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Objective: We hypothesized that different body composition and fitness of firefighters would affect immune and inflammatory activity after working in the heat., Methods: Forty-two firefighters worked in the heat (100 ± 5 °C). Changes in leukocytes, platelets, tumor necrosis factor (TNF-α), and C-reactive protein (CRP) were analyzed based on body composition (DXA) and aerobic fitness (VO2max)., Results: Higher baseline leukocytes were observed for high body fat (P = 0.002) and low lean mass (P = 0.023) resulting in the highest peak values. Additionally, significantly lower values for TNF-α were observed with high lean mass at all time points. Platelets were unaffected by fitness or body composition. Furthermore, body mass index (BMI) and VO2max played no role., Conclusions: Minimizing body fat and increasing lean mass may reduce immune and inflammatory activity of firefighters in the heat.

Background: Firefighters regularly re-enter fire scenes during long duration emergency events with limited rest between work bouts. It is unclear whether this practice is impacting on the safety of firefighters., Objectives: To evaluate the effects of multiple work bouts on firefighter physiology, strength, and cognitive performance when working in the heat., Methods: Seventy-seven urban firefighters completed two 20-minute simulated search and rescue tasks in a heat chamber (105 ± 5°C), separated by a 10-minute passive recovery. Core and skin temperature, rate of perceived exertion (RPE), thermal sensation (TS), grip strength, and cognitive changes between simulations were evaluated., Results: Significant increases in core temperature and perceptual responses along with declines in strength were observed following the second simulation. No differences for other measures were observed., Conclusions: A significant increase in thermal strain was observed when firefighters re-entered a hot working environment. We recommend that longer recovery periods or active cooling methods be employed prior to re-entry.

When firefighters work in hot conditions, altered immune and inflammatory responses may increase the risk of a cardiac event. The present study aimed to establish the time course of such responses. Forty-two urban firefighters completed a repeat work protocol in a heat chamber (100 ± 5°C). Changes to leukocytes, platelets, TNFα, IL-6, IL-10, LPS and CRP were evaluated immediately post-work and also after 1 and 24 h of rest. Increases in core temperatures were associated with significant increases in leukocytes, platelets and TNFα directly following work. Further, platelets continued to increase at 1 h (+31.2 ± 31.3 × 10(9) l, p < 0.01) and remained elevated at 24 h (+15.9 ± 19.6 × 10(9) l, p < 0.01). Sustained increases in leukocytes and platelets may increase the risk of cardiac events in firefighters when performing repeat work tasks in the heat. This is particularly relevant during multi-day deployments following natural disasters. Practitioner Summary: Firefighters regularly re-enter fire affected buildings or are redeployed to further operational tasks. Should work in the heat lead to sustained immune and inflammatory changes following extended rest periods, incident controllers should plan appropriate work/rest cycles to minimise these changes and any subsequent risks of cardiac events.

Firefighters are exposed to hot environments, which results in elevated core temperatures. Rapidly reducing core temperatures will likely increase safety as firefighters are redeployed to subsequent operational tasks. This study investigated the effectiveness of cold-water immersion (CWI) and iced-slush ingestion (SLUSH) to cool firefighters post-incident. Seventy-four Australian firefighters (mean ± SD age: 38.9 ± 9.0 years) undertook a simulated search and rescue task in a heat chamber (105 ± 5 °C). Testing involved two 20-min work cycles separated by a 10-min rest period. Ambient temperature during recovery periods was 19.3 ± 2.7 °C. Participants were randomly assigned one of three 15-min cooling protocols: (i) CWI, 15 °C to umbilicus; (ii) SLUSH, 7 g·kg(-1) body weight; or (iii) seated rest (CONT). Core temperature and strength were measured pre- and postsimulation and directly after cooling. Mean temperatures for all groups reached 38.9 ± 0.9 °C at the conclusion of the second work task. Both CWI and SLUSH delivered cooling rates in excess of CONT (0.093 and 0.092 compared with 0.058 °C·min(-1)) and reduced temperatures to baseline measurements within the 15-min cooling period. Grip strength was not negatively impacted by either SLUSH or CONT. CWI and SLUSH provide evidence-based alternatives to passive recovery and forearm immersion protocols currently adopted by many fire services. To maximise the likelihood of adoption, we recommend SLUSH ingestion as a practical and effective cooling strategy for post-incident cooling of firefighters in temperate regions.

Eccentric exercise can lead to muscle damage including dramatic changes to mitochondrial calcium content (MCC) and impaired respiratory function. Heat acclimation can create a cross-tolerance to a number of stresses including eccentric exercise but little is known about any protection to mitochondria. We hypothesised that intermittent heat exposure will lead to improved control of MCC and to preserved mitochondrial function following eccentric exercise. Sprague-Dawley rats were exposed to 3 weeks of intermittent heat exposure (36°C, 40% relative humidity, 6 h/day, 5 days a week) or kept in cool conditions (20°C). Animals were then assigned to a control or exercise group (-14°C decline treadmill exercise for 90 min). MCC, mitochondrial respiration and mitochondrial permeability transition pore opening (mPTP) were measured in mitochondria isolated from the red quadriceps in animals killed immediately, 2 h and 48 h post-exercise. Results showed that heat exposure was associated with lower plasma creatine kinase levels (p < 0.05) post-exercise suggesting lower levels of muscle damage. There was a significant (~500%) rise in MCC (p < 0.001) and a reduction in mitochondrial respiratory control ratio (p < 0.001) 48 h post-exercise. mPTP displayed increased (p < 0.05) sensitivity to calcium immediately and 48 h post-exercise. Thus, decline running led to significant impairment of mitochondria respiration and calcium loading which was more pronounced 48 h post-exercise compared with earlier time points. MCC levels and mitochondrial function were not altered by heat exposure. In conclusion, intermittent heat exposure does not appear to provide protection against mitochondrial dysfunction resulting from eccentric exercise.