Incidence and predictors of exertional hyperthermia after a 15-km road race in cool environmental conditions

Objectives Current knowledge about the incidence and risk factors for exertional hyperthermia (core body temperature ≥40 °C) is predominantly based on military populations or small-sized studies in athletes. We assessed the incidence of exertional hyperthermia in 227 participants of a 15-km running race, and identified predictors for exertional hyperthermia. Design Observational study. Methods We measured intestinal core body temperature before and immediately after the race. To identify predictive factors of maximum core body temperature, we entered sex, age, BMI, post-finish dehydration, number of training weeks, fluid intake before and during the race, finish time, and core body temperature change during warming-up into a backward linear regression analysis. Additionally, two subgroups of hyperthermic and non-hyperthermic participants were compared. Results In a WBGT of 11 °C, core body temperature increased from 37.6 ± 0.4 °C at baseline to 37.8 ± 0.4 °C after warming-up, and 39.2 ± 0.7 °C at the finish. A total of 15% of all participants had exertional hyperthermia at the finish. Age, BMI, fluid intake before the race and the core body temperature change during warming-up significantly predicted maximal core body temperature (p < 0.001). Participants with hyperthermia at the finish line had a significantly greater core body temperature rise (p < 0.01) during the warming-up compared to non-hyperthermic peers, but similar race times (p = 0.46). Conclusions 15% of the recreational runners developed exertional hyperthermia, whilst core body temperature change during the warming-up was identified as strongest predictor for core body temperature at the finish. This study emphasizes that exertional hyperthermia is a common phenomenon in recreational athletes, and can be partially predicted

Within-subject Variation of Thermoregulatory Responses during Repeated Exercise Bouts

Aim: To assess the within-subject variation of thermoregulatory responses during 2 consecutive 15-km road races. Secondly, we explored whether gastrointestinal temperature (TGI) data from the first race could improve our previously established predictive model for finish TGI in the second race. Methods: We measured TGI before and immediately after both races in 58 participants and determined correlation coefficients. Finish TGI in the second race was predicted using a linear regression analysis including age, BMI, pre-race fluid intake, TGI increase between baseline and the start of the race and finish TGI in the first race. Results: Under cool conditions (WBGT 11–12°C), TGI was comparable between both races at baseline (37.6±0.4°C vs. 37.9±0.4°C; p=0.24) and finish (39.4±0.6°C vs. 39.4±0.6°C; p=0.83). Finish TGI correlated significantly between both races (r=0.50; p<0.001). The predictive model (p<0.001) could predict 32.2% of the finish TGI in the second race (vs. 17.1% without finish TGI in race 1). Conclusion: Our findings demonstrate that the use of previously obtained thermoregulatory responses results in higher predictability of finish core body temperatures in future races, enabling better risk assessment for those athletes that are most likely to benefit from preventive measures

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

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

PURPOSE: Telemetric temperature capsule systems are wireless, relatively non-invasive 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 during Trial 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) (p0.05). Comparable inertia characteristics were found for CorTemp (25±4 sec), e-Celsius (21±13 sec) and myTemp (19±2 sec), while the VitalSense system responded more slowly (39±6 sec) to changes in water bath temperature (p<0.001). CONCLUSION: 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

Validity and reliability of the myTemp ingestible temperature capsule.

OBJECTIVES: An accurate and non-invasive measurement of core body temperature (Tc) is of great importance to quantify exercise-induced increases in Tc in athletes or to assess changes in Tc in patient populations. The use of ingestible gastrointestinal telemetric temperature capsules is widely accepted as a surrogate marker for Tc, but widespread implementation is lacking due to the high costs of these disposable capsules. A new and cheaper temperature capsule system (i.e. myTemp) was recently introduced. The aim of present study is to determine the validity and test-retest reliability of the myTemp system. DESIGN: Ex-vivo experimental study. METHODS: Fifteen ingestible temperature capsules (myTemp, Nijmegen, Netherlands) were tested in a highly temperature controlled water bath, in which the water temperature gradually increased from 34°C to 44°C. The study protocol was performed twice for each temperature capsule. RESULTS: Mean difference between myTemp temperature and water bath temperature was -0.001±0.005°C (Limit of Agreement (LOA): ±0.011°C) during Trial 1 (p=0.11) and -0.001±0.006°C (LOA: ±0.012°C) during Trial 2 (p=0.039). Furthermore, an Intraclass Correlation Coefficient (ICC) of 1.00 was found for both trials. A systematic difference between Trials 1 and 2 of 0.004±0.008°C (LOA: ±0.015°C) was found (p<0.001), whereas the ICC between both trials was 1.00 and the standard error of measurement was 0.005°C. CONCLUSIONS: Although we found a systematic bias for the sensitivity (-0.001°C) and reliability (0.004°C), these values can be considered insignificant from a physiological and clinical perspective. Thus, the myTemp ingestible temperature capsule is a valid technique to measure (water) temperature under controlled circumstances

Changes in BNP and cardiac troponin I after high-intensity interval and endurance exercise in heart failure patients and healthy controls

Exercise training represents a cornerstone of contemporary cardiac rehabilitation. Recently, high-intensity interval training (HIT) has been popularized for heart failure (HF) patients (1) and may serve as a superior mode of exercise compared to traditional endurance exercise training. However, there is controversy regarding the safety (2) and the direct effects of HIT on the heart. Previous studies have demonstrated that an acute bout of exercise leads to an increase in cardiac troponin (cTn), a biomarker for cardiac injury, and B-type natriuretic peptide (BNP), a marker for cardiomyocyte stress (3,4). Exercise-induced elevation in these biomarkers is related to exercise intensity and duration (4,5), and may occur to a larger extend in patients with cardiovascular risk factors (6). To date, no previous study: 1. compared changes in cTn and BNP between endurance exercise and HIT, and 2. explored differences in exercise-induced changes in cTn and BNP between HF patients and controls

Impact of 2-Weeks Continuous Increase in Retrograde Shear Stress on Brachial Artery Vasomotor Function in Young and Older Men

Background Although acute elevation in retrograde shear rate (SR) impairs endothelial function, no previous study has explored the effect of prolonged elevation of retrograde SR on conduit artery vascular function. We examined the effect of 2‐weeks elevation of retrograde SR on brachial artery endothelial function in young and in older men. Methods and Results Thirteen healthy young (23±2 years) and 13 older men (61±5 years) were instructed to continuously wear a compression sleeve around the right forearm to chronically (2 weeks) elevate brachial artery retrograde SR in 1 arm. We assessed SR, diameter, and flow‐mediated dilation in both the sleeve and contralateral control arms at baseline and after 30 minutes and 2 weeks of continuous sleeve application. The sleeve intervention increased retrograde SR after 30 minutes and 2 weeks in both young and older men (P=0.03 and 0.001, respectively). In young men, brachial artery flow‐mediated dilation % was lower after 30 minutes and 2 weeks (P=0.004), while resting artery diameter was reduced after 2 weeks (P=0.005). The contralateral arm showed no change in retrograde SR or flow‐mediated dilation % (P=0.32 and 0.26, respectively), but a decrease in diameter (P=0.035). In older men, flow‐mediated dilation % and diameter did not change in either arm (all P>0.05). Conclusions Thirty‐minute elevation in retrograde SR in young men caused impaired endothelial function, while 2‐week exposure to elevated levels of retrograde SR was associated with a comparable decrease in endothelial function. Interestingly, these vascular changes were not present in older men, suggesting age‐related vascular changes to elevation in retrograde SR

Elevation in blood flow and shear rate prevents hyperglycemia-induced endothelial dysfunction in healthy subjects and those with type 2 diabetes

Hyperglycemia, commonly present after a meal, causes transient impairment in endothelial function. We examined whether increases in blood flow (BF) protect against the hyperglycemia- mediated decrease in endothelial function in healthy subjects and patients with type 2 diabetes mellitus (T2DM). Ten healthy subjects and 10 age- and sex-matched T2DM patients underwent simultaneous bilateral assessment of brachial artery endothelial function by means of flow- mediated dilation (FMD), using high-resolution echo-Doppler. FMD was examined before and 60, 120 and 150 minutes after a 75-gr oral glucose challenge. We unilaterally manipulated BF by heating one arm between minute 30 and 60. Oral glucose administration caused a statistically significant, transient increase in blood glucose in both groups (P<0.001). Forearm skin temperature, brachial artery BF and shear rate significantly increased in the heated arm (P<0.001), and to a greater extent compared to the non-heated arm in both groups (interaction- effect, P<0.001). The glucose load caused a transient decrease in FMD% (P<0.05), whilst heating significantly prevented the decline (interaction-effect: P<0.01). Also when correcting for changes in diameter and shear rate, we found that the hyperglycemia-induced decrease in FMD can be prevented by local heating (P<0.05). These effects on FMD were observed in both groups. Our data indicate that non-metabolically driven elevation in BF and shear rate can similarly prevent the hyperglycemia-induced decline in conduit artery endothelial function in healthy volunteers and in patients with type 2 diabetes. Additional research is warranted to confirm that other interventions increasing BF and shear rate equally protect the endothelium when challenged by hyperglycemia

Exploratory assessment of left ventricular strain-volume loops in severe aortic valve diseases.

Objectives The purpose of this study was to examine left ventricular (LV) strain (ԑ)-volume loops to provide novel insight into the haemodynamic cardiac consequences of aortic valve stenosis (AS) and aortic valve regurgitation (AR). Methods 27 participants were retrospectively recruited: AR (n = 7), AS (n = 10) and controls (n = 10). Standard transthoracic echocardiography was utilised to obtain apical 4 chamber images to construct ԑ-volume relationships were assessed by: Early systolic ԑ (ԑ_ES), slope of ԑ-volume relation during systole (Sslope), End-systolic peak ԑ (peak ԑ), Diastolic uncoupling (systolic ԑ-diastolic ԑ at same volume) during early diastole (UNCOUP_ED) and late diastole (UNCOUP_LD). ROC-curves were used to determine the ability to detect impaired LV function. Results Whilst LV ejection fraction was comparable between groups, longitudinal peak ԑ was similarly reduced compared to controls. In contrast, ԑ_ES and Sslope were lower in both pathologies compared to controls (P  0.05) to distinguish AS vs Controls, AR vs Controls and AS vs AR, respectively. Conclusions Temporal changes in ԑ-volume characteristics provide novel insight into the haemodynamic cardiac impact of AS and AR. Contrary to traditional measures (i.e. ejection fraction, peak ԑ), these novel measures successfully distinguish between the haemodynamic cardiac impact of AS and AR. This article is protected by copyright. All rights reserved