Cold Ambient Temperature Does Not Alter Subcutaneous Abdominal Adipose Tissue Lipolysis and Blood Flow in Endurance-Trained Cyclists.

This study sought to investigate the effect of cold ambient temperature on subcutaneous abdominal adipose tissue (SCAAT) lipolysis and blood flow during steady-state endurance exercise in endurance-trained cyclists. Ten males (age: 23 ± 3 years; peak oxygen consumption: 60.60 ± 4.84 ml·kg-1·min-1; body fat: 18.4% ± 3.5%) participated in baseline lactate threshold (LT) and peak oxygen consumption testing, two familiarization trials, and two experimental trials. Experimental trials consisted of cycling in COLD (3 °C; 42% relative humidity) and neutral (NEU; 19 °C; 39% relative humidity) temperatures. Exercise consisted of 25 min cycling at 70% LT and 25 min at 90% LT. In situ SCAAT lipolysis and blood flow were measured via microdialysis. Heart rate, core temperature, carbohydrate and fat oxidation, blood glucose, and blood lactate were also measured. Heart rate, core temperature, oxygen consumption, and blood lactate increased with exercise but were not different between COLD and NEU. SCAAT blood flow did not change from rest to exercise or between COLD and NEU. Interstitial glycerol increased during exercise (p < .001) with no difference between COLD and NEU. Fat oxidation increased (p < .001) at the onset of exercise and remained elevated thereafter with no difference between COLD and NEU. Carbohydrate oxidation increased with increasing exercise intensity and was greater at 70% LT in COLD compared to NEU (p = .030). No differences were observed between conditions for any other variable. Cycling exercise increased SCAAT lipolysis but not blood flow. Ambient temperature did not alter SCAAT metabolism, SCAAT blood flow, or fat oxidation in well-trained cyclists, though cold exposure increased whole-body carbohydrate oxidation at lower exercise intensities.

Alaska Backcountry Expeditionary Hunting Promotes Sustained Muscle Protein Synthesis.

INTRODUCTION: We have previously described negative energy balance (ie, -9.7±3.4 MJ/d) and weight loss (Δ-1.5 ± 0.7 kg) influenced by high levels of energy expenditure (ie, 17.4±2.6 MJ/d) during remote expeditionary hunting in Alaska. Despite negative energy balance, participants retained skeletal muscle. The purpose of this pilot study was to measure skeletal muscle protein synthesis and examine molecular markers of skeletal muscle protein metabolism under similar conditions of physical and nutrient stress. METHODS: The "virtual biopsy method" was used to evaluate integrated fractional synthetic rates (FSRs) of muscle protein from blood samples in 4 participants. Muscle biopsies were taken to measure molecular markers of muscle protein kinetics (ie, FSTL1, MEF2, MYOD1, B2M, and miR-1-3p, -206, -208b, 23a, and 499a) using real-time polymerase chain reaction. RESULTS: Our findings in 4 participants (2 females [28 and 62 y of age; 66.2 and 71.8 kg body weight; 25.5 and 26.7 kg/m2 body mass index] and 2 males [47 and 56 y of age; 87.5 and 91.4 kg body weight; 26.1 and 28.3 kg/m2 body mass index]) describe mean muscle FSRs of serum carbonic anhydrase (2.4%) and creatine kinase M-type (4.0%) and positive increments in molecular regulation. CONCLUSIONS: Preservation of skeletal muscle under conditions of physical and nutrient stress seems to be supported by positive inflection of skeletal muscle FSR and molecular activation.

Training in a Hot Environment Fails to Elicit Changes in the Blood Oxidative Stress Response.

Environmental temperature can impact exercise-induced blood oxidative stress; however, the effects of heat acclimation on this response have not been fully elucidated. The purpose of the study was to investigate the effects of hot (33°C) and room temperature (20°C) environments on post-exercise blood oxidative stress responses following 15 temperature acclimation sessions. Untrained participants (n = 38, 26 ± 7 years, VO2peak = 38.0 ± 7.2 years) completed 15 temperature acclimation sessions of a cycling bout at an intensity perceived as "hard" in either a hot (33°C) or room temperature (20°C) environment. Pre and post acclimation exercise tolerance trials were conducted, which involved cycling at 50% Wpeak for one hour. Blood sampling occurred before exercise, immediately after, two hours, and four hours after the exercise tolerance trials. Blood samples were analyzed for oxidative stress markers including lipid hydroperoxides, 8-isoprostanes, protein carbonyls, 3-nitrotyrosine, ferric-reducing ability of plasma, and Trolox-equivalent antioxidant capacity. Exercise-dependent increases were observed in lipid hydroperoxides, Trolox-equivalent antioxidant capacity, and ferric-reducing ability of plasma (p < 0.001). Considering exercise-induced elevations in markers of blood oxidative stress, there were no differences observed between environmental temperatures before or after the acclimation training period.

Physiology of the Wildland Firefighter: Managing Extreme Energy Demands in Hostile, Smoky, Mountainous Environments.

Wildland firefighters (WLFFs) are inserted as the front-line defense to minimize loss of natural resources, property, and human life when fires erupt in forested regions of the world. The WLFF occupation is physically demanding as exemplified by total daily energy expenditures that can exceed 25 MJ/day (6000 calories). WLFFs must also cope with complex physical and environmental situations (i.e., heat, altitude, smoke, compromised sleep, elevated stress) which challenge thermoregulatory responses, impair recovery, and increase short- and long-term injury/health risks while presenting logistical obstacles to nutrient and fluid replenishment. The occupation also imposes emotional strain on both the firefighter and their families. The long-term implications of wildfire management and suppression on the physical and mental health of WLFFs are significant, as the frequency and intensity of wildland fire outbreaks as well as the duration of the fire season is lengthening and expected to continue to expand over the next three decades. This article details the physical demands and emerging health concerns facing WLFFs, in addition to the challenges that the U.S. Forest Service and other international agencies must address to protect the health and performance of WLFFs and their ability to endure the strain of an increasingly dangerous work environment. © 2023 American Physiological Society. Compr Physiol 13:4587-4615, 2023.

Independent effects of acute normobaric hypoxia and hypobaric hypoxia on human physiology.

The purpose of this study was to examine the effects of acute normobaric (NH, decreased FiO2) and hypobaric (HH, 4200 m ascent) hypoxia exposures compared to sea level (normobaric normoxia, NN). Tissue oxygenation, cardiovascular, and body fluid variables measured during rest and a 3-min step-test following 90-min exposures (NH, HH, NN). Muscle oxygenated hemoglobin (O2Hb) decreased, and muscle deoxygenated hemoglobin (HHb) increased environmentally independent from rest to exercise (p < 0.001). During exercise, brain O2Hb was lower at HH compared to NN (p = 0.007), trending similarly with NH (p = 0.066), but no difference between NN and NH (p = 0.158). During exercise, HR at NH (141 ± 4 beats·min-1) and HH (141 ± 3 beats·min-1) were higher than NN (127 ± 44 beats·min-1, p = 0.002), but not each other (p = 0.208). During exercise, stroke volume at HH (109.6 ± 4.1 mL·beat-1) was higher than NH (97.8 ± 3.3 mL·beat-1) and NN (99.8 ± 3.9 mL·beat-1, p ≤ 0.010) with no difference between NH and NN (p = 0.481). During exercise, cardiac output at NH (13.8 ± 0.6 L) and HH (15.5 ± 0.7 L) were higher than NN (12.6 ± 0.5 L, p ≤ 0.006) with HH also higher than NH (p = 0.001). During acute hypoxic stimuli, skeletal muscle maintains oxygenation whereas the brain does not. These differences may be mediated by environmentally specific cardiovascular compensation. Thus, caution is advised when equating NH and HH.

Septuagenarians Approach 4 Times the Basal Metabolic Rate During Race Across America.

BACKGROUND: Previous data have demonstrated that Tour de France riders maintain total daily energy expenditure (TDEE) between 3.5 and 5.5 times the basal metabolic rate (×BMR). In contrast, TDEE for healthy male septuagenarians has been reported to average 1.3 to 2.0 ×BMR. PURPOSE: Measure the TDEE and water efflux during ultraendurance work in an older population during the cross-continent cycling Race Across America. METHODS: A 4-man septuagenarian team (70 [1.6] y, 72.0 [5.1] kg) received an oral dose of doubly labeled water prior to completing the Race Across America (4817 km, 51,816 m of climbing) for TDEE calculation. Nude body weight measures were coupled with collected urine samples. RESULTS: The race was completed in approximately 6.5 days (official time: 6 d, 13 h, and 13 min) with an average speed of 30.6 (0.7) km·h-1 (age-group course record). Body weight remained unchanged (prerace: 70.4 [5.8] kg, postrace: 70.0 [5.3] kg). TDEE was calculated over 3 race segments. TDEE varied between individual riders and segments throughout the continuous event (24.7 [4.2] MJ·24 h-1, 5900 [1015] kcals·24 h-1, 3.4 [0.5] ×BMR). Water efflux averaged 10.2 (0.8) L·24 h-1 resulting in a total turnover of 45.3 (3.9) L amounting to 1.5 (0.2) times initial total body water during the race. CONCLUSIONS: Highly active septuagenarians maintain body weight prerace to postrace, suggesting near energy balance when TDEE approaches 4 ×BMR. These values exceed twice those of previously observed healthy but less active septuagenarian men and are comparable to professional riders during portions of the Tour de France. Advanced age and high metabolic output are not mutually exclusive.

Deterioration of Lipid Metabolism Despite Fitness Improvements in Wildland Firefighters.

OBJECTIVE: Determine serum lipid and general health/fitness alterations following a 5-month wildfire suppression season. METHODS: We recruited 100 wildland firefighters (WLFFs) to a 5-month pre- to post-season observational study. Nude body mass, blood pressure (BP), grip strength, and steptest heart rate (HR) were recorded. Blood samples were collected for lipid panel analysis (total cholesterol, high density lipoproteins (HDL)-cholesterol, low density lipoproteins-cholesterol, very low density lipoproteinscholesterol, triglycerides, triglyceride:HDL-cholesterol ratio). Two-tailed dependent t tests determined statistical significance (P < 0.05). RESULTS: There were pre- to post-season changes in nude body mass (+2 ±â€Š4%, P  = 0.001), systolic BP (-2 ±â€Š10%, P  = 0.01), step-test HR (-5 ±â€Š10%, P  < 0.001), and all serum lipids (total cholesterol: +5 ±â€Š14%, P  = 0.02, HDL-cholesterol: = 1 ±â€Š17%, P  = 0.04, low density lipoproteins-cholesterol: +8 ±â€Š22%, P  = 0.02, very low density lipoproteins-cholesterol: +31 ±â€Š49%, P  < 0.001, triglycerides: +30 ±â€Š49%, P  < 0.001, triglyceride:HDL-cholesterol ratio: +37 ±â€Š58%, P  < 0.001). Pre- to post-season diastolic BP (P = 0.12) and grip strength (P = 0.60) remained stable. CONCLUSIONS: WLFFs demonstrate maladaptive serum lipids and body mass alterations despite subtle aerobic fitness improvements.

Nutrient Intake of Wildland Firefighters During Arduous Wildfire Suppression: Macronutrient and Micronutrient Consumption.

Wildland firefighters (WLFFs) perform in adverse environments making rapid adjustments to dietary needs. The National Mobile Food Services (NMFS) contract details WLFF dietary provisions on wildfire incidents. OBJECTIVE: Determine the nutrient content of food and drink provided to and consumed by WLFFs under the NMFS contract. METHODS: Individual (n = 122) dietary provisions and consumption was recorded during 1 workday. Nutritional analysis of items provided was compared with consumption and the recommended dietary allowance (RDA). RESULTS: WLFFs consumed significantly (P < 0.05) fewer macronutrients than provided for calories, protein, and fat. Provided and consumed micronutrients were below the RDA for vitamins D and E, magnesium, and manganese. CONCLUSION: Most dietary recommendations were met by NMFS provisions. Next steps include WLFF nutrition education to improve consumption and contract revisions to meet micronutrient recommendations.

Workshift Changes in Hydration Status During Wildfire Suppression.

OBJECTIVE: Document wildland firefighters (WLFFs) hydration status during a singular workshift (13.7 ±â€Š1.4 hours). METHODS: WLFF researchers documented real-time WLFF (n = 71) urine metrics and fluid consumption. Body weight and blood samples (n = 25) were also collected. Two-tailed dependent t tests determined statistical significance (P < 0.05). RESULTS: Body weight significantly decreased (-0.3 ±â€Š1.1%, P > 0.05). Fluid consumption totaled 6.2 ±â€Š2.3 L including food and 5.0 ±â€Š2.1 L without food. Morning versus afternoon urine frequency (2.6 ±â€Š1.3, 3.1 ±â€Š1.9 voids), urine volume (1.2 ±â€Š0.7, 1.3 ±â€Š0.8 L), urine volume per void (440 ±â€Š157, 397 ±â€Š142 mL), and urine specific gravity (1.010 ±â€Š0.007, 1.010 ±â€Š0.007) were not significantly different (P > 0.05). Pre- to post-workshift serum chloride (103.2 ±â€Š1.9, 101.4 ±â€Š1.7 mM) and blood glucose (5.2 ±â€Š0.4, 4.5 ±â€Š0.7 mM) significantly decreased (P < 0.05), while serum sodium (141.5 ±â€Š2.4, 140.8 ±â€Š2.0 mM) and serum potassium (4.3 ±â€Š0.3, 4.2 ±â€Š0.3 mM) remained stable (P > 0.05). CONCLUSIONS: WLFFs can ingest fluid and food amounts that maintain workshift euhydration and electrolyte status.

Evaluation of Environmental Conditions on Self-Selected Work and Heat Stress in Wildland Firefighting.

INTRODUCTION: The purpose of this study was to evaluate heat stress occurring in wildfire management activities with variable environmental conditions. METHODS: Direct observation and real-time wireless physiological monitoring allowed for weather and physiological metrics, including heart rate, core temperature (Tc), skin temperature, and physiological strain index (PSI), of male (n=193) and female (n=28) wildland firefighters (WLFFs) to be recorded during wildfire management activities. Accelerometry data were used to categorize intensity level of activity. RESULTS: Ambient temperature and relative humidity values were used to compute the heat index (HI; n=3891 h) and divided into quartiles (Q1: 13.3-25.1°C; Q2: 25.2-26.4°C; Q3: 26.5-28.9°C; Q4: 29.0-49.1°C). Activity levels remained relatively constant across all HI quartiles. The percentage of time spent performing moderate/vigorous activities was lowest during the hotter Q4 (Q1: 3%; Q2: 2%; Q3: 2%; Q4: 1%). Heart rate, Tc, PSI, and skin temperature associations with HI varied by resource type. Sixty-one percent of WLFFs (n=134) experienced a Tc ≥38.0°C, and 50% of WLFFs (n=111) experienced a PSI ≥6.0. CONCLUSIONS: Heat stress was prevalent as WLFFs performed job tasks of varying intensities in all ambient conditions. Spontaneous bouts of arduous labor, duration of work shifts, and other occupation characteristics present the possibility for substantial durations of hyperthermia, although no heat-related injuries occurred in this study. Despite chronic exposure to rugged sloped terrain, load carriage, and environmental conditions, self-regulation and individual attention to managing work:rest appears to be the primary management strategy in mitigating excessive accumulation of body heat in this occupation.

Blood oxidative stress and post-exercise recovery are unaffected byhypobaric and hypoxic environments.

Hypobaria and hypoxia exert independent effects on oxidative stress during exercise, while combined effectson the post-exercise recovery period remain unclear.Accordingly, this study examined the recovery period during lab-simulated hypoxic and hypobaric conditions following exercise-induced oxidative stress. Participants (n=13) performed 60-minutes of cycling (70% watts max) in a normobaric normoxic environment followed by a four-hour recovery under three conditions; 1000m normobaric normoxia (NN, 675mmHg), 4400m normobaric hypoxia (NH, 675mmHg), or 4400m hypobaric hypoxia (HH, 440mmHg). Blood samples collected at Pre, Post, 2-Hours (2-HR), and 4-Hours (4-HR) post-exercise were analyzed fora potential increase in biochemical modifications of proteins(protein carbonyls, PC; 3-nitrotyrosines, 3NT) lipids (lipid hydroperoxides, LOOH; 8-isoprostanes, 8-ISO), and antioxidant capacity (FRAP, TEAC). Gene transcripts (EPAS, HMOX1, SOD2, NFE2L2) were quantified by qRT-PCR from muscle biopsies taken Pre and Post exercise. Hypoxia and hypobaria had no effect throughout recovery. Post-exercise TEAC (p=0.041), FRAP (p=0.013), and 8-ISO (p=0.044) increased, while PC (p=0.002) and 3-NT (p=0.032) were decreased. LOOH was lower in Post (p=0.018) NH trial samples. Exercise-dependent increases occurred in NFE2L2 (p=0.003), HMXO1 (p<0.001), SOD2 (p=0.046), and EPAS (p=0.038). Exercise recovery under conditions of NH and HH did not impact blood oxidative stress or redox-sensitive gene transcripts.

Influence of Fluid Delivery Schedule and Composition on Fluid Balance, Physiologic Strain, and Substrate Use in the Heat.

INTRODUCTION: Wildfire suppression is characterized by high total energy expenditure and water turnover rates. Hydration position stands outline hourly fluid intake rates. However, dose interval remains ambiguous. We aimed to determine the effects of microdosing and bolus-dosing water and microdosing and bolus-dosing carbohydrate-electrolyte solutions on fluid balance, heat stress (physiologic strain index [PSI]), and carbohydrate oxidation during extended thermal exercise. METHODS: In a repeated-measures cross-over design, subjects completed four 120-min treadmill trials (1.3 m·s-1, 5% grade, 33°C, 30% relative humidity) wearing a US Forest Service wildland firefighter uniform and a 15-kg pack. Fluid delivery approximated losses calculated from a pre-experiment familiarization trial, providing 22 doses·h-1 or 1 dose·h-1 (46±11, 1005±245 mL·dose-1). Body weight (pre- and postexercise) and urine volume (pre-, during, and postexercise) were recorded. Heart rate, rectal temperature, skin temperature, and steady-state expired air samples were recorded throughout exercise. Statistical significance (P<0.05) was determined via repeated-measures analysis of variance. RESULTS: Total body weight loss (n=11, -0.6±0.3 kg, P>0.05) and cumulative urine output (n=11, 677±440 mL, P>0.05) were not different across trials. The micro-dosed carbohydrate-electrolyte trial sweat rate was lower than that of the bolus-dosed carbohydrate-electrolyte, bolus-dosed water, and microdosed water trials (n=11, 0.8±0.2, 0.9±0.2, 0.9±0.2, 0.9±0.2 L·h-1, respectively; P<0.05). PSI was lower at 60 than 120 min (n=12, 3.6±0.7 and 4.5±0.9, respectively; P<0.05), with no differences across trials. The carbohydrate-electrolyte trial's carbohydrate oxidation was higher than water trial's (n=12, 1.5±0.3 and 0.8±0.2 g·min-1, respectively; P<0.05), with no dosing style differences. CONCLUSIONS: Equal-volume diverse fluid delivery schedules did not affect fluid balance, PSI, or carbohydrate oxidation during extended thermal work.

Alaska backcountry expeditionary hunting promotes rapid improvements in metabolic biomarkers in healthy males and females.

We have previously reported negative energy balance and health benefits during an Alaska backcountry expeditionary hunting (ABEH) immersion in two males. The purpose of our present study was to increase the number of participants, include females, and evaluate macronutrient intake and serum lipids. Four men (age: 46 ± 6 year, BMI: 26 ± 1 kg/m2 ) and three women (age: 46 ± 11 year, BMI: 25 ± 3 kg/m2 ) were recruited. Doubly labeled water methodology and dietary recall were utilized to assess energy expenditure and energy intake, respectively. Data were collected during pre- and post-ABEH visits. Body composition was measured using dual-energy x-ray absorptiometry and the cross-sectional area of skeletal muscle in the upper leg (XT), and intrahepatic lipid (IHL) was determined using magnetic resonance imaging and/or spectroscopy (MRI/MRS). Blood parameters were measured by LabCorp. Paired T-tests were used for statistical analysis. Data are reported as mean ± SD and considered significant at p < 0.05. Total energy intake was 7.7 ± 3.4 MJ/day and total energy expenditure was 17.4 ± 2.6 MJ/day, resulting in a negative energy balance of -9.7 ± 3.4 MJ/day. Protein intake(grams)/body weight(kilograms)/day was 1.0 ± 0.4. There were reductions in body weight (Δ-1.5 ± 0.7 kg), BMI (Δ-0.3 ± 0.2 kg/m2 ), fat mass (Δ-1.7 ± 0.9 kg), and IHL (Δ-0.3 ± 0.3% water peak). There were no changes in lean tissue mass (Δ0.6 ± 1.4 kg) or XT (Δ-1.3 ± 3.3 cm2 ). There were significant reductions in total cholesterol (Δ-44 ± 35 mg/dl), LDL-cholesterol (Δ-25 ± 14 mg/dl), VLDL-cholesterol (Δ-7 ± 7 mg/dl), and triglycerides (Δ-35 ± 33 mg/dl). The ABEH immersion resulted in considerable negative energy balance and provided comprehensive benefits in metabolic health without any reduction in skeletal muscle.

Total Energy Intake and Self-Selected Macronutrient Distribution During Wildland Fire Suppression.

INTRODUCTION: Wildland firefighters (WLFF) work long hours in extreme environments, resulting in high daily total energy expenditure. Increasing work-shift eating episodes and/or providing rations that promote convenient eating has shown augmented self-selected work output, as has regular carbohydrate (CHO) consumption. It remains unclear how current WLFF feeding strategies compare to more frequent nutrient delivery. Our aim was to determine WLFFs' self-selected field total energy intake (TEI), composition, and feeding patterns during wildland fire suppression shifts. METHODS: WLFF were deployed to fire incidents across the United States throughout the 2018 fire season. Preshift food inventories collected at basecamp provided item-specific nutrient content (kilocalories, CHO, fat, protein). Work shift consumption (TEI, feeding frequency, episodic composition) was monitored in real time by field researchers on fireline via observational data capture using mobile tablets. Shift work output was also quantified via actigraph accelerometry. RESULTS: Eighty-six WLFF (27.5±6.4 y; 16 female, 70 male) worked 14.0±1.1 h shifts, with a TEI of 6.3±2.5 MJ (1494±592 kcal) (51±10, 37±9, 13±4% for CHO, fat, and protein, respectively). WLFF averaged 4.3±1.6 eating episodes (1.4±1.3 MJ [345±306 kcal] and 44±38 g CHO·episode-1). WLFF who consumed >20 kcal·kg-1 averaged less sedentary activity than those consuming <16 kcal·kg-1. Data are presented as mean±SD. CONCLUSIONS: Not including fire camp meals (breakfast, dinner), the present work-shift TEI approximates 33% of previously determined WLFF total energy expenditure and demonstrates that current WLFF consumption patterns may not deliver adequate nutrients for occupational demands.

Skeletal Muscle mRNA Response to Hypobaric and Normobaric Hypoxia After Normoxic Endurance Exercise.

Background: The physiological effects of hypoxia may be influenced by how hypoxia is achieved. The purpose of this study was to determine the effects of recovery in hypobaric hypoxia (HH), normobaric hypoxia (NH), and normobaric normoxia (NN) after endurance exercise on gene expression related to mitochondrial biogenesis, myogenesis, and proteolysis. Methods: Fifteen recreationally trained subjects each cycled for 1 hour before recovering for 4 hours in NN (laboratory atmospheric conditions, 975 m), HH (depressurized to simulate 4420 m), and NH (fraction of O2 reduced to simulate 4420 m). Muscle biopsy samples were obtained before exercise and after 4 hours of recovery. Results: Blood oxygenation (SpO2) was lower in HH (76.02 ± 0.58%) than NH (79.45 ± 0.56, p < 0.001), which were both lower than in NN (96.3 ± 0.17, p < 0.001). Heart rate was higher in HH (82 ± 2 bpm) than NH (77 ± 1 bpm, p < 0.001), which were both higher than in NN (67 ± 1 bpm, p < 0.001). Mitochondrial transcription factor A (TFAM) mRNA was lower after NN than HH (p = 0.034) or NH (p = 0.005), but was not different between HH and NH (p = 0.460). Myostatin (MSTN) mRNA decreased from pre- to postexercise (p < 0.001) in all conditions and was lower in HH compared with NH (p = 0.035) and NN (p = 0.017). No other differences were noted in genes related to mitochondrial biogenesis, myogenesis, or proteolysis (p > 0.05). Conclusion:TFAM mRNA is lower with hypoxia exposure, but effected by the type of hypoxia. MSTN gene expression is lower after exposure to HH than NH or NN. These data support previous work and caution the translation of NH data obtained in a NH environment to a HH environment.

Wildland Firefighting: Adverse Influence on Indices of Metabolic and Cardiovascular Health.

OBJECTIVE: The purpose of this study was to evaluate pre- and postseason measures of body composition, skeletal muscle, and blood parameters/liver lipid in wildland firefighters (WLFF) over the fire season. METHODS: Alaskan WLFF (N = 27) crews were evaluated pre- and postwildfire season, which included 63 ±â€Š10 operational days. Body composition, thigh muscle area, and liver lipid were quantified using dual-energy radiograph absorptiometry and magnetic resonance imaging, respectively. Blood metabolic and lipid panels were also collected and analyzed. RESULTS: Total body, fat, and visceral fat mass increased from pre- to postseason (P < 0.05). Total cholesterol, LDL, and total globulin also increased (P < 0.05). There was a trend (P = 0.06) towards an increase in intrahepatic lipid. CONCLUSIONS: The observed maladaptive changes in adipose tissue, blood lipids, and hepatic function may reflect adaptations/consequences to occupational demands/conditions and warrant evaluation of appropriate countermeasures.

Assessment of urinary protein composition in response to consecutive days of wildland firefighting.

The purpose of this study was to examine the pattern of urinary protein excretion induced by 3 consecutive days of wildland firefighting. Eighteen male active-duty military personnel served as the participants. All testing on the 3 consecutive days was conducted at a Northwestern USA fire camp. All participants consumed military-based foods containing 2620-2864 kcal/day. The work activity was evaluated with an accelerometer in association with body weight and hydration markers over the experimental period. Urinary samples were collected pre and post workshift on days 1 and 3 to assess glomerular and tubular protein excretion (total protein, albumin, ß2-microglobulin, N-acetyl-ß-d-glucosaminidase and creatinine). The urinary levels of glomerular and tubular protein were not significantly different. The main findings of the present study indicate that similar alterations of urinary protein composition can be observed over consecutive days of wildland firefighting, which appears to be dependent on intensity rather than total work output.

Short term heat acclimation reduces heat stress, but is not augmented by dehydration.

Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg-1 15 min-1, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg-1 15 min-1, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance. Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn. Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ±â€¯0.1-39.0 ±â€¯0.1 °C: P < 0.001) and EUH acclimation (39.5 ±â€¯0.1-38.9 ±â€¯0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ±â€¯0.06-1.89 ±â€¯0.09 L h-1) compared to EUH acclimation (1.57 ±â€¯0.06-1.79 ±â€¯0.08 L h-1: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83). In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation.

The energy requirements and metabolic benefits of wilderness hunting in Alaska.

The purported healthy aspects of subsistence foods have led to the popularity of the Paleo diet. There has been very little focus, surprisingly, on health benefits derived from the nomadic nature of humans during the Paleolithic era. The purpose of our study was to examine total energy expenditure (TEE), total energy intake (TEI), body composition, blood lipids, and intrahepatic lipid in humans during a 12-day Alaskan backcountry expeditionary hunting (ABEH) immersion. Four healthy men (age: 42 ± 3 year, BMI: 27 ± 1 kg/m2 ) were recruited for the study. TEE was measured using the doubly labeled water method and a food diary was utilized to assess TEI. Body composition was measured using dual energy X-ray absorptiometry (DXA); cross-sectional area of the thigh (XT) and intrahepatic lipid (IHL) were measured using molecular imaging. Blood samples were collected for the measurement of blood lipids. DXA, XT, IHL, and blood data were collected pre- and immediately post-ABEH. Results were analyzed using paired t-tests and considered significant at P < 0.05. TEE and TEI averaged 18.1 ± 1.2 and 9.1 ± 2.5 MJ/day, respectively, indicating substantial negative energy balance (-9.0 ± 1.3 MJ/day). There was a reduction in percent body fat (∆-3.3 ± 0.2%), total fat mass (∆-3.3 ± 0.4 kg), and visceral fat volume (Δ-261 ± 188 cm3 ). Lean tissue mass and XT was unchanged. There was a decrease in IHL (Δ-0.5 ± 0.1% water peak), and a trend (P = 0.055) toward reduction in LDL-cholesterol. We conclude that constancy of physical activity during negative energy balance may provide metabolic benefits above and beyond variations in diet that exist with the hunter-gatherer lifestyle.