Competitive match-play tennis under heat stress: A challenge for all players

centre court and the rest of the grounds during the first week of the Australian Open in Melbourne. Following days of scorching hot weather and air tempera-tures nearing 43°C, play was suspended for several hours when the ‘Extreme Heat Policy ’ was invoked. This entailed a stop-page in play, except that sets in progress had to carry on until completion, along with closing of the roofs over the arenas so that some matches could continue. The stoppage of play, however, occurred only after a plastic bottle had reportedly started melting on court, a ball boy and a male player fainted, a female playe

Reliability and validity of the MX3 portable sweat sodium analyser during exercise in warm conditions

Purpose: Accurately measuring sweat sodium concentration ([Na+]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na+]. This study aimed to assess the validity and reliability of the MX3 hydration testing system. Methods: Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected from three measurement sites using absorbent patches. The samples were then analysed for sweat [Na+] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample. Results: The mean difference between measurements was 0.1 mmoL·L−1 (95% limits of agreement (LoA): − 9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L−1. When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of − 1.7 mmoL·L−1 (95% LoA: − 0.25X¯, 0.25X¯) and the CV was 9.8%. Conclusion: The MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity.</p

Effect of heat and heat acclimatization on cycling time trial performance and pacing

PURPOSE: This study aimed to determine the effects of heat acclimatization on performance and pacing during outdoor cycling time trials (TT, 43.4 km) in the heat. METHODS: Nine cyclists performed three TT in hot ambient conditions (TTH, approximately 37°C) on the first (TTH-1), sixth (TTH-2), and 14th (TTH-3) days of training in the heat. Data were compared with the average of two TT in cool condition (approximately 8°C) performed before and after heat acclimatization (TTC). RESULTS: TTH-1 (77 ± 6 min) was slower (P = 0.001) than TTH-2 (69 ± 5 min), and both were slower (P < 0.01) than TTC and TTH-3 (66 ± 3 and 66 ± 4 min, respectively), without differences between TTC and TTH-3 (P > 0.05). The cyclists initiated the first 20% of all TT at a similar power output, irrespective of climate and acclimatization status; however, during TTH-1, they subsequently had a marked decrease in power output, which was partly attenuated after 6 d of acclimatization and was further reduced after 14 d. HR was higher during the first 20% of TTH-1 than that in the other TT (P < 0.05), but there were no differences between conditions from 30% onward. Final rectal temperature was similar in all TTH (40.2°C ± 0.4°C, P = 1.000) and higher than that in TTC (38.5°C ± 0.6°C, P < 0.001). CONCLUSIONS: After 2 wk of acclimatization, trained cyclists are capable of completing a prolonged TT in a similar time in the heat compared with cool conditions, whereas in the unacclimatized state, they experienced a marked decrease in power output during the TTH

Thermal and cardiovascular strain mitigate the potential benefit of carbohydrate mouth rinse during self-paced exercise in the heat

Purpose: To determine whether a carbohydrate mouth rinse can alter self-paced exercise performance independently of a high degree of thermal and cardiovascular strain. Methods: Eight endurance-trained males performed two 40-km cycling time trials in 35°C, 60% RH while swilling a 20-ml bolus of 6.5% maltodextrin (CHO) or a color- and taste-matched placebo (PLA) every 5 km. Heart rate, power output, rectal temperature (T(re)), and mean skin temperature (T(sk)) were recorded continuously; cardiac output, oxygen uptake (VO(2)), mean arterial pressure (MAP), and perceived exertion (RPE) were measured every 10 min. Results: Performance time and mean power output were similar between treatments, averaging 63.9 ± 3.2 and 64.3 ± 2.8 min, and 251 ± 23 and 242 ± 18 W in CHO and PLA, respectively. Power output, stroke volume, cardiac output, MAP, and VO(2) decreased during both trials, increasing slightly or remaining stable during a final 2-km end-spurt. T(re), T(sk), heart rate, and RPE increased throughout exercise similarly with both treatments. Changes in RPE correlated with those in T(re) (P < 0.005) and heart rate (P < 0.001). Conclusions: These findings suggest that carbohydrate mouth rinsing does not improve ~1-h time trial performance in hot-humid conditions, possibly due to a failure in down-regulating RPE, which may be influenced more by severe thermal and cardiovascular strain

Prediction of Critical Power and W′ in Hypoxia: Application to Work-Balance Modelling

Purpose: Develop a prediction equation for critical power (CP) and work above CP (W′) in hypoxia for use in the work-balance ([Formula: see text]) model. Methods: Nine trained male cyclists completed cycling time trials (TT; 12, 7, and 3 min) to determine CP and W′ at five altitudes (250, 1,250, 2,250, 3,250, and 4,250 m). Least squares regression was used to predict CP and W′ at altitude. A high-intensity intermittent test (HIIT) was performed at 250 and 2,250 m. Actual and predicted CP and W′ were used to compute W′ during HIIT using differential ([Formula: see text]) and integral ([Formula: see text]) forms of the [Formula: see text] model. Results: CP decreased at altitude (P < 0.001) as described by 3rd order polynomial function (R(2) = 0.99). W′ decreased at 4,250 m only (P < 0.001). A double-linear function characterized the effect of altitude on W′ (R(2) = 0.99). There was no significant effect of parameter input (actual vs. predicted CP and W′) on modelled [Formula: see text] at 2,250 m (P = 0.24). [Formula: see text] returned higher values than [Formula: see text] throughout HIIT (P < 0.001). During HIIT, [Formula: see text] was not different to 0 kJ at completion, at 250 m (0.7 ± 2.0 kJ; P = 0.33) and 2,250 m (−1.3 ± 3.5 kJ; P = 0.30). However, [Formula: see text] was lower than 0 kJ at 250 m (−0.9 ± 1.3 kJ; P = 0.058) and 2,250 m (−2.8 ± 2.8 kJ; P = 0.02). Conclusion: The altitude prediction equations for CP and W′ developed in this study are suitable for use with the [Formula: see text] model in acute hypoxia. This enables the application of [Formula: see text] modelling to training prescription and competition analysis at altitude

Validation of an ingestible temperature data logging and telemetry system during exercise in the heat

Aim: Intestinal temperature telemetry systems are promising monitoring and research tools in athletes. However, the additional equipment that must be carried to continuously record temperature data limits their use to training. The purpose of this study was to assess the validity and reliability of a new gastrointestinal temperature data logging and telemetry system (e-Celsius™) during water bath experimentation and exercise trials. Materials and Methods: Temperature readings of 23 pairs of e-Celsius (T(eC)) and VitalSense (T(VS)) ingestible capsules were compared to rectal thermistor responses (T(rec)) at 35, 38.5 and 42°C in a water bath. Devices were also assessed in vivo during steady-state cycling (n = 11) and intermittent running (n = 11) in hot conditions. Results: The water bath experiment showed T(VS) and T(eC) under-reported T(rec) (P<0.001). This underestimation of T(rec) also occurred during both cycling (mean bias vs T(VS): 0.21°C, ICC: 0.84, 95% CI: 0.66–0.91; mean bias vs. T(eC): 0.44°C, ICC: 0.68, 95% CI: 0.07–0.86, P<0.05) and running trials (mean bias vs. T(VS): 0.15°C, ICC: 0.92, 95% CI: 0.83–0.96; mean bias vs. T(eC): 0.25, ICC: 0.86, 95% CI: 0.61–0.94, P<0.05). However, calibrating the devices attenuated this difference during cycling and eliminated it during running. During recovery following cycling exercise, T(eC) and T(VS) were significantly lower than T(rec) despite calibration (P<0.01). Conclusion: These results indicate that both T(eC) and T(VS) under-report T(rec) during steady-state and intermittent exercise in the heat, with T(eC) predicting T(rec) with the least accuracy of the telemetry devices. It is therefore recommended to calibrate these devices at multiple temperatures prior to use

Lymphocyte and Monocyte Hsp72 Responses to Exercise in Athletes with Prior Exertional Heat Illness

ABSTRACT Introduction. Exertional heatstroke is a serious disorder that can be fatal especially if treatment is delayed. Heat shock protein 72 (Hsp72) is strongly induced by heat, and can be protective against a subsequent stress that may be the same or of a different form. In animal models it has been shown that upregulation of Hsp72 is protective against heatstroke. There is a natural variability in the amount and/or inducibility of Hsp72 in cells and tissues between individuals, and it is possible that impaired expression levels could make some athletes more prone to heat illness. The purpose of this study was to examine Hsp72 expression in lymphocytes and monocytes of young (\u3c40 years) athletes who had previously experienced, but recovered from serious heatstroke during exercise in the heat. Methods. Fourteen athletes ran on a treadmill for 60 min at 72% maximal oxygen uptake (o2max) in warm conditions (30°C, 40% relative humidity). One group consisted of athletes who had a previous history of exertional heat illness (EHI), while the control group (CON) had no previous history of EHI. Both groups were of similar age (29.7 ± 1.2 and 29.1 ± 2 years, CON vs EHI) and fitness (o2max 65.7 ± 2 and 64.5 ± 3 ml.kg-1.min-1, CON vs EHI). Rectal temperature was measured using a thermistor inserted to a depth of 10 cm past the anal sphincter. Hsp72 levels were measured in both monocytes and lymphocytes by flow cytometry before and immediately after the 60-min run, then after 60 min of recovery at an ambient temperature of 24°C. Results. Rectal temperature increased during the exercise period but there was no difference between groups, demonstrating that the EHI group had recovered from their heat illness and were not heat intolerant. Lymphocyte Hsp72 was lower in the EHI group after 60 min of exercise (p\u3c0.05), while monocyte Hsp72 was not different between groups. Conclusion. Our study found a lower lymphocyte Hsp72 concentration during exercise in athletes who had previously collapsed with serious EHI. Further research is needed to determine whether lower lymphocyte Hsp72 is a factor that may predispose athletes to develop EHI