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The effects of hydration on cognitive performance during a simulated wildfire suppression shift in temperate and hot conditions
Abstract
The effects on dehydration and cognitive performance from heat and/or physical activity are well established in the laboratory, although have not yet been studied for personnel working in occupations such as wildland firefighting regularly exposed to these types of conditions. This study aimed to investigate the effects of temperature and dehydration on seventy-three volunteer firefighters (35.7 ± 13.7 years, mean ± standard deviation) during a simulation of wildfire suppression under either control or hot (18-20; or 33-35 °C) temperature conditions. Results showed cognitive performance on the psychomotor vigilance task declined when participants were dehydrated in the heat and Stroop task performance was impaired when dehydrated late in the afternoon. Firefighters may be at risk of deteriorations in simple cognitive functions in the heat whilst dehydrated, although may also experience impairments in complex cognitive functions if dehydrated late in the day, irrespective of the environmental temperature.
... 2 Exercise included in Cvirn et al. (2019) was categorised as moderate for the purpose of this review due to the intermittent nature of the task, including lengthy rest periods between bouts, however no physiological data is provided to support the categorisation of the exercise dose, nor reference to the intensity of the tasks included. Physiological data was also not reported in Chandra et al. (2010) and exercise dose was categorised as light based upon the authors description and seemingly non-taxing nature of the task. ...
... Across the twenty studies, sample sizes ranged from 8 to 73, with an average of 19 participants. Of the 366 participants in total, only 41 were females from 6 of the studies (Adam et al., 2008;Cvirn et al., 2019;Gerhart et al., 2020;Macleod, Cooper, Bandelow, Malcolm, & Sunderland, 2018;Parker et al., 2013;Tikuisis & Keefe, 2005). Eight studies focused on healthy, physically active individuals, seven on professional/well-trained athletes and/or referees, three on military personnel, and two on emergency service personnel. ...
... on cognition (from pre-to-post and/or to during exercise) in the heat are presented in Table 2. Of the sixteen studies that included a hot condition fifteen included comparisons with a temperate condition, and one study included only a manipulation within hot conditions (Chandra, Ghosh, Barman, Iqbal, & Sadhu, 2010). Three studies looked at temperatures between 28 • C and 30 • C (Taylor et al., 2014;Tikuisis & Keefe, 2005;Watkins et al., 2014), eight between 31 • C and 38 • C (Cvirn et al., 2019;Donnan, Williams, & Stanger, 2020;Gerhart et al., 2020;Macleod et al., 2018;McMorris et al., 2006;Parker et al., 2013;Roh, So, Cho, & Suh, 2017;Shibasaki et al., 2019), three between 39 • C and 42 • C (Radakovic et al., 2007;Tamm et al., 2014Tamm et al., , 2015, and one at 48 • C (20%rh) (Caldwell, Patterson, & Taylor, 2012). Another observed the effect of progressive heat exposure in only hot conditions (28.6-33.2 ...
To date, no review has focused specifically on the potential modulating role of environmental temperature on the effects of exercise on cognitive function. Despite this, a range of occupations and performance contexts exist (e.g., military personnel, emergency services, sport) where the maintenance of cognitive function in environmentally challenging environments is crucial. Therefore, this systematic review aimed to evaluate the experimental research investigating how manipulating environmental temperature influenced the effects of acute bouts exercise on cognitive functioning from pre-to post-exercise, or during exercise. Studies to be included were assessed by two authors reviewing title, abstract, and then full-text. From the searches conducted, twenty articles were identified which met the inclusion criteria. For the purpose of this review, exercise involved in each study was categorised into low, moderate, and vigorous dosages (dependent on intensity and duration). The results indicate that moderate dosages of exercise help stimulate improved cognitive performance from pre-to-post exercise in temperate conditions, where cold exposure appears to blunt these effects. In addition, hot environments led to cognitive decrements during and post exercise which were often identified in studies that implemented prolonged moderate or vigorous exercise protocols. Therefore, suggesting a combination of heightened physiological strain from increased dose of exercise, alongside heat exposure, can be detrimental to optimal cognitive functioning, whereby executive functioning tasks appeared to be most affected. The findings from this systematic review highlight the potential modulating role of environmental temperature on the effects of exercise on cognitive function. Thus, highlighting the importance of considering the role of environmental temperature for individuals either exercising to elicit desired cognitive benefits or for those involved in physically demanding occupations or performance domains.
... The majority of research shows that the physical performance of firefighters is largely unaffected in hot conditions [12]. However, cognitive performance is negatively affected under hot conditions [13][14][15]. This is concerning given firefighters are often tasked with making safety critical decisions [4]. ...
... Statistical significance was defined as p < 0.05 and post hoc pairwise comparisons were performed using a Bonferroni correction. The data analysed in the current study were secondary to the primary aims of the study, with primary outcomes published elsewhere [8,[12][13][14][15][48][49][50][51][52][53][54][55][56][57]. ...
Firefighters are exposed to numerous stressors during wildfire suppression, including working in hot temperatures and sleep restricted conditions. Research has shown that when sleep restricted, individuals choose foods higher in carbohydrates, fat, and sugar, and have increased cravings for calorie dense foods. However, there is currently no research on the combined effect of heat and sleep restriction on snacking behaviour. Conducting secondary analyses from a larger study, the current study aimed to investigate the impact of heat and sleep restriction on snacking behaviour and food cravings. Sixty-six firefighters completed three days of simulated physically demanding firefighting work and were randomly allocated to either the control (n = 18, CON; 19 °C, 8h sleep opportunity), sleep restricted (n = 16, SR; 19 °C, 4-h sleep opportunity), hot (n = 18, HOT; 33 °C, 8h sleep opportunity), or hot and sleep restricted (n = 14 HOT + SR; 33 °C, 4-h sleep opportunity) condition. During rest periods firefighters were able to self-select sweet, savoury, or healthy snacks from a ration pack and were asked to rate their hunger, fullness, and cravings every two hours (eating block). Mixed model analyses revealed no difference in total energy intake between conditions, however there was a significant interaction between eating block and condition, with those in the CON, HOT, and HOT + SR condition consuming significantly more energy between 1230 and 1430 compared to the SR condition (p = 0.002). Sleep restriction and heat did not impact feelings of hunger and fullness across the day, and did not lead to greater cravings for snacks, with no differences between conditions. These findings suggest that under various simulated firefighting conditions, it is not the amount of food that differs but the timing of food intake, with those that are required to work in hot conditions while sleep restricted more likely to consume food between 1230 and 1430. This has potential implications for the time of day in which a greater amount of food should be available for firefighters.
... Second, we did not consider the qualitative aspects of sleep, which may be equally crucial as the quantities. Many quality indicators can be used to evaluate sleep (Cudney et al. 2022). In addition, the sleep data were only acquired from the participants' sleep diaries. ...
The cognitive ability to self-monitor one's current performance is important for hospital nurses to maintain safety and health. However, studies on the effects of rotating shift work on self-monitoring ability are insufficient. We examined the differences in self-monitoring accuracy across shifts in a rotating three-shift system among 30 female ward nurses (mean age 28.2 years). Their self-monitoring ability was calculated by subtracting the predicted reaction times of the psycho-motor vigilance task performed just before exiting the workplace from the actual reaction times. A mixed-effect model was employed to assess the effects of shift, awake hours, and prior sleep duration on self-monitoring ability. We observed impaired self-monitoring ability in nurses, particularly after the night shift. Although actual performance remained high across all shifts, their self-predictions on reaction times became pessimistic in the night shift, resulting in a difference of approximately−100 msec. The effect of the shift on self-monitoring was obvious even after adjusting for sleep duration and hours awake. Our findings indicate that the misalignment between their working hours and circadian rhythms may affect even professional nurses. Occupational management that emphasizes maintaining circadian rhythms will improve the safety and health of nurses. ARTICLE HISTORY
... Cvirn et al found that participants exposed to high temperature (33-35°C) for a long time were not only prone to dehydration, but also likely to suffer from complex cognitive impairment. 11 Cyril et al found that those increasingly hot environmental conditions induce adverse cognitive functions and negatively affect behavioral performance results, and additionally found an inverted U-shaped relationship between temperature and cognitive performance. 12 The medical field has always experienced heavy demands, high-pressure, and complications, meaning the fatigue of medical staff have long been a topic of interest in the academic field. ...
Background:
COVID-19 has brought greater workload pressures to the medical field, such as medical staff being required to wear personal protective equipment (PPE). While PPE can protect the safety of staff during the pandemic, it can also accelerate the accumulation of fatigue among operators.
Objective:
This study explores the influence of different protection states on the mental fatigue of nurses.
Methods:
In this study, 10 participants (5 males and 5 females) were randomly selected among applicants to monitor mental fatigue during the nurses' daily work in four different PPE states (low temperature and low protection; low temperature and high protection; high temperature and low protection; high temperature and high protection). The NASA subjective mental fatigue scale was used for subjective evaluation. Reaction time, attention concentration, attention distribution, memory, and main task completion time were used for objective evaluation.
Results:
The results demonstrated a significant difference in the effects of different protection states on mental fatigue. The state of high temperature and high protection had the greatest influence on mental fatigue, the state of low temperature and low protection had the least, and states of high (low) temperature and low (high) protection had intermediate effects on mental fatigue. Furthermore, the correlation between the subjective and objective fatigue indices was analyzed using a multiple regression model.
Conclusion:
This study clarified the influence of different protection states on the mental fatigue of nurses, and verified that nurses require more time and energy to complete the same work as before under high protection states. It provides a basis for evaluating the mental fatigue of nurses in the unique period of the COVID-19 pandemic and specific ideas for optimizing the nursing process.
... Hydration in the workplace is a specific concern since dehydration can affect productivity, safety, and morale (Kenefick & Sawka, 2007). Most previous studies investigating the workers' hydration status in the workplace have focused on those performing physical activities in hot and humid environments (Butler-Dawson et al., 2019;Cvirn et al., 2019;Polkinghorne et al., 2013;Wagoner et al., 2020); however, only a few studies have investigated the hydration state of health care professionals (HCPs) working in several indoor workplaces where the temperature and humidity are controlled (Alomar et al., 2013;El-Sharkawy et al., 2016). ...
Objective: Dehydration has a risk of reducing cognitive function, which can lead to misjudgment by nurses. Nurses are required to be in optimal physical and mental conditions since their misjudgments affect the lives of patients. Therefore, it is desirable to prevent dehydration in nurses; however, the prevalence and factors of dehydration in nurses have not been clarified. This study aimed to clarify dehydration prevalence in nurses and examine dehydration factors before and after their shift. Methods: Data were collected during the day shift of 115 registered nurses in 19 wards of 2 hospitals in Japan. Urine specific gravity (USG) and body weight were measured before and after the shift to determine dehydration. Questionnaires, including demographic characteristics and fluid intake, were recorded before and after their shift. Multivariate analysis was performed based on the fluid intake, number of steps, and years of experience as dehydration factors. Results: Overall, 59 (51.3%) and 82 (71.3%) nurses were dehydrated before and after their shift, respectively. USG before the shift (odds ratio [OR]: 2.328, 95% confidence interval [CI]: 1.424-3.807) and years of experience (OR: 0.946, 95% CI: 0.899-0.996) were factors related to dehydration at the end of the shift. USG before the shift (OR: 2.573, 95% CI: 1.347-4.914) was also a factor related to dehydration factors after the shift for beginner nurses. Conclusions: Over 70% of nurses were dehydrated after their shift. USG before the shift and years of experience were related to dehydration after the shift. To prevent dehydration, it is desirable for managers to encourage beginner nurses to drink water.
... In other words, no cognitive impairments were observed with repeated exposures to low and moderate hypohydration beyond exercise-induced EUH. This observation is particularly important for firefighters [43], military personnel [44] or individuals that are exposed to hot environments with limited access to hydration over long or consecutive shifts/days. In fact, it suggests that limited access to fluids for 3 days per week over a period of several weeks is unlikely to be detrimental to cognitive performance, compared with the maintenance of euhydration during exercise. ...
We investigated the effect of repeated exposures to hypohydration upon cognitive performance. In a randomized crossover design, ten physically active adults completed two 4-week training blocks, one where they maintained euhydration (EUH) and the other where they were water-restricted (DEH) during walking/running at 55% VO2max, 40 °C. Three sessions per week were performed: (1) 1 h of exercise, (2) exercise until 2% or (3) 4% of body mass has been lost or replaced. Limited to the first and fourth training week, a 12 min walking/running time-trial was completed following the 2 and 4% exercise bouts. Trail making, the Wisconsin card sort, the Stop signal task, Simple visual reaction time and Corsi block-tapping tests were performed immediately following the time-trials. Body mass loss was maintained < 1% with EUH and reached 2.7 and 4.7% with DEH following the time-trials. Except for a lower percentage of correct responses (% accuracy) during the Wisconsin card sort test (p < 0.05) with DEH compared to EUH, no statistically significant decline in cognitive performance was induced by low and moderate levels of hypohydration. Compared to week 1, no statistical differences in cognitive responses were observed after repeated exposures to hypohydration (all p > 0.05). From a practical perspective, the gains in cognitive performance following training to DEH were mostly unclear, but under certain circumstances, were greater than when EUH was maintained. Based on the battery of cognitive tests used in the current study, we conclude that whether physically active individuals are habituated or not to its effect, exercise-induced hypohydration of 2 and 4% has, in general, no or unclear impact on cognitive performance immediately following exercise. These results encourage further research in this area.
... The inability to lose the increasing amount of trapped body heat leads to peripheral vasodilation to decrease the level of thermal strain, potentially leading to increased cardiovascular demands, which can cause a cardiovascular event or thermal emergency [61]. Furthermore, a high thermal load can result in dehydration, mental confusion and physical fatigue, which can affect firefighter's performance [44]. Pryor et al. [68] highlighted that is important to monitor the body temperature of firefighters to prevent the onset for heatrelated conditions. ...
In recent years, the necessity to prevent work-related diseases has led to the use of sensor-based systems to measure important features during working activities. This topic achieved great popularity especially in hazardous and demanding activities such as those required of firefighters. Among feasible sensor systems, wearable sensors revealed their advantages in terms of possibility to conduct measures in real conditions and without influencing the movements of workers. In addition , the advent of robotics can be also exploited in order to reduce work-related disorders. The present literature review aims at providing an overview of sensor-based systems used to monitor physiological and physical parameters in firefighters during real activities, as well as to offer ideas for understanding the potentialities of exoskeletons and assistive devices.
... Communicated by George Havenith. 1993, Martin et al. 2019, and although has been assumed to be as a function of elevated core temperature (Hocking et al. 2001, Schmit et al. 2017, Martin et al. 2019, it could also be related to perceptual and/or cardiovascular effects of high skin and mean body temperature (Gaoua 2010, Gaoua et al. 2017, dehydration (Cian et al. 2001, Ganio et al. 2011, Nolte et al. 2013, Cvirn et al. 2019, nutritional status (van Dokkum et al. 1996, Owen et al. 2004, Bandelow, Maughan et al. 2010, experience (Hancock and Vasmatzidis 2003), solar radiation (Piil et al. 2020), physical (Grego et al. 2005, Eddy et al. 2015, Yanovich et al. 2015, Bhattacharyya et al. 2017) and cognitive fatigue (Lieberman et al. 2006, Head et al. 2017, carried loads (Williams et al. 1997) and sleep deprivation (Lieberman et al. 2005), among other factors. The role of core temperature on cognition remains unclear. ...
PurposeCognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition.Methods
Eight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory.ResultsNo differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO2Hb-deO2Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions.Conclusion
Moderately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.
... During their job firefighters are exposed to a high thermal load due to heavy physical activity, external heat exposure from fires and the wear of highly insulated protective clothing. High thermal load can cause heat stress (McQuerry et al., 2018) (Costello et al., 2015) (Yazdi and Sheikhzadeh, 2014) (Nunneley, 1989) (Levels et al., 2014), resulting in heat exhaustion, dehydration, mental confusion, physical fatigue and loss of consciousness which affects productivity and risk perception (Chang et al., 2017) (Cvirn et al., 2019) (Epstein andMoran, 2006) (McInnes et al., 2017) (Barr et al., 2010). To monitor and prevent heat stress among firefighters, a reliable and continuous thermometer which is able to measure the real-time core temperature of firefighters is desirable. ...
This study aims (1) to test the validity of a new non-invasive core thermometer, Cosinuss°, in rest and (2) during firefighting simulation tasks, against invasive temperature pill and inner-ear temperature and (3) to compare the change in core temperature of firefighters when working in two types of protective clothing (traditional turnout gear versus new concept). 11 active firefighters performed twice a selection of tasks during their periodic preventive medical examination and a fire-extinguishing task. Without correction no correlation between the Cosinuss° and thermometer pill (ICC≤0.09, p ≥ 0.154, LoA≥1.37) and a moderate correlation between Cosinuss° and inner-ear infrared (ICC = 0.40, p = 0.044, LoA±1.20) was observed. With individual correction both correlations were excellent (ICC≥0.84, p = 0.000, LoA≤0.30). However, during and after working all correlations were poor and non-significant (ICC≤0.38, p ≥ 0.091, LoA≥1.71). During firefighting tasks, the Cosinuss° is invalid for measuring the core temperature. No differences in heat development in the two types of protective clothing was proven.
... Neurobehavioural performance was measured using the Psychomotor Vigilance Task (PVT). The PVT is a neurobehavioural measure of vigilance which measures response time (RT) to visual stimulus at random intervals between 2 and 10s (Dinges and Powell, 1985), and has previously been used to assess cognitive performance in emergency service workers (Cvirn et al., 2017(Cvirn et al., , 2019. The PVT-B, a shorter modified version (3 min duration with inter-stimulus intervals between 2 and 5s), has been validated against the 10-min version and has previously been used in research on sleep inertia (Hilditch et al. 2016a). ...
Sleep inertia, the state of reduced alertness upon waking, can negatively impact on-call workers. Anticipation of a stressful task on sleep inertia, while on-call was investigated. Young, healthy males (n = 23) spent an adaptation, control and two counterbalanced on-call nights in the laboratory. When on-call, participants were told they would be woken to a high or low stress task. Participants were not woken during the night, instead were given a 2300-0700 sleep opportunity. Participants slept ∼7.5-h in all conditions. Upon waking, sleep inertia was quantified using the Karolinska Sleepiness Scale and Psychomotor Vigilance and Spatial Configuration Tasks, administered at 15-min intervals. Compared to control, participants felt sleepier post waking when on-call and sleepiest in the low stress compared to the high stress condition (p < .001). Spatial performance was faster when on-call compared to control (p < .001). Findings suggest that anticipating a high-stress task when on-call, does not impact sleep inertia severity.
Working well under tremendous strain for relatively short periods is a topic of great importance in firefighting. This study put firefighters through a series of stressful solo smoke dives around a dark, winding simulation track to examine how their stress reactions affected their cognitive function. Male firefighters' heart rates were recorded during a smoke-diving exercise and compared with baseline readings and maximal rates. Male firefighters were used to studying these stressors. The firefighters thought aloud as they performed the smoke-diving maneuver to demonstrate their mental acuity. This study used a content analysis review of the literature published between the years 2017 to 2021 to define the problem, outline its complexities, and find needed solutions from dispersed sources.
Introduction: Over the years, the evolution of forest fires has occurred as a result of the evolution of the human species. However, forest fires are still a major challenge for society, placing firefighters with greater occupational exposure. The present study has as main objective to carry out a systematic review of the literature on the main techniques and variables for assessing the occupational exposure of firefighters, during the fight against forest fires.Methodology: The systematic review utilised The Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statementmethodology. This methodology was applied in the Scopus, Web of Science, Pubmed and Academic Search Complete databases with different keywords. The review will include articles written in English only. Results: In the present study, 34 articles were included, in which it was found that exposure to smoking is the most studied variable, and it was in 2019 that a greater evolution of studies in this area of research was observed. Regarding the variables, the studies were organised in groups. Here it is possible to check the different variables selected by the authors and the methods and equipment applied.Discussion: The fact that firefighters carry out their tasks in diverse scenarios and extreme conditions has hindered the application of innovative equipment. It is necessary to combine different variables and equipment for the assessment of occupational exposure. However, it is not always possible to develop this type of equipment in order to be inserted from the user's perspective, from the perspective of the environment, where it will be applied, and from an economic perspective, making it difficult to effectively apply it in the field. Conclusion: As future perspectives, it is recommended that new variables are introduced together, in order to improve the assessment of occupational exposure, namely, through the use of carbon monoxide (CO) and lactate assessment.
Tujuan penelitian ini membuktikan efek dehidrasi sampai dengan 2.8% terhadap prestasi lari 400 meter. Permasalahan dalam penelitian secara praktis kesadaran akan hidrasi ketika melakukan aktivitas jasmani terutama olahraga masih kurang, sehingga perlu bukti untuk mengetahui pengaruh dehidrasi terhadap kinerja terutama pelaku olahraga. Metode penelitian dengan quasi one group pretest post test desain. Sampel terdiri dari 25 mahasiswa pendidikan kepelatihan olahraga 6 putri dan 19 putra. Dilakukan prosedur, pengukuran berat badan, tes lari 400 meter, penghitungan dehidrasi 2.8% dari berat badan, dan tes lari 400 meter. Treatment dehidrasi sampai 2.8% berjemur pasif dengan mengenakan jas hujan. Hasil penelitian menunjukkan bahwa data tidak berdistribusi normal. Data dianalisis dengan Uji non parameterik Wilcoxon. Hasil perhitungan menunjukkan nilai signifikansi sebesar 0.000 yang menunjukkan terjadi perbedaan prestasi lari sebelum dan sesudah dehidrasi. Waktu tempuh rerata 112.48 detik menjadi 146.32 detik, terjadi kenaikan waktu tempuh 30%. Implikasi hasil penelitian ini adalah untuk olahraga prestasi, perlu diperhatikan level hidrasi atlet agar prestasi tidak mengalami penurunan drastic dan perlu upaya untuk mengatur asupan cairan.
Purpose:
To examine the effects of sleep restriction on firefighters' physical task performance, physical activity, and physiological and perceived exertion during simulated hot wildfire conditions.
Methods:
31 firefighters were randomly allocated to either the hot (n = 18, HOT; 33 °C, 8-h sleep opportunity) or hot and sleep restricted (n = 13, HOT + SR; 33 °C, 4-h sleep opportunity) condition. Intermittent, self-paced work circuits of six firefighting tasks were performed for 3 days. Firefighters self-reported ratings of perceived exertion. Heart rate, core temperature, and physical activity were measured continuously. Fluids were consumed ad libitum, and all food and fluids consumed were recorded. Urine volume and urine specific gravity (USG) were analysed and sleep was assessed using polysomnography (PSG).
Results:
There were no differences between the HOT and HOT + SR groups in firefighters' physical task performance, heart rate, core temperature, USG, or fluid intake. Ratings of perceived exertion were higher (p < 0.05) in the HOT + SR group for two of the six firefighting tasks. The HOT group spent approximately 7 min more undertaking moderate physical activity throughout the 2-h work circuits compared to the HOT + SR group.
Conclusion:
Two nights of sleep restriction did not influence firefighters' physical task performance or physiological responses during 3 days of simulated wildfire suppression. Further research is needed to explore firefighters' pacing strategies during real wildfire suppression.
Wildland firefighters perform physical work while being subjected to multiple stressors and adverse, volatile working environments for extended periods. Recent research has highlighted sleep as a significant and potentially modifiable factor impacting operational performance. The aim of this review was to (1) examine the existing literature on firefighters' sleep quantity and quality during wildland firefighting operations; (2) synthesise the operational and environmental factors that impact on sleep during wildland firefighting; and (3) assess how sleep impacts aspects of firefighters' health and safety, including mental and physical health, physical task performance, physical activity and cognitive performance. Firefighters' sleep is restricted during wildfire deployments, particularly when shifts have early start times, are of long duration and when sleeping in temporary accommodation. Shortened sleep impairs cognitive but not physical performance under simulated wildfire conditions. The longer-term impacts of sleep restriction on physiological and mental health require further research. Work shifts should be structured, wherever possible, to provide regular and sufficient recovery opportunities (rest during and sleep between shifts), especially in dangerous working environments where fatigue-related errors have severe consequences. Fire agencies should implement strategies to improve and manage firefighters' sleep and reduce any adverse impacts on firefighters' work.
Objective
The aim of the study was to assess the sleep quality, quantity, and fatigue levels of Canadian wildland firefighters while on deployment.
Methods
Objective and subjective sleep and fatigue measures were collected using actigraphy and questionnaires during non-fire (Base) and fire (Initial Attack and Project) deployments.
Results
Suboptimal sleep quality and quantity were more frequently observed during high-intensity, Initial Attack fire deployments. Suboptimal sleep was also exhibited during non-fire (Base) work periods, which increases the risk of prefire deployment sleep debt. Self-reported, morning fatigue scores were low-to-moderate and highest for Initial Attack fire deployments.
Conclusions
The study highlights the incidence of suboptimal sleep patterns in wildland firefighters during non-fire and fire suppression work periods. These results have implications for the health and safety practices of firefighters given the link between sleep and fatigue, in a characteristically hazardous occupation.
This study was designed to examine the effects of ambient heat on firefighters' physical task performance, and physiological and perceptual responses when sleep restricted during simulated wildfire conditions. Thirty firefighters were randomly allocated to the sleep restricted (n = 17, SR; 19 • C, 4-h sleep opportunity) or hot and sleep restricted (n = 13, HOT + SR; 33 • C, 4-h sleep opportunity) condition. Firefighters performed two days of simulated, intermittent, self-paced work circuits comprising six firefighting tasks. Heart rate, and core temperature were measured continuously. After each task, firefighters reported their rating of perceived exertion and thermal sensation. Effort sensation was also reported after each work circuit. Fluids were consumed ad libitum. Urine volume and urine specific gravity were analysed. Sleep was monitored using polysomnography. There were no differences between the SR and HOT + SR groups in firefighters' physiological responses, hydration status, ratings of perceived exertion, motivation, and four of the six firefighting tasks (charged hose advance, rake, hose rolling, static hose hold). Black out hose and lateral repositioning were adversely affected in the HOT + SR group. Working in hot conditions did not appear to consistently impair firefighters work performance, physiology, and perceptual responses. Future research should determine whether such findings remain true when individual tasks are performed over longer durations.
Little is currently known about the physical activity patterns of workers in physically
demanding populations. The aims of this study were to (a) quantify firefighters’ physical activity
and sedentary time within (2-h periods) and across planned burn shifts; and (b) examine whether
firefighters’ activity levels during one shift or 2-h period was associated with their activity levels
in the following shift or 2-h period. Thirty-four salaried firefighters (26 men, 8 women) wore an
Actical accelerometer for 28 consecutive days. Time spent sedentary (SED) and in light- (LPA),
moderate- (MPA) and vigorous-intensity physical activity (VPA) were derived using validated
cut-points. Multilevel analyses (shift, participant) were conducted using generalised linear latent
and mixed models. Firefighters spent the majority of a planned burn shift (average length 10.4 h) or
2-h period engaged in LPA (69% and 70%, respectively). No significant associations were observed
between SED and physical activity levels between consecutive planned burned shifts or 2-h periods.
The physical activity that a firefighter engaged in during one shift (or 2-h period) did not subsequently
affect their physical activity levels in the subsequent shift (or 2-h period). Further research is needed
to establish how workers in physically demanding populations are able to sustain their activity levels
over long periods of time.
The 10 min psychomotor vigilance task (PVT) is commonly used in laboratory studies
to assess the impact of sleep loss, sustained wakefulness, and/or time of day on neurobehavioral
performance. In field settings, though, it may be impractical for participants
to perform a test of this length. The aim of this study was to identify a
performance measure that is sensitive to the effects of fatigue but less burdensome
than a 10 min test. Sixteen participants (11 female, 5 male; mean age ¼ 21.7 years)
slept in the sleep laboratory overnight then remained awake for 28 h from 08:00 h.
During every second hour, participants completed three PVTs of differing duration
(10 min, 5 min, 90 sec). For the 5 min/10 min comparison, ANOVA indicated that
response time was significantly affected by test length (F1,14 ¼ 26.9, p , .001) and
hours of wakefulness (F13,182 ¼ 46.1, p , .001) but not by their interaction
(F13,182 ¼ 1.7, ns). There was a strong correlation between response time on the 5
and 10 min PVTs (r ¼ .88, p , .001). For the 90 sec/10 min comparison, ANOVA
indicated that response time was significantly affected by test length (F1,14 ¼ 65.9,
p , .001) and hours of wakefulness (F13,182 ¼ 29.7, p , .001) as well as by their interaction
(F13,182 ¼ 6.0, p , .001). There was a strong correlation between response time
on the 90 sec and 10 min PVTs (r ¼ .77, p , .001). The effects of hours of wakefulness
on neurobehavioral performance were similar for the 5 min and 10 min PVTs. In contrast,
performance on the 90 sec PVT was less affected by hours of wakefulness than on
the 10 min PVT. In addition, performance on the 10 min PVT was more highly correlated
with the 5 min PVT than the 90 sec PVT. These data indicate that the 5 min PVT
may provide a reasonable substitute for the 10 min PVT in circumstances where a test
shorter than 10 min is required.
In this study, we evaluated the sensitivity of a 5-min personal digital assistant–psychomotor vigilance test
(PDA–PVT) to severe sleep loss. Twenty-one participants completed a 10-min PVT-192 and a 5-min PDA–PVT
at two hourly intervals during 62 h of sustained wakefulness. For both tasks, response speed and number of
lapses (RTs . 500) per minute significantly increased with increasing hours of wakefulness. Overall, standardised response speed scores on the 5-min PDA–PVT closely tracked those of the PVT-192; however, the PDA–PVT was generally associated with more lapses/minute. Closer inspection of the data indicated that when the level of sleep loss and fatigue became more severe (i.e., Day 3), the 5-min PDA–PVT was not quite as sensitive as the 10-min PVT-192 when 2- to 10-sec foreperiods were used for both. It is likely, however, that the observed differences between the two devices was due to differences in task length. Thus, the findings provide further evidence of the validity of the 5-min PDA–PVT as a substitute for the 10-min PVT-192, particularly in circumstances in which a shorter test is required and/or the PVT-192 is not as practical.
Planned burning is a preventative strategy aimed at decreasing fuel loads to reduce the severity of future wildfire events. During planned burn operations, firefighters can work long shifts. Furthermore, remote burning locations may require firefighters to sleep away from home between shifts. The existing evidence surrounding firefighters' sleep during such operations is exclusively anecdotal. The aims of the study were to describe firefighters' sleep during planned burn operations and evaluate the impact of the key operational factors (shift start time, shift length and sleeping location) that may contribute to inadequate sleep. Thirty-three salaried firefighters were recruited from Australia's fire agencies and sleep was measured objectively using wrist actigraphy for four weeks. All variables were examined in two conditions: (1) burn days, and (2) non-burn days. Time in bed, total sleep time, sleep latency and sleep efficiency were evaluated objectively. Subjective reports of pre- and post-sleep fatigue, sleep location, sleep quality, sleep quantity, number of times woken and sleep timing were also recorded. Analyses revealed no differences in measures of sleep quantity and quality when comparing non-burn and burn days. Total sleep time was less when planned burn shifts were >12 h. However, on burn days, work shift start time as well as sleeping location did not impact firefighters' sleep quantity. Self-reported levels of pre- and post-sleep fatigue were greater on burn days compared to non-burn days. These findings indicate that sleep quantity and quality are not compromised during planned burn operations <12 h in duration.
Cognitive function defines performance in objective tasks that require conscious mental effort. Extreme environments, namely heat, hypoxia, and cold can all alter human cognitive function due to a variety of psychological and/or biological processes. The aims of this Focused Review were to discuss; (1) the current state of knowledge on the effects of heat, hypoxic and cold stress on cognitive function, (2) the potential mechanisms underpinning these alterations, and (3) plausible interventions that may maintain cognitive function upon exposure to each of these environmental stressors. The available evidence suggests that the effects of heat, hypoxia, and cold stress on cognitive function are both task and severity dependent. Complex tasks are particularly vulnerable to extreme heat stress, whereas both simple and complex task performance appear to be vulnerable at even at moderate altitudes. Cold stress also appears to negatively impact both simple and complex task performance, however, the research in this area is sparse in comparison to heat and hypoxia. In summary, this focused review provides updated knowledge regarding the effects of extreme environmental stressors on cognitive function and their biological underpinnings. Tyrosine supplementation may help individuals maintain cognitive function in very hot, hypoxic, and/or cold conditions. However, more research is needed to clarify these and other postulated interventions.
The aim of this study was to examine the associations between firefighters’ physical activity levels
across consecutive shifts during a multi-day emergency wildfire and to determine whether sleep
duration moderated these associations. Forty volunteer firefighters (31 males, 9 females) wore an
activity monitor to concurrently measure physical activity and sleep duration. Sedentary time and time
spent in light- (LPA), moderate- (MPA), and vigorous-intensity physical activity (VPA) during each
shift were determined using monitor-specific cut points. During any given shift, every additional 60
min spent in LPA was associated with 7.2 min more LPA and 27.6 min MPA the following shift.
There were no other significant positive or negative associations. No significant moderating effect of
total sleep time was observed. Firefighters are able to maintain and/or increase their physical activity
intensity between consecutive shifts. Further research is needed to understand firefighters pacing and
energy conservation strategies during emergency wildfire deployments.
This study examined firefighters' sleep quantity and quality throughout multi-day wildfire suppression, and assessed the impact of sleep location, shift length, shift start time, and incident severity on these variables. For four weeks, forty-one volunteer firefighters sleep was assessed using wrist actigraphy. Analyses revealed that the quantity of sleep obtained on fire days was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. On fire days, total sleep time was less when: i) sleep location was in a tent or vehicle, ii) shifts were greater than 14 h, and iii) shifts started between 05:00-06:00 h. This is the first empirical investigation providing objective evidence that firefighters' sleep is restricted during wildfire suppression. Furthermore, sleep location, shift length, and shift start time should be targeted when designing appropriate controls to manage fatigue-related risk and preserve firefighter health and safety during wildfire events. Practitioner Summary During multi-day wildfire suppression, firefighters' sleep quantity was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. Furthermore, total sleep time was less when: i) sleep occurred in a tent/vehicle, ii) shifts were >14 h, and iii) shifts started between 05:00-06:00 h.
This study assessed the accumulated effect of ambient heat on the performance of, and physiological and perceptual responses to, intermittent, simulated wildfire fighting tasks over three consecutive days. Firefighters (n = 36) were matched and allocated to either the CON (19°C) or HOT (33°C) condition. They performed three days of intermittent, self-paced simulated firefighting work, interspersed with physiological testing. Task repetitions were counted (and converted to distance or area) to determine work performance. Participants were asked to rate their perceived exertion and thermal sensation after each task. Heart rate, core temperature (Tc), and skin temperature (Tsk) were recorded continuously throughout the simulation. Fluids were consumed ad libitum. Urine volume was measured throughout, and urine specific gravity (USG) analysed, to estimate hydration. All food and fluid consumption was recorded. There was no difference in work output between experimental conditions. However, significant variation in performance responses between individuals was observed. All measures of thermal stress were elevated in the HOT, with core and skin temperature reaching, on average, 0.24 ± 0.08°C and 2.81 ± 0.20°C higher than the CON group. Participants' doubled their fluid intake in the HOT condition, and this was reflected in the USG scores, where the HOT participants reported significantly lower values. Heart rate was comparable between conditions at nearly all time points, however the peak heart rate reached each circuit was 7 ± 3% higher in the CON trial. Likewise, RPE was slightly elevated in the CON trial for the majority of tasks. Participants' work output was comparable between the CON and HOT conditions, however the performance change over time varied significantly between individuals. It is likely that the increased fluid replacement in the heat, in concert with frequent rest breaks and task rotation, assisted with the regulation of physiological responses (e.g., heart rate, core temperature).
To examine the effects of sleep restriction on firefighters' physical task performance during simulated wildfire suppression.
Thirty-five firefighters were matched and randomly allocated to either a control condition (8-hour sleep opportunity, n = 18) or a sleep restricted condition (4-hour sleep opportunity, n = 17). Performance on physical work tasks was evaluated across three days. In addition, heart rate, core temperature, and worker activity were measured continuously. Rate of perceived and exertion and effort sensation were evaluated during the physical work periods.
There were no differences between the sleep-restricted and control groups in firefighters' task performance, heart rate, core temperature, or perceptual responses during self-paced simulated firefighting work tasks. However, the sleep-restricted group were less active during periods of non-physical work compared to the control group.
Under self-paced work conditions, 4 h of sleep restriction did not adversely affect firefighters' performance on physical work tasks. However, the sleep-restricted group were less physically active throughout the simulation. This may indicate that sleep-restricted participants adapted their behaviour to conserve effort during rest periods, to subsequently ensure they were able to maintain performance during the firefighter work tasks. This work contributes new knowledge to inform fire agencies of firefighters' operational capabilities when their sleep is restricted during multi-day wildfire events. The work also highlights the need for further research to explore how sleep restriction affects physical performance during tasks of varying duration, intensity, and complexity.
Global warming will increase heat stress at home and at work. Few studies have addressed the health consequences in tropical low and middle income settings such as Thailand. We report on the association between heat stress and workplace injury among workers enrolled in the large national Thai Cohort Study in 2005 (N=58,495). We used logistic regression to relate heat stress and occupational injury separately for males and females, adjusting for covariate effects of age, income, education, alcohol, smoking, Body Mass Index, job location, job type, sleeping hours, existing illness, and having to work very fast. Nearly 20% of workers experienced occupational heat stress which strongly and significantly associated with occupational injury (adjusted OR 2.12, 95%CI 1.87-2.42 for males and 1.89, 95%CI 1.64-2.18 for females). This study provides evidence connecting heat stress and occupational injury in tropical Thailand and also identifies several factors that increase heat exposure. The findings will be useful for policy makers to consider work-related heat stress problems in tropical Thailand and to develop an occupational health and safety program which is urgently needed given the looming threat of global warming.
Background:
The water-deficit equation {WD(1) = 0.6 × B(m) × [1 - (140 ÷ Na(+))]; B(m) denotes body mass} is used in medicine and nutrition to estimate the volume (L) of water required to correct dehydration during the initial stages of fluid-replacement therapy. Several equation assumptions may limit its accuracy, but none have been systematically tested.
Objectives:
We quantified the potential error in WD(1) for the estimation of free water (FW) and total body water (TBW) losses and systematically evaluated its assumptions.
Design:
Thirty-six euhydrated volunteers were dehydrated (2.2-5.8% B(m)) via thermoregulatory sweating. Assumptions within WD(1) were tested by substituting measured euhydrated values for assumed or unknown values. These included the known (premorbid) B(m) (WD(2)), a proposed correction for unknown B(m) (WD(3)), the TBW estimated from body composition (WD(4)), the actual plasma sodium (WD(5)), the substitution of plasma osmolality (Posm) for sodium (WD(6)), and actual Posm (WD(7)).
Results:
Dehydration reduced TBW by 3.49 ± 0.91 L, 57% of which (2.02 ± 0.96 L) was FW loss, and increased plasma sodium from 139 (range: 135-143 mmol/L) to 143 (range: 141-148 mmol/L) mmol/L. Calculations for WD(1) through WD(7) all underestimated TBW loss by 1.5-2.5 L (P < 0.05). WD(1) through WD(5) underestimated FW by 0.5 L to 1.0 L (P < 0.05), but WD(6) and WD(7) estimated FW loss to within 0.06-0.16 L (P > 0.05).
Conclusions:
WD(1) grossly underestimates TBW and FW losses. Corrections for unknowns and assumptions (WD(2) through WD(5)) improved estimates little. The use of WD(6) = 0.6 × B(m) × [1 - (290 ÷ Posm)] accurately estimates FW but still underestimates TBW losses by >40%.
Submitted 8 healthy, endurance trained men (mean age 27.4 yrs), unacclimated to heat, to variations in body hydration. The Ss were kept euhydrated, dehydrated by controlled passive hyperthermia or exercise on a treadmill up to a weight loss of 2.8%, or hyperhydrated using a solution containing glycerol, with a total ingested volume equal to 21.4 ml/kg of body weight. On completion of a 90-min recovery period, the Ss were assigned a pedaling exercise and psychological tests of perceptive discrimination, psycho-motor skill, memory, fatigue and mood, were administered. Both dehydration conditions impaired cognitive abilities without any relative differences between them. Following arm crank exercise, further effects of dehydration were found for tracking performance only. Moreover, long-term memory was impaired in both control and hydration situations, whereas there was no decrement in performance in the hyperhydration condition. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic function of the internal environment. This can adversely affect cognitive performance, not only in groups more vulnerable to dehydration, such as children and the elderly, but also in young adults. However, few studies have examined the impact of mild or moderate dehydration on cognitive performance. This paper reviews the principal findings from studies published to date examining cognitive skills. Being dehydrated by just 2% impairs performance in tasks that require attention, psychomotor, and immediate memory skills, as well as assessment of the subjective state. In contrast, the performance of long-term and working memory tasks and executive functions is more preserved, especially if the cause of dehydration is moderate physical exercise. The lack of consistency in the evidence published to date is largely due to the different methodology applied, and an attempt should be made to standardize methods for future studies. These differences relate to the assessment of cognitive performance, the method used to cause dehydration, and the characteristics of the participants.
Due to their schedules, train drivers are likely to experience elevated fatigue at work, which can have marked safety consequences. This study investigated the effects of fatigue on the ability to negotiate speed restrictions. Twenty male train drivers drove a realistic rail simulator and their performance was evaluated in fatigue three fatigue groups; low, moderate and high. Overall, fatigue had a marked effect on performance during speed restrictions. In general, drivers in the high fatigue group used the brake less and traveled at faster speeds. In addition, it appears that speed restrictions following moderate to heavy descending grades are more likely to be sensitive to fatigue. In contrast, performance was less affected during undulating territory, where a higher level of interaction was required to control the train. Overall, results suggested that there are certain types of track sections where fatigue is most likely to have serious effect.
Limited information is available regarding the effects of mild dehydration on cognitive function. Therefore, mild dehydration was produced by intermittent moderate exercise without hyperthermia and its effects on cognitive function of women were investigated. Twenty-five females (age 23.0 ± 0.6 y) participated in three 8-h, placebo-controlled experiments involving a different hydration state each day: exercise-induced dehydration with no diuretic (DN), exercise-induced dehydration plus diuretic (DD; furosemide, 40 mg), and euhydration (EU). Cognitive performance, mood, and symptoms of dehydration were assessed during each experiment, 3 times at rest and during each of 3 exercise sessions. The DN and DD trials in which a volunteer attained a ≥1% level of dehydration were pooled and compared to that volunteer's equivalent EU trials. Mean dehydration achieved during these DN and DD trials was -1.36 ± 0.16% of body mass. Significant adverse effects of dehydration were present at rest and during exercise for vigor-activity, fatigue-inertia, and total mood disturbance scores of the Profile of Mood States and for task difficulty, concentration, and headache as assessed by questionnaire. Most aspects of cognitive performance were not affected by dehydration. Serum osmolality, a marker of hydration, was greater in the mean of the dehydrated trials in which a ≥1% level of dehydration was achieved (P = 0.006) compared to EU. In conclusion, degraded mood, increased perception of task difficulty, lower concentration, and headache symptoms resulted from 1.36% dehydration in females. Increased emphasis on optimal hydration is warranted, especially during and after moderate exercise.
The present study assessed the effects of mild dehydration on cognitive performance and mood of young males. A total of twenty-six men (age 20·0 (sd 0·3) years) participated in three randomised, single-blind, repeated-measures trials: exercise-induced dehydration plus a diuretic (DD; 40 mg furosemide); exercise-induced dehydration plus placebo containing no diuretic (DN); exercise while maintaining euhydration plus placebo (EU; control condition). Each trial included three 40 min treadmill walks at 5·6 km/h, 5 % grade in a 27·7°C environment. A comprehensive computerised six-task cognitive test battery, the profile of mood states questionnaire and the symptom questionnaire (headache, concentration and task difficulty) were administered during each trial. Paired t tests compared the DD and DN trials resulting in >1 % body mass loss (mean 1·59 (sd 0·42) %) with the volunteer's EU trial (0·01 (sd 0·03) %). Dehydration degraded specific aspects of cognitive performance: errors increased on visual vigilance (P = 0·048) and visual working memory response latency slowed (P = 0·021). Fatigue and tension/anxiety increased due to dehydration at rest (P = 0·040 and 0·029) and fatigue during exercise (P = 0·026). Plasma osmolality increased due to dehydration (P < 0·001) but resting gastrointestinal temperature was not altered (P = 0·238). In conclusion, mild dehydration without hyperthermia in men induced adverse changes in vigilance and working memory, and increased tension/anxiety and fatigue.
Well-recognized markers for static (one time) or dynamic (monitoring over time) dehydration assessment have not been rigorously tested for their usefulness in clinical, military, and sports medicine communities.
This study evaluated the components of biological variation and the accuracy of potential markers in plasma, urine, saliva, and body mass (B(m)) for static and dynamic dehydration assessment.
We studied 18 healthy volunteers (13 men and 5 women) while carefully controlling hydration and numerous preanalytic factors. Biological variation was determined over 3 consecutive days by using published methods. Atypical values based on statistical deviations from a homeostatic set point were examined. Measured deviations in body fluid were produced by using a separate, prospective dehydration experiment and evaluated by receiver operating characteristic (ROC) analysis to quantify diagnostic accuracy.
All dehydration markers displayed substantial individuality and one-half of the dehydration markers displayed marked heterogeneity of intraindividual variation. Decision levels for all dehydration markers were within one SD of the ROC criterion values, and most levels were nearly identical to the prospective group means after volunteers were dehydrated by 1.8-7.0% of B(m). However, only plasma osmolality (P(osm)) showed statistical promise for use in the static dehydration assessment. A diagnostic decision level of 301 plusmn 5 mmol/kg was proposed. Reference change values of 9 mmol/kg (P(osm)), 0.010 [urine specific gravity (U(sg))], and 2.5% change in B(m) were also statistically valid for dynamic dehydration assessment at the 95% probability level.
P(osm) is the only useful marker for static dehydration assessment. P(osm), U(sg), and B(m) are valid markers in the setting of dynamic dehydration assessment.
The occupation of firefighting is one that has repeatedly attracted the research interests of ergonomics. Among the activities encountered are attention to live fires, performing search and rescue of victims, and dealing with emergencies. The scientific literature is reviewed to highlight the investigative models used to contribute to the knowledge base about the ergonomics of firefighting, in particular to establish the multi-variate demands of the job and the attributes and capabilities of operators to cope with these demands. The job requires individuals to be competent in aerobic and anaerobic power and capacity, muscle strength, and have an appropriate body composition. It is still difficult to set down thresholds for values in all the areas in concert. Physiological demands are reflected in metabolic, circulatory, and thermoregulatory responses and hydration status, whilst psychological strain can be partially reflected in heart rate and endocrine measures. Research models have comprised of studying live fires, but more commonly in simulations in training facilities or treadmills and other ergometers. Wearing protective clothing adds to the physiological burden, raising oxygen consumption and body temperature, and reducing the time to fatigue. More sophisticated models of cognitive function compatible with decision-making in a fire-fighting context need to be developed. Recovery methods following a fire-fighting event have focused on accelerating the restoration towards homeostasis. The effectiveness of different recovery strategies is considered, ranging from passive cooling and wearing of cooling jackets to immersions in cold water and combinations of methods. Rehydration is also relevant in securing the safety of firefighters prior to returning for the next event in their work shift.
Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La-]b, and plasma catecholamine [CA]pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La-]b, and [CA]pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La-]b, and [CA]pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = -0.651) and noradrenaline concentrations (r = -0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La-]b and [CA]pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT.
The aim of the present study was to examine the effect of increased arousal induced by a prolonged exercise at ventilatory threshold simple reaction time performance performed during a running task. 11 well trained triathletes completed two testing sessions within a 2-wk. period. The first session was a protocol of VO2 max determination conducted on a treadmill. This protocol was used to assess the velocity associated with ventilatory threshold (vVvt). The second session was a 90-min. running test performed at vVvt. This last session was composed of five submaximal treadmill runs (10-min. long, 0% grade) separated by four overground runs (10-min.). Before, during each treadmill run, and after exercise, subjects performed three blocks of 20 simple reaction time. Furthermore, at the end of each overground run, perceived exertion (RPE) was recorded. Analysis showed a significant impairment in Simple RT performance during the first treadmill run only. After this first run a significant effect of exercise duration on Simple RT was observed. After 40-min. of exercise a significant improvement in reaction time during exercise was recorded, Furthermore, when Simple RT was recorded at rest, there was no difference pre-exercise and postexercise. These results suggest that a simple cognitive performance could be improved during exercise, despite the negative effect of the dual task. This improvement in reaction time could be explained mainly by an increase in arousal induced by a prolonged exercise.
The aim of the present study was to examine the effects of prolonged exercise at the ventilatory threshold and carbohydrate ingestion on single (SRT) and choice (CRT) reaction time. Eight well-trained triathletes completed three testing sessions within a 3-week period. Maximal oxygen uptake was determined in the first test, whereas the second and the third sessions were composed of a 100-min run (treadmill 15 min, overground 70 min, treadmill 15 min) performed at the velocity associated with the ventilatory threshold. During these submaximal tests, the subjects ingested (in random order) 8 ml x kg(-1) body weight of either a placebo (Pl) or 5.5% carbohydrate (CHO) solution prior to the first submaximal run and 2 ml x kg(-1) body weight every 15 min after that. The cognitive tasks were performed before and after exercise for CRT, and before, during each submaximal run and after exercise for SRT. Furthermore, at the end of each submaximal test subjects were asked to report their rating of perceived exertion (RPE). Results showed a significant positive effect of CHO ingestion on RPE and CRT performance at the end of exercise, while no effect of exercise duration was found in the Pl condition. After a 100-min run, during the CHO condition, CRT mean (SD) group values decreased from 688.5 (51) ms to 654 (63) ms, while during the Pl condition, RPE mean group values increased from 11 (2) to 16 (1.02) and CRT mean values remained stable [688 (104) ms vs 676 (73.4) ms, P > 0.05]. No similar effect was observed for SRT. These results suggest that CHO-electrolyte ingestion during a 100-min run results in an improvement in the complex cognitive performance measured at the end of that run.
A review was conducted of studies that assessed the effects of acute bouts of physical activity on adults' cognitive performance. Three groups of studies were constituted on the basis of the type of exercise protocol employed. Each group was then evaluated in terms of information-processing theory. It was concluded that submaximal aerobic exercise performed for periods up to 60 min facilitate specific aspects of information processing; however, extended exercise that leads to dehydration compromises both information processing and memory functions. The selective effects of exercise on cognitive performance are explained in terms of Sanders' [Acta Psychol. 53 (1983) 61] cognitive-energetic model.
Our lab has recently documented the total energy expenditure during arduous wildfire suppression using the doubly labeled water methodology. The elevated rates of isotopic elimination indicate an arduous working environment that may often compromise energy balance and overall hydration.
The purpose of this investigation was to determine the effects of arduous wildfire suppression on water turnover and changes in body composition in wildland firefighters (WLFF).
WLFF (N = 14) were studied during a 5-d period of arduous fire suppression work. A comparison group (N = 13) of recreationally active college students (RACS) was also studied. Water turnover was measured from rates of 2H elimination (rH2O). Urine osmolality, specific gravity, and skinfold measures were also collected.
WLFF demonstrated a decrease in nude body weight (pre = 71.9 +/- 10.4 kg, post = 70.9 +/- 10.2 kg, P = 0.0001) and total body water (pre = 42.9 +/- 7.2 kg, post = 42.0 +/- 6.7 kg, P = 0.0046). RACS maintained total body water and body weight during the experimental period. Isotope (2H2O) dilution demonstrated that rH2O was significantly higher for the WLFF (rH2O = 6.7 +/- 1.4 and 3.8 +/- 1.0 L.24 h-1 for the WLFF and RACS, respectively).
These results demonstrate an arduous work environment that threatens hydration, energy balance, and perhaps normal glycogen status.
The purpose of the present study was to examine the influence of submaximal aerobic exercise duration on simple and complex cognitive performance. Eight well-trained male subjects agreed to participate in this study (trial group). A control group of eight regularly trained male subjects was included for comparative purposes. For the trial group, the experiment involved a critical flicker fusion test (CFF) and a map recognition task performed before, every 20 min during, and immediately after, a 3-h cycling task at an intensity corresponding to approximately 60 % of VO2max. Data were obtained over two experimental sessions with fluid ingestion (F) or no fluid (NF) ingestion. For the control group the experiment was the same but without exercise and fluid ingestion. In the trial group, a significant effect of hydration status was observed on physiological parameters (p <0.05). No effect was found on cognitive performance. A significant decrease in CFF performance was observed after 120 min of exercise when compared with the first 20 min (respectively for CFFmdi: 2.6 vs. 3.8 Hz), irrespective of experimental condition. A significant improvement in speed of response (respectively: 3291 vs. 3062 msec for 20 and 120 min, respectively) and a decrease in error number (21.5 % vs. 6.0 % for 20 and 120 min, respectively) during the map recognition task were recorded between 80 min and 120 min when compared with the first 20 min of exercise. After 120 min the number of recorded errors was significantly greater indicating a shift in the accuracy-speed trade-off (6.0 % vs. 14.1 % for 120 and 180 min, respectively). These results provide some evidence for exercise-induced facilitation of cognitive function. However this positive effect disappears during prolonged exercise--as evidenced within our study by an increase in errors during the complex task and an alteration in perceptual response (i.e. the appearance of symptoms of central fatigue).
Whether mental performance is affected by slowly progressive moderate dehydration induced by water deprivation has not been examined previously. Therefore, objective and subjective cognitive-motor function was examined in 16 volunteers (8 females, 8 males, mean age: 26 yr) twice, once after 24 h of water deprivation and once during normal water intake (randomized cross-over design; 7-day interval). Water deprivation resulted in a 2.6% decrease in body weight. Neither cognitive-motor function estimated by a paced auditory serial addition task, an adaptive 5-choice reaction time test, a manual tracking test, and a Stroop word-color conflict test nor neurophysiological function assessed by auditory event-related potentials P300 (oddball paradigm) differed (P > 0.1) between the water deprivation and the control study. However, subjective ratings of mental performance changed significantly toward increased tiredness (+1.0 points) and reduced alertness (-0.9 points on a 5-point scale; both: P < 0.05), and higher levels of perceived effort (+27 mm) and concentration (+28 mm on a 100-mm scale; both: P < 0.05) necessary for test accomplishment during dehydration. Several reaction time-based responses revealed significant interactions between gender and dehydration, with prolonged reaction time in women but shortened in men after water deprivation (Stroop word-color conflict test, reaction time in women: +26 ms, in men: -36 ms, P < 0.01; paced auditory serial addition task, reaction time in women +58 ms, in men -31 ms, P = 0.05). In conclusion, cognitive-motor function is preserved during water deprivation in young humans up to a moderate dehydration level of 2.6% of body weight. Sexual dimorphism for reaction time-based performance is present. Increased subjective task-related effort suggests that healthy volunteers exhibit cognitive compensating mechanisms for increased tiredness and reduced alertness during slowly progressive moderate dehydration.
In recent years, there has been an increasing need for a reliable and practical tool for assessing fatigue-related impairment in the field. This study investigated the sensitivity of one potential tool, a 5-min version of the psychomotor vigilance task (PVT) specifically designed for use on personal digital assistants (PDA), to 28 h of sustained wakefulness.
There were 15 participants who slept in the laboratory overnight then remained awake from 08:00 (Day 1) to 12:00 (Day 2). During every second hour, they completed a 10-min PVT, a sustained attention task that is sensitive to the effects of sleep loss and fatigue, and a 5-min PDA-PVT.
While performance on both tasks significantly varied as a function of hours of wakefulness, responses on the PDA-PVT were typically slower than on the PVT. When performance scores were standardized, the negative impact of increasing hours of wakefulness on performance on the 5-min PDA-PVT and 10-min PVT did not significantly differ.
The findings suggest that the 5-min PDA-PVT may provide a reasonable substitute for the 10-min PVT, particularly in circumstances where a shorter test is required and/or the standard PVT is not as practical.
This field-portable reaction time test and analysis software run on devices using the Palm operating system. It is designed to emulate a test and commercial device widely used in sleep deprivation, shift work, fatigue, and stimulant drug research but provides additional capabilities. Experimental comparisons with the standard commercial device in a 40-hour total sleep deprivation study show it to be comparably sensitive to selected experimental variables. A Pocket PC-compatible version is under developement.
(i) To evaluate firefighters' pre- and post-shift hydration status across two shifts of wildfire suppression work in hot weather conditions. (ii) To document firefighters' fluid intake during and between two shifts of wildfire suppression work. (iii) To compare firefighters' heart rate, activity, rating of perceived exertion (RPE), and core temperature across the two consecutive shifts of wildfire suppression work.
Across two consecutive days, 12 salaried firefighters' hydration status was measured immediately pre- and post-shift. Hydration status was also measured 2h post-shift. RPE was also measured immediately post-shift on each day. Work activity, heart rate, and core temperature were logged continuously during each shift. Ten firefighters also manually recorded their food and fluid intake before, during, and after both fireground shifts.
Firefighters were not euhydrated at all measurement points on Day one (292±1 mOsm l(-1)) and euhydrated across these same time points on Day two (289±0.5 mOsm l(-1)). Fluid consumption following firefighters' shift on Day one (1792±1134ml) trended (P = 0.08) higher than Day two (1108±1142ml). Daily total fluid intake was not different (P = 0.27), averaging 6443±1941ml across both days. Core temperature and the time spent ≥ 70%HRmax were both elevated on Day one (when firefighters were not euhydrated). Firefighters' work activity profile was not different between both days of work.
There was no difference in firefighters' pre- to post-shift hydration within each shift, suggesting ad libitum drinking was at least sufficient to maintain pre-shift hydration status, even in hot conditions. Firefighters' relative hypohydration on Day one (despite a slightly lower ambient temperature) may have been associated with elevations in core temperature, more time in the higher heart rate zones, and 'post-shift' RPE.
© The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.
Firefighters' fluid balance was measured while they attempted to suppress well-developed experimental bushfires of intensities commonly faced by hand-tool crews, and also while they built fireline in the same way without fire, during three summers in Australian eucalypt forests. They consistently sweated at rates of 1-2 kg h-1 while building fireline and at half these rates for the whole work day. Drinking and dehydration were proportional to sweat loss: on average firefighters replaced 43% of their sweat loss during fireline construction and 63% for the whole work day. During fireline construction they dehydrated at an average rate of 654 g (0.9% body mass) per hour and a maximum rate of 2 kg per hour (2.6% body mass). The scientific observers sweated less than half as much as the firefighters but also drank less and became almost as dehydrated. These findings emphasise the need for work practices that guarantee an adequate water intake before, during, and after firefighting. Regression equations are presented for predicting sweat rate (hence water requirements) from activity, fire, body mass, and air temperature.
Unlabelled:
The purpose of this study was to examine 1) wildfire fighters' ability to consume the prescribed fluid volume (1200 mL h(-1)), 2) the effect of fluid intake on plasma sodium and hydration, and 3) the effect of fluid intake on firefighters' heart rate, core temperature and activity during emergency suppression shifts.
Methods:
Thirty-four firefighters were divided into ad libitum (AD, n = 17) and prescribed (PR, n = 17) drinking groups.
Results:
PR drinkers did not meet the prescribed fluid target, yet consumed over double the volume of AD drinkers. No differences between groups in plasma sodium or hydration were noted. PR drinking resulted in lower core temperature between 2 and 6 h. This did not coincide with reduced cardiovascular strain, greater work activity or larger distances covered when compared to AD drinkers.
Conclusion:
Extra fluid consumption (above AD) did not improve firefighter activity or physiological function (though PR firefighters core temperature was lower earlier in their shift). Firefighter can self-regulate their fluid consumption behavior and work rate to leave the fireground euhydrated.
The Institute of Pennsylvania Hospital and University of Pennsylvania, Philadelphia, Pennsylvania There is a need for brief,
portable performance measures that are free of practice effects but that reliably show the impact of sleep loss on performance
during sustained work. Reaction time (RT) tasks hold considerable promise in meeting this need, if the extensive number of
responses they typically yield can be processed in ways that quickly provide the essential analyses. While testing the utility
of a portable visual RT task during a sustained, quasi-continuous work schedule of 54 h, we developed a microcomputer software
system that inputs, edits, transforms, analyzes, and reduces the data from the RT portable audiotapes, for each 10-min trial
on the task. With relatively minor modifications, the software system can be used on a minimally configured microcomputer
system that supports BASIC. The software is flexible and capable of retrieving distorted data, and it generates a variety
of dependent variables reflecting intratrial optimum response capacity, lapsing, and response slowing.
To curtail the spread of wildfire, firefighters are often required to work long hours in hot, smoky conditions with little rest between consecutive shifts. In isolation, heat, smoke, and sleep disruption can have a detrimental impact on cognitive and physical abilities. Far less is known, however, about the combined impact that heat, smoke, and sleep disruption can have on firefighters' performance during wildfire suppression or on human performance in general. The available literature, though scant, suggests that audio and visual tracking may be degraded after sustained heat exposure following one night of sleep deprivation. Exposure to heat and carbon monoxide, in contrast, appears to have only limited impact on cognitive performance, even after physical exercise. Heat and carbon monoxide exposure does, however, increase physiological exertion to a given work or exercise bout. To the authors' knowledge, there are no published studies that have explored the impacts of heat exposure following sleep disruption on physical work performance, sleep disruption and smoke exposure on physical or cognitive work, or the combined impacts of sleep disruption, smoke and heat exposure on cognitive or physical work. While more integrative research is needed, the current review provides a summary of the available evidence and an indication of the degree of confidence agencies can have in the research. This will allow both the scientific community and agencies to make informed recommendations regarding the management of wildland firefighters' health and safety on the fireground.
Wildfire fighters are known to report to work in a hypohydrated state, which may compromise their work performance and health.
To evaluate whether ingesting a bolus of fluid before the shift had any effect on firefighters' fluid consumption, core temperature, or the time they spent in high heart rate and work activity zones when fighting emergency wildfires.
Thirty-two firefighters were divided into non-bolus (AD) and pre-shift drinking bolus (PS, 500 ml water) groups.
Firefighters began work hypohydrated as indicated by urine colour, specific gravity and plasma osmolality (P(osm)) results. Post-shift, firefighters were classified as euhydrated according to P(osm) and hypohydrated by urinary markers. No significant differences existed between the drinking groups in pre- or post-shift hydration status, total fluid intake, activity, heart rate or core temperature.
Consuming a bolus of fluid, pre-shift provided no benefit over non-consumption as both groups had consumed equivalent ad libitum volumes of fluid, 2.5 h into the shift. No benefits of bolus consumption were observed in firefighter activity, heart rate response or core temperature response across the shift in the mild weather conditions experienced. Ad libitum drinking was adequate to facilitate rehydration in firefighters upon completion of their emergency firefighting work shift.
To identify and characterize the physically demanding tasks undertaken during multi-day wildfire (known as bushfire in Australia) suppression by Australian rural firefighters.
During semi-structured group interviews, thirty-one experienced male firefighters reviewed 53 firefighting tasks that could be performed during tanker-based bushfire suppression. Participants were asked to nominate the most physically demanding tasks and then define their typical frequencies, durations, operational importance and the dominant actions and activity types in each task.
Seven tasks were identified as physically demanding. They were further categorized into three hose and four handtool (e.g., rakehoe) related activities. These tasks were assessed as moderately important to critical and were thought to occur less than one up to 700 times in a four-month bushfire 'season'. Each task's duration was estimated to last approximately 2-30 min depending on the task. Dominant actions were carry, drag, dig/rake actions in seven, three and four of the demanding tasks, respectively. 'Strength-endurance' was the dominant activity type for five of the seven tasks.
Seven fireground tasks, three using a hose and four using handtools were classified as physically demanding by incumbent firefighters. The combination of hose and handtool work indicates that the tanker-based bushfire suppression tactics used by Australian rural firefighters appears to be a hybrid of structural and wildfire firefighting techniques and may require a dedicated physiological analyses before the job demands for these firefighters can be quantified.
The purpose of this study was to compare the effects of a water + electrolyte solution versus plain water on changes in drinking behaviors, hydration status, and body temperatures during wildfire suppression.
Eight participants consumed plain water, and eight participants consumed water plus an electrolyte additive during 15 hours of wildfire suppression. Participants wore a specially outfitted backpack hydration system equipped with a digital flow meter system affixed inline to measure drinking characteristics (drinking frequency and volume). Body weight and urine-specific gravity were collected pre- and postshift. Ambient, core, and skin temperatures were measured continuously using a wireless system. Work output was monitored using accelerometry.
There were no differences between groups for body weight, drinking frequency, temperature data, activity, or urine-specific gravity (1.019 +/- 0.007 to 1.023 +/- 0.010 vs. 1.019 +/- 0.005 to 1.024 +/- 0.009 for water and water + electrolyte groups pre- and postshift, respectively; P < .05). There was a main effect for time for body weight, demonstrating an overall decrease (78.1 +/- 13.3 and 77.3 +/- 13.3 kg pre- and postshift, respectively; P < .05) across the work shift. The water group consumed more total fluid (main effect for treatment) than the water + electrolyte group (504 +/- 472 vs. 285 +/- 279 mL.h(-1) for the water and water + electrolyte groups, respectively; P < .05).
The addition of an electrolyte mixture to plain water decreased the overall fluid consumption of the water + electrolyte group by 220 mL.h(-1) (3.3 L.d(-1)). Supplementing water with electrolytes can reduce the amount of fluid necessary to consume and transport during extended activity. This can minimize carrying excessive weight, possibly reducing fatigue during extended exercise.
Variation in mental performance under different levels of heat stress-induced dehydration was recorded in 11 subjects heat acclimatized to the tropicals. Dehydration was induced by a combination of water restriction and exercise in heat. The psychological functions--arithmetic ability, short-term memory, and visuomotor tracking--were assessed in a thermoneutral room after the subjects recovered fully from the effects of exercise in heat, as reflected by their oral temperature and heart rate. The results indicated significant deterioration in mental functions at 2% or more body dehydration levels.
The effect of primary dehydration of various levels (1, 2 and 3% body-weight deficits) on mental functions of different complexities were studied in eight heat-acclimatized subjects drawn from tropical regions of India. These subjects were also studied after a bout of exercise in heat under two conditions viz., Hot Dry (45°C DB, 30% rh), and Hot Humid (39DC DB, 60% rh) at 34°C WBGT. No significant change in routine mental work was seen either under dehydration per se of any level or after subsequent exercise under heat when compared with the normal state. On the other hand, at 2 and 3% levels of primary dehydration a further reduction was noted in all the functions though it was not significant. Inter-variations in Hot Humid and Hot Dry conditions were not significant except for more pronounced reductions in the concentration component in Hot Humid conditions.
The effect of heat stress on reaction time to centrally and to peripherally presented stimuli was determined for lean and obese subjects whose work levels on a treadmill in a heat chamber produced either a 2.5 or 5% loss of body weight in six hours. Peripheral reaction time improved with practice, but central reaction time was not affected. Obesity, eccentricity of the peripheral stimulus, and the level of dehydration did not have significant effects on reaction time. It was concluded that, for short periods of time, the effects of heat stress can be overcome for highly motivated and experienced subjects.
To determine whether: a) plasma osmolarity (Posm) is sensitive to small incremental changes in hydration status, b) urine specific gravity (Usg) can accurately identify a state of euhydration, c) Usg is a sensitive indicator of a change in hydration status, and d) Usg correlates with Posm.
Euhydrated (Posm = 288 +/- 4 mOsm.L-1) subjects (N = 12) were dehydrated by 5% of their body weight via exercise in the heat (40 degrees C, 20% RH). Posm, urine osmolarity (Uosm), and Usg were measured at 1%, 3%, and 5% dehydration, and 30 and 60 min of recovery (rec). Subjects consumed water in recovery equal to their loss of body weight.
Posm increased incrementally with each successive increase in percent body weight loss (%BWL). Usg was not significantly different from baseline until 3% BML. Uosm was not significantly different from baseline until 5% BWL. Usg correlated moderately (r = 0.46, P > 0.10) with Posm but reasonably well (r = 0.68, P < 0.02) with Uosm.
Posm accurately identifies a state of euhydration and is sensitive to changes in hydration status during acute dehydration and rehydration. Usg and Uosm are also sensitive to changes in hydration status but lag behind during periods of rapid body fluid turnover and therefore correlate only moderately with Posm during acute dehydration.
This study investigated the effects of heat exposure, exercise-induced dehydration and fluid ingestion on cognitive performance. Seven healthy men, unacclimatized to heat, were kept euhydrated or were dehydrated by controlled passive exposure to heat (H, two sessions) or by treadmill exercise (E, two sessions) up to a weight loss of 2.8%. On completion of a 1-h recovery period, the subjects drank a solution containing 50 g l(-1) glucose and 1.34 g l(-1) NaCl in a volume of water corresponding to 100% of his body weight loss induced by dehydration. (H1 and E1) or levels of fluid deficit were maintained (H0, E0). In the E0, H0 and control conditions, the subject drank a solution containing the same quantity of glucose diluted in 100 ml of water. Psychological tests were administered 30 min after the dehydration phase and 2 h after fluid ingestion. Both dehydration conditions impaired cognitive abilities (i.e. perceptive discrimination, short-term memory), as well as subjective estimates of fatigue, without any relevant differences between the methods. By 3.5 h after fluid deficit, dehydration (H0 and E0) no longer had any adverse effect, although the subjects felt increasingly tired. Thus, there was no beneficial effect of fluid ingestion (H1 and E1) on the cognitive variables. However, long-term memory retrieval was impaired in both control and dehydration situations, whereas there was no decrement in performance in the fluid ingestion condition (H1, E1).
Little is known about the relation of hydration status to cognitive performance in older adults, who may be more vulnerable to poor hydration and cognitive impairment. We examined whether hydration status was related to cognitive functioning in 28 healthy community-dwelling older adults. Hierarchical regression models demonstrated that lower hydration status was related to slowed psychomotor processing speed and poorer attention/memory performance, after controlling for demographic variables and blood pressure.