Objective: The purpose of this investigation was to characterize the effects of self-selected work activity on energy expenditure, water turnover, and thermal strain during wildland fire suppression. A secondary aim was to contrast current data with data collected 15 years ago using similar methods to determine whether job demands have changed. Methods: Participants (n = 15, 26 ± 3 years, 179 ± 6 cm, 78.3 ± 8.6 kg) were monitored for 3 days for total energy expenditure, water turnover, core and chest skin temperature, physical activity, and heart rate. Participants arrived to the mobile laboratory each morning, submitted a nude weight, ingested a temperature transmitter, provided a urine sample, and were equipped with a physiological and activity monitor. Participants completed live wildland fire suppression during their work shifts. Results: Mean core temperature was 37.6° ± 0.2°C, mean chest skin temperature was 34.1° ± 1.0°C, mean heart rate was 112 ± 13 beats/min, and the mean physiological strain index score was 3.3 ± 1.0. Wildland firefighters spent 49 ± 8%, 39 ± 6%, and 12 ± 2% in the sedentary, light, and moderate-vigorous intensity categories, respectively. The mean total energy expenditure was 19.1 ± 3.9 MJ/d, similar to 1997 (17.5 ± 6.9 MJ/d). The mean water turnover in 2012 was 9.5 ± 1.7 L/d, which was higher ( P < .05) compared with 1997–98 (7.0 ± 1.7 L/d). Conclusions: Wildland firefighters do not induce consistently high cardiovascular and thermal strain while completing arduous work in a hot environment despite fairly high chest skin temperatures. The total energy expenditure in the current study suggests job demands are similar to those of 15 years ago, while the increased water turnover may reflect a change in drinking habits.

Context: Telemetric core-temperature monitoring is becoming more widely used as a noninvasive means of monitoring core temperature during athletic events. Objective: To determine the effects of sensor ingestion timing on serial measures of core temperature during continuous exercise. Design: Crossover study. Setting: Outdoor dirt track at an average ambient temperature of 4.4°C ± 4.1°C and relative humidity of 74.1% ± 11.0%. Patients or Other Participants: Seven healthy, active participants (3 men, 4 women; age = 27.0 ± 7.5 years, height = 172.9 ± 6.8 cm, body mass = 67.5 ± 6.1 kg, percentage body fat = 12.7% ± 6.9%, peak oxygen uptake [V˙o_2peak] = 54.4 ± 6.9 mL•kg⁻¹•min⁻¹) completed the study. Intervention(s): Participants completed a 45-minute exercise trial at approximately 70% V˙o_2peak. They consumed core-temperature sensors at 24 hours (P1) and 40 minutes (P2) before exercise. Main Outcome Measure(s): Core temperature was recorded continuously (1-minute intervals) using a wireless data logger worn by the participants. All data were analyzed using a 2-way repeated-measures analysis of variance (trial × time), Pearson product moment correlation, and Bland-Altman plot. Results: Fifteen comparisons were made between P1 and P2. The main effect of time indicated an increase in core temperature compared with the initial temperature. However, we did not find a main effect for trial or a trial × time interaction, indicating no differences in core temperature between the sensors (P1 = 38.3°C ± 0.2°C, P2 = 38.3°C ± 0.4°C). Conclusions: We found no differences in the temperature recordings between the 2 sensors. These results suggest that assumed sensor location (upper or lower gastrointestinal tract) does not appreciably alter the transmission of reliable and repeatable measures of core temperature during continuous running in the cold.

S, N = 6 females) performed a graded exercise test on a treadmill (TM) and cycle ergometer (CE) to determine ventilatory threshold (VT) and V˙O2peak. In a double-blind, randomized crossover design, subjects received either CHO [20% maltodextrin (0.6 g·kg−1 FFM·h−1)] or flavored placebo (PLA) drink each hour across 10 h of exercise. Exercise intensity was 71.3 ± 3% and 72.4 ± 4% VT for TM and CE, respectively. Hourly exercise included 9 min of upper-body ergometery, 19 min of cycling, and 20 min of treadmill walking, with a 1-min transition between modes, followed by a 10-min rest and feeding period. The protocol was selected to simulate arduous occupational settings. Vastus lateralis biopsies were obtained before and after exercise. Expired gases were collected every other hour to establish average rates of whole-body CHO and fat oxidation. Blood glucose (BG) was measured continuously. Results: Whole-body CHO oxidation was maintained during CHO trial compared with the PLA trial. Net muscle glycogen use was 52% higher for the PLA trial (176.0 ± 16.7, 117.0 ± 20.9 and 164.5 ± 11.0, 133.8 ± 10.9 mmol·kg−1 w.w. for PLA and CHO, respectively, P < 0.05). There were no significant sex-specific differences in glycogen use, whole-body substrate oxidation, or BG values. Conclusion: The ingestion of CHO during long-duration exercise decreases net muscle glycogen use while better maintaining whole-body carbohydrate oxidation, and potentially increasing performance in field settings. There are limited differences in sex-specific substrate oxidation....