Optimal break structures and cooling strategies to mitigate heat stress during a Rugby League match simulation.

OBJECTIVES: To examine, 1) optimal structure of break periods to mitigate physiological heat strain during rugby league play (Stage 1); and ii) effectiveness of three different cooling strategies applied during breaks (Stage 2). DESIGN: Counter-balanced crossover design. METHODS: In 37 °C, 50% RH, 11 males completed six simulated 80-min (two 40-min halves) rugby league matches on a treadmill with different break structures: regular game (RG) (12-min halftime), 1-min or 3-min "quarter-time" breaks halfway through each half with a 12-min halftime break (R1C and R3C), a 20-min halftime break (EH), or 1-min or 3-min quarter-time breaks with a 20-min halftime break (E1C and E3C) [Stage 1]. Nine participants completed Stage 2, which assessed the application of either ice towels (ICE), an electric fan (FAN) or a misting fan (MST) during breaks in the E3C protocol which, in Stage 1, prevailed as the optimal break structure. RESULTS: Stage 1: Irrespective of quarter-time break duration, reductions in rectal temperature (-0.24 °C ±â€¯0.24) and heart rate (-61 ±â€¯10 bpm) during the halftime break were greater with a 20-min compared to a 12-min break (-0.08 ±â€¯0.13 °C, p = 0.005; -55 ±â€¯-9 bpm, p = 0.021). Stage 2: End-game rises in rectal temperature were smaller (p < 0.006) in MST (1.41 ±â€¯0.22 °C), FAN (1.55 ±â€¯0.36 °C) and ICE (1.60 ±â€¯0.21 °C) than in CON (1.80 ±â€¯0.39 °C). The end-halftime heart rate was lower (p < 0.001) in ICE (89 ±â€¯13 bpm), MST (90 ±â€¯10 bpm) and FAN (92 ±â€¯13 bpm) than in CON (99 ±â€¯18 bpm). CONCLUSIONS: Combining an extended halftime period and quarter-time breaks with MST application is the optimal cooling strategy for rugby league players in hot, humid conditions.

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.