearm water immersion and a low dose of ice slurry ingestion on physiological response and subsequent exercise performance in the heat. Eight non-heat-acclimated males participated in this study. After reaching a rectal temperature of 38.5 °C through a bout of cycling exercise in the heat (35 °C, 60% relative humidity), the participants were subjected to one of the following four conditions for a 15-min period: W: forearm cooling; ICE: ice slurry (-1 °C) ingestion; MIX: both W and ICE, and CON: no cooling intervention. After the intervention, the participants performed time to exhaustion (TTE) cycling exercise at 75% V˙O2max. The rate of decrease in rectal temperature in the MIX group was significantly lower than that in the CON group from 6 min to the end of the cooling intervention period (P < 0.05). In addition, mean skin temperature, heart rate, physiological strain index, and perceptual strain were significantly reduced for MIX and W compared with ICE and CON. However, TTE was longer for ICE compared with the other interventions. These results suggest the effectiveness of the newly developed cooling strategy combining external and internal cooling for reducing thermal strain in a short-term recovery period during exercise in the heat.

Impact of Ice Slurry Ingestion During Break-Times on Repeated-Sprint Exercise in the Heat.

The study aimed to investigate the effects of ice slurry ingestion during break times and half-time (HT) on repeated-sprint performance and core temperature in the heat. Seven males performed two different trials as follows: ice slurry (-1°C) or room temperature water ingestion at each break and HT break at 36.5°C, 50% relative humidity. Participants performed 30 sets of 1-min periods of repeated- sprint exercises protocol using a cycling ergometer. Each period consisted of 5 sec of maximal pedaling, 25 sec of pedaling with no workload, and 30 sec of rest; two sets of exercise periods were separated by 10 min of rest. Each break was implemented for 1 min after every 5 sets. The rectal temperature in ice slurry ingestion was significantly lower than that of the room temperature water at 45 set (p=0.04). Total and mean work done was greater in ice slurry ingestion compared to room temperature water ingestion (p < 0.05). These results suggested that ice slurry ingestion during break times and HT break may be an effective cooling strategy to attenuate the rise of core temperature in the second half of exercise and improve the repeated-sprint exercise capacity in the heat.