Physiological criteria for functioning of hands in the cold: a review

The application of heating film to hands reduces the decline in manual dexterity performance associated with cold exposure

PURPOSE

Exposure to cold temperatures decreases finger temperature (Tfing) and dexterity. Decreased manual function and dexterity can be serious safety risks, especially in tasks that require fine motor movements that must be performed outdoors. The aim of this study was to determine whether hand heating with a minimal power requirement (14.8 W) results in a smaller reduction in Tfing and manual dexterity performance during mild cold exposure compared to a non-heated control condition.

METHODS

In a randomized crossover design, twenty-two healthy participants were exposed to a moderately cold environment (5  ºC) for 90 min. One condition had no intervention (CON), while the other had the palmar and dorsal hands heated (HEAT) by using electric heating films. Tfing and cutaneous vascular conductance (CVC) were continuously monitored using laser Doppler flowmetry. Manual dexterity performance and cognitive function were assessed by the Grooved Pegboard Test (GPT) and Stroop Color-Word (SCW) test, respectively, during the baseline period and every 30 min during the cold exposure.

RESULTS

After the cold exposure, Tfing was higher in HEAT relative to CON (CON 9.8 vs. HEAT 13.7 ºC, p < 0.0001). GPT placing time, as an index of dexterity performance, was also shorter in HEAT by 14.5% (CON 69.10 ± 13.08 vs. HEAT 59.06 ± 7.99 s, p < 0.0001). There was no difference in CVC between the two conditions during the cold exposure (p > 0.05 for all). Cognitive function was similar between two conditions (p > 0.05 for all).

CONCLUSION

The proposed hand heating method offers a practical means of heating fingers to maintain dexterity throughout prolonged cold exposure.

The effect of exposure to cold on dexterity and temperature of the skin and hands

Objectives. This study aimed to determine the impact of low temperature (-1 °C, +5 °C) on manual dexterity and hand skin temperature after 1 h of exposure when using two types of protective gloves. Methods. Ten male participants wore double gloves or single gloves, when spending 1 h in a climatic chamber at -1, +5 or +20 °C. Before and after the cold exposure, measurements of mean weighted body skin temperature, hand skin temperature, the Purdue Pegboard Test and hand grip strength were performed. Results. There were statistically significant differences in the values of mean weighted body skin temperature and left and right hand skin temperature between the study variants. Conclusion. No effect of cold exposure (-1 °C, +5 °C) on manual dexterity was observed, but there was an effect of -1 °C temperature change on weighted mean skin temperature and hand skin temperature during 1 h of exposure. The decrease in both right and left hand skin temperature after cold exposure was the largest for -1 °C while using single gloves, and differed significantly from the other variants.

Combined effects of mild hypothermia and nitrous-oxide-induced narcosis on manual and cognitive performance

Divers are at enhanced risk of suffering from acute cognitive deterioration because of the low ambient temperatures and the narcotic action of inert gases inspired at high pressures. Yet, the behavioral effects of cold and inert gas narcosis have commonly been assessed in isolation and during short-term provocations. We therefore evaluated the interactive influence of mild hypothermia and narcosis engendered by a subanesthetic dose of nitrous oxide (N2O; a normobaric intervention analog of hyperbaric nitrogen) on cognitive function during prolonged iterative exposure. Fourteen men partook in two ∼12-h sessions (separated by ≥4 days), wherein they performed sequentially three 120-min cold (20°C) water immersions (CWIs), while inhaling, in a single-blinded manner, either normal air or a normoxic gas mixture containing 30% N2O. CWIs were separated by a 120-min rewarming in room-air breathing conditions. Before the first CWI and during each CWI, subjects performed a finger dexterity test, and the Spaceflight Cognitive Assessment Tool for Windows (WinSCAT) test assessing aspects of attention, memory, learning, and visuospatial ability. Rectal and skin temperatures were, on average, reduced by ∼1.2 °C and ∼8 °C, respectively (P < 0.001). Cooling per se impaired (P ≤ 0.01) only short-term memory (∼37%) and learning (∼18%); the impairments were limited to the first CWI. N2O also attenuated (P ≤ 0.02) short-term memory (∼37%) and learning (∼35%), but the reductions occurred in all CWIs. Furthermore, N2O invariably compromised finger dexterity, attention, concentration, working memory, and spatial processing (P < 0.05). The present results demonstrate that inert gas narcosis aggravates, in a persistent manner, basic and higher-order cognitive abilities during protracted cold exposure.

Cold-induced vasodilation during sequential immersions of the hand

A common practice for those operating in cold environments includes repetitive glove doffing and donning to perform specific tasks, which creates a repetitive cycle of hand cooling and rewarming. This study aimed to determine the influence of intraday repeated hand cooling on cold-induced vasodilation (CIVD), sympathetic activation, and finger/hand temperature recovery. Eight males and two females (mean ± SD age: 28 ± 5 year; height: 181 ± 9 cm; weight: 79.9 ± 10.4 kg) performed two 30-min hand immersions in cold (4.3 ± 0.92 °C) water in an indoor environment (18 °C). Both immersions (Imm1; Imm2) were performed on the same day and both allowed for a 10-min recovery. CIVD components were calculated for each finger (index, middle, ring) during each immersion. CIVD onset time (index, p = 0.546; middle, p = 0.727; ring, p = 0.873), minimum finger temperature (index, p = 0.634; middle, p = 0.493; ring, p = 0.575), and mean finger temperature (index, p = 0.986; middle, p = 0.953; ring, p = 0.637) were all similar between immersions. Recovery rates generally demonstrated similar responses as well. Findings suggest that two sequential CIVD tests analyzing the effect of prior cold exposure of the hand does not impair the CIVD response or recovery. Such findings appear promising for those venturing into cold environments where hands are likely to be repeatedly exposed to cold temperatures.

Investigating manual performance when using push buttons following cold water hand immersion

The purpose of this study was to investigate manual performance of humans when using push buttons following cold water hand immersion. An experiment involving 29 human participants was carried out to measure the activation rate of twelve different shaped push buttons mounted on a novel test apparatus after their dominant hand was immersed in cold (2 °C) and thermoneutral (34 °C) water for 2 min. A series of standardized hand dexterity tests were completed to assess the participants' baseline tactile sensitivity in a dry thermoneutral state. The mean baseline performance of participants indicates that they were representative of the general population. The button test apparatus was developed specifically for this experiment and was comprised of 12 different buttons at different locations on the panel which were varying in size, surface shape and texture. After the participants immersed their dominant hand in the assigned temperature condition, their index finger was guided to the centre of the panel, and they were instructed to find and press as many buttons as they could in a 2-min time period using only their index finger. For the button panel test, the participants' view was obstructed from seeing the buttons. The results of the study indicate that temperature does not influence the activation rate of the push buttons on the button test apparatus. In addition, button size (large) was the most significant factor, followed by shape (protruding), however button texture was not a significant parameter. Given that exposure to cold water reduces manual performance, along with anecdotal evidence from survival training centres that users sometimes struggle to activate PLBs, the motivation for this research was to understand how humans interact with these devices in cold water emergency situations. It is expected that the results of this research will be useful for designers of emergency signalling devices used for rescue at sea.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Prevalence of hypothermia and critical hand temperatures during military cold water immersion training

Cold-weather military operations can quickly undermine warfighter readiness and performance. Specifically, accidental cold-water immersion (CWI) contributes to rapid body heat loss and impaired motor function. This study evaluated the prevalence of hypothermia and critical hand temperatures during CWI. One-hundred seventeen (N = 117) military personnel (mean ± SD age: 27 ± 6 yr, height: 176 ± 8 cm, weight: 81.5 ± 11.6 kg) completed CWI and rewarming during cold-weather training, which included a 10-min outdoor CWI (1.3 ± 1.4°C) combined with cold air (-4.2 ± 8.5°C) exposure. Following CWI, students removed wet clothing, donned dry clothing, and entered sleeping systems. Core (T_c) and hand (T_hand) temperatures were recorded continuously during the training exercise. T_c for 96 students (mean ± SD lowest T_c = 35.6 ± 0.9°C) revealed that 24 students (25%) experienced T_c below 35.0°C. All of 110 students (100%) experienced T_hand below 15.0°C, with 71 students (65%) experiencing T_hand at or below 8.0°C. Loss of hand function and hypothermia should be anticipated in warfighters who experience CWI in field settings. Given the high prevalence of low T_hand, focus should be directed on quickly rewarming hands to recover function.

We are all exposed, but some are more exposed than others

This paper defines functional cold exposure zones that illustrate whether a person is at risk of developing physical performance loss or cold weather injuries. Individual variation in body characteristics, activity level, clothing and protective equipment all contribute to variation in the effective exposure. Nevertheless, with the right education, training, and cold-adapted behaviours the exposure differences might not necessarily lead to increased risk for cold injury. To support the preparation process for cold weather operations, this paper presents a biophysical analysis explaining how much cold exposure risk can vary between individuals in the same environment. The results suggest that smaller persons are prone to be underdressed for moderate activity levels and larger persons are prone to be overdressed. The consequences of these discrepancies place people at different risks for performance loss or cold weather injuries. Nonetheless, even if all are well-dressed at the whole-body level, variation in hand morphology is also expected to influence hand skin temperatures that can be maintained; with smaller hands being more prone to reach skin temperatures associated with dexterity loss or cold weather injuries. In conclusion, this work focusses on bringing cold science to the Arctic warrior, establishing that combating cold stress is not a one size fits all approach.

The impact of cold, hypoxia, and physical exertion on pistol accuracy and tactical performance

The purpose of this study was to examine the impact of independent cold and combined cold and hypoxic exposures on operational-specific task performance including pistol marksmanship, pistol magazine reload ability, and subjective and objective thermal indices before and after a whole-body physical exertional task. Twelve participants were exposed to Thermoneutral Normoxic (24 °C; FiO2 21%), Cold Normoxic (10 °C; FiO2 21%), and Cold Hypoxic (10 °C; FiO2 14%) conditions for 30min before performing pistol marksmanship at distances of 6.40 and 13.72m and a pistol magazine reload task before and after 3 sets of sandbag deadlifts at 50% body mass. Thermal perception and hand temperatures were collected before and after the physical exertion task. There were no significant differences in Pistol Accuracy performance at distances of 6.40 and 13.72m due to physical exertion, cold, or hypoxia. Following physical exertion, Pistol Accuracy was similar between Thermoneutral and Cold Normoxic conditions but lead to 17% and a 10% reduction in performance during the Cold Hypoxic condition, compared to Thermoneutral and Cold Normoxic conditions. There was no change in Pistol Accuracy for the Thermoneutral Normoxic condition. The pistol magazine reload task was not impacted by physical exertion, but there was a reduction in performance in Cold Normoxic 21% (4.04s) and Cold Hypoxic 16% (3.08s) conditions. Physical exertion did not impact hand temperature but did increase thermal perception scores for all conditions. These findings indicate that cold exposure reduced both tactical dexterity and pistol marksmanship, however, physical exertion may offset these deficits via an increase in thermal perception. Additionally, hypoxemia was the primary mediator of marksmanship performance in cold hypoxic environments following an acute bout of physical exertion. Thus, in cold mountainous environments, marksmen should be aware of their elevation and utilize brief episodes of physical activity to enhance their thermal state when marksmanship is a priority for operational success.

Tourniquet self-application assessment in cold weather conditions

BACKGROUND

Our study aimed to assess the ability of nonmedical civilians to self-apply extremity tourniquets in cold weather conditions while wearing insulating technical clothing after receiving basic training.

METHODS

A field study was conducted among 37 voluntary participants of an expedition party to the Spanish Antarctic base. The researchers assessed the participant's ability to self-apply five commercial extremity tourniquets (CAT, OMNA, RMT, SWAT-T, and RATS) over cold-weather clothing and their achieved effectiveness for vascular occlusion. Upper extremity self-application was performed with a single-handed technique (OHT), and lower extremity applying a two-handed technique (THT). Perceptions of self-application ease mean values ± standard deviation (SD) were compared by applying a 5% statistical significance threshold. Frequency count determined tourniquet preference.

RESULTS

All the tested ETs, except the SWAT-T, were properly self-applied with an OHT, resulting in effective vascular occlusion in the upper extremity. The five devices tested were self-applied correctly in the lower extremities using THT. The ratcheting marine-designed OMNA ranked the highest for application easiness on both the upper and lower extremities, and the windlass CAT model was the preferred device by most participants.

CONCLUSIONS

Civilian extremity tourniquet self-application on both upper and lower extremities can be accomplished in cold weather conditions despite using cold-weather gloves and technical clothing after receiving brief training. The ratcheting marine-designed OMNA ranked the highest for application ease, and the windlass CAT model was the preferred device.

Efficacy of closed cell wet-suit at various depths and gas mixtures for thermoprotection during military training dives

Purpose: To evaluate a closed-cell wet-suit for thermal protective capability during extreme cold water exposure at various depths. Methods: Thirteen (n = 13) elite military divers who were tasked with cold-water training, participated in this study. To mimic various depths, the Ocean Simulation Facility (OSF) at the Navy Experimental Diving Unit (NEDU) was pressurized to simulate dive depths of 30, 50, and 75fsw. Water temperature remained at 1.8-2.0°C for all dives. Four divers dove each day and used the MK16 underwater breathing apparatus with gas mixes of either N202 (79:21) or HeO2 (88:12). Mean skin temperature (T_SK) (Ramanathan, 1964), core temperature (Tc), hand and foot readings were obtained every 30 min for 30 and 50fsw and every 15 min during the 75fsw dive. Results: T_C was significantly reduced across all dives (p = 0.004); however, was preserved above the threshold for hypothermia (post dive Tc = 36.5 ± 0.4). There was no effect of gas mix on T_C. T_SK significantly decreased (p < 0.001) across all dives independent of depth and gas. Hand and foot temperatures resulted in the termination of three of the dives. There were no significant main effects for depth or gas, but there were significant main effects for time on hand temperature (p < 0.001) and foot temperature (p < 0.001). Conclusion: Core temperature is maintained above threshold for hypothermia. Variatioins in T_C and T_SK are a function of dive duration independent of depth or gas for a closed-cell wet-suit in cold water at various depths. However, both hand and foot temperatures reached values at which dexterity is compromised.

Influence of acute beetroot juice supplementation on cold-induced vasodilation and fingertip rewarming

PURPOSE

Vasoactive ingredients in beetroot (BR) such as nitrate are known to induce vasodilation in temperate conditions. This study investigated the effect of BR ingestion on cold induced vasodilation (CIVD) and rewarming of finger skin temperature (T_fing) during and after hand immersion in cold water.

METHODS

Twenty healthy males (mean ± SD; age 22.2 ± 0.7 years, height 172.6 ± 6.0 cm, body mass 61.3 ± 11.7 kg) repeated a hand cold water immersion test twice with prior BR or water beverage ingestion (randomised order). They rested for 2 h in thermoneutral conditions (27 °C, 40% relative humidity) after consuming the beverage, then immersed their non-dominant hand in 8 °C water for 30 min. They then rewarmed their hand in the ambient air for 20 min. Skin temperature at seven body sites, T_fing, finger skin blood flow (SkBF_fing), and blood pressure were measured.

RESULTS

During hand immersion parameters of CIVD (T_fing and SkBF_fing) were not different between BR and water conditions although skin temperature gradient from proximal to distal body sites was significantly smaller with BR (P < 0.05). During rewarming, SkBF_fing and cutaneous vascular conductance were significantly higher with BR than with water (P < 0.05). The rewarming speed in T_fing and SkBF_fing was significantly faster with BR at 15- (BR 1.24 ± 0.22 vs water 1.11 ± 0.26 °C/min) and 20-min rewarming (P < 0.05). Additionally, individuals with slower rewarming speed with water demonstrated accelerated rewarming with BR supplementation.

CONCLUSION

BR accelerated rewarming in T_fing and SkBF_fing after local cold stimulus, whereas, CIVD response during hand cold immersion was not affected by BR ingestion.

Modeling of heat transfer and thermal regulation for an electric heating glove against a cold environment

An electric heating glove can protect the health of workers without affecting flexibility of the hand in a cold environment. A heat transfer model of an electric heating glove with a function of intelligent temperature control was established. The model was verified by a test device for simulating cold-contact exposure. The results showed good agreement between the simulated values and the experimental values. Based on the numerical model, the basic parameters of the electric heating glove were analyzed. It was found that the pressure, thickness and thermal conductivity of the outer fabric were the key factors affecting the thermal regulative performance of the electric heating glove. The power consumption of the electric heating glove was mainly determined by the thickness of the outer fabric. The developed model provides a theoretical basis for the design of an electric heating glove for a thermal regulative effect and energy saving.

Biomarkers for warfighter safety and performance in hot and cold environments

Exposure to extreme environmental heat or cold during military activities can impose severe thermal strain, leading to impairments in task performance and increasing the risk of exertional heat (including heat stroke) and cold injuries that can be life-threatening. Substantial individual variability in physiological tolerance to thermal stress necessitates an individualized approach to mitigate the deleterious effects of thermal stress, such as physiological monitoring of individual thermal strain. During heat exposure, measurements of deep-body (T_c) and skin temperatures and heart rate can provide some indication of thermal strain. Combining these physiological variables with biomechanical markers of gait (in)stability may provide further insight on central nervous system dysfunction - the key criterion of exertional heat stroke (EHS). Thermal strain in cold environments can be monitored with skin temperature (peripheral and proximal), shivering thermogenesis and T_c. Non-invasive methods for real-time estimation of T_c have been developed and some appear to be promising but require further validation. Decision-support tools provide useful information for planning activities and biomarkers can be used to improve their predictions, thus maximizing safety and performance during hot- and cold-weather operations. With better understanding on the etiology and pathophysiology of EHS, the microbiome and markers of the inflammatory responses have been identified as novel biomarkers of heat intolerance. This review aims to (i) discuss selected physiological and biomechanical markers of heat or cold strain, (ii) how biomarkers may be used to ensure operational readiness in hot and cold environments, and (iii) present novel molecular biomarkers (e.g., microbiome, inflammatory cytokines) for preventing EHS.

Extreme environmental temperatures and motorcycle crashes: a time-series analysis

Extreme temperature could affect traffic crashes by influencing road safety, vehicle performance, and drivers' behavior and abilities. Studies evaluating the impacts of extreme temperatures on the risk of traffic crashes have mainly overlooked the potential role of vehicle air conditioners. The aim of this study, therefore, was to evaluate the effect of exposure to extreme cold and hot temperatures on seeking medical attention due to motorcycle crashes. The study was conducted in Iran by using medical attendance for motorcycle crashes from March 2011 to June 2017. Data on daily minimum, mean and maximum temperature (°C), relative humidity (%), wind velocity (km/h), and precipitation (mm/day) were collected. We developed semi-parametric generalized additive models following a quasi-Poisson distribution with the distributed nonlinear lag model to estimate the immediate and lagged associations (reported as relative risk [RR], and 95% confidence interval [CI]). Between March 2011 and June 2017, 36,079 medical attendances due to motorcycle road traffic crashes were recorded (15.8 ± 5.92 victims per day). In this time period, the recorded temperature ranged from -11.2 to 45.4 °C (average: 25.5 ± 11.0 °C). We found an increased risk of medical attendance for motorcycle crashes (based on maximum daily temperature) at both extremely cold (1st percentile) and hot (99th percentile) temperatures and also hot (75th percentile) temperatures, mainly during lags 0 to 3 days (e.g., RR: 1.12 [95% CI: 1.05: 1.20]; RR: 1.08 [95% CI: 1.01: 1.16]; RR: 1.20 [95% CI: 1.09: 1.32] at lag0 for extremely cold, hot, and extremely hot conditions, respectively). The risk estimates for extremely hot temperatures were larger than hot and extremely cold temperatures. We estimated that 11.01% (95% CI: 7.77:14.06) of the medical attendance for motorcycle crashes is estimated to be attributable to non-optimal temperature (using mean temperature as exposure variable). Our findings have important public health messaging, given the considerable burden associated with road traffic injury, particularly in low- and middle-income countries.

Duration limits for exposure for the whole body and extremities with a military extreme cold protection clothing ensemble at an ambient temperature of -40°C

Manual performance and body temperature responses were assessed in a 1-h trial at an ambient temperature (TAMB) of -40°C for 7 male participants (32 ± 14 (mean ± SD) years) wearing a typical military extreme cold protection clothing ensemble. The purpose was to establish duration limited exposure (DLIM) for these conditions, and it was hypothesized that (i) core temperature (TCORE) would remain normothermic, whereas extremity skin temperature (TSK) would decrease; (ii) decrements of manual performance would be in proportion to decreases of hand TSK; and (iii) DLIM would be determined by the hand or foot TSK responses. Linear regression was employed to assess associations of manual performance scores and body temperatures with DLIM assessed using the Required Clothing Insulation (IREQ) model and extremity temperatures in ISO 11079-2007. Results showed TCORE remained at ~37.3°C, whereas there were significant (0.0001 < p < 0.05) decreases in extremity TSK. Associations between manual performance and hand TSK showed coefficients of determination (R2) ranging from 0.48 < R2 < 0.98; 0.00005 ≤ p ≤ 0.08. The DLIM for the whole-body ensemble ranged from 2.2 h to > 8 h, whereas the DLIM for the extremities was 0.56 ± 0.20 h for TSK decreasing 15°C. In conclusion, the hypotheses of a stable core temperature and decreases of extremity skin temperature giving decrements in manual performance were accepted as was the hypothesis that duration limits for exposure would be determined by extremity skin temperatures of the hand and foot.

Finger anthropometrics may not be a primary influence on the thermal responses to cooling and rewarming

The fingers have a large surface area to volume ratio (SA:V), minimal muscle mass, and potent vasoconstrictor capacity. These qualities make the fingers prone to heat loss and freezing injuries during whole-body or local cold exposure. Anthropologists have proposed that the large inter-individual variability in human finger anthropometrics may be an ecogeographic evolutionary adaptation, where shorter and thicker digits (i.e. smaller SA:V ratio) provide a favorable adaptation for cold climate natives. We hypothesized that the SA:V ratio of a digit has an inverse relationship with finger blood flux and finger temperature (Tfinger) during cooling and rewarming from cold. Fifteen healthy adults with no or limited cold experiment experience performed 10 min of baseline immersion in warm water (35.0 ± 0.1°C), 30 min in cold water (8.4 ± 0.2°C), and a final 10 min of rewarming in ambient air (~22°C, ~40% relative humidity). Tfinger and finger blood flux were measured continuously across multiple digits per participant. Average Tfinger (p = 0.05; R2 = 0.06) and area under the curve for Tfinger (p = 0.05; R2 = 0.07) during hand cooling showed significant, negative correlations to digit SA:V ratio. There was no relationship between digit SA:V ratio and blood flux (i.e. average blood flux and AUC) during cooling as well as between SA:V ratio and digit temperature (i.e. average Tfinger and AUC) or blood flux (i.e. average blood flux and AUC) during rewarming. Overall, digit anthropometrics do not appear to play a dominant role in extremity cold response.

The Impact of Protective Gloves on Manual Dexterity in Cold Environments-A Pilot Study

Our research aimed to determine the impact of two types of protective gloves. The research tested the glove performance on men exposed to a range of temperatures reflecting the working conditions in fruit and vegetable processing. The gloves were assessed for performance within the time required to complete a specific manual task and for performance relative to the subjective thermal sensations in the male subjects. Six males participated in a total of 3 study variants: at +5 °C (with double gloves and single glove), at -1 °C (with double gloves and single glove) and in reference conditions +20 °C (without gloves), in which they performed manual tasks. The measurement of manual task performance time was used to assess manual dexterity. Subjective thermal sensations were determined. Differences in the time required to complete specific tasks were observed between the variants with gloves (both at a temperature of +5 °C and -1 °C), and without gloves (p < 0.05). The type of protective gloves had an impact on the time needed to complete manual tasks and therefore may affect manual dexterity.

Advanced Functional Materials for Intelligent Thermoregulation in Personal Protective Equipment

The exposure to extreme temperatures in workplaces involves physical hazards for workers. A poorly acclimated worker may have lower performance and vigilance and therefore may be more exposed to accidents and injuries. Due to the incompatibility of the existing standards implemented in some workplaces and the lack of thermoregulation in many types of protective equipment that are commonly fabricated using various types of polymeric materials, thermal stress remains one of the most frequent physical hazards in many work sectors. However, many of these problems can be overcome with the use of smart textile technologies that enable intelligent thermoregulation in personal protective equipment. Being based on conductive and functional polymeric materials, smart textiles can detect many external stimuli and react to them. Interconnected sensors and actuators that interact and react to existing risks can provide the wearer with increased safety, protection, and comfort. Thus, the skills of smart protective equipment can contribute to the reduction of errors and the number and severity of accidents in the workplace and thus promote improved performance, efficiency, and productivity. This review provides an overview and opinions of authors on the current state of knowledge on these types of technologies by reviewing and discussing the state of the art of commercially available systems and the advances made in previous research works.

A digital tool for prevention and management of cold weather injuries-Cold Weather Ensemble Decision Aid (CoWEDA)

This paper describes a Cold Weather Ensemble Decision Aid (CoWEDA) that provides guidance for cold weather injury prevention, mission planning, and clothing selection. CoWEDA incorporates current science from the disciplines of physiology, meteorology, clothing, and computer modeling. The thermal performance of a cold weather ensemble is defined by endurance times, which are the time intervals from initial exposure until the safety limits are reached. These safety limits correspond to conservative temperature thresholds that provide a warning of the approaching onset of frostbite and/or hypothermia. A validated six-cylinder thermoregulatory model is used to predict human thermal responses to cold while wearing different ensembles. The performance metrics, model, and a database of clothing properties were integrated into a user-friendly software application. CoWEDA is the first tool that allows users to build their own ensembles from the clothing menu (i.e., jackets, footwear, and accessories) for each body region (i.e., head, torso, lower body, hands, feet) and view their selections in the context of physiological strain and the operational consequences. Comparison of predicted values to skin and core temperatures, measured during 17 cold exposures ranging from 0 to -40°C, indicated that the accuracy of CoWEDA prediction is acceptable, and most predictions are within measured mean ± SD. CoWEDA predicts the risk of frostbite and hypothermia and ensures that a selected clothing ensemble is appropriate for expected weather conditions and activities. CoWEDA represents a significant enhancement of required clothing insulation (IREQ, ISO 11079) and wind chill index-based guidance for cold weather safety and survival.

The effect of harness suspension on a simulated maintenance task efficacy in the renewable energy industry

Building, bridge or wind turbine maintenance requires manual dexterity tasks by a specialist rope-access trained workforce via two principal means: harness suspension of individual workers from above, or deployment of a suspended platform or cradle from which workers access the structure to be maintained. Currently no published research compares accuracy and efficiency of simulated maintenance tasks between these modalities. This study investigated manual dexterity task performance of peg placement and shape delineation in seated, standing and suspended environments in 16 healthy controls and 26 professional rope-access trained individuals. Both seated and standing assessments were superior to those suspended, and height of suspension, total mass and years of experience had no influence on the task outcome. These findings suggest that, where feasible, cradle suspension mechanisms which permit standing maintenance are favourable in terms of task efficacy and where feasible, should be considered for deployment in wind energy and other engineering applications.

Independent and interactive effects of thermal stress and mental fatigue on manual dexterity

Many occupations and sports require high levels of manual dexterity under thermal stress and mental fatigue. Yet, multistressor studies remain scarce. We quantified the interactive effects of thermal stress and mental fatigue on manual dexterity. Seven males (21.1 ± 1.3 yr) underwent six separate 60-min trials characterized by a combination of three air temperatures (hot, 37°C; neutral, 21°C; cold, 7°C) and two mental fatigue states (MF, mental fatigue induced by a 35-min cognitive battery; no-MF, no mental fatigue). Participants performed complex (O'Connor test) and simple (hand-tool test) manual tasks pre- and posttrial to determine stressor-induced performance changes. We monitored participants' rectal temperature and hand skin temperature (T_hand) continuously and assessed the reaction time (hand-click test) and subjective mental fatigue (5-point scale). Thermal stress (P < 0.0001), but not mental fatigue (P = 0.290), modulated T_hand (heat, +3.3°C [95% CI: +0.2, +6.5]; cold, -7.5°C [-10.7, -4.4]). Mental fatigue (P = 0.021), but not thermal stress (P = 0.646), slowed the reaction time (∼10%) and increased subjective fatigue. Thermal stress and mental fatigue had an interactive effect on the complex manual task (P = 0.040), with cold-no-MF decreasing the performance by -22% [-39, -5], whereas neutral-MF, cold-MF, and heat-MF by -36% [-53, -19], -34% [-52, -17], and -36% [-53, -19], respectively. Only mental fatigue decreased the performance in the simple manual task (-30% [-43, -16] across all thermal conditions; P = 0.002). Cold stress-induced impairments in complex manipulation increase with mental fatigue; yet combined stressors' effects are no greater than those of mental fatigue alone, which also impairs simple manipulation. Mental fatigue poses a greater challenge to manual dexterity than thermal stress.

Evaluation of Three Field Rewarming Techniques During Cold Weather Military Training

INTRODUCTION

The purpose of this work was to evaluate the effectiveness of 3 rewarming techniques to determine how warfighters, and perhaps other populations in wilderness environments, should prioritize field rewarming options after a brief accidental immersion in cold water.

METHODS

As part of a cold weather military training exercise, 31 military personnel (mean±SD age: 26±5 y, height: 180±10 cm, weight: 83.2±10.9 kg) completed a 10-min immersion in cold (0°C) water and subsequently rewarmed for 60 min using 3 different field rewarming techniques (sleeping bag, sleeping bag + warm fluids, or exercise). Heart rate, core and skin temperatures, thermal and shivering sensations, and manual dexterity (intravenous setup and insertion) were measured during the training exercise.

RESULTS

Cold water immersion decreased core temperature (pre: 37.4±0.4; post: 36.4±1.0°C; P<0.001) and mean skin temperature (pre: 27.9±1.3; post: 15.6±1.8°C; P<0.001) and impaired manual dexterity (intravenous insertion time, pre: 71±12, post: 166±48 s; P<0.001). Recovery from mild cold stress was similar among all 3 rewarming techniques for all measurements.

CONCLUSIONS

Findings suggesting similar rewarming responses in field settings are beneficial for the warfighter, and perhaps others, in that rewarming options exist and can be implemented with no compromise in recovery from cold stress.

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.

Effects of muscle cooling on kinetics of pulmonary oxygen uptake and muscle deoxygenation at the onset of exercise

This study investigated effects of skeletal muscle cooling on the metabolic response and kinetics of pulmonary oxygen uptake (V˙O₂) and skeletal muscle deoxygenation during submaximal exercise. In the cooling condition (C), after immersion of the lower body into 12°C water for 30 min, eight healthy males performed 30‐min cycling exercise at the lactate threshold while undergoing thigh cooling by a water‐circulating pad. In the normal condition (N) as control, they conducted the same exercise protocol without cooling. Blood lactate concentration was significantly higher in C than N at 10 min after onset of exercise (4.0 ± 1.7 and 2.4 ± 1.2 mmol/L in C and N, P < 0.05). The percent change in the tissue oxygen saturation of the vastus lateralis, measured by a near‐infrared spectroscopy, was significantly lower in C at 2, 8, 10, and 20 min after the exercise onset compared with N (P < 0.05). The percent change in deoxy hemoglobin+myoglobin concentration (Deoxy[Hb+Mb]) showed a transient peak at the onset of exercise and significantly higher value in C at 10, 20, and 30 min after the exercise onset (P < 0.05). Compared to N, slower V˙O₂ kinetics (mean response time) was observed in C (45.6 ± 7.8 and 36.1 ± 7.7 sec in C and N, P < 0.05). The mean response time in C relative to N was significantly correlated with the transient peak of Deoxy[Hb+Mb] in C (r = 0.84, P < 0.05). These results suggest that lower oxygen delivery to the hypothermic skeletal muscle might induce greater glycolytic metabolism during exercise and slower V˙O₂ kinetics at the onset of exercise.

Cold-induced vasodilation responses before and after exercise in normobaric normoxia and hypoxia

PURPOSE

Cold-induced vasodilation (CIVD) is known to protect humans against local cold injuries and improve manual dexterity. The current study examined the effects of metabolic heat production on cold-induced vasodilation responses in normobaric hypoxia and normoxia.

METHODS

Ten participants immersed their non-dominant hand into 5 °C water for 15 min. Minimum finger temperature (T_min), maximum finger temperature (T_max), onset time, amplitude, and peak time were measured before and after exercise under normoxia (21% O₂) and two levels of normobaric hypoxia (17% O₂ and 13% O₂).

RESULTS

Neither T_min nor amplitude was affected by hypoxia. However, T_max was significantly decreased by hypoxia while reduction in onset time and peak time trended towards significance. T_min, T_max, and amplitude were significantly higher during post-exercise CIVD than pre-exercise CIVD.

CONCLUSION

The CIVD response may be negatively affected by the introduction of hypoxia whereas metabolic heat production via exercise may counteract adverse effects of hypoxia and improve CIVD responses.

Effect of localized microclimate heating on peripheral skin temperatures and manual dexterity during cold exposure

Reduced dexterity is a major problem in cold weather, with a need for a countermeasure that increases hand (T_hand) and finger (T_fing) temperatures and improves dexterity. The purpose of this study was to determine whether electric heat (set point, 42°C) applied to the forearm (ARM, 82 W), face (FACE, 9.2 W), or combination of both (COMB, 91.2 W), either at the beginning of cold exposure (COLD; 0.5°C, 120 min; 2 clo insulation, seated, bare-handed) or after T_fing fell to 10.5°C [delayed trials (D)], improves T_hand, T_fing, dexterity, and finger key pinch strength (S_fing). Volunteers ( n = 8; 26 ± 9 yr) completed 7 experimental trials in COLD: ARM, ARM-D, FACE, FACE-D, COMB, COMB-D, and no heating (CON). Temperatures were measured before (BASE) and throughout COLD. Tests of dexterity [Purdue Pegboard assembly (PP) and magazine loading (MAGLOAD)] and S_fing were measured at BASE and after 45 and 90 min of COLD. Data presented are at minute 90. T_hand was warmer ( P < 0.001) during ARM (18.0 ± 2.6°C) and COMB (18.9 ± 2.0°C) versus CON (15.3 ± 1.5°C) and FACE (15.8 ± 1.5°C) for heating that was initiated at the beginning of COLD. T_fing was higher ( P < 0.04) during COMB (12.7 ± 5.1°C) versus CON (9.7 ± 2.1°C) and FACE (8.9 ± 2.2°C). The change from BASE for PP (no. of pieces) was less ( P < 0.005) in COMB (-4.5 ± 3.3) and ARM (-5.0 ± 6.0) versus CON (-13.0 ± 7.3) and FACE (-10.0 ± 8.3), and for MAGLOAD, it tended ( P = 0.06) to be less in COMB (-8.9 ± 6.2 cartridges) versus CON (-14.8 ± 3.7 cartridges). There was no change in S_fing from BASE (10.5 kg) to minute 90 in ARM or COMB (0.7 ± 1.4 and -0.2 ± 1.7 kg, respectively) but a decrease ( P < 0.01) in CON and FACE (-2.1 ± 2.0 and -1.6 ± 1.9 kg, respectively). There were no differences in T_hand, T_fing, dexterity, and S_fing at minute 90 when comparing heating that was initiated at the beginning of COLD versus delayed heating. In conclusion, heating using either COMB or ARM, compared with CON and FACE, improved T_hand and T_fing and reduced the decline in dexterity by 20%-50% and S_fing by 90%. Furthermore, delayed heating had no deleterious effect on T_hand, T_fing, dexterity, and S_fing compared with heating that started at the beginning of cold exposure. NEW & NOTEWORTHY The present study demonstrated that, during sedentary cold air exposure, localized heating that was applied from the beginning of cold exposure on the forearm increases hand and finger temperatures and finger strength, leading to subsequent improvements in manual dexterity. In addition, localized heating that was delayed until finger temperatures cooled significantly also caused higher peripheral temperatures, leading to better strength and manual dexterity, compared with no heating.

Towards a wearable sensor system for continuous occupational cold stress assessment

This study investigated the usefulness of continuous sensor data for improving occupational cold stress assessment. Eleven volunteer male subjects completed a 90-120-min protocol in cold environments, consisting of rest, moderate and hard work. Biomedical data were measured using a smart jacket with integrated temperature, humidity and activity sensors, in addition to a custom-made sensor belt worn around the chest. Other relevant sensor data were measured using commercially available sensors. The study aimed to improve decision support for workers in cold climates, by taking advantage of the information provided by data from the rapidly growing market of wearable sensors. Important findings were that the subjective thermal sensation did not correspond to the measured absolute skin temperature and that large differences were observed in both metabolic energy production and skin temperatures under identical exposure conditions. Temperature, humidity, activity and heart rate were found to be relevant parameters for cold stress assessment, and the locations of the sensors in the prototype jacket were adequate. The study reveals the need for cold stress assessment and indicates that a generalised approached is not sufficient to assess the stress on an individual level.

The influence of digit size and proportions on dexterity during cold exposure

OBJECTIVES

The current study investigated whether size and proportions of the hands and digits affect dexterity during severe cold exposure. As wide hands are known to lose less heat than narrow hands, and narrow digits are associated with greater dexterity, this study aimed to test whether there was a direct trade-off between dexterity and thermoregulation that shapes hand morphology.

METHODS

Participants (25 women, 15 men) carried out the Purdue Pegboard test before and after a 3-min ice-water immersion of the hand. Their hand length, hand width, digit lengths, and digit widths were measured using standard anthropometric methods.

RESULTS

Wide first and third digits associated with significantly reduced dexterity after immersion relative to individuals with narrower first and third digits. Second digit width positively correlated with average digit temperature after immersion. Hand length and hand width did not influence dexterity.

CONCLUSION

The current study suggests that digit width influences dexterity in cold conditions, reflecting patterns found at room temperature. Hand and digit morphology may be the product of two significant constraints on the hand: dexterity and thermoregulation. In cold conditions, hand morphology appears to be predominantly constrained by thermal stress, at the expense of dexterity. This may have important implications for interpreting the morphology of extinct and extant hominins.

Body size and body composition effects on heat loss from the hands during severe cold exposure

OBJECTIVES

This study investigated the influence of body size and composition on maintaining hand temperature during severe cold exposure. The hand's high surface area-to-volume ratio predisposes the hand to heat loss, increasing the risk of cold injury and even hypothermia, which are major selective pressures in cold environments. While vasoregulation may reduce heat loss from the hand, the effect of body form, tissue thermogenesis, and body insulation on heat loss is unknown.

MATERIALS AND METHODS

Thermal imaging was used to determine heat loss during a 3-min ice-water hand immersion test carried out on 114 volunteers (female = 63, male = 51). Established anthropometric measures were used to quantify body size, and bioelectrical impedance analysis determined skeletal muscle and fat mass.

RESULTS

Skeletal muscle mass relative to body mass was a highly significant predictor of heat loss, while body mass, fat mass, and stature were not. Body composition and body size had little to no significant influence during rewarming after immersion.

DISCUSSION

The thermogenic properties of muscle mass support maintenance of hand temperature during severe cold exposure. The findings here suggest that muscular individuals are less susceptible to heat loss and cold injury, and may be better at manual tasks in cold conditions than nonmuscular individuals.

The Combined Effect of Cold and Moisture on Manual Performance

Objective The aim of this study was to investigate the combined effect of cold and moisture on manual performance and tactile sensitivity. Background People working in the ocean environment often perform manual work in cold and wet conditions. Although the independent effects of cold and moisture on hand function are known, their combined effect has not been investigated. Method Participants completed sensory (Touch-Test, two-point discrimination) and motor (Purdue Pegboard, Grooved Pegboard, reef knot untying) tests in the following conditions: dry hand, wet hand, cold hand, and cold and wet hand. Results For the Purdue Pegboard and knot untying tasks, the greatest decrement in performance was observed in the cold-and-wet-hand condition, whereas the decrements seen in the cold-hand and wet-hand conditions were similar. In the Grooved Pegboard task, the performance decrements exhibited in the cold-and-wet-hand condition and the cold-hand condition were similar, whereas no decrement was observed in the wet-hand condition. Tactile sensitivity was reduced in the cold conditions for the Touch-Test but not the two-point discrimination test.

CONCLUSION

The combined effect of cold and moisture led to the largest performance decrements except when intrinsic object properties helped with grasp maintenance. The independent effects of cold and moisture on manual performance were comparable. Application Tools and equipment for use in the cold ocean environment should be designed to minimize the effects of cold and moisture on manual performance by including object properties that enhance grasp maintenance and minimize the fine-dexterity requirements.

Internal and external cooling methods and their effect on body temperature, thermal perception and dexterity

Objective

The present study aimed to compare a range of cooling methods possibly utilised by occupational workers, focusing on their effect on body temperature, perception and manual dexterity.

Methods

Ten male participants completed eight trials involving 30 min of seated rest followed by 30 min of cooling or control of no cooling (CON) (34°C, 58% relative humidity). The cooling methods utilised were: ice cooling vest (CV₀), phase change cooling vest melting at 14°C (CV₁₄), evaporative cooling vest (CV_EV), arm immersion in 10°C water (AI), portable water-perfused suit (WPS), heliox inhalation (HE) and ice slushy ingestion (SL). Immediately before and after cooling, participants were assessed for fine (Purdue pegboard task) and gross (grip and pinch strength) manual dexterity. Rectal and skin temperature, as well as thermal sensation and comfort, were monitored throughout.

Results

Compared with CON, SL was the only method to reduce rectal temperature (P = 0.012). All externally applied cooling methods reduced skin temperature (P<0.05), though CV₀ resulted in the lowest skin temperature versus other cooling methods. Participants felt cooler with CV₀, CV₁₄, WPS, AI and SL (P<0.05). AI significantly impaired Purdue pegboard performance (P = 0.001), but did not affect grip or pinch strength (P>0.05).

Conclusion

The present study observed that ice ingestion or ice applied to the skin produced the greatest effect on rectal and skin temperature, respectively. AI should not be utilised if workers require subsequent fine manual dexterity. These results will help inform future studies investigating appropriate pre-cooling methods for the occupational worker.

Thermal comfort sustained by cold protective clothing in Arctic open-pit mining-a thermal manikin and questionnaire study

Workers in the Arctic open-pit mines are exposed to harsh weather conditions. Employers are required to provide protective clothing for workers. This can be the outer layer, but sometimes also inner or middle layers are provided. This study aimed to determine how Arctic open-pit miners protect themselves against cold and the sufficiency, and the selection criteria of the garments. Workers' cold experiences and the clothing in four Arctic open-pit mines in Finland, Sweden, Norway and Russia were evaluated by a questionnaire (n=1,323). Basic thermal insulation (I_cl) of the reported clothing was estimated (ISO 9920). The I_cl of clothing from the mines were also measured by thermal manikin (standing/walking) in 0.3 and 4.0 m/s wind. The questionnaire showed that the I_cl of the selected clothing was on average 1.2 and 1.5 clo in mild (-5 to +5°C) and dry cold (-20 to -10°C) conditions, respectively. The I_cl of the clothing measured by thermal manikin was 1.9-2.3 clo. The results show that the Arctic open-pit miners' selected their clothing based on occupational (time outdoors), environmental (temperature, wind, moisture) and individual factors (cold sensitivity, general health). However, the selected clothing was not sufficient to prevent cooling completely at ambient temperatures below -10°C.

Cardiovascular and thermal strain during 3-4 days of a metabolically demanding cold-weather military operation

BACKGROUND

Cardiovascular (CV) and thermal responses to metabolically demanding multi-day military operations in extreme cold-weather environments are not well described. Characterization of these operations will provide greater insights into possible performance capabilities and cold injury risk.

METHODS

Soldiers from two cold-weather field training exercises (FTX) were studied during 3-day (study 1, n = 18, age: 20 ± 1 year, height: 182 ± 7 cm, mass: 82 ± 9 kg) and 4-day (study 2, n = 10, age: 20 ± 1 year, height: 182 ± 6 cm, mass: 80.7 ± 8.3 kg) ski marches in the Arctic. Ambient temperature ranged from -18 to -4 °C during both studies. Total daily energy expenditure (TDEE, from doubly labeled water), heart rate (HR), deep body (T_pill), and torso (T_torso) skin temperature (obtained in studies 1 and 2) as well as finger (T_fing), toe (T_toe), wrist, and calf temperatures (study 2) were measured.

RESULTS

TDEE was 6821 ± 578 kcal day^-1 and 6394 ± 544 for study 1 and study 2, respectively. Mean HR ranged from 120 to 140 bpm and mean T_pill ranged between 37.5 and 38.0 °C during skiing in both studies. At rest, mean T_pill ranged from 36.0 to 36.5 °C, (lowest value recorded was 35.5 °C). Mean T_fing ranged from 32 to 35 °C during exercise and dropped to 15 °C during rest, with some T_fing values as low as 6-10 °C. T_toe was above 30 °C during skiing but dropped to 15-20 °C during rest.

CONCLUSIONS

Daily energy expenditures were among the highest observed for a military training exercise, with moderate exercise intensity levels (~65% age-predicted maximal HR) observed. The short-term cold-weather training did not elicit high CV and T_pill strain. T_fing and T_toe were also well maintained while skiing, but decreased to values associated with thermal discomfort at rest.

Neuromuscular function during knee extension exercise after cold water immersion

Background

Human adaptability to cold environment has been focused on in the physiological anthropology and related research area. Concerning the human acclimatization process in the natural climate, it is necessary to conduct a research assessing comprehensive effect of cold environment and physical activities in cold. This study investigated the effect of cold water immersion on the exercise performance and neuromuscular function during maximal and submaximal isometric knee extension.

Methods

Nine healthy males participated in this study. They performed maximal and submaximal (20, 40, and 60% maximal load) isometric knee extension pre- and post-immersion in 23, 26, and 34 °C water. The muscle activity of the rectus femoris (RF) and vastus lateralis (VL) was measured using surface electromyography (EMG). The percentages of the maximum voluntary contraction (%MVC) and mean power frequency (MPF) of EMG data were analyzed.

Results

The post-immersion maximal force was significantly lower in 23 °C than in 26 and 34 °C conditions (P < 0.05). The post-immersion %MVC of RF was significantly higher than pre-immersion during 60% maximal exercise in 23 and 26 °C conditions (P < 0.05). In the VL, the post-immersion %MVC was significantly higher than pre-immersion in 23 and 26 °C conditions during 20% maximal exercise and in 26 °C at 40 and 60% maximal intensities (P < 0.05). The post-immersion %MVC of VL was significantly higher in 26 °C than in 34 °C at 20 and 60% maximal load (P < 0.05). The post-immersion MPF of RF during 20% maximal intensity was significantly lower in 23 °C than in 26 and 34 °C conditions (P < 0.05), and significantly different between three water temperature conditions at 40 and 60% maximal intensities (P < 0.05). The post-immersion MPF of VL during three submaximal trials were significantly lower in 23 and 26 °C than in 34 °C conditions (P < 0.05).

Conclusions

The lower shift of EMG frequency would be connected with the decrease in the nerve and muscle fibers conduction velocity. To compensate for the impairment of each muscle fibers function, more muscle fibers might be recruited to maintain the working load. This might result in the greater amplitude of EMG after the cold immersion.

Thermal stress, human performance, and physical employment standards

Many physically demanding occupations in both developed and developing economies involve exposure to extreme thermal environments that can affect work capacity and ultimately health. Thermal extremes may be present in either an outdoor or an indoor work environment, and can be due to a combination of the natural or artificial ambient environment, the rate of metabolic heat generation from physical work, processes specific to the workplace (e.g., steel manufacturing), or through the requirement for protective clothing impairing heat dissipation. Together, thermal exposure can elicit acute impairment of work capacity and also chronic effects on health, greatly contributing to worker health risk and reduced productivity. Surprisingly, in most occupations even in developed economies, there are rarely any standards regarding enforced heat or cold safety for workers. Furthermore, specific physical employment standards or accommodations for thermal stressors are rare, with workers commonly tested under near-perfect conditions. This review surveys the major occupational impact of thermal extremes and existing employment standards, proposing guidelines for improvement and areas for future research.

Relationships of self-identified cold tolerance and cold-induced vasodilatation in the finger

This study was conducted to investigate relationships of self-identified cold tolerance and cold-induced vasodilatation (CIVD) in the finger. Nine males and 34 females participated in the following 2 tests: a CIVD test and a self-reported survey. The CIVD test was conducted 30-min cold-water immersion (3.8 ± 0.3 °C) of the middle finger at an air temperature of 27.9 ± 0.1 °C. The self-reported questionnaire consisted of 28 questions about whole and local body cold and heat tolerances. By a cluster analysis on the survey results, the participants were divided into two groups: high self-identified cold tolerance (HSCT, n = 25) and low self-identified cold tolerance (LSCT, n = 18). LSCT had lower self-identified cold tolerance (P < 0.001), preferred hot thermal stimulation (P = 0.006), and wore heavier clothing during daily life (P < 0.001) than HSCT. LSCT had significantly lower maximal finger temperatures (T max) (P = 0.040), smaller amplitude (P = 0.029), and delayed onset time of CIVD (P = 0.080) when compared to HSCT. Some questions examining the self-identified cold or heat tolerance had relationships with cold tolerance index, T max, and amplitude (P < 0.1). These results indicate that self-identified cold tolerance classified through a standardized survey could be a good index to predict physiological cold tolerance.

Cold Stress Effects on Exposure Tolerance and Exercise Performance

Cold weather can have deleterious effects on health, tolerance, and performance. This paper will review the physiological responses and external factors that impact cold tolerance and physical performance. Tolerance is defined as the ability to withstand cold stress with minimal changes in physiological strain. Physiological and pathophysiological responses to short-term (cold shock) and long-term cold water and air exposure are presented. Factors (habituation, anthropometry, sex, race, and fitness) that influence cold tolerance are also reviewed. The impact of cold exposure on physical performance, especially aerobic performance, has not been thoroughly studied. The few studies that have been done suggest that aerobic performance is degraded in cold environments. Potential physiological mechanisms (decreases in deep body and muscle temperature, cardiovascular, and metabolism) are discussed. Likewise, strength and power are also degraded during cold exposure, primarily through a decline in muscle temperature. The review also discusses the concept of thermoregulatory fatigue, a reduction in the thermal effector responses of shivering and vasoconstriction, as a result of multistressor factors, including exhaustive exercise.

Thermoregulatory modeling for cold stress

Modeling for cold stress has generated a rich history of innovation, has exerted a catalytic influence on cold physiology research, and continues to impact human activity in cold environments. This overview begins with a brief summation of cold thermoregulatory model development followed by key principles that will continue to guide current and future model development. Different representations of the human body are discussed relative to the level of detail and prediction accuracy required. In addition to predictions of shivering and vasomotor responses to cold exposure, algorithms are presented for thermoregulatory mechanisms. Various avenues of heat exchange between the human body and a cold environment are reviewed. Applications of cold thermoregulatory modeling range from investigative interpretation of physiological observations to forecasting skin freezing times and hypothermia survival times. While these advances have been remarkable, the future of cold stress modeling is still faced with significant challenges that are summarized at the end of this overview.

The influence of cooling forearm/hand and gender on estimation of handgrip strength

Handgrip strength is essential in manual operations and activities of daily life, but the influence of forearm/hand skin temperature on estimation of handgrip strength is not well documented. Therefore, the present study intended to investigate the effect of local cooling of the forearm/hand on estimation of handgrip strength at various target force levels (TFLs, in percentage of MVC) for both genders. A cold pressor test was used to lower and maintain the hand skin temperature at 14°C for comparison with the uncooled condition. A total of 10 male and 10 female participants were recruited. The results indicated that females had greater absolute estimation deviations. In addition, both genders had greater absolute deviations in the middle range of TFLs. Cooling caused an underestimation of grip strength. Furthermore, a power function is recommended for establishing the relationship between actual and estimated handgrip force. Statement of relevance: Manipulation with grip strength is essential in daily life and the workplace, so it is important to understand the influence of lowering the forearm/hand skin temperature on grip-strength estimation. Females and the middle range of TFL had greater deviations. Cooling the forearm/hand tended to cause underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force. Practitioner Summary: It is important to understand the effect of lowering the forearm/hand skin temperature on grip-strength estimation. A cold pressor was used to cool the hand. The cooling caused underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force.

STATEMENT OF RELEVANCE

Manipulation with grip strength is essential in daily life and the workplace, so it is important to understand the influence of lowering the forearm/hand skin temperature on grip-strength estimation. Females and the middle range of TFL had greater deviations. Cooling the forearm/hand tended to cause underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force.

PRACTITIONER SUMMARY

It is important to understand the effect of lowering the forearm/hand skin temperature on grip-strength estimation. A cold pressor was used to cool the hand. The cooling caused underestimation, and a power function is recommended for establishing the relationship between actual and estimated handgrip force

Hands and feet: physiological insulators, radiators and evaporators

The purpose of this review is to describe the unique anatomical and physiological features of the hands and feet that support heat conservation and dissipation, and in so doing, highlight the importance of these appendages in human thermoregulation. For instance, the surface area to mass ratio of each hand is 4-5 times greater than that of the body, whilst for each foot, it is ~3 times larger. This characteristic is supported by vascular responses that permit a theoretical maximal mass flow of thermal energy of 6.0 W (136 W m(2)) to each hand for a 1 °C thermal gradient. For each foot, this is 8.5 W (119 W m(2)). In an air temperature of 27 °C, the hands and feet of resting individuals can each dissipate 150-220 W m(2) (male-female) of heat through radiation and convection. During hypothermia, the extremities are physiologically isolated, restricting heat flow to <0.1 W. When the core temperature increases ~0.5 °C above thermoneutral (rest), each hand and foot can sweat at 22-33 mL h(-1), with complete evaporation dissipating 15-22 W (respectively). During heated exercise, sweat flows increase (one hand: 99 mL h(-1); one foot: 68 mL h(-1)), with evaporative heat losses of 67-46 W (respectively). It is concluded that these attributes allow the hands and feet to behave as excellent radiators, insulators and evaporators.

Influence of indoor and outdoor temperatures on the fingertip blood flow rate

A total of 58 healthy subjects participated to elucidate the influence of indoor and outdoor temperatures on blood flow. After walking outdoors for 20 min, the blood flow rate of a subject was measured. The subject then entered a classroom and studied for 120 min, and afterwards, the blood flow rate was measured again. The subjects were exposed to outdoor temperature ranging from -2.5 to 33.7°C. During the summer, the average blood flow rate after walking outdoors was 45.95 ± 25.790 TPU (tissue perfusion units); after the class, this decreased to 36.14 ± 21.837 TPU (p<0.05). During the autumn, the blood flow rate decreased from 27.69 ± 12.334 TPU to 12.47 ± 12.255 TPU (p<0.001). When the outside air temperature was below 3°C, the blood flow rate indoors increased significantly from 6.74 ± 3.540 TPU to 13.95 ± 11.522 TPU (p<0.05). In a comfortable and healthy environment, the blood flow rate was not constant but fluctuated between 15 TPU and 40 TPU.

Protective jacket enabling decision support for workers in cold climate

The cold and harsh climate in the High North represents a threat to safety and work performance. The aim of this study was to show that sensors integrated in clothing can provide information that can improve decision support for workers in cold climate without disturbing the user. Here, a wireless demonstrator consisting of a working jacket with integrated temperature, humidity and activity sensors has been developed. Preliminary results indicate that the demonstrator can provide easy accessible information about the thermal conditions at the site of the worker and local cooling effects of extremities. The demonstrator has the ability to distinguish between activity and rest, and enables implementation of more sophisticated sensor fusion algorithms to assess work load and pre-defined activities. This information can be used in an enhanced safety perspective as an improved tool to advice outdoor work control for workers in cold climate.