Optimal cooling strategies for players in Australian Tennis Open conditions.

OBJECTIVES: We compared the utility of four cooling interventions for reducing heat strain during simulated tennis match-play in an environment representative of the peak conditions possible at the Australian Open (45°C, <10% RH, 475W/m2 solar radiation). DESIGN: Nine trained males undertook four trials in a climate chamber, each time completing 4 sets of simulated match-play. METHODS: During ITF-mandated breaks (90-s between odd-numbered games; 120-s between sets), either iced towels (ICE), an electric fan (FANdry), a fan with moisture applied to the skin (FANwet), or ad libitum 10°C water ingestion only (CON) was administered. Rectal temperature (Tre), mean skin temperature (Tsk), heart rate (HR), thermal sensation (TS), perceived exertion (RPE) and whole body sweating (WBSR) were measured. RESULTS: After set 3, Tre was lower in ICE (38.2±0.3°C) compared to FANdry (38.7±0.5°C; p=0.02) and CON (38.5±0.5°C; p=0.05), while Tre in FANwet (38.2±0.3°C) was lower than FANdry (p=0.05). End-exercise Tre was lower in ICE (38.1±0.3°C) and FANwet (38.2±0.4°C) than FANdry (38.9±0.7°C; p<0.04) and CON (38.8±0.5°C; p<0.04).Tsk for ICE (35.3±0.8°C) was lower than all conditions, and Tsk for FANwet (36.6±1.1°C) was lower than FANdry (38.1±1.3°C; p<0.05). TS for ICE and FANwet were lower than CON and FANdry (p<0.05). HR was suppressed in ICE and FANwet relative to CON and FANdry (p<0.05). WBSR was greater in FANdry compared to FANwet (p<0.01) and ICE (p<0.001). CONCLUSIONS: Fan use must be used with skin wetting to be effective in hot/dry conditions. This strategy and the currently recommended ICE intervention both reduced Tre by ∼0.5-0.6°C and Tsk by ∼1.0-1.5°C while mitigating rises in HR and TS.

In-Play Cooling Interventions for Simulated Match-Play Tennis in Hot/Humid Conditions.

PURPOSE: This study aimed to assess the efficacy of different in-play cooling strategies for mitigating heat strain during simulated tennis match-play activity in a hot/humid environment representing the most extreme conditions during the US Open (36°C, 50% relative humidity). METHODS: On three occasions, nine males completed an intermittent treadmill protocol with an exercise intensity and activity profile simulating a four-set tennis match, with 90-s breaks between odd-numbered games and 120-s breaks between sets, according to International Tennis Federation rules. During breaks, 1) the currently used cooling strategy-an ice-filled damp towel around the neck and a cold-damp towel on the head and thighs (ICE); 2) wetting of arms, neck, face, and lower legs with a sponge in front of an electric fan (FANwet); or 3) no cooling (CON) were applied. Rectal (Tre) and mean skin (Tsk) temperature and HR were measured throughout. Thermal sensation and RPE were assessed during breaks. Trials were terminated upon reaching a Tre ≥ 39.5°C or volitional exhaustion. RESULTS: Seven, five, and one participant completed FANwet, ICE, and CON, respectively. By end set 1, ΔTre was lower in FANwet (0.92°C ± 0.15°C) compared with CON (1.09°C ± 0.09°C, P = 0.01), and by end set 2, ΔTre was lower (P < 0.001) in FANwet (1.55°C ± 0.23°C) and ICE (1.59°C ± 0.17°C) compared with CON (1.99°C ± 0.19°C). Mean RPE (FANwet = 13.9 ± 2.2, ICE = 13.6 ± 1.8, CON = 16.6 ± 1.8), HR (FANwet = 163 ± 21, ICE 164 ± 22, CON = 175 ± 19 bpm), Tsk (FANwet = 36.56°C ± 0.69°C, ICE 36.12°C ± 0.44°C, CON = 37.21°C ± 0.42°C), and thermal sensation were lower in FANwet and ICE (P < 0.05) compared with CON by end set 2. CONCLUSIONS: The currently recommended ICE strategy successfully mitigates thermal strain during simulated tennis match play in hot/humid conditions. The FANwet intervention is an equally effective alternative that may be more practical in limited resource settings.

Occupational heat stress in Australian workplaces.

The aim of this review was to summarize the current state of knowledge on heat stress risk within typical Australian occupational settings. We assessed identified occupations (mining, agriculture, construction, emergency services) for heat production and heat loss potential, and resultant levels of physiological heat strain. A total of 29 reports were identified that assessed in-situ work settings in Northern Territory, South Australia, Western Australia, Queensland, New South Wales and Victoria, that measured physiological responses and characterized the thermal environment. Despite workers across all industries being regularly exposed to high ambient temperatures (32-42°C) often coupled with high absolute humidity (max: 33 hPa), physiological strain is generally low in terms of core temperature (<38°C) and dehydration (<1 % reduction in mass) by virtue of the low energy demands of many tasks, and self-regulated pacing of work possible in most jobs. Heat stress risk is higher in specific jobs in agriculture (e.g. sheep shearing), deep underground mining, and emergency services (e.g., search/rescue and bushfire fighting). Heat strain was greatest in military-related activities, particularly externally-paced marching with carried loads which resulted in core temperatures often exceeding 39.5°C despite being carried out in cooler environments. The principal driver of core temperature elevations in most jobs is the rate of metabolic heat production. A standardized approach to evaluating the risk of occupational heat strain in Australian workplaces is recommended defining the individual parameters that alter human heat balance. Future research should also more closely examine female workers and occupational activities within the forestry and agriculture/horticulture sector.

Heat stress and strain in exercise and sport.

Heat stress arising from the thermal environment is of concern to sports medicine and to sports administration because of the perceived risk of heat casualties, in particular heat stroke. Many sports organizations recommend environmental indices such as the WBGT for assessing risk and setting environmental limits for training and competition. But the limits are not justified by evidence. This article describes the nature of heat stress in sport and how it may be assessed objectively. Heat stress and the principal human responses to exercise heat stress are reviewed briefly. Metabolic heat production and the thermal environment provoke separate and largely independent physiological strains. Metabolic heat production drives body core temperature, and the thermal environment drives skin temperature; the combined stresses are integrated to drive sweat rate. Control of core temperature depends on adequate sweat production and the capacity of the environment to evaporate the sweat. The nature of exercise heat stress is demonstrated by rational analysis of the physical heat exchanges between the body and the environment. The principles of this analysis are applied to critical review of current practice in the assessment of heat stress in sport. The article concludes with discussion of research to establish methods for objective sport-specific assessment of heat stress.

Heat-related injuries resulting in hospitalisation in Australian sport.

The aim of this study was to summarise the extent and characteristics of cases of illness due to environmental heat, significant enough to result in hospitalisation, and arising during sporting activity in Australia. Cases were identified from the hospital separations database compiled by the Australian Institute of Health and Welfare, using the allocated external cause and diagnosis codes and the activity code "While engaged in sports". Hospital separations for the 2 years 2002-2003 and 2003-2004 were used. One hundred and forty eight cases were identified (68% male). Cases were fairly evenly distributed across 10-year age groups starting from age 15 years, apart from fewer cases between 55 and 64 years. Nearly two thirds of the cases occurred in the summer months (December to February inclusive). The most commonly involved individual sports were lawn bowls, cricket, softball, golf, marathon running and walking, and the rate was highest for triathlons, lawn bowls, cricket, and running. Rates for persons aged 65 years or older were more than twice the rates at younger ages. Heat-related disorders are an uncommon cause of significant morbidity in Australians participating in sporting activity. However, particular sports have a relatively high rate of occurrence and these sports would provide an appropriate focus for prevention activity. The availability of a specific code in the International Classification of Diseases and Injuries to cover excessive endogenous production of heat would assist future analyses of the role of thermoregulatory disturbance in leading to morbidity in persons participating in sporting activity.

Air temperature and physiological and subjective responses during competitive singles tennis.

OBJECTIVES: This report describes the thermal stresses and strains during competitive singles tennis. METHODS: Thermoregulatory responses were investigated during best of three set tennis matches among 25 players. A total of 86 observations were made from 43 matches played, covering each season, with ambient temperatures ranging from 14.5 to 38.4 degrees C. Core body temperature and skin temperature were recorded each minute throughout the match, whilst heart rate was logged every 15 s. Body mass and fluid intake were measured before the match, after 30 min of play and at the completion of the match to determine sweat rate. Subjective ratings of thermal strain included thermal comfort, sweatiness and perceived exertion. The thermal environment was assessed by dry bulb, wet bulb and natural wet bulb temperatures, globe temperature and wind speed. RESULTS: Mean (SD) core temperature after 30 min of play was 38.4 degrees C (0.4 degrees C), and demonstrated no association with air temperature or wet bulb globe temperature. Mean skin temperature was 31.8 degrees C (2.3 degrees C) ranging from 25.7 to 36.5 degrees C, and showed a positive association with air temperature (p<0.001). Heart rate varied widely during play, resulting in a mean (SD) response of 136.1 (13.7) beats/min and no association with air temperature. Sweat rate averaged 1.0 (0.4) litres/h (0.2-2.4 litres/h) or 12.8 (5.5) ml/kg/h (2.7-26.0 ml/kg/h), and demonstrated a positive relationship with air temperature (p<0.001). All subjective responses showed positive correlations with air temperature (p<0.001). CONCLUSIONS: Stressful environmental conditions produce a high skin temperature and rating of thermal discomfort. However, overall thermoregulatory strain during tennis is moderate, with core temperature remaining within safe levels.