Heat strain in professional firefighters: physiological responses to a simulated smoke dive in extremely hot environments and the subsequent recovery phase

Firefighters risk heat strain during occupational tasks when exposed to extremely hot environmental conditions and performing high-intensity work. Relevant training scenarios are therefore essential. This study investigated the effect of a single simulated smoke dive and the following recovery phase on physiological and perceptual responses. Nineteen professional male firefighters (43 ± 8 yr) performed a 2-min stair walk and a15-min simulated smoke dive in a two-floor heat chamber (110 °C to 272°C) (HEAT), followed by a 5-min stair walk outside the heat chamber. Heart rate (HR), gastrointestinal temperature (Tgi) and skin temperatures were registered continuously during the test. The Tgi increased significantly from the start (37.5 ± 0.3°C) to the end of HEAT (38.4 ± 0.4°C) and further increased after the heat exposure (39.6 ± 0.5°C).The HR also increased significantly from the start (92 ± 14 bpm) to the end of HEAT (185 ± 13 bpm) and increased after the heat exposure to a maximum of 190 ± 13 bpm. The simulated smoke dive induced high physiological strain on the firefighters, and the increase in Tgi and HR after the hot exposure must be considered during live fire events when repeated smoke dives are required.

Training videos to prevent cold weather injuries

Cold weather injuries (CWIs) are a challenge during military training, exercises and operations in Arctic conditions. Soldier performance in these challenging conditions depends on protective equipment, knowledge, personal experience, routines, and leadership. Despite the Norwegian Armed Forces' goal of zero freezing cold injuries (FCIs), there has been a persistently high incidence of FCIs among the younger soldiers with an average of 120-150 new FCIs recorded each year. Therefore, an expert working group with representatives from medical, defence and research background was established in 2020. Their task was to develop a communication package to help prevent CWIs among military personnel. Training videos and an updated and improved official website were created with a focus on practical recommendations and advice to prevent CWIs and especially FCIs. Risks, prevention and symptoms of FCIs were emphasised. The main goal of the training videos was to supplement current teaching on guidance for CWI prevention in CWOs to prevent FCIs, but following the advice may prevent non-freezing cold injuries (NFCIs) and hypothermia. This informative paper describes the background, working methods and possible implications of the training videos, which may be a potential way forward to improve cold weather training and operations.

Heat tolerance during uncompensable heat stress in men and women wearing firefighter personal protective equipment

Firefighters run a risk of heat strain during occupational tasks. The number of female firefighters has been increasing, but research relevant to this group is still scarce. We aimed to investigate whether there are any sex differences in heat tolerance or physiological responses during uncompensable heat stress while wearing firefighter personal protective equipment. Twelve female (28 ± 7 years, 66 ± 5 kg, 51.7 ± 4.7 mL kg^-1 min^-1) and 12 male (27 ± 7 years, 83 ± 8 kg, 58.8 ± 7.5 mL kg^-1 min^-1) participants performed walking (maximum of 60 min) at 6W·kg^-1, 40 °C, and 14% relative humidity. No differences were observed between groups in heat tolerance, rectal temperature, heart rate, percent body mass loss, thermal sensation, and rate of perceived exertion. Thus, when personnel are selected using gender-neutral physical employment standards, sex is not an independent factor influencing heat tolerance when wearing firefighter personal protective equipment during uncompensable heat stress.

The Use of Wearable Sensor Technology to Detect Shock Impacts in Sports and Occupational Settings: A Scoping Review

Shock impacts during activity may cause damage to the joints, muscles, bones, or inner organs. To define thresholds for tolerable impacts, there is a need for methods that can accurately monitor shock impacts in real-life settings. Therefore, the main aim of this scoping review was to present an overview of existing methods for assessments of shock impacts using wearable sensor technology within two domains: sports and occupational settings. Online databases were used to identify papers published in 2010-2020, from which we selected 34 papers that used wearable sensor technology to measure shock impacts. No studies were found on occupational settings. For the sports domain, accelerometry was the dominant type of wearable sensor technology utilized, interpreting peak acceleration as a proxy for impact. Of the included studies, 28 assessed foot strike in running, head impacts in invasion and team sports, or different forms of jump landings or plyometric movements. The included studies revealed a lack of consensus regarding sensor placement and interpretation of the results. Furthermore, the identified high proportion of validation studies support previous concerns that wearable sensors at present are inadequate as a stand-alone method for valid and accurate data on shock impacts in the field.

The effect of mild whole-body cold stress on isometric force control during hand grip and key pinch tasks

Prolonged exposure to cold can impair manual performance, which in turn can affect work task performance. We investigated whether mild whole-body cold stress would affect isometric force control during submaximal hand grip and key pinch tasks. Twelve male participants performed isometric hand grip and key pinch tasks at 10% and 30% of maximal voluntary contraction (MVC) for 30 and 10 s respectively, in cold (8 °C) and control (25 °C) conditions. Finger temperature decreased significantly by 18.7 ± 2.1 °C and continuous low-intensity shivering in the upper trunk increased significantly in intensity and duration during cold exposure. Rectal temperature decreased similarly for the 8 °C and 25 °C exposures. Force variability (FCv) was <2% for the hand grip tasks, and <3% for the key pinch tasks. No significant changes in FCv or force accuracy were found between the ambient temperatures. In conclusion, isometric force control during hand grip and key pinch tasks was maintained when participants experienced mild whole-body cold stress compared with when they were thermally comfortable.

Metabolic rate and muscle activation level when wearing state-of-the-art cold-weather protective clothing during level and inclined walking

Use of cold-weather personal protective clothing (PPC) in cold climates is essential but can add metabolic cost to the wearer. This study measured the effect of wearing state-of-the-art PPC and personal protective equipment (PPE), with the possible effect of clothing layers and fit, on physiological responses including metabolic rate (MR) and muscle activation level. 19 male participants (80.2 ± 5.9 kg, 181.5 ± 5.1 cm) wore five different clothing ensembles during level (0°) and inclined (6°) walking. Compared to a base layer ensemble (388.7 ± 42.7 W/737.8 ± 57.9 W), wearing a 3-layer PPC ensemble (421.5 ± 44.7 W/811.7 ± 69.2 W) significantly increased MR, and adding PPE (458.3 ± 59.8 W/864.5 ± 71.2 W) further increased MR during level/inclined walking. Independent of the extra weight, adding a middle layer between base layer and outer clothing significantly increased MR during inclined walking only, and no effect of oversized outer clothing was measured.

Effect of ambient temperature on endurance performance while wearing cross-country skiing clothing

This study assessed the effects of exposure to cold (-14 and -9 °C), cool (-4 and 1 °C) and moderate warm (10 and 20 °C) environments on aerobic endurance performance-related variables: maximal oxygen consumption (VO(2max)), running time to exhaustion (TTE), running economy and running speed at lactate threshold (LT). Nine male endurance athletes wearing cross-country ski racing suit performed a standard running test at six ambient temperatures in a climatic chamber with a wind speed of 5 m s(-1). The exercise protocol consisted of a 10-min warm-up period followed by four submaximal periods of 5 min at increasing intensities between 67 and 91 % of VO(2max) and finally a maximal test to exhaustion. During the time course mean skin temperature decreased significantly with reduced ambient temperatures whereas T (re) increased during all conditions. T (re) was lower at -14 °C than at -9 and 20 °C. Running economy was significantly reduced in warm compared to cool environments and was also reduced at 20 °C compared to -9 °C. Running speed at LT was significantly higher at -4 °C than at -9, 10 and 20 °C. TTE was significantly longer at -4 and 1 °C than at -14, 10 and 20 °C. No significant differences in VO(2max) were found between the various ambient conditions. The optimal aerobic endurance performance wearing a cross-country ski racing suit was found to be -4 and 1 °C, while performance was reduced under moderate warm (10 and 20 °C) and cold (-14 and -9 °C) ambient conditions.