Work-rest regimens for work in hot environments: A scoping review.

BACKGROUND: To limit exposures to occupational heat stress, leading occupational health and safety organizations recommend work-rest regimens to prevent core temperature from exceeding 38°C or increasing by ≥1°C. This scoping review aims to map existing knowledge of the effects of work-rest regimens in hot environments and to propose recommendations for future research based on identified gaps. METHODS: We performed a search of 10 databases to retrieve studies focused on work-rest regimens under hot conditions. RESULTS: Forty-nine articles were included, of which 35 were experimental studies. Most studies were conducted in laboratory settings, in North America (71%), on healthy young adults, with 94% of the 642 participants being males. Most studies (66%) employed a protocol duration ≤240 min (222 ± 162 min, range: 37-660) and the time-weighted average wet-bulb globe temperature was 27 ± 4°C (range: 18-34). The work-rest regimens implemented were those proposed by the American Conference of Governmental and Industrial Hygiene (20%), National Institute of Occupational Safety and Health (11%), or the Australian Army (3%). The remaining studies (66%) did not mention how the work-rest regimens were derived. Most studies (89%) focused on physical tasks only. Most studies (94%) reported core temperature, whereas only 22% reported physical and/or mental performance outcomes, respectively. Of the 35 experimental studies included, 77% indicated that core temperature exceeded 38°C. CONCLUSIONS: Although work-rest regimens are widely used, few studies have investigated their physiological effectiveness. These studies were mainly short in duration, involved mostly healthy young males, and rarely considered the effect of work-rest regimens beyond heat strain during physical exertion.

On-Duty Resting Heart Rate Variability at the Fire Station Is Related to Cardiorespiratory Fitness and Physical Activity Levels in Firefighters.

OBJECTIVE: The aim of the study is to measure the association between the physical activity (PA) levels and cardiorespiratory fitness on the firefighters' cardiac autonomic function at rest at the fire station. METHODS: Anthropometry, heart rate variability, fitness, and PA levels were assessed at the fire station in 98 career Québec male firefighters. RESULTS: Partial correlations, adjusted for age, waist circumference, and perceived stress revealed that heart rate and several heart rate variability indices were significantly correlated to estimated maximal oxygen consumption and to high-intensity PA but not to moderate-intensity PA. CONCLUSIONS: These results suggest that both cardiorespiratory fitness and high-intensity physical training are related to the cardiac autonomic function of firefighters. Therefore, fire department should promote PA programs to improve physical fitness among firefighters.

Cardiovascular disease risk factors in career firefighters: A 6-year follow-up study.

This study sought to investigate the evolution of cardiovascular disease (CVD) risk factors in career firefighters. A questionnaire was sent to a cohort of 233 Québec career firefighters in 2015 and 2021 to collect demographic and occupational information and the presence of CVD risk factors. Ninety-six (96) firefighters (1 female) responded to the questionnaire in 2015 and 2021. Body weight (2015: 88.3 ± 10.9, 2021: 89.6 ± 10.7 kg, p = 0.01), body mass index (2015: 27.6 ± 3.2, 2021: 28.0 ± 3.0 kg/m2, p = 0.01), number of CVD risk factors (2015: 1.1 ± 1.0, 2021: 1.3 ± 0.9 CVD risk factors, p = 0.05), and proportion of firefighters with at least 1 CVD risk factor (2015: 71, 2021: 82%, p = 0.02) increased. Overall, our results highlight an aggravation of several CVD risk factors in Québec career firefighters over the years.

Physical Activity, Occupational Stress, and Cardiovascular Risk Factors in Law Enforcement Officers: A Cross-sectional Study.

OBJECTIVE: This cross-sectional study aimed to assess the interrelationship between leisure-time physical activity (LTPA), occupational stress, and cardiovascular disease (CVD) risk factors in law enforcement officers (LEOs). METHODS: A total of 229 LEOs completed a survey assessing their LTPA level, occupational stress, and CVD risk factors. RESULTS: After adjusting for age and sex, physically inactive LEOs are more likely to have one or more CVD risk factors. While high occupational stress was associated with greater odds of CVD risk factors in physically inactive LEOs, stress was not significantly associated with the prevalence of CVD risk factors in active LEOs. CONCLUSIONS: Our results suggest that occupational stress is associated with the prevalence of CVD risk factors in LEOs. Nevertheless, LTPA might have the potential to mitigate the impact of occupational stress on CVD risk factors.

Change in heart rate variability during two firefighting work cycles.

This study aimed to determine whether the change in heart rate variability from pre to post firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-min work bouts intercalated by a passive recovery period of either 20 min (T20) or 5 min (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, p = 0.02). Post-firefighting aural temperature was greater (p = 0.05) in T5 (37.18 ± 0.53 °C) than in T20 (36.88 ± 0.49 °C). In conclusion, a shorter recovery period of 5 min between firefighting work bouts decreases post-firefighting heart rate variability, possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Health, Safety, and Wellness Concerns Among Law Enforcement Officers: An Inductive Approach.

Background: Although studies have assessed the impact of occupational risk factors on the health of law enforcement officers (LEO's), few have involved (LEO's) as informants in ways that allow their points of view to be heard directly. Thus, the objective of this study is to explore the occupational health, safety, and wellness (OHSW) concerns of (LEO's). Methods: (LEO's) working in Quebec, Canada were invited to answer an open-ended question regarding their OHSW concerns. Using a multi-stage content analysis, the collected answers were analyzed and coded by two members of the research team to identify the most recurrent concerns of (LEO's). Findings: Five themes relating to the OHSW concerns of (LEO's) were identified, namely, the work schedule, occupational stress, work equipment, workplace health promotion, and operational risks. Furthermore, our analyses highlighted differences in the concerns of (LEO's) based on their level of experience and sex. Conclusions/Application to Practice: This study addresses a gap in the literature on the OHSW concerns from the perspective of (LEO's). Overall, our results support that the work schedule and occupational stress associated with law enforcement are the two most recurrent concerns of (LEO's). Thus, the results of this study further stress the need for police organizations to implement strategies and policies, which could mitigate the deleterious effects of these hazards on the overall wellness of (LEO's).

Passive heat acclimation does not modulate processing speed and executive functions during cognitive tasks performed at fixed levels of thermal strain.

This study evaluated if passive controlled hyperthermia heat acclimation modulates cognitive performance during passive heat stress. Eight healthy adults (25 ± 4 years) underwent 7 consecutive days of hot water immersion (core temperature ≥38.6 °C) and a 7-day time-control period. On days 1 and 7 of heat acclimation, participants performed a digital Stroop test at baseline, when core temperature reached 38.6 °C, and after 60 minutes at a core temperature ≥38.6 °C to evaluate reaction time during tasks targeting processing speed (reading and counting) and executive functions (inhibition and switching). On days 1 and 7 of the time-control intervention, participants performed the Stroop test with equivalent amounts of time separating each task as for heat acclimation. During day 1 of heat acclimation, reaction time was quicker during the reading (-44 ms [-71 to -17], P < 0.01) and counting (-39 ms [-76 to -2], P = 0.04) tasks when the rectal temperature reached 38.6 °C, but after a further 60 minutes of heat exposure, reaction time only remained quicker during the reading task (-56 ms [-83 to -29], P < 0.01). Changes in reaction time during heat exposure were unaffected by subsequent heat acclimation (interaction, all P ≥ 0.09). In conclusion, 7 days of heat acclimation does not modulate processing speed and executive functions during passive heat exposure. Novelty: Whether heat acclimation improves cognitive performance during heat exposure remains unclear. We tested the hypothesis that heat acclimation modulates reaction time during cognitive tasks performed at matched levels of thermal strain. Despite the classical signs of heat acclimation, reaction time during heat exposure is unaffected by heat acclimation.

Fitness components associated with performance of a law enforcement physical employment standard in police cadets.

BACKGROUND: The physical preparation of cadets for both physical employment standards (PES) and police job performance is a major concern for police organizations. Identifying fitness components associated with both PES performance and work performance can provide essential information for the physical training of police cadets. Therefore, the objective of this study was to assess the association of fitness components with performance of the Standardized Physical Abilities Test (SPAT), a new law enforcement PES. METHODS: A sample of 41 police cadets was recruited to take part in this cross-sectional study. First, the participants were assessed using six fitness assessments (standing broad jump, medicine ball put, grip strength test, visuomotor reaction time (VMRT) test, modified agility T-test, and 600-meter run). In a second experiment, participants performed the SPAT. RESULTS: Bivariate correlation analysis showed moderate to strong associations between each fitness assessment and SPAT performance. Based on stepwise multiple regression analysis, results at the VMRT Test, the medicine ball put, and the agility T-test accounted for 66.0% of the variability in SPAT performance (R2=0.660; P<0.001). CONCLUSIONS: Overall, our results suggest that exercise prescriptions for police cadets should focus on power, agility, and VMRT. Furthermore, our results show that performance in a PES can be estimated rather precisely based on low-cost fitness assessments. Therefore, such methodology could be used to develop fitness assessments specific to PES requirements.

Revisiting the evaluation of central versus peripheral thermoregulatory control in humans.

Human thermoregulatory control is often evaluated through the relationship between thermoeffector output and core or mean body temperature. In addition to providing a general indication of whether a variable of interest alters thermoregulatory control, this relationship is often used to determine how this alteration may occur. This latter interpretation relies upon two parameters of the thermoeffector output-body temperature relationship: the onset threshold and thermosensitivity. Traditionally, changes in the onset threshold and thermosensitivity are interpreted as "central" or "peripheral" modulation of thermoregulatory control, respectively. This mini-review revisits the origins of the thermoeffector output-body temperature relationship and its use to interpret "central" or "peripheral" modulation of thermoregulatory control. Against this background, we discuss the strengths and weaknesses of this approach and highlight that "central" thermoregulatory control reflects the neural control of body temperature whereas "peripheral" thermoregulatory control reflects properties specific to the thermoeffector organs. We highlight studies that employed more direct approaches to investigate the neural control of body temperature and peripheral properties of thermoeffector organs. We conclude by encouraging future investigations interested in studying thermoregulatory control to more directly investigate the component of the thermoeffector loop under investigation.heat; human; skin blood flow; sweat; thermoregulatory.

Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment.

We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% V˙O2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

Seven days of hot water heat acclimation does not modulate the change in heart rate variability during passive heat exposure.

We examined if the change in heart rate variability during passive heat exposure is modified by hot water heat acclimation (HA). Sixteen healthy adults (28 ± 5 years, 5 females/11 males) underwent heat exposure in a water-perfused suit, before and after 7 days of HA (60 min at rectal temperature ≥38.6 °C). During passive heat exposure, heart rate, the standard deviation of NN intervals (SDNN), the square root of the mean squared differences of successive NN intervals (RMSSD), and the power in the high-frequency range (HF) were measured. No difference in heart rate (P = 0.22), SDNN (P = 0.87), RMSSD (P = 0.79), and HF (P = 0.23) was observed at baseline. The increase in HR (pre-HA, 43 ± 10; post-HA, 42 ± 9 bpm; P = 0.57) and the decrease of SDNN (pre-HA, -54.1 ± 41.0; post-HA, -52.2 ± 36.8 ms; P = 0.85), RMSSD (pre-HA, -70.8 ± 49.5; post-HA, -72.7 ± 50.4 ms; P = 0.91) and HF (pre-HA, -28.0% ± 14.5; post-HA, -23.2% ± 17.1%; P = 0.27) were not different between experimental visits at fixed increases in esophageal temperature. These results suggest that 7 consecutive days of hot water HA does not modify the change in heart rate variability indices during passive heat exposure. Novelty: It remains unclear if HA alters the change in heart rate variability that occurs during passive heat exposure. At matched levels of thermal strain, 7 consecutive days of hot water immersion did not modulate the change in indices of heart rate variability during passive heat exposure.

Shortened Recovery Period Between Firefighting Work Bouts Increases Cardiac Response Disproportionately With Metabolic Rate.

OBJECTIVE: To compare physiological responses between two firefighting simulations with different recovery periods, one having work bouts intercalated by a shortened recovery period. METHODS: Thirteen male firefighters participated in two different simulations, which comprised two identical 25-minute effort bouts (E1 and E2) intercalated by a recovery period of either 20 (T20) or 5 (T5) minutes. RESULTS: From E1 to E2, the increase of mean heart rate (HR) (26 ±â€Š5 vs 14 ±â€Š5 bpm, P < 0.001) and mean VO2 (1.8 ±â€Š0.4 vs 1.3 ±â€Š0.4 mL kg min, P < 0.001) was higher in T5 than in T20. CONCLUSION: Results indicate that a shortened recovery time between firefighting work bouts intensifies cardiac strain disproportionately with metabolic rate, since mean HR increased by 19.3% and 10.8% while mean VO2 increased by only 7.2% and 5.0% in T5 and T20, respectively.

Cardiovascular health profile among Québec male and female police officers.

To document the cardiovascular health profile of Québec police officers (PO). Participants answered an online questionnaire evaluating the presence of cardiovascular disease (CVD) risk factors and symptoms. Two thousand, ninety-nine (2,099) male (age: 40.8 ± 9.2 years) and 756 female (age: 37.9 ± 7.9 years) PO participated in this study. The prevalence of obesity (body mass index ≥30 kg/m2) and diagnosed hypertension was respectively 21.1, and 14.3% in male and 7.3 and 4.1% in female PO. According to 2013 American College of Sports Medicine guidelines, 27.0 and 48.0% of male and 12.1 and 56.7% of female PO were categorized as being at moderate and high CVD risk, respectively. These findings suggest that Québec police departments should help PO to adopt and maintain a healthy lifestyle to decrease CVD risk.

Physiological and Psychological Adaptations of Trained Cyclists to Spring Cycling Camps.

The purpose of our study was to assess physiological adaptations and measure mood outcomes following a cycling training camp in competitive athletes. Fourteen competitive athletes (8 males, 6 females) performed 2 incremental tests to exhaustion before and after a training camp. Volume and intensity (load) of the training regimen were recorded. Submaximal and maximal metabolic data were analysed, as well as economy variables (gross mechanical efficiency and cycling economy). Skeletal muscle adaptations were assessed using near infrared spectroscopy (NIRS). For both genders (n = 14), peak power output, peak power output-W/kg ratio and peak power output-B[La] were significantly increased (p < 0.05) after the cycling training camp (p < 0.05). Significant increases occurred for gross mechanical efficiency measured at the lactate threshold (+4.9%) and at the same precamp lactate threshold power output (+2.9%). At the lactate threshold and Post Camp Lactate Threshold Power, cycling economy increased by 5.2 and 2.9%, respectively (p < 0.05). These power measurements were significantly correlated with individual fluctuations in deoxyhaemoglobin in the vastus lateralis for male cyclists only. Profile of Mood State questionnaire results showed that subcategories "Tension-Anxiety", "Confusion", "Fatigue" and "Total Global Score" significantly decreased after the training camp. Cycling training camps were associated with positive adaptations (increased cycling economy, gross mechanical efficiency and power output) as well as some mental benefits. This indicates that despite some significant physiological adaptations participants probably did not overreach during their CTC.

Cardiovascular Disease Risk Factors in Québec Male Firefighters.

OBJECTIVE: We aimed to document the prevalence of cardiovascular disease (CVD) risk factors and symptoms in Québec firefighters. METHODS: Seven hundred and seventy-nine (779) male firefighters (age: 41.6 ±â€Š10.4 years; body mass index [BMI]: 28.0 ±â€Š3.6 kg/m) answered an online questionnaire evaluating lifestyle and the presence of CVD risk factors and symptoms. RESULTS: The prevalence of obesity (BMI is more than or equal to 30 kg/m), diagnosed hypertension, diagnosed dyslipidemia, and diagnosed type 2 diabetes mellitus was respectively 23.6%, 12.2%, 17.4%, and 1.7%. Among survey participants, 34.5% were categorized as moderate and 43.6% as high CVD risk, according to American College of Sports Medicine guidelines. CONCLUSIONS: A high proportion of Québec firefighters are at moderate to high risk of CVD. These findings suggest that Québec fire departments should help all firefighters to adopt and maintain a healthy lifestyle.