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The use of wearable sensors for real-time monitoring of exercise-related measures has been extensively studied in recent years (e.g., performance enhancement, optimizing athlete's training, and preventing injuries). Surface electromyography (sEMG), which measures muscle activity, is a widely researched technology in exercise monitoring. However, due to their cumbersome nature, traditional sEMG electrodes are limited. In particular, facial EMG (fEMG) studies in physical training have been limited, with some scarce evidence suggesting that fEMG may be used to monitor exercise-related measurements. Altogether, sEMG recordings from facial muscles in the context of exercise have been examined relatively inadequately. In this feasibility study, we assessed the ability of a new wearable sEMG technology to measure facial muscle activity during exercise. Six young, healthy, and recreationally active participants (5 females), performed an incremental cycling exercise test until exhaustion, while facial sEMG and vastus lateralis (VL) EMG were measured. Facial sEMG signals from both natural expressions and voluntary smiles were successfully recorded. Stable recordings and high-resolution facial muscle activity mapping were achieved during different exercise intensities until exhaustion. Strong correlations were found between VL and multiple facial muscles' activity during voluntary smiles during exercise, with statistically significant coefficients ranging from 0.80 to 0.95 (p<0.05). This study demonstrates the feasibility of monitoring facial muscle activity during exercise, with potential implications for sports medicine and exercise physiology, particularly in monitoring exercise intensity and fatigue. [ABSTRACT FROM AUTHOR]

Purpose: Heat intolerance (HI) is determined in the Israel Defense Force according to a heat tolerance test (HTT) before returning to duty after an exertional heat stroke (EHS) event. Recently, increased numbers of female combatants resulted in an increased number of EHS cases among women and a higher percentage of heat intolerance (HI) individuals. We aimed to evaluate the differences between tolerance to heat among women performing an HTT in relation to their menstrual cycle phase. Method: Thirty-three female participants were sorted into two groups: HI and heat tolerant (HT) according to two HTTs performed during both the luteal and follicular phases of the menstrual cycle or while consuming and during a break from consuming contraceptives. Results: HT women had an 18% higher maximal oxygen uptake (p < .005, 95% CI [2.6,9.8]) and 1.2% lower skin temperature in the HTT at the during and follicular phases (p < .01, 95% CI [0.12,0.77]) and 1.7% lower at the off and luteal phases (p < .001, 95% CI [0.34,0.92]). The mean sweat rate was 14% lower among the HI group only at the HTT at the during and follicular phases (p < .05, 95% CI (3,88)]). Conclusion: We found that HT can be predicted using aerobic capacity and core body temperature. Moreover, during the luteal phase, women presented altered thermoregulation that decreased the probability of being HT. This emphasizes the importance of considering the HT/HI criteria in the HTT for women, according to their aerobic ability and menstrual-cycle phase. [ABSTRACT FROM AUTHOR]

In various occupations, workers may be exposed to extreme environmental conditions and physical activities. Under these conditions the ability to follow the workers' body temperature may protect them from overheating that may lead to heat related injuries. The "Dräger" Double Sensor (DS) is a novel device for assessing body-core temperature (T c ). The purpose of this study was to evaluate the accuracy of the DS in measuring T c under heat stress. Seventeen male participants performed a three stage protocol: 30 min rest in a thermal comfort environment (20–22 °C, 50% relative humidity), followed by an exposure to a hot environment of 40 °C, 40% relative humidity −30 min at rest and 60 min of exercise (walking on a treadmill at 5 km/h and 2% elevation). Simultaneously temperatures measured by the DS (T DS ) and by rectal temperature (T re ) (YSI-401 thermistor) were recorded and then compared. During the three stages of the study the average temperature obtained by the DS was within±0.3 °C of rectal measurement. The correlation between T DS and T re was significantly better during the heat exposures phases than during resting under comfort conditions. These preliminary results are promising for potential use of the DS by workers under field conditions and especially under environmental heat stress or when dressed in protective garments. For this goal, further investigations are required to validate the accuracy of the DS under various levels of heat stress, clothing and working levels. [ABSTRACT FROM AUTHOR]

Background: The heat tolerance test (HTT) is a standardized physiological test that constitutes one of the considerations in the Israel Defence Forces (IDF) for return to duty after a heat injury. The HTT consists of a 2h controlled exercise-heat stress with a threshold of maximal rectal temperature (Tc) and heart rate (HR) values above which subjects are referred to as heat intolerant; the dynamics of the HR and Tc during the test, which tend to plateau during the 2nd hour of the test, is also considered. Since “tendency to plateau” is a subjective measure, this study aimed to quantify the tendency to plateau during a HTT. Material and methods: The physiological results of 102 HTT subjects (83 normal and 19 heat-intolerant) served as the database for analysis. The first 28 subjects, who were considered heat tolerant (HT) by an experienced examiner, served to evaluate a “normal” dynamic of Tc and HR during a HTT. Then, we applied the results on seven heat tolerant and seven heat intolerant (HI) subjects in order to determine which of the two variables (dTc or dHR) in different time intervals (t 120–0, t 60–0, t 120–60, and t 120–100) may best distinguish heat tolerant from heat intolerant subjects. During the 3rd stage of the study 60 random test results (post factum: 48 heat tolerant and 12 heat intolerant subjects) were evaluated. Post-hoc results of heat tolerance determined by dTc were compared to the expert diagnosis of the test. Results: A rise of less than 0.45°C in Tc during the 2nd hour of the HTT was found acceptable to define a tendency to plateau of the Tc with a 100% sensitivity and specificity. We did not find a numerical value of HR increase over time during the HTT acceptable to define a tendency of the HR to plateau. Conclusion: During the last hour of the heat tolerance test, there is a tendency to plateau in Tc in heat tolerant individuals. It is concluded that a rise in Tc of less than 0.45°C during this period (Tc120–60) can be used as a supporting measure to distinguish between heat tolerant and heat intolerant individuals. [ABSTRACT FROM AUTHOR]

Summary This is the first study to provide valuable insights into the effects of the Israeli Navy's 20‐h rotating watch schedule on submariners’ alertness, mood states, risk‐taking behaviours, and sleep. Specifically, we assessed the impact of the non‐circadian‐aligned schedule on cognitive performance, mood, and behavioural outcomes in a highly controlled submarine environment. A total of 20 male submariners participated in an at‐sea mission, where their cognitive performance, mood states, risk‐taking propensity, and caffeine consumption were measured. A psychomotor vigilance task (PVT) assessed alertness, the propensity for risky behaviour (Evaluation of Risks Scale) measured risk‐taking behaviours, and the Profile of Mood States evaluated mood disturbances. Actigraphy was used to monitor sleep times. Data were analysed according to seven watch schedule segments. Submariners slept a mean (standard error of the mean [SEM]) of 8.3 (0.2) h/24 h, fragmented into 3.7 (0.8) h epochs. Caffeine consumption decreased at sea (mean [SEM] 149.3 [6.0] mg) compared to land (mean [SEM] 205.5 [7.2] mg; p = 0.027). In the PVT, premature responses significantly increased during Watch VI (5:00–8:00 p.m.) and Watch VII (8:00 p.m.–12:00 a.m.; p = 0.014). In the mood subscales, tension was significantly higher during Watch II (4:00–8:00 a.m.; p = 0.002), indicating greater stress. Risk‐taking propensity significantly increased during afternoon shifts (p = 0.050). The 20‐h watch schedule led to fragmented sleep, reduced alertness in the evening, worsened mood states in the early morning, and increased risk‐taking propensity in the afternoon. These findings suggest the need for the Israeli Navy to establish evidence‐based caffeine guidelines and optimise the watch schedule to improve submariners’ sleep, performance, and overall well‐being. [ABSTRACT FROM AUTHOR]

To assess the utility of self-reported symptoms in identifying positive coronavirus disease 2019 (COVID-19) cases among predominantly healthy young adults in a military setting. A questionnaire regarding COVID-19 symptoms and exposure history was administered to all individuals contacting the Israeli Defence Forces Corona call-centre, before PCR testing. Surveyed symptoms included cough, fever, sore throat, rhinorrhoea, loss of taste or smell, chest pain and gastrointestinal symptoms. Factors were compared between positive and negative cases based on confirmatory test results, and positive likelihood ratios (LR) were calculated. Results were stratified by sex, body mass index, previous medical history and dates of questioning, and a multivariable analysis for association with positive test was conducted. Of 24 362 respondents, 59.1% were men with a median age of 20.5 years (interquartile range 19.6–22.4 years). Significant positive LRs were associated with loss of taste or smell (LR 3.38, 95% CI 3.01–3.79), suspected exposure (LR 1.33, 95% CI 1.28–1.39) and fever (LR 1.26, 95% CI 1.17–1.36). Those factors were also associated with positive PCR result in a multivariable analysis (OR 3.51, 95% CI 3.04–4.06; OR 1.86, 95% CI 1.65–2.09; and OR 1.34, 95% CI 1.19–1.51, respectively). Reports of loss of taste or smell increased gradually over time and were significantly more frequent during the late period of the study (63/5231, 1.21%; 156/7941, 1.96%; and 1505/11 190, 13.45%: p < 0.001). Loss of taste or smell, report of a suspicious exposure and fever (>37.5°C) were consistently associated with positive LRs for a positive SARS-CoV-2 PCR test result, in a population of predominantly young and healthy adults. [ABSTRACT FROM AUTHOR]

Objectives: The high values of thermal resistance (Rct) and/or vapor resistance (Ret) of chemical protective clothing (CPC) induce a considerable thermal stress. The present study compared the physiological strain induced by CPCs and evaluates the relative importance of the fabrics’ Rct, Ret, and air permeability in determining heat strain. Methods: Twelve young (20–30 years) healthy, heat-acclimated male subjects were exposed fully encapsulated for 3h daily to an exercise-heat stress (35°C and 30% relative humidity, walking on a motor-driven treadmill at a pace of 5 km h1 and a 4% inclination, in a work–rest cycle of 45min work and 15min rest). Two bipack CPCs (PC1 and PC2) were tested and the results were compared with those attained by two control suits—a standard cotton military BDU (CO1) and an impermeable material suit (CO2). Results: The physiological burden imposed by the two bilayer garments was within the boundaries set by the control conditions. Overall, PC2 induced a lower strain, which was closer to CO1, whereas PC1 was closer to CO2. Air permeability of the PC2 cloth was almost three times higher than that of PC1, enabling a better heat dissipation and consequently a lower physiological strain. Furthermore, air permeability characteristic of the fabrics, which is associated with its construction and weave, significantly correlated with the physiological strain, whereas the correlation with Rct, Ret, and weight was poor. Conclusions: The results emphasize the importance of air permeability in reducing the physiological strain induced by CPCs. [ABSTRACT FROM AUTHOR]

The coronavirus disease 2019 (COVID-19) pandemic, first reported in China, soon spread worldwide, has evolved into one of the most complex global public health crises the world has encountered in the last several decades. Conducting military medical research is vital to study the unique influences of military service conditions on soldiers' health and to improve the medical response in various emergency periods. The Israel Defense Forces (IDF) Medical Corps maintains an Institutional Review Board (IRB) which reviews clinical studies conducted within the IDF. During the COVID-19 pandemic, the IRB of the IDF had to rapidly implement procedural modifications in order to comply with expanding urgent demands for research without compromising ethical standards. The ethical dilemmas and the IDF policy and perspective are outlined in this article. [ABSTRACT FROM AUTHOR]

Aerobic exercise under muscle fatigue can lead to muscular damage and injuries. Finding the correlations between central and peripheral microcirculation variables, as well as with electromyography signals of leg muscles during aerobic exercise, may contribute to early muscle fatigue identification. The goal of this study was to characterize the peripheral compensation following intensive exercise for assessment of muscle performance based on non-invasive techniques. The experimental protocol included two days of measurements. Electrocardiography tests and anthropometric measurements of the volunteers (N = 14) were carried out. The maximal aerobic ability (first day), as well as electromyography and cutaneous hemodynamic variables (second day) were measured during treadmill run. A score-based Bayesian network machine-learning algorithm was used to predict ventilation values based on cutaneous hemodynamic measurements. Transcutaneous oxygen tension can be used to identify anaerobic threshold for both trained and untrained subjects during treadmill running, while electromyography can be used to identify anaerobic threshold only of trained subjects. Predicted values of ventilation, based on the transcutaneous oxygen tension, showed high correlation with actual values. Prediction accuracy was better among trained subjects, compared to the untrained ones. Transcutaneous oxygen tension could be used for prediction of maximal oxygen consumption during intense exercise and thus may provide improved assessment of premature fatigue during exercise. • Cutaneous variables could reflect local compensation mechanisms due to exercise. • Electromyography and cutaneous oxygenation can identify the anaerobic threshold. • A coupling between the peripheral and the central systems was observed. • Cutaneous oxygenation may predict minute ventilation during intensive exercise. • The results may have an impact on muscle performance assessment during exercise. [ABSTRACT FROM AUTHOR]

Sleep deprivation (SD) is suggested to be associated with reduced thermo-regulatory functions. This study aimed to quantify the effect of partial (PSD) and total (TSD) 24 h SD using a standard heat tolerance test (HTT). Eleven participants underwent HTT after well-rested state, PSD and TSD. No significant physiological differences were found between the exposures but subjective discomfort was higher after TSD. Evening chronotypes' temperature during HTT was higher after TSD compared with PSD ( p = 0.017). After TSD, evening chronotypes compared to intermediate chronotypes' temperature was higher during the first hour of the HTT ( p < 0.05), suggesting that thermo-regulatory function during exercise in the heat is influenced by chronotype. [ABSTRACT FROM AUTHOR]

Athletes, soldiers, and workers who perform intense physical activities under extreme hot conditions might encounter increased physiological thermal strain. Consequently, the increase in body core temperature (T c) might result in heat exhaustion and heatstroke. Thus, continuously following changes in T c is of utmost importance. Recently, the Tcore sensor (Dräger, Germany), which employs a unique dual-sensor heat flux technology, became commercially available to measure T c , in a hospital-controlled environment. This study aimed to evaluate the possibility of using the Tcore sensor to accurately monitor rectal temperature (T re), reflecting T c , under exercise-heat stress. Thirteen healthy young males completed the study protocol, consisting of 90 min of moderate exercise (walking on a treadmill - 5 km/h, 4% elevation) under controlled hot/dry and hot/wet climatic conditions (30 °C/60% rh, 34 °C/40% rh, and 40 °C/40% rh). Tcore sensors were placed on the forehead and the left wrist. Temperatures from both Tcore sensors were recorded continuously together with T re using a rectal thermistor. The original algorithm used by the company to estimate T re from the Tcore sensor was found to be inadequate under the study's conditions and new models for the forehead and the wrist measurements were developed. Nearly 150,000 measurement sets (after filtering) were used to build independent MATLAB software algorithms and test their reliability according to the cross-validation algorithm. Bland-Altman analysis was used to compare between the results obtained by the new models to T re. The database consisted of a large T re range (36.5–38.9 °C). The mean errors of the models were close to zero, and the mean absolute errors were 0.20 ± 0.16 °C and 0.27 ± 0.20 °C for the forehead and wrist, respectively. 95% of the measurements from the forehead model and 86% from the wrist model were within ±0.5 °C of T re , and 78% (forehead) and 64% (wrist) were within ±0.3 °C. Root Mean Square Deviation (RMSD) values were 0.29 °C and 0.40 °C for the forehead and wrist models, respectively. The developed models show the feasibility to use the Tcore sensor for assessing T re under exercise-heat conditions. Furthermore, the sensor was found to be adequate for use on the wrist as well, which might be more practical for use in field conditions. • Assessing rectal temperature (T re) non-invasively, using the Tcore sensor positioned on the forehead and wrist. • New models were developed to reflect T re from the Tcore sensor under the study's heat-exercise conditions. • Assessing T re noninvasively was within acceptable error (±0.3 °C to ±0.5 °C) [ABSTRACT FROM AUTHOR]