John G. Fox (1931-2004)

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on–off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30°C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 ± 5 W · m^?2. Water temperature to the LCG was held constant at 21°C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 ± 0.2°C) in NC, which was greater than IC (0.5 ± 0.2°C) and CC (0.5 ± 0.3°C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 ± 0.4°C) than IC (33.7 ± 0.6°C) and CC (32.6 ± 0.6°C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 ± 9 b · min^?1) was greater than IC (110 ± 10 b · min^?1) and CC (107 ± 9 b · min^?1) ( p < 0.05). Cooling by conduction (K) during NC (94 ± 4 W · m^?2) was lower than IC (142 ± 7 W · m^?2) and CC (146 ± 4 W · m^?2) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.     

Impact of fluid replacement on heat storage while wearing protective clothing

This study used partitional calorimetry to determine the influence of fluid replacement on heat storage during uncompensable heat stress. Eight males performed either light (L; level treadmill walking at 0.97 m x s(-1) (3.5 km x h(-1)) or heavy (H; 1.33 m x s(-1) (4.8 km x h(-1)) at a 4% grade) exercise at 40 degrees C and 30% relative humidity while wearing nuclear, biological and chemical (NBC) protective clothing. Subjects received either no fluid (NF), or 200 or 250 ml of fluid (F) as warm water at approximately 35 degrees C immediately before and every 15 min during the L and H trials respectively. Similar reductions in heart rate were observed at both metabolic rates with F but rectal temperature responses were not different between F and NF. Tolerance time was extended during L/F (106.5 +/- 22.1 min) compared with L/NF (93.1 +/- 20.8 min) but fluid replacement had no influence during H (59.8 +/- 9.5 min and 58.3 +/- 11.1 min for F and NF respectively). Fluid replacement also had no effect on the rate of heat storage during L (108.2 +/- 20.6 W x m(-2) and 111.0 +/- 22.6 W x m(-2) for F and NF respectively) and H (172.5 +/- 11.5 W x m(-2) and 182.1 +/- 15.8 W x m(-2) for F and NF respectively). However, heat storage expressed per unit of mass was significantly increased during L/F (18.5 +/- 4.0 kJ x kg(-1) ) compared with the other trials (16.3 +/- 4.8 kJ x kg(-1), 16.6 +/- 3.0 kJ x kg(-1) and 16.7 +/- 4.0 kJ x kg(-1) for L/NF, H/F and H/NF respectively). It was concluded that fluid replacement does not alter the rate of heat storage during uncompensable heat stress but does increase the heat storage capacity during light exercise when tolerance times are > 60 min.     

Thermal comfort and sensation in men wearing a cooling system controlled by skin temperature

OBJECTIVE: The study was done to determine whether thermal comfort (TC), thermal sensation (TS), and subjective factors gauging environmental stress were negatively affected with different cooling methods in men exercising in chemical protective clothing. BACKGROUND: Previous studies have reported that intermittent regional cooling improved the efficacy of cooling as compared with constant cooling (CC), but no studies have addressed whether there is any improvement in thermal comfort. METHODS: Eight male volunteers exercised at moderate work intensity (425 W) in three microclimate cooling tests. The circulating fluid in the cooling garment was provided during exercise to the head (6% body surface area [BSA]), torso (22% BSA), and thighs (44% BSA) and manipulated under three methods: (a) CC, (b) pulsed cooling (PC), and (c) PC activated by mean skin temperature (T(sk)) control (PC(skin)). TC and TS ratings were recorded every 20 min during the 80-min test. RESULTS: TC and TS ratings were not different for PC(skin) and CC; thus the participants perceived PC(skin) as being similar to CC. TS was significantly warmer with PC than with PC(skin) and CC (p < .001). In PC(skin), T(sk) was significantly higher than in PC and CC (p < .001), and PC(skin) was rated as being not as warm as PC according to TS. CONCLUSION: This indicates that the PC(skin) method was perceived as being as cool as CC and cooler than PC. APPLICATION: These findings indicate that the PC(skin) cooling method is an acceptable alternative to CC and PC based on human perceptions.     

The impact of various rehydration volumes for firefighters wearing protective clothing in warm environments

This study examined different fluid replacement quantities during intermittent work while wearing firefighting protective clothing and self-contained breathing apparatus in the heat (35 degrees C, 50% relative humidity). Twelve firefighters walked at 4.5 km per h with 0% elevation on an intermittent work (50 min) and rest (30 min) schedule until they reached a rectal temperature of 39.5 degrees C during work periods and 40.0 degrees C during rest, heart rates of 95% of maximum and/or exhaustion. During the heat-stress trials subjects received one of four fluid replacement quantities, high (H), moderate (M), low (L), and no hydration (NH), where H, M and L represented 78%, 63% and 37% of fluid loss, respectively. The total tolerance time (work + rest) was significantly greater during H (111.8 +/- 3.5), M (112.9 +/- 5.2) and L (104.2 +/- 5.8) compared to NH (95.3 +/- 3.8). In addition, work time (min), which excluded rest periods, was significantly greater in H (82.6 +/- 3.5), and M (82.9 +/- 5.2) compared to NH (65.3 +/- 3.8). It is concluded that incorporating even partial fluid replacement strategies while wearing firefighting protective clothing and self-contained breathing apparatus in the heat improves tolerance time.     

Effectiveness of rest pauses and cooling in alleviation of heat stress during simulated fire-fighting activity

This study examined whether cooling a fire-fighter with a high velocity fan, during 10 min rest pauses between, and following, 10 min work periods, decreases heat stress during repetitive fire-fighting activity. Twelve professional fire-fighters (mean age 31.8 +/- 6.7 years) completed two, 40 min work/recovery trials in an environmental chamber at 40 degrees C and 70% relative humidity (RH). One trial was termed an enhanced recovery (ER) trial and the other was termed a normal recovery (NR) trial. In both conditions subjects wore full protective clothing and breathing apparatus during the work. In the ER trial a subject removed his protective coat and sat in front of a fan during each recovery period. In the NR trial a subject merely unbuckled his coat and was not cooled by a fan during either recovery period. The group mean metabolic cost (VO2), and the exercise and recovery heart rates were significantly lower (p < or = 0.05) during the ER trial than in the NR condition. Group mean rectal temperature increased by 1.5 degrees C in the NR trial but by only 0.8 degree C during the ER trial. The latter group's more effective cooling indicates the potential of fan cooling to reduce physiological strain and decrease the risk of heat exhaustion during repetitive fire-fighting activity. The results suggest that a fire-fighter's short 10 min exposure to heavy work in a hot environment of 40 degrees C and 70% RH produces minimal heat stress in a healthy fire-fighter. However, a period of fire-fighting exposure greater than 10 min without adequate rest and cooling may lead to a significant accumulation of heat stress and fatigue during further fire-fighting activity, irrespective of physical prowess.     

Cardiovascular and thermal consequences of protective clothing: a comparison of clothed and unclothed states

We have undertaken a laboratory-based examination of the cardiovascular and thermal impact of wearing thermal (heat) protective clothing during fatiguing exercise in the heat. Seven males completed semi-recumbent, intermittent cycling (39.6 degrees C, 45% relative humidity) wearing either protective clothing or shorts (control). Mean core and skin temperatures, cardiac frequency (f(c)), stroke volume (Q), cardiac output (Q), arterial pressure, forearm blood flow (Q(f)), plasma volume change, and sweat rates were measured. In the clothed trials, subjects experienced significantly shorter times to fatigue (52.5 vs. 58.9 min), at lower peak work rates (204.3 vs. 277.4 W), and with higher core (37.9 degrees vs. 37.5 degrees C) and mean skin temperatures (37.3 degrees vs. 36.9 degrees C). There was a significant interaction between time and clothing on f(c), such that, over time, the clothing effect became more powerful. Clothing had a significant main affect on Q, but not Q, indicating the higher Q was chronotropically driven. Despite a greater sweat loss when clothed (923.0 vs. 547.1 g.m(-2) x h(-1); P<0.05), Q(f) and plasma volume change remained equivalent. Protective clothing reduced exercise tolerance, but did not affect overall cardiovascular function, at the point of volitional fatigue. It was concluded that, during moderately heavy, semi-recumbent exercise under hot, dry conditions, the strain on the unclothed body was already high, such that the additional stress imparted by the clothing ensemble represented a negligible, further impact upon cardiovascular stability.     

Heat stress while wearing long pants or shorts under firefighting protective clothing

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8 km x h(-1), 5% grade), moderate (M, 4.5 km x h(-1), 2.5% grade), light (L, 4.5 km x h(-1)) or very light (VL, 2.5 km x h(-1)) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35 degrees C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (Tre) or heart rate response during heavy or moderate exercise where exposure times were less than 1 h (40.8 +/- 5.8 and 53.5 +/- 9.2 min for H and M, respectively while wearing P, and 43.5 +/- 5.3 and 54.2 +/- 8.4 min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise Tre was reduced by as much as 0.4 degrees C after 80 min of exercise while wearing S. Exposure times were significantly increased from 65.8 +/- 9.6 and 83.5 +/- 11.6 min during L and VL, respectively while wearing P to 73.3 +/- 8.4 and 97.0 +/- 12.5 min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10 - 15% during light exercise. However, during heavier exercise where exposure times were less than 1 h replacing P with S was of little benefit.     

Subjective perceptions and ergonomics evaluation of a liquid cooled garment worn under protective ensemble during an intermittent treadmill exercise

While a personal protective equipment (PPE) ensemble effectively provides workers with protection from occupational hazards, working in a vapour-resistant ensemble increases the risk of heat illness/injuries and physiological burdens. The purpose of this study was to investigate the effect of body cooling via a liquid-cooled garment (LCG) underneath a PPE ensemble on perceived thermal strain, physiological responses and ergonomics during an intermittent treadmill exercise in warm environmental conditions. The results of the present study indicated that the concomitant wearing of LCG underneath the PPE ensemble significantly reduced subjective perception of heat and alleviated overall increase in body temperature and heart rate while no impact of wearing LCG on ergonomic features was found. The extension of the present findings to practical applications in occupational settings requires further research on a LCG system design and performance evaluations while the LCG is incorporated within the PPE ensemble.

Statement of Relevance: Implementation of a LCG underneath PPE for body cooling was investigated, focusing on its impact on individuals' perceived thermal strain, physiological responses and ergonomics. The findings of the present study indicated that body cooling via a wearable LCG underneath PPE significantly alleviated both perceived thermal and physiological strain in uncompensable heat stress condition.     

A comparison between intermittent and constant wheelchair propulsion strategies

The purpose of this study was to investigate the effect of different synchronous push strategies on physiological parameters and temporal timing characteristics. Eight novice male able-bodied participants completed four counter-balanced conditions: two push strategies (constant pushing) and intermittent pushing (INT) at two push frequencies (40 and 70 pushes/min) at 27 W. The ANOVA main effects for frequency indicated that regardless of push strategy, oxygen cost and mechanical efficiency increased with an increase in push frequency (p < 0.01). The INT40 strategy resulted in the lowest heart rate (115 +/- 19 beats/min). With increased frequency the push angle was reduced (91 degrees vs. 78 degrees respectively) and the push was initiated at a more anterior position of the wheel (p < 0.05). The results suggest that regardless of push strategy, the over-riding factor that influences both the physiological and timing parameters measured was push frequency.     

Multi-loop control of liquid cooling garment systems

In this study the effects of multi-loop control of liquid cooling garments (LCGs) under exercise heat stress conditions were investigated by experiments and theoretical analysis. A triple-loop LCG, by which the torso, arms and legs could be independently cooled, was used in the two series of experiments carried out in a hot environment (35 degrees C/40% RH). The experiment consisted of rest, exercise on an ergometer at 70 W and exercise at 110 W. In the first experiment, each water inlet temperature (TWI) was adjusted according to the local thermal sensation. In the second experiment, TWI for the torso including arms and TWI for the legs were regulated by a skin temperature controller with set-point adjustment via heart rate. The experiments showed that a multi-loop LCG is more effective than a single-loop LCG in providing thermal sensation and comfort adjusted to the requirements of the different parts of the body, and that a skin temperature controller could be applied to a multi-loop system. The theoretical analysis was carried out using a mathematical model of thermoregulation. The results showed that a strong cooling of the surface over the working muscles (legs) provided the greatest thermoregulatory advantage during low body exercise, because most of the heat generated within the working muscles can be removed directly by heat conduction to the skin. Optimization of a human/LCG system could be attained by an optimal configuration and control. However, an optimal configuration always depends on the application purpose of an LCG system.     

Intermittent microclimate cooling during rest increases work capacity and reduces heat stress

Requirements for special protective equipment while working in hazardous environments can present a significantly increased thermal burden and early onset of physical fatigue. Ambulatory (backpack) or tethered personal cooling can accelerate metabolic heat removal, but is often not practical from an ergonomic standpoint. The efficacy of incorporating personal cooling during non-ambulatory rest periods was evaluated in subjects (n=8) with varying levels of fitness. Treadmill work (≈475 W, 40% [Vdot]O₂max) was alternately performed for 30 min followed by 30 min of rest. Subjects walked and rested under three separate experimental conditions: (1) control (C), in which light clothing was worn; (2) CPE, in which a chemical protective ensemble (CPE) was worn, and (3) CPE plus intermittent microclimate cooling (COOL). The WBGTcondition for all trials was 31°C. During the COOL trial the subjects additionally wore a personal cooling vest which allowed for the circulation of chilled liquid over the torso during rest. Under C conditions, relatively modest changes in rectal temperature (T _re ) were observed, which stabilized over time. CPE wear resulted in a progessive rise in T _re and early fatigue. The addition of intermittent cooling during each rest cycle (COOL trial) significantly attenuated heat storage such that an oscillating, but equilibrated T _re was established and work capacity was at least doubled. Moreover, the perceived cooling effect was appreciable for all subjects. Therefore, intermittent personal cooling provided a useful means of enhancing work productivity and may have application for certain military and industrial personnel performing heavy work in hot environments. This approach should provide a practical alternative for reducing stress/fatigue when work/rest cycles are employed.     

Gender differences in the circadian variations in muscle strength assessed with and without superimposed electrical twitches

The circadian rhythm in muscle strength was analysed in 12 males (28 +/- 4 years, 79.6 +/- 12.3 kg, 1.80 +/- 0.05 m) and eight females (28 +/- 4 years, 60.3 +/- 5.5 kg, 1.61 +/- 0.08 m). After two familiarization sessions, participants were tested at six different times of the day (02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours), the order of which was randomly assigned over 3-4 days. Rectal temperature (T(rec)) was measured over 30 min before each test. Peak isokinetic torques (PT) of knee extensors and flexors were then measured at 1.05 rad s(-1) and 3.14 rad s(-1) through a 90 degrees range of motion. Maximal isometric voluntary contraction (MVC) of knee extensors and flexors was measured at 60 degrees of knee flexion and the MVC of knee extensors was also assessed with superimposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) in order to control for motivational effects. Three trials were performed in each condition, separated by 3 min recovery, and the highest values were retained for subsequent analyses. A significant circadian rhythm was observed for T(rec) in both males and females (acrophase, Phi, 17:29 and 16:40 hours; mesor, Me, 37.0 and 36.8 degrees C; amplitude, A, 0.28 and 0.33 degrees C for males and females, respectively). The mesor of T(rec) was higher in males than in females (p < 0.05). Significant circadian rhythms were observed for knee extensor PT at 3.14 rad s(-1) in males (Phi, 17:06 hours; Me, 178.2 N m; A, 4.7 N m) and for knee extensor PT at 1.05 rad s(-1) in females (Phi, 15:35 hours; Me, 128.7 N m; A, 3.7 N m). In males, the MVC of knee extensors demonstrated a significant circadian rhythm, but only when electrical twitches were superimposed (Phi, 16:17 h; Me, 302.1 N m; A, 13.6 N m). Acrophases of all indices of muscle strength were not statistically different between the two groups and were located in the afternoon (12:47 < Phi < 17:16 hours). The amplitude (percentage of mesor) of extensors MVC (electrically stimulated) was higher in males (6.4%) than in females (4.2%; p < 0.05). Significant circadian rhythms were not consistently observed for all indices of muscle strength whatever the gender. Our group of female subjects tended to show lower circadian amplitudes than the males. In males, maximal voluntary contraction of electrically stimulated muscles followed a circadian curve, which was not significant without the superimposed twitches. These results suggest that motivation could have a masking effect on the circadian rhythm in muscle performance and strengthen the view that peripheral factors are implicated in this rhythm.     

Thermal function of a clothing ensemble during work: dependency on inner clothing layer fit

A tight-fitting crewneck undergarment (U) and a loose-fitting shirt (S) were studied as part of a commonly used clothing ensemble (Itot = 0.22 m2 K W-1). Ten clothed male subjects performed standardized packing work (VO2 = 0.761 min-1) at three climatic conditions, 20 degrees C and Va = 0.45 m s-1 (0-30 min), at 5 degrees C and Va = 0.39 m s-1 (30-60 min) and at 5 degrees C and Va = 1.23 m s-1 (76-90 min). From 60-75 min the subjects rested at 20 degrees C. The physiological and subjective responses varied with the environment from slightly warm to cool. U resulted in warmer responses than S: torso and upper arm skin temperatures were higher at both 5 degrees C and 20 degrees C, evaporation rate was higher at 20 degrees C, mean skin temperature was higher during work at 20 degrees C, sweating tended to begin earlier and skin wettedness to be higher with U than with S. No differences were observed in core temperature, heart rates, and subjective thermal evaluations. It was concluded that a tight-fitting inner layer (U) compared to a loose-fitting one (S) allows for less cooling of the skin in both a cool and a slightly warm environment.     

Physiological responses of fire-fighter instructors during training exercises

Thirteen male instructors were monitored during a total of 44 live fire training exercises (ambient temperature 74+/-42 degrees C). Exposure time during the 'Hot Fire' (HF), 'Fire Behaviour' and 'Fire Attack' exercises was 33.0+/-7.9 min (n=30); 26.3+/-5.5 min (n=6); and 7.3+/-2.6 min (n=8) respectively. At the end of the exercises, mean core temperature (t(core)) was 38.5+/-0.9 degrees C (n=32), however eight instructors had a t(core) above 39 degrees C. The mean maximum temperature under the fire hood was 41.2+/-4.6 degrees C (n=40). Mean maximum heart rate (HR) was 138+/-26 bpm (n=34) however, in five exercises, HR exceeded 90% of the instructors' HR reserve. Mean fluid deficit was 0.62+/-0.6 l (n=30) at the end of the HF exercises, the maximum being 2.54 l. Four instructors doubted their ability to perform a rescue at the end of the exercise. The energy cost of performing simulated rescues of a 50 kg dummy in the cool was investigated in a pilot study. Mean HR during the rescues was 79+/-7% of the instructors' HR reserve and it was estimated that this could increase t(core) by 0.4 to 0.6 degrees C. The physiological responses to the fire-fighting exercises varied considerably and reflected the differences in work performed and external heat load. The results obtained from some individuals give cause for concern, and signs of heat strain were seen in at least two individuals.     

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXTPPE and GXTPT). Maximal oxygen consumption (VO2max) during GXTPPE was 17.3% lower than the GXTPT in regular exercise clothing (43.0 +/- 5.7 vs. 52.4 +/- 8.5 ml/kg per min, respectively). The lower VO2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 +/- 18.0 vs. 167.1 +/- 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 +/- 10.4 vs. 3.2 +/- 0.4 l). Breathing frequency at peak exercise was unchanged (55 +/- 7 vs. 53 +/- 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.     

Exercise thermoregulation and hyperprolactinaemia

The anterior pituitary hormone prolactin (PRL), measured in the peripheral blood circulation, reflects alterations in central brain 5-hydroxytryptamine (serotonin) and dopaminergic activity and is used as a marker of 'central fatigue' during active heat exposure. Significant correlations have consistently been found between PRL and core temperature (T(CORE)) during prolonged exercise. There has been no investigation into the relationship between PRL and other key thermoregulatory variables during exercise, such as weighted mean skin (T(SK)) and mean body temperature (T(B)), heat storage (HS), thermal gradient (T(GRAD)), heart rate (HR) and skin blood flow (cutaneous vascular conductance, CVC). Therefore, the aim of this study was to ascertain if a significant relationship exists between PRL and these thermoregulatory variables during prolonged exercise. Nine active male subjects conducted three trials of approximately 60% VO(2peak) at 70-80 rpm for 45 min on a semi-recumbent cycle ergometer at three different ambient temperatures [6 degrees C (Cold), 18 degrees C (Neutral) and 30 degrees C (Hot)] to elicit varying levels of thermoregulatory stress during exercise. Significant differences existed in T(SK), T(B), HS, T(GRAD) and CVC across the environmental conditions (p < 0.001). Core temperature (T(CORE)), HR and PRL were significantly elevated only in Hot (p < 0.05). Moderate correlations were found for T(CORE), T(SK), T(B), HS, T(GRAD), HR and CVC with post-exercise PRL (rho = 0.358-0.749). The end-of-exercise <38.0 degrees C T(CORE) responses were not (rho = -0.129, p > 0.05) but the >38.0 degrees C T(CORE) responses were (rho = 0.845, p < 0.001) significantly related to their corresponding PRL responses. The significant relationships between PRL release and T(SK), T(B), HS, T(GRAD), HR and CVC have extended previous research on T(CORE) and PRL release and indicate an association between these thermoregulatory variables, as well as T(CORE), and serotonergic/dopaminergic activity during prolonged exercise.     

Localized temperatures and water vapour pressures within clothing during alternate exercise/rest in the cold.

The purpose of this study was to determine the variation of localized skin temperatures, clothing surface temperatures and water vapour pressures within a clothing system when worn during alternating work/rest cycles in a cold environment. A two-layer prototype clothing system comprising underwear and a uniform was studied on eight subjects (Ta = Tr = 5 degrees C; Tdp = -3.5 degrees C; va = 0.32 m s-1; Itot = 0.24 m2 K W-1). The 2 h experiment comprised a twice-repeated bout of 40 min cycle exercise (W = 56 W m-2; M = 313 W m-2) followed by 20 min of rest (M = 62 W m-2). Esophageal, skin, clothing, and ambient temperatures, as well as dew-point temperatures near the skin, in the clothing and in the environment were monitored. In addition, evaporation of sweat and sweat accumulated in the clothing were determined. The temperatures and water vapour pressures in all clothing layers varied significantly with the human thermoregulatory responses (skin temperature, sweating) to alternating work/rest cycles. Different courses of localized corresponding temperatures and water vapour pressures indicated that various forms of heat transport and heat exchange in the skin-clothing-environment system are of significance in different body areas.     

Effects of daytime ingestion of melatonin on short-term athletic performance

The immediate effects of ingesting melatonin in the daytime include decreased alertness and body temperature. To date, no researcher has examined whether daytime ingestion of melatonin leads to impairments in variables relevant to short-term (<10 min) athletic performance. Twelve physically active participants (mean +/- s age = 25.2 +/- 5.0 years, body mass = 81.4 +/- 12.1 kg and chronotype = 33.8 +/- 6.3 units) ingested 5 mg of melatonin or placebo at 11:45 hours in a double-blind experiment. At 13:00 and 17:00 hours, subjective alertness was measured, together with intra-aural temperature, reaction time (two-, four- and eight-choice), short-term memory recall and grip strength. Performance, ratings of perceived exertion (RPE) and heart rate were also recorded during a 4-km cycling time trial. At 13:00 hours, the mean +/- s intra-aural temperature was 0.49 +/- 0.79 degrees C lower after ingestion of melatonin than after placebo (p = 0.015), but this difference was not apparent at 17:00 hours. At both 13:00 and 17:00 hours, melatonin reduced (p < 0.05) alertness, short-term memory and exercise heart rate by 1.5 +/- 1.8 units, 1 +/- 1 digits and 6 +/- 9 beats.min(-1), respectively (mean +/- s). Eight-choice reaction time was also slower at both times of day after ingesting melatonin. Melatonin did not influence time trial performance or RPE (p > 0.05). The effects of 5 mg of melatonin seem more pronounced for mental rather than physical components of short-term athletic performance, although the cardiovascular responses to exercise are affected. Some effects of melatonin were apparent 5 h after ingestion when the hypothermic effects of melatonin had dissipated.     

Limits of and possibilities to improve the IREQ cold stress model (ISO/TR 11079). A validation study in the field

Estimated insulation (Icl) of clothing worn by workers daily exposed to air temperatures between 0 and 15 degrees C was compared with the corresponding insulation calculated for thermal neutrality using the IREQ-model (IREQneutral, ISO/TR 11079). The goal was to determine possible limitations of the applicability of the IREQ-model and to stress to necessities and possibilities to improve the model. Sixteen female and 59 male workers (16-56 yr) were monitored during their work. According to their cold stress at the workplace they were allocated to three groups (33 persons were exposed to constant temperatures of more than 10 degrees C, 32 to less than 10 degrees C, and 10 persons experienced frequent temperature changes of 13 degrees C. Another categorization concerned workload (8 persons worked at metabolic rates of less than 100 W/m2, 50 persons worked at 101-164 W/m2, and 17 worked at more than 165 W/m2, respectively). The analysis of the differences between estimated worn insulation (Icl) and calculated IREQneutral revealed that the IREQ-model applies for air temperatures up to 15 degrees C and for temperature changes of 13 degrees C (at least) but needs to be improved with respect to gender. The IREQ model does not apply sufficiently for high and largely varying workloads (165 W/m2 and more). However, these situations are beyond the currently available possibilities to protect workers adequately with conventional clothing material. A suitable short-term measure is a more even work flow by avoiding activities with very high and low metabolic rates.     

Heat stress and bulkiness of chemical protective clothing impair performance of medical personnel in basic lifesaving tasks

The study examined the impact of chemical protective (CP) clothing on the performance of lifesaving tasks in thermoneutral and cold conditions. Eleven males performed pre-exercise followed by lifesaving tasks wearing either field combat uniform at 21 degrees C (U) or CP clothing at 21 degrees C (CPN) and -5 degrees C (CPC). The tasks were ventilating a doll (VA) and connecting an intravenous line (IV). Mean skin temperature was significantly higher for CPN compared to U and CPC during pre-exercise, VA and IV. Changes in blood pressure were significantly greater with CP clothing than without during VA and IV. The number of breaths per min (in VA) and time needed for IV increased by 19% (p < 0.05) and 18%, respectively, for CPN compared to U. Due to the cold, the additional increment was 5% and 17%, respectively, for CPC. Wearing of CP clothing in thermoneutral or in cold conditions may not prevent but, especially in the cold, significantly impede the performance of basic medical tasks. The findings of this study showed that performing medical tasks while wearing nuclear, biological and chemical protective clothing is impaired due to significant changes in physiological strain. This suggests that realistic training in local conditions as well as in cold conditions is needed to realise the restrictions due to protective clothing.