Coen C. W. G. Bongers

Precooling and percooling (cooling during exercise) both improve performance in the heat: a meta-analytical review

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 cooling before (precooling) and during exercise (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.

Cooling interventions for athletes: An overview of effectiveness, physiological mechanisms, and practical considerations

ABSTRACT 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.

Cooling during Exercise in Temperate Conditions: Impact on Performance and Thermoregulation

Exercise-induced increase in core body temperature may lead to the development of hyperthermia (>40.0°C) and/or decreased performance levels. This study examined the effects of wearing a cooling vest during a 5-km time trial on thermoregulatory responses and performance. 10 male masters athletes (42±10 years) performed a 5-km time trial on a motorized treadmill in a climate chamber (25°C, 55% relative humidity) with and without a cooling vest. Split times, heart rate, core-, skin- and cooling vest temperature were measured every 500 m. Subjects also rated thermal comfort and level of perceived exertion. The cooling vest significantly decreased heart rate (p<0.05), decreased skin temperature (p<0.001) and improved thermal comfort (p<0.005) during the time trial. Time to finish the 5-km time trial and pacing strategy did not differ between the control (1 246±96 s) and cooling vest condition (1 254±98 s, p=0.85). Additionally, thermoregulatory responses, maximum core body temperature and level of perceived exertion were not different across conditions (p=0.85, p=0.49, p=0.11, respectively). In conclusion, we demonstrated that wearing a cooling vest during exercise improves thermal comfort but does not enhance performance or decrease core body temperature in male masters athletes under temperate ambient conditions.

Effects of Cooling During Exercise on Thermoregulatory Responses of Men With Paraplegia

Background People with spinal cord injury (SCI) have an altered afferent input to the thermoregulatory center, resulting in a reduced efferent response (vasomotor control and sweating capacity) below the level of the lesion. Consequently, core body temperature rises more rapidly during exercise in individuals with SCI compared with people who are able-bodied. Cooling strategies may reduce the thermophysiological strain in SCI. Objective The aim of this study was to examine the effects of a cooling vest on the core body temperature response of people with a thoracic SCI during submaximal exercise. Methods Ten men (mean age=44 years, SD=11) with a thoracic lesion (T4–T5 or below) participated in this randomized crossover study. Participants performed two 45-minute exercise bouts at 50% maximal workload (ambient temperature 25°C), with participants randomized to a group wearing a cooling vest or a group wearing no vest (separate days). Core body temperature and skin temperature were continuously measured, and thermal sensation was assessed every 3 minutes. Results Exercise resulted in an increased core body temperature, skin temperature, and thermal sensation, whereas cooling did not affect core body temperature. The cooling vest effectively decreased skin temperature, increased the core-to-trunk skin temperature gradient, and tended to lower thermal sensation compared with the control condition. Limitations The lack of differences in core body temperature among conditions may be a result of the relative moderate ambient temperature in which the exercise was performed. Conclusions Despite effectively lowering skin temperature and increasing the core-to-trunk skin temperature gradient, there was no impact of the cooling vest on the exercise-induced increase in core body temperature in men with low thoracic SCI.

Validity, Reliability, and Inertia of Four Different Temperature Capsule Systems.

Purpose 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). Methods 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. Results 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). Conclusions 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.

Impact of acute versus repetitive moderate intensity endurance exercise on kidney injury markers

Exercise may lead to kidney injury through several mechanisms. Urinary Kidney Injury Molecule‐1 (uKIM1) and Neutrophil Gelatinase‐Associated Lipocalin (uNGAL) are known biomarkers for acute kidney injury, but their response to repetitive exercise remains unknown. We examined the effects of a single versus repetitive bouts of exercise on markers for kidney injury in a middle‐aged population. Sixty subjects (aged 29–78 years, 50% male) were included and walked 30, 40 or 50 km for three consecutive days. At baseline and after exercise day 1 and 3, a urine sample was collected to determine uNGAL and uKIM1. Furthermore, urinary cystatin C, creatinine, and osmolality were used to correct for dehydration‐related changes in urinary concentration. Baseline uNGAL was 9.2 (5.2–14.7) ng/mL and increased to 20.7 (11.0–37.2) ng/mL and 14.2(8.0–26.3) ng/mL after day 1 and day 3, respectively, (P ≤ 0.001). Baseline uKIM1 concentration was 2.6 (1.4–6.0) ng/mL and increased to 5.2 (2.4–9.1) ng/mL (P = 0.002) after day 1, whereas uKIM1 was not different from baseline at day 3 (2.9 [1.4–6.4] ng/mL (P = 0.52)). Furthermore, both uNGAL and uKIM1 levels were higher after day 1 compared to day 3 (P < 0.01). When corrected for urinary cystatin C, creatinine, and osmolality, uNGAL demonstrated a similar response compared to the uncorrected data, whereas differences in uKIM1 between baseline, day 1 and day 3 (Ptime = 0.63) were no longer observed for cystatin C and creatinine corrected data. A single bout of prolonged exercise significantly increased uNGAL concentration, whereas no changes in uKIM1 were found. Repetitive bouts of exercise show that there is no cumulative effect of kidney injury markers.

The Impact of Central and Peripheral Cyclooxygenase Enzyme Inhibition on Exercise-Induced Elevations in Core Body Temperature.

PURPOSE Exercise increases core body temperature (TC) due to metabolic heat production. However, the exercise-induced release of inflammatory cytokines including interleukin-6 (IL-6) may also contribute to the rise in TC by increasing the hypothalamic temperature set point. This study investigated whether the exercise-induced increase in TC is partly caused by an altered hypothalamic temperature set point. METHODS Fifteen healthy, active men age 36 ± 14 y were recruited. Subjects performed submaximal treadmill exercise in 3 randomized test conditions: (1) 400 mg ibuprofen and 1000 mg acetaminophen (IBU/APAP), (2) 1000 mg acetaminophen (APAP), and (3) a control condition (CTRL). Acetaminophen and ibuprofen were used to block the effect of IL-6 at a central and peripheral level, respectively. TC, skin temperature, and heart rate were measured continuously during the submaximal exercise tests. RESULTS Baseline values of TC, skin temperature, and heart rate did not differ across conditions. Serum IL-6 concentrations increased in all 3 conditions. A significantly lower peak TC was observed in IBU/APAP (38.8°C ± 0.4°C) vs CTRL (39.2°C ± 0.5°C, P = .02) but not in APAP (38.9°C ± 0.4°C) vs CTRL. Similarly, a lower ΔTC was observed in IBU/APAP (1.7°C ± 0.3°C) vs CTRL (2.0°C ± 0.5°C, P < .02) but not in APAP (1.7°C ± 0.5°C) vs CTRL. No differences were observed in skin temperature and heart-rate responses across conditions. CONCLUSIONS The combined administration of acetaminophen and ibuprofen resulted in an attenuated increase in TC during exercise compared with a CTRL. This observation suggests that a prostaglandin-E2-induced elevated hypothalamic temperature set point may contribute to the exercise-induced rise in TC.

Changes in cytokine levels after prolonged and repeated moderate intensity exercise in middle-aged men and women

Previous studies have shown that exercise‐induced changes in cytokine profiles depend on exercise duration and intensity. Studies are generally limited to a single day, and insight into the time course during multiple days of exercise is lacking. Therefore, this study assessed cytokine responses during multiple days of moderate intensity exercise in men and women. Fifty males (58.9 ± 9.9 years) and fifty females (50.9 ± 11.2 years) were monitored on 4 consecutive days at which they walked on average ~9 h/d at a self‐determined pace. Blood samples were collected 1 or 2 days prior to the start of the exercise (baseline) and every walking day immediately post‐exercise. Blood samples were analyzed for IL‐6, IL‐8, IL‐10, IL‐1β, and TNF‐α concentrations. All cytokine concentrations increased from baseline to post‐exercise at day 1 (P < .001). Thereafter, concentrations decreased from day 1 to day 2 (P < .01), remaining rather stable during the next days. IL‐1β and TNF‐α were higher in men at baseline and during all days. In conclusion, exercise‐induced cytokine increases attenuated on subsequent days, although daily workload remained constant. Men and women showed different baseline levels but similar exercise responses. These results suggest that individuals adapt rapidly to this type of repeated exercise.

Time-motion analysis in the big data era: A promising method to assess the effects of heat stress on physical performance

The negative effects of heat stress on health, physiologic function and capacity to perform prolonged exercise or work are well described in literature. However, it remains difficult to quantify the detrimental effects of heat exposure on physical functioning without using invasive measurement equipment. Alternatively, timemotion analysis, in which movement and time spent on each movement is examined using video analysis, can be used to obtain insight into the physiological demands and movement patterns of an individual [1]. In the current study, Ioannou and colleagues explored the applicability of time-motion analysis to determine the impact of heat stress on labor loss in agriculture workers [2]. For this purpose, the authors assessed the impact of wet bulb globe temperature (WBGT) on work time spent in irregular work breaks of grape-picking workers [2]. Quantitative information was extracted from timemotion analysis of video data to examine the impact of heat stress on occupational productivity. Ioannou et al. demonstrated that 12.4% of the total work shift time was lost on irregular breaks in which the majority of the breaks were observed in the middle 4-h period of the work shift. More importantly, a higher total break time and a decreased duration of uninterrupted labor was found with an increasing WBGT and skin temperature [2]. These findings show that workplace heat stress leads to a reduced productivity of agriculture workers. The present study also demonstrates that time-motion analysis is a valuable tool to provide detailed insight into behavioral thermoregulation and its impact on physical performance. An important limitation of this research technique is the time needed to perform the frame by frame analysis of video footage. For example, 1,920 minutes of data were collected per subject (n = 7), whereas the ratio of video recording to time-motion analyses was 1:1.33 due to regular breaks for the researchers that performed the analyses. This time-consuming manual process may hamper implementation of time-motion analysis in larger occupational studies and/or the field of thermo-physiology in general. On the other hand, technological advances in data sciences may contribute to the introduction of (semi-)automated analyses of video frames in the present big data era. Artificial intelligence derived algorithms can already recognize human motion from video [3]. Future application of machine learning and deep learning techniques may further aid the development of software that can process video footage more quickly. In the absence of time constraints, time-motion analysis could be a valuable tool to monitor the effects of heat stress on physical performance in occupational and sports settings. Information about thermal stress induced changes in an athlete’s individual speed, duration of each movement, total distance covered and work-rest ratio provides insight in the detrimental effects of the heat. For example, tennis players are allowed to have a time interval of maximally 20

Impact of acute versus prolonged exercise and dehydration on kidney function and injury

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 eGFRcystatin C did not differ between baseline and acute exercise (118 ± 11 vs. 116 ± 12 mL/min/1.73 m2, P = 0.12), whereas eGFRcystatin 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 eGFRcystatin C and kidney injury biomarkers, whereas prolonged exercise is associated with a decline in eGFRcystatin C and increased biomarkers for kidney injury.