CARDIORESPIRATORY RESPONSES TO THE USFS WILDLAND FIREFIGHTER ARDUOUS PACK TEST

C.J. Alfiero,C.L. Dumke FACSM, B.C. Ruby FACSM, M.W. Bundle University of Montana, Missoula, MT US wildland firefighters administer over 30,000 physical tests per year to qualify candidates for the occupational demands of fire suppression. The primary assessment is the arduous pack test (APT) a 4.83 km hike that must be completed in 45 min while wearing a 20.45 kg pack. Delivery of individual feedback to guide the physical training of candidates is hampered by two factors; first, passing the pack test is widely considered the minimum performance level necessary needed for this occupation, and second, the binary nature of the assessment presents candidates with a task representing an unknown and self-selected exercise intensity. PURPOSE: To determine the cardiorespiratory response elicited by the APT within a subject population whose aerobic capacity and body masses vary. METHODS: 61 young (age = 22.8 ± 3.2 yrs) adults (36 males, Mb = 79.5 ± 8.8kg; 25 females, Mb = 67.5 ± 13.5kg; study range: 55.4 - 119.6 kg) performed the APT and subsequently underwent a hiking inclined-treadmill test to VO2peakwhile wearing a skin mounted heart rate (HR) monitor and 20.45-kg pack. RESULTS: 50 of the 63 subjects achieved the 45-min cutoff with a finishing time of 41.8 ± 2.1min, the non-passers had a mean time of 47.7 ± 2.7 min. Non-passers were 77% female and 23% male. The VO2peakvalues of the passing and non-passing groups were 49.4 ± 7.2 and 42.6 ± 9.6 mlO2kg-1 min-1, respectively; the study range was 62.1 to 30.8 mlO2kg-1 min-1. HR, whether expressed as a fraction of the subject’s maximum rate (passers = 81.2 ± 17.1 and non-passers = 79.9 ± 12.7% of HRmax), or as the fraction of the HR reserve (passers = 68.0 ± 7.9 and non-passers = 67.7 ± 15.3% of HR reserve) were not different between the groups. Regression of VO2peakon completion time yielded a negative relationship (R2 = 0.45). In contrast, the HR responses and completion time were consistent among the participants (R2\u3c 0.01 for both % of HRmaxand % of HR reserve). CONCLUSION: To successfully complete the APT candidates must achieve a HR reserve of 68% or less while maintaining a walking speed of 1.8 m s-1. These data suggest that monitoring HR during load carriage may be used to identify candidates with adequate and inadequate pre-fire season readiness

THE IMPACT OF HYDRATION STATUS DURING HEAT ACCLIMATION ON PHYSIOLOGICAL STRAIN AND EXERCISE PERFORMANCE

M.W. Schleh, M. Johannsen, B.C. Ruby FACSM, C.L. Dumke FACSM The University of Montana, Missoula, MT Heat acclimation improves thermal tolerance and attenuates the physiological and perceptual strain associated with exercise in the heat. A limited fluid delivery strategy during heat acclimation may promote further adaptations to attenuate heat stress over long periods, decreasing the probability of heat related illness. PURPOSE: To determine i) the effect of fluid delivery by inducing dehydration (DEH=0.5 ml*kg-1*min-15) compared to euhydration (EUH=2.0 ml * kg-1 * 15 min-1) following three heat acclimation bouts on heat stress factors, and ii) to determine the effect of aerobic performance in the heat following DEH and EUH acclimation trials. METHODS: Eight aerobically fit males (23.0±0.9 yrs, 82.1 ± 2.0 kg, 184.0 ± 2.5 cm, 53.2 ± 1.5 ml*kg-1*min-1 VO2 max) completed 90-minute heat stress test (HST) in hot conditions (T=40°C, RH=30%) at 50% VO2 max prior to and following three-days of EUH and DEH acclimation trials. Acclimation trials consisted of three heat exposures in the same environmental conditions, intensity, and duration as previously stated on alternating days. Participants wore standard wildland firefighter (WLFF) Nomex: yellow shirt, green pants, and a cotton T-shirt. Following each HST, aerobic performance was assessed by a graded ramp protocol by increasing treadmill grade by 1% until 15%, and then increased 1 mph every minute until volitional exhaustion. Core temperature (Tc) and Skin temperature (Tsk) were measured continuously, and reported as peak TC and TSk at 90 minutes. Sweat rate by ∆nude weight, and post acclimation performance measured in time to exhaustion. All data was analyzed by a two-way analysis of variance (ANOVA) 2 (trt) x 2 (time). RESULTS: Peak Tc and Tsk during HST significantly decreased in effect for time in DEH & EUH groups (p\u3c0.001, p=0.003) respectively. Sweat rate was significantly greater in DEH compared to EUH (trt*time: p=0.034). Aerobic performance increased greater in EUH compared to DEH (trt*time: p= 0.034). CONCLUSION: Short-term heat acclimation is an effective strategy to attenuate physiological strain associated with heat stress, and also improve aerobic performance in the heat. Fluid delivery strategies during acclimation do not affect thermal strain, but may increase sweat capacity. Controlled dehydration during acclimation did not however increase performance. This project was supported by the US Forest Service

THE EFFECT OF DEHYDRATION ON HEAT ACCLIMATION

R. Berland, C. Briscoe, M. Schleh, B.C. Ruby FACSM, C.L. Dumke FACSM The University of Montana, Missoula, MT With the prevalence of occupations occurring in hot environments, it is crucial to develop a protocol to protect these individuals from heat related illness. We hypothesize that heat acclimation with mitigated fluid delivery will improve cardiovascular and perceptual strain associated with heat stress, and hydration maintenance. PURPOSE: To determine the impact of hydration status during heat acclimation on hydration retention and cardiovascular and perceptual drift. METHODS: Eight aerobically fit male subjects (23 ± 1.00 yrs, 82.1±2.14 kg, 53.18 ± 1.63 mL•kg-1•min-1 VO2 max, 13.8% ± 1.31% BF) completed a heat stress test (HST) two days prior to and following three acclimation bouts, in alternating days to allow for rehydration. HST and acclimation bouts consisted of 90 min treadmill walking at 50% VO2 max in hot conditions (40℃, 30% RH). Fluid delivery during acclimation bouts was administered in a randomized crossover design, where fluids were administered to promote a dehydrated (DEH = 0.5 mL/kg) or a euhydrated (EUH = 2.0 mL/kg) state. A five week washout period separated DEH from EUH acclimation periods. Participants wore standard wildland firefighter (WLFF) NoMex clothing with a cotton shirt. Peak heart rate (HR), peak rate of perceived exertion (RPE), percent dehydration (%DEH), and ΔBW were analyzed by a 2(trt) X 2(trial) ANOVA. RESULTS: HR decreased from PRE to POST (p\u3c0.001) (178.9±13.3, 165.1±16.0, 182.3±11.8, 162.9±16.0, for DEH vs EUH pre-post respectively) but there was not an effect of treatments. RPE decreased between trials (p\u3c0.001)(17.8±2.3, 14.5±2.6, 16.9±2.5, 13.6±2.3 for DEH vs EUH pre-post respectively) but no significance between treatments. ΔBW demonstrated a time and trtXtime interaction (p=0.030) with greater ΔBW in the DEH trial following acclimation (1.15±0.27, 1.83±0.39, 1.35±0.35, 1.57±0.38 for DEH vs EUH pre-post respectively). %DEH demonstrated a time and trtXtime interaction (p=0.033) with greater %DEH in the DEH trial following acclimation (1.48±0.38, 2.15±0.48, 1.72±0.49, 1.99±0.52 for DEH vs EUH pre-post respectively). CONCLUSION: Our data suggests that heat acclimation reduces cardiovascular and perceptual strain, however mitigated fluid delivery during acclimation did not alter this adaptation. Mitigated fluid delivery increases ΔBW and %DEH suggesting greater sweat capacity following the acclimation trials. This suggests that controlled dehydration may result in greater adaptations during short term heat acclimation. Funding provided by the US Forest Service

METABOLIC COST OF LOAD CARRIAGE: EVALUATING EXISTING MODELS WITH EMPERICAL DATA

J.T. Strang, C.J. Alfiero, C.L. Dumke FACSM, B.C. Ruby FACSM, M.W. Bundle University of Montana, Missoula, MT PURPOSE: Despite extensive and ongoing scientific study into the metabolic requirements of load carriage, an understanding quantifying the effect of speed, load, sex and body mass has yet to come forth and the extent to which established models predict these requirements is largely untested. Specifically, because existing experimental efforts have typically focused on relatively modest walking speeds using loads representing a fixed portion of the subject’s mass, extending the available predictions to applications where individuals complete a common task carrying an identical absoluteload provides estimates of unknown accuracy. Here, we measured the energy use in a large subject group walking at speeds surrounding the 1.8 m s-1necessary to successfully complete the 4.83 km USFS wildland firefighter arduous pack (20.5kg) test, and compared these results to estimates available from the prevailing models. METHODS: We measured VO2from 61 young (age = 22.8±3.2 yrs) adults (36 males, Mb = 79.5±8.8kg; 25 females, Mb = 67.5±13.5kg; study range: 55.4-119.6 kg) as they performed four, 5min trials, with a 20.5kg pack, on a level treadmill at 1.7, 1.8, 1.9 m s-1, and their individual average speed from a previously administered pack test. We used the methods of Pandolf et al. 1977 and Ludlow & Weyand 2017 to generate VO2estimates for the 217 individual trials we administered. RESULTS: Measured values of VO2increased from 22.5±3.3 and 24.2±4.1 ml kg-1 min-1at 1.7 m s-1,to 31.3±5.2 and 30.5±4.3 ml kg-1 min-1at the fastest speed administered for males and females respectively. In contrast, the accuracy of the predictive models decreased with speed and yielded prediction errors of -12.1 and -22.6% at 1.7 m s-1 for the Pandolf and Ludlow & Weyand methods respectively, these errors were -17.2 and -31.0% at the fastest speeds administered. When evaluated at the speed subjects used in the field trial the prediction models underestimated energy expenditure by 5.7±4.6 and 9.8±4.8 ml kg-1 min-1respectively. CONCLUSION: We conclude that existing predictive models do not retain their internal accuracy, and substantially underestimate measured values when applied to a group of male and female subjects undertaking relatively fast walking speeds with a heavy load. Supported by US Forest Service Agreement # 16-CR-11138200-005, to CD, BR and M

THE EFFECT OF HYDRATION STATUS ON PHYSIOLOGICAL MARKERS DURING HEAT ACCLIMATION

C. Alfiero, K. Nickol, M.Schleh, B. Ruby FACSM, C.L. Dumke FACSM University of Montana, Missoula, MT The hydration status of wildland firefighters (WLFF) during heat acclimation trials may impact long-term work performance by attenuating physiological strain. By inducing dehydration by a mitigated fluid delivery method in a controlled setting, physiological adaptations such as increased sweat rate and cardiovascular strain may be ameliorated. PURPOSE: To investigate the impact of fluid delivery that affects hydration status (dehydrated/ euhydrated) on levels of hydration (% dehydration), sweat rate (SR), heart rate (HR), and rating of perceived exertion (RPE). METHODS: In a randomized cross-over protocol, five aerobically fit male subjects (age=23.0±0.9, weight=82.1±4.6kg, 53.2±1.6) underwent three heat acclimation trials on alternate days in an environmental chamber (40°C, 30%RH) for 90 min at 50%VO2max. Fluid delivery was administered to promote either dehydration (DEH=0.5 ml*kg-1*15 min-1) or euhydration (EUH=2.0 ml*kg-1*15 min-1). After a five week washout period three subsequent trials were held in the alternate hydrated state. Participants wore standard WLFF Nomex green pants, yellow shirt with 100% cotton base layer. Rating of perceived exertion (RPE) and heart rate (HR) were measured every 30 min throughout the 90 min trial. Pre and post bodyweight were measured to determine sweat rate and percent dehydration. Statistics were performed as a 2 (trt) x 3 (day) analysis of variance (ANOVA) with repeated measures. RESULTS: There was a significant trt*day interaction (p=0.009) in average RPE (DEH=13.4±0.2, 12.7±0.2, 12.7±0.4, EUH=12.33±.252, 12.17±.252, 11.9±0.4) between DEH and EUH over the three days. There was a significant effect of treatment (p-1) for acclimation bouts 1, 2, and 3 respectively. CONCLUSIONS: Our data suggests that controlled dehydration during 3 days of heat acclimation results in elevated RPE and percent dehydration, but does not jeopardize HR or SR. This project was supported by the US Forest Service

EFFECT OF HIGH INTENSITY INTERVAL TRAINING ON MAXIMAL FATTY ACID OXIDATION VERSUS STEADY STATE EXERCISE

K. Beisel, E. Donahue, A. Kalafatis, K. Christison, C.L. Dumke, FACSM University of Montana, Missoula, MT Previous evidence suggests high intensity intervals and steady state exercise can enhance fat oxidation. These two stimuli have not been examined in the same exercise bout. PURPOSE: This study examines the effect of high intensity interval training (HIIT) on fatty acid oxidation compared to steady state at each individuals maximal fatty acid oxidation (MFAO). METHODS: Twelve fasted, uncaffeinated individuals (8 males, 4 females, average VO2max = 44.3±2.3 ml·kg-1·min-1, average age =23.8±0.8 years) underwent a randomized crossover design study with 2 trials; trial A included cycling for 60 minutes at MFAO workload (0.55±0.05 g·min-1; 58.6±1.1 % VO2max; 126.7±9.6 W) and trial B included 3 minute intervals at 90% and 30% of maximal workload during the first 30 minutes, and the last 30 minutes the subjects cycled at the MFAO workload. Total work was matched between the two trials. Heart rate (HR), respiratory exchange ratio (RER), rating of perceived exertion (RPE), absolute fat (FAO) and carbohydrate oxidation (CHOO) were recorded every 15 minutes, lactate and glucose taken every 30 minutes. Data was analyzed using a 2X2 repeated measures ANOVA and paired samples T-test for overall trial differences. RESULTS: There was a main effect of time on lactate (p=0.002), RPE (p=0.027), HR (45 min: 164.6±2.8 bpm vs. 60 min: 168.0±2.9 bpm, 45 min: 159.4±3.6 bpm vs. 60 min:159.8±4.6 bpm, p=0.028), and FAO (45 min: 0.55±0.05 g/min vs. 60 min: 0.66±0.06 g/min, 45 min: 0.62±0.04 g/min vs. 60 min: 0.63±0.04 g/min, p=0.044). There was a trial effect of RPE (45 min: 13.5±0.3 vs 60 min: 13.8±0.4, 45 min: 11.4±0.8 vs 60 min: 12.5±0.6, p =0.014), and sweat rate (0.91±0.07 L·min-1 vs 0.69±0.03 L·min-1, p=0.03) All listed values are trial A vs. trial B respectively. A trial by time interaction was found for lactate (pCONCLUSION:These data suggest as exercise endurance increases, MFAO is elevated. Despite elevated lactate in the HIIT trial FAO did not differ between trials. Despite matched work between trials, significant reductions in RPE, HR and SR, suggests subjects had reduced metabolic stress at MFAO workloads following HIIT

MAXIMAL FAT OXIDATION DURING STEADY STATE EXERCISE

A. Kalafatis, K. Beisel, E. Donahue, K. Christison, C.L. Dumke, FACSM University of Montana, Missoula, MT Research has demonstrated multiple factors contributing to maximal fatty acid oxidation (MFAO). However, less is known about factors that regulate changes in fatty acid oxidation during exercise. PURPOSE: The purpose of this study is better understand how cycling at MFAO for 60 minutes will alter fat oxidation. METHODS: Twelve fasted, uncaffeinated individuals (8 males, 4 females, average VO2max = 44.3± 2.3 mL·kg-1·min-1, average age =23.7±0.8) underwent two laboratory visits. They first underwent a VO2 max test in which heart rate (HR), rating of perceived exhaustion (RPE), absolute fat (FAO) and carbohydrate oxidation (CHOO) were recorded. Hydrostatic weighing was used to determine body fat percentage. The second visit included a 60-minute exercise on a cycle ergometer at the subjects predetermined maximal fatty acid oxidation (MFAO) workload (0.55±0.05 g·min-1; 58.6±1.1 % VO2max; 126.7±9.6 W). HR, RPE, and the respiratory exchange ratio were recorded every fifteen minutes, with water provided at 3 ml·kg-1 at 15, 30, and 45 minutes. Lactate and glucose were measured at 30 and 60 minutes. Data were analyzed using repeated measures ANOVA, and paired samples T-test for pre- and post changes. RESULTS: There was a main effect of time on HR (154.7±3.5 at 15min, vs 168.0±2.9 bpm at 60min; p=0.005), RPE (11.2±0.3 at 15 min vs 13.8±0.4 at 60 min; p=0.001) and FAO (0.46±0.05 at 15 min vs. 0.65±0.06 at 60 min; p\u3c0.001). FAO at the end of 60 mins of exercise was significantly greater than MFAO (p=0.04) from the VO2max test. The change in FAO during exercise did not correlate with subject characteristics. However, MFAO was superior in the tallest (r=0.67, p=0.02), heaviest (r=0.78, p=0.003), and those with the greatest maximum workload (r=0.82, p=0.001). Correlation was found between the tallest and weight loss during the trial (r=0.66, p=0.019). CONCLUSION: These data suggest that during the 60 minute bike ride that FAO exceeds the MFAO during a VO2max test. In addition, the largest subjects with the greatest maximum workload had the highest MFAO and FAO during the one hour trials

SEASONAL CHANGES IN CARDIOVASCULAR FUNCTION, RISK FACTORS, AND OXIDATIVE STRESS OF WILDLAND FIREFIGHTERS

C.M. Williamson-Reisdorph, K.S. Christison, S.C. Gurney, K.G.S. Tiemessen, J.A. Sol, T.S. Quindry, C.G. Palmer, M.W. Bundle, C.L. Dumke, FACSM, J.C. Quindry, FACSM University of Montana, Missoula, MT Wildland firefighters (WLFF) experience extreme physiological strain throughout a typical season due to intense occupational demands and consistent woodsmoke exposure. There is a rationale to indicate that accumulated physiological strain, and oxidative stress, throughout a WLFF season has the potential to negatively alter cardiovascular function and risk factors. PURPOSE: The purpose of the study was to examine the effects of a season on cardiovascular function, risk factors, and markers of oxidative stress in WLFF. METHODS: Fourteen members of a Type I interagency hotshot crew participated in the study (males: n=13, females: n=1, age: 30.1 years ± 4.8). Pre- and post-seasonal resting measurements (May, October) were obtained for heart rate variability (lnRMSSD, lnHF, lnHF, LF:HF), pulse wave velocity (PWV), blood lipid panels (TC, TG, LDL, HDL), metabolic biomarkers (blood glucose, HbA1c), blood pressure (SBP, DBP) and blood oxidative stress (3-nitrotyrosine, 8-isoprostane, lipid hydroperoxides). Paired samples t-tests were used to identify differences among pre- and post- seasonal values. RESULTS: There were no seasonal effects observed on resting heart rate variability, PWV, 3-nitrotyrosine, 8-isoprostane, TC, TG, LDL, blood glucose, SBP, or DBP (p\u3e0.05). A significant reduction occurred in HDL (Pre: 53 mg/dL ± 14, Post: 45 mg/dL ± 18, p=0.043) and both HbA1c (Pre: 5.2% ± 0.2 , Post: 5.3% ± 0.2, p=0.034) and lipid hydroperoxides (Pre: 2.5 ± 0.5, Post: 4.9 ± 0.6, p = 0.003 ) increased from pre- to post-season. CONCLUSION: These data suggest a WLFF season did not impact resting markers of heart rate variability, pulse wave velocity, 3-nitrotyrosine, and 8-isoprostane. Alterations in metabolic biomarkers of cardiovascular risk factors (HDL and HbA1c) and lipid hydroperoxides demonstrate unfavorable seasonal changes, suggesting that the WLFF season may increase cardiovascular risk. Funded by the USFS 16-CR-11138200-005

METABOLIC AND CARDIOVASCULAR ALTERATIONS DURING CRITICAL TRAINING IN WILDLAND FIREFIGHTERS

S.C. Gurney, K.S. Christison, C.M. Williamson-Reisdorph, K.G.S. Tiemessen, J.A. Sol, T.S. Quindry, M.W. Bundle, C.G. Palmer, J.C. Quindry, FACSM, C.L. Dumke, FACSM University of Montana, Missoula, MT Wildland firefighters (WLFF) are confronted with numerous physical and mental stressors. Pre-fire season includes an intense 2- week critical training (CT) period; a preparatory phase that can result in injury, illness, and rhabdomyolysis. PURPOSE: To identify physiologic changes in metabolic biomarkers that occur during 2 weeks of CT in WLFF. METHODS: Eighteen male (29.4±1.1 yr, 182.1±1.6 cm) and three female (26.7±2.6 yr, 169.5±4.2 cm) participants were recruited from a Type I interagency hotshot fire crew and monitored over their 2-week CT. Fitness was assessed via BLM Fitness Challenge (push-ups, pull- ups, sit-ups, 1.5 mi run). Subjects were asked to fast and abstain from caffeine for blood draws on days 1, 4, 8, and 11. Plasma was analyzed for changes in the metabolic profile and oxidative stress markers 3-Nitrotyrosine (3NT), 8-Isoprostane (8ISO), and Lipid Hydroperoxides (LOOH). A one-way repeated measures ANOVA was used to analyze 8ISO, 3NT, and LOOH. Paired samples t-tests were used to compare metabolic biomarkers. Data presented as mean±SEM. RESULTS: CT elicited decrease in total cholesterol (TC) (173.6±12.1 to 153.4±8.6 mg·dL-1, p=0.01), hemoglobin A1c (5.2±0.1 5.1±0.1 %, p=0.003), hemoglobin (15.5±0.4 to 14.3±0.3 g·dL- 1, p=0.003), and estimated plasma volume to (53.8±0.7 to 50.7±1.4 %, p=0.005) from day 1 to 11. No difference was observed in high- density lipoprotein cholesterol. A main effect for time was observed in 8ISO (p- 1). 3NT was significantly elevated from day 4 to day 8 (d4: 2.4±0.6, d8: 2.9±0.6 mg·mL-1). LOOH showed a significant increase across all days (d1: 2.2±0.4, d4: 2.8±0.5, d8: 3.4±0.5, d11: 4.0±0.6 mM). Fitness was significantly correlated with DTC (r=0.58, p=0.046) and D8ISO (r=0.60, p=0.050). CONCLUSION: These data suggest the exertion required of WLFF during CT results in positive alterations to the metabolic profile. The changes in oxidative stress markers may reflect rapid adaptation to the CT stressors. These data suggest that WLFF are able to adapt quickly to the physical stress of CT, where fitness may be a protector of metabolic perturbations. Funded by the US Forest Service 16-CR-11138200-005