Prescribed fluid consumption and its effects on the physiology and work behaviour of Australian wildland firefighters

The present study examined firefighters\u27 ability to consume a prescribed fluid volume (1200 ml &middot; h-1) during a wildland fire suppression shift and compare the effect of this additional fluid prescription with self-paced drinking on firefighters\u27 hydration status and plasma sodium concentration post shift and their heart rate, core temperature and physical activity during their shift. Thirty-four firefighters were evenly divided into two drinking groups: self paced and prescribed. Prescribed drinkers did not meet the required 1200 ml&middot;h-1 intake, yet they consumed twice the fluid drank by the self-paced group. No differences were noted between groups in plasma sodium levels or hydration status before or after their shift. Prescribed fluid consumption resulted in significantly lower core temperature between two and six hours into the shift. This did not coincide with lower cardiovascular strain, greater physical activity when compared to the self-paced drinking group. Additional fluid consumption (above self-paced intake) did not improve firefighter activity or physiological function (though it may buffer rising core temperature). It seems that wildland firefighters, at least in mild to warm weather conditions, can self-regulate their fluid consumption and work behaviour to leave the fireground hydrated at the conclusion of their shift.<br /

Design of a valid simulation for researching physical, physiological and cognitive performance in volunteer firefighters during bushfire deployment.

Every year, Australian firefighters protect our nation from the devastation of bushfire. Understanding the impact of consecutive long shifts in hot, smoky conditions is essential for making decisions during campaign fires. At present, the evidence-base for such decisions is limited to laboratory studies with little relevance to bushfire suppression or field research where the impact of environmental and workload stressors cannot be measured. To counter these limitations, we have developed a three-day simulation that mimics the work and environment of campaign bushfire suppression. Construction of the simulation involved three stages; 1) data collection and analysis; 2) design and development; and 3) trial and refinement. The frequency, intensity, duration and type of physical work performed on the fireground is well documented and a modified applied cognitive task analysis, using experienced firefighters was used as a framework to describe in detail the non-physical aspects of the work. The design and development of the simulation incorporated the physical and non-physical aspects of the work into simulated tasks. Finally, experienced firefighters participated in trials of the simulation and reviewed digital recordings to ensure that the simulation accurately represented campaign bushfire suppression work. The outcome of this project is a valid, realistic, and reliable simulation of the physiological, physical and cognitive aspects of a volunteer firefighter on a three-day bushfire deployment.<br /

Frequency, intensity and duration of physical tasks performed by Australian rural firefighters during bushfire suppression

The current study combined, for the first time, video footage of individual firefighters wearing heart rate monitors and personal GPS units to quantify the frequency, duration and intensity of tasks performed by Australian rural fire crews when. suppressing bushfires. Across the four fireground \u27shifts\u27, the firefighters performed 34 distinct fireground tasks. Per shift, the task frequency ranged from once (raking fireline in teams, carrying a quick fill pump) to 103 times {lateral repositioning of a 38-mm charged firehose) .. The tasks lasted between 4 &plusmn; 2 s (bowling out 3-8-mm firehose) and 461 &plusmn; 387 s (raking fireline in teams). The task intensity~ as measured by average heart rate ranged between 97 &plusmn; 16 beats&middot;min-1 (55.7 &plusmn; 8.7. %HRmax) and 157 &plusmn; 15 beats&middot;min-1 (86.2 &plusmn; 10.8 %HRmax)&middot; The tasks were performed a speeds that ranged from 0.12 &plusmn; 0.08 m&middot;s-1 (manual hose retraction of 38-mm charged firehose) to 0.79 &plusmn; 0.40 m&middot;s-1 (carrying a 38-mm coiled hose). Tasks found to be simultaneously frequent, long and intense (or two of these three) are likely to form the basis for job-specific testing of Australian rural firefighters suppressing bushfires.<br /

Heat shock protein response during fixed intensity and self-paced exercise in the heat in young, healthy women on oral contraceptives compared with young healthy men

Background: Heat shock proteins respond to a variety of physiological and environmental stresses, including heat stress, ischemia and endotoxic shock. Hormonal changes during the female menstrual cycle can have a thermogenic effect on body temperature. The monophasic oral contraceptive (OC) pill provides low doses of progesterone and oestrogen over the course of the normal menstrual phase. There is little evidence regarding the combined effects of OC on exercise performance and heat stress with respect to heat shock protein response. Objectives: This study aimed to determine the response of heat shock proteins (Hsp72) during fixed-intensity and self-paced exercise in the heat in young, healthy women on oral contraceptives compared with young healthy men. Methods: Sixteen physically active men and women performed 30 min fixed-intensity cycling at 50% of maximum workload, followed by 30 min of a self-paced time trial (TT) interspersed by 30 s maximal sprint at 9, 19 and 29 min respectively. Trials were undertaken in cool (20°C; 48±3% relative humidity (RH)) and warm (32°C; 66±2% RH) ambient conditions. Core (Tc) and skin temperature, heart rate (HR) and subjective responses were measured before, during and post exercise. Results: The distance, mean and peak power output, mean and peak speed during the self-paced time trial showed no difference between the ambient temperatures for men and women. Hsp72 in females was higher than males at all sample points at both 20°C and 32°C, except for pre-exercise at 20°C (p&lt; 0.04). Women also attained a higher Tc than men at the end of the TT in the heat (38.5°C v 37.9°C for women and men, respectively; p&lt;0.03), higher mean HR and perceived exertion. Conclusion: This study indicates that females who use oral contraceptives (OC) had higher levels of Hsp72 than males when tested under the same environmental conditions

Acute effects of a dopamine/norepinephrine reuptake inhibitor on neuromuscular performance following self-paced exercise in cool and hot environments

Abstract Dopamine/norepinephrine (DA/NE) reuptake inhibitors have been used to manipulate the central mechanisms affecting arousal and motivation during exercise. Eight healthy, physically active males performed 30 min fixed-intensity cycling at 50% Wmax followed by 30 min of self paced time trial (TT) with each section interspersed with a 30 s maximal sprint at 9, 19 and 29 min. The DA/NE re-uptake inhibitor administered was bupropion (BUP) versus a placebo (PLA) in either warm (32 &deg;C, BUP32 or PLA32) or moderate (20 &deg;C; BUP20, PLA20) ambient conditions. Core and skin temperature, heart rate and perceptual responses, neuromuscular and hormonal measures were assessed at multiple times throughout the trials and post exercise. Time trial performance remained unchanged across conditions (12.7&ndash;13.1 km) although core temperature was elevated in the fixed intensity section of the trials for BUP32 and BUP20 but continued to rise only in BUP32 during the time trial reaching 38.6 &deg;C (P&lt;0.05). NE increased in all conditions from pre-exercise with BUP32 values peaking at the end of TT to 1245.3&plusmn;203.1 pg/mL (P&lt;0.05) compared to the other conditions. Neuromuscular responses were similar among conditions although peak force was significantly reduced from pre (262&plusmn;31 N) to post (202&plusmn;31 N, P&lt;0.05) exercise along with contraction duration (22%, P&lt;0.05) in BUP20. We conclude that DA/NE re-uptake inhibitors influenced thermoregulation in the heat but not exercise performance. DA/NE re-uptake inhibitors are likely to act centrally to override the inhibitory signals for the cessation of exercise with these drugs acting peripherally to reduce the twitch characteristics of skeletal muscle in cooler conditions