Most studies projecting human survivability limits to extreme heat with climate change use a 35 °C wet-bulb temperature (T_w) threshold without integrating variations in human physiology. This study applies physiological and biophysical principles for young and older adults, in sun or shade, to improve current estimates of survivability and introduce liveability (maximum safe, sustained activity) under current and future climates. Our physiology-based survival limits show a vast underestimation of risks by the 35 °C T_w model in hot-dry conditions. Updated survivability limits correspond to T_w~25.8–34.1 °C (young) and ~21.9–33.7 °C (old)—0.9–13.1 °C lower than T_w = 35 °C. For older female adults, estimates are ~7.2–13.1 °C lower than 35 °C in dry conditions. Liveability declines with sun exposure and humidity, yet most dramatically with age (2.5–3.0 METs lower for older adults). Reductions in safe activity for younger and older adults between the present and future indicate a stronger impact from aging than warming.

Exercise-induced increases in core body temperature could negative impact performance and may lead to development of heat-related illnesses. The use of cooling techniques prior (pre-cooling), during (per-cooling) or directly after (post-cooling) exercise may limit the increase in core body temperature and therefore improve exercise performance. The aim of the present review is to provide a comprehensive overview of current scientific knowledge in the field of pre-cooling, per-cooling and post-cooling. Based on existing studies, we will discuss 1) the effectiveness of cooling interventions, 2) the underlying physiological mechanisms and 3) practical considerations regarding the use of different cooling techniques. Furthermore, we tried to identify the optimal cooling technique and compared whether cooling-induced performance benefits are different between cool, moderate and hot ambient conditions. This article provides researchers, physicians, athletes and coaches with important information regarding the implementation of cooling techniques to maintain exercise performance and to successfully compete in thermally stressful conditions.

Background: Exercise increases core body temperature (Tc), which is necessary to optimise physiological processes. However, excessive increase in Tc may impair performance and places participants at risk for the development of heat-related illnesses. Cooling is an effective strategy to attenuate the increase in Tc. This meta-analysis compares the effects of coolingbefore(precooling) andduringexercise (percooling) on performance and physiological outcomes.Methods: A computerised literature search, citation tracking and hand search were performed up to May 2013. 28 studies met the inclusion criteria, which were trials that examined the effects of cooling strategies on exercise performance in men, while exercise was performed in the heat (>30°C). 20 studies used precooling, while 8 studies used percooling.Results: The overall effect of precooling and percooling interventions on exercise performance was +6.7±0.9% (effect size (ES)=0.43). We found a comparable effect (p=0.82) of precooling (+5.7±1.0% (ES=0.44)) and percooling (+9.9±1.9% (ES=0.40)) to improve exercise performance. A lower finishing Tc was found in precooling (38.9°C) compared with control condition (39.1°C, p=0.03), while Tc was comparable between conditions in percooling studies. No correlation between Tc and performance was found. We found significant differences between cooling strategies, with a combination of multiple techniques being most effective for precooling (p<0.01) and ice vest for percooling (p=0.02).Conclusions: Cooling can significantly improve exercise performance in the heat. We found a comparable ES for precooling and percooling on exercise performance, while the type of cooling technique importantly impacts the effects. Precooling lowered the finishing core temperature, while there was no correlation between Tc and performance.

Telemetric temperature capsule systems are wireless, relatively noninvasive, and easily applicable in field conditions and have therefore great advantages for monitoring core body temperature. However, the accuracy and responsiveness of available capsule systems have not been compared previously. Therefore, the aim of this study was to examine the validity, reliability, and inertia characteristics of four ingestible temperature capsule systems (i.e., CorTemp, e-Celsius, myTemp, and VitalSense). Ten temperature capsules were examined for each system in a temperature-controlled water bath during three trials. The water bath temperature gradually increased from 33°C to 44°C in trials 1 and 2 to assess the validity and reliability, and from 36°C to 42°C in trial 3 to assess the inertia characteristics of the temperature capsules. A systematic difference between capsule and water bath temperature was found for CorTemp (0.077°C ± 0.040°C), e-Celsius (−0.081°C ± 0.055°C), myTemp (−0.003°C ± 0.006°C), and VitalSense (−0.017°C ± 0.023°C; P < 0.010), with the lowest bias for the myTemp system (P < 0.001). A systematic difference was found between trial 1 and trial 2 for CorTemp (0.017°C ± 0.083°C; P = 0.030) and e-Celsius (−0.007°C ± 0.033°C; P = 0.019), whereas temperature values of myTemp (0.001°C ± 0.008°C) and VitalSense (0.002°C ± 0.014°C) did not differ (P > 0.05). Comparable inertia characteristics were found for CorTemp (25 ± 4 s), e-Celsius (21 ± 13 s), and myTemp (19 ± 2 s), whereas the VitalSense system responded more slowly (39 ± 6 s) to changes in water bath temperature (P < 0.001). Although differences in temperature and inertia were observed between capsule systems, an excellent validity, test–retest reliability, and inertia was found for each system between 36°C and 44°C after removal of outliers.

Background: An inadequate protein intake may offset the muscle protein synthetic response after physical activity, reducing the possible benefits of an active lifestyle for muscle mass. We examined the effects of 12 weeks of daily protein supplementation on lean body mass, muscle strength, and physical performance in physically active older adults with a low habitual protein intake (<1.0 g/kg/day).Methods: A randomized double‐blinded controlled trial was performed among 116 physically active older adults [age 69 (interquartile range: 67–73) years, 82% male] who were training for a 4 day walking event of 30, 40, or 50 km/day. Participants were randomly allocated to either 31 g of milk protein or iso‐caloric placebo supplementation for 12 weeks. Body composition (dual‐energy X‐ray absorptiometry), strength (isometric leg extension and grip strength), quadriceps contractile function, and physical performance [Short Physical Performance Battery, Timed Up‐and‐Go test, and cardiorespiratory fitness (Åstrand–Rhyming submaximal exercise test)] were measured at baseline and after 12 weeks. We assessed vitamin D status and markers of muscle damage and renal function in blood and urine samples before and after intervention.Results: A larger increase in relative lean body mass was observed in the protein vs. placebo group (∆0.93 ± 1.22% vs. ∆0.44 ± 1.40%, P_Interaction = 0.046). Absolute and relative fat mass decreased more in the protein group than in the placebo group (∆−0.90 ± 1.22 kg vs. ∆−0.31 ± 1.28 kg, P_Interaction = 0.013 and ∆−0.92 ± 1.19% vs. ∆−0.39 ± 1.36%, P_Interaction = 0.029, respectively). Strength and contractile function did not change in both groups. Gait speed, chair‐rise ability, Timed Up‐and‐Go, and cardiorespiratory fitness improved in both groups (P < 0.001), but no between‐group differences were observed. Serum urea increased in the protein group, whereas no changes were observed in the placebo group (P_Interaction < 0.001). No between‐group differences were observed for vitamin D status, muscle damage, and renal function markers.Conclusions: In physically active older adults with relatively low habitual dietary protein consumption, an improvement in physical performance, an increase in lean body mass, and a decrease in fat mass were observed after walking exercise training. A larger increase in relative lean body mass and larger reduction in fat mass were observed in participants receiving 12 weeks of daily protein supplementation compared with controls, whereas this was not accompanied by differences in improvements between groups in muscle strength and physical performance.

Exercise and dehydration may be associated with a compromised kidney function and potential signs of kidney injury. However, the kidney responses to exercise of different durations and hypohydration levels are not yet known. Therefore, we aimed to compare the effects of acute versus prolonged exercise and dehydration on estimated glomerular filtration rate (eGFR) and kidney injury biomarkers in healthy male adults. A total of 35 subjects (23 ± 3 years) were included and invited for two study visits. Visit 1 consisted of a maximal cycling test. On Visit 2, subjects performed a submaximal exercise test at 80% of maximal heart rate until 3% hypohydration. Blood and urine samples were taken at baseline, after 30 min of exercise (acute effects; low level of hypohydration) and after 150 min of exercise or when 3% hypohydration was achieved (prolonged effects, high level of hypohydration). Urinary outcome parameters were corrected for urinary cystatin C, creatinine, and osmolality. Subjects dehydrated on average 0.6 ± 0.3% and 2.9 ± 0.7% after acute and prolonged exercise, respectively (P < 0.001). The eGFR_{cystatin C} did not differ between baseline and acute exercise (118 ± 11 vs. 116 ± 12 mL/min/1.73 m², P = 0.12), whereas eGFR_{cystatin C} was significantly lower after prolonged exercise (103 ± 16 mL/min/1.73 m², P < 0.001). We found no difference in osmolality corrected uKIM1 concentrations after acute and prolonged exercise (P > 0.05), and elevated osmolality corrected uNGAL concentrations after acute and prolonged exercise (all P‐values < 0.05). In conclusion, acute exercise did barely impact on eGFR_{cystatin C} and kidney injury biomarkers, whereas prolonged exercise is associated with a decline in eGFR_{cystatin C} and increased biomarkers for kidney injury.