Abstract
BackgroundCardiovascular (CV) and thermal responses to metabolically demanding multi-day military operations in extreme cold-weather environments are not well described. Characterization of these operations will provide greater insights into possible performance capabilities and cold injury risk.MethodsSoldiers from two cold-weather field training exercises (FTX) were studied during 3-day (study 1, n = 18, age: 20 ± 1 year, height: 182 ± 7 cm, mass: 82 ± 9 kg) and 4-day (study 2, n = 10, age: 20 ± 1 year, height: 182 ± 6 cm, mass: 80.7 ± 8.3 kg) ski marches in the Arctic. Ambient temperature ranged from −18 to −4 °C during both studies. Total daily energy expenditure (TDEE, from doubly labeled water), heart rate (HR), deep body (Tpill), and torso (Ttorso) skin temperature (obtained in studies 1 and 2) as well as finger (Tfing), toe (Ttoe), wrist, and calf temperatures (study 2) were measured.ResultsTDEE was 6821 ± 578 kcal day−1 and 6394 ± 544 for study 1 and study 2, respectively. Mean HR ranged from 120 to 140 bpm and mean Tpill ranged between 37.5 and 38.0 °C during skiing in both studies. At rest, mean Tpill ranged from 36.0 to 36.5 °C, (lowest value recorded was 35.5 °C). Mean Tfing ranged from 32 to 35 °C during exercise and dropped to 15 °C during rest, with some Tfing values as low as 6–10 °C. Ttoe was above 30 °C during skiing but dropped to 15–20 °C during rest.ConclusionsDaily energy expenditures were among the highest observed for a military training exercise, with moderate exercise intensity levels (~65% age-predicted maximal HR) observed. The short-term cold-weather training did not elicit high CV and Tpill strain. Tfing and Ttoe were also well maintained while skiing, but decreased to values associated with thermal discomfort at rest.
Highlights
Cardiovascular (CV) and thermal responses to metabolically demanding multi-day military operations in extreme cold-weather environments are not well described
Of the 10 volunteers in the thermal strain group, there were 5 in the carbohydrate supplementation group (CHO) group, 2 in the PRO group, and 3 in the control group (CON) group. The data for these three feeding groups were pooled for the analyses reported in this paper as there were no differences for the groups
This study showed that 3–4 days of ski marching in below freezing temperatures elicited only mild cardiovascular and thermal strain, suggesting that the Soldiers’ clothing and equipment provided good protection under the environmental and physical conditions studied
Summary
Cardiovascular (CV) and thermal responses to metabolically demanding multi-day military operations in extreme cold-weather environments are not well described. During light, moderate, and heavy exercise intensities over 6-h work days [13], rectal temperature was lowest during light work (~275 W) and highest during work eliciting ~435 W and finger (Tfing) and toe (Ttoe) temperatures followed the same pattern These field studies cited were conducted during limited cold exposure, that is, exposure durations less than 6 to 8 h over a 24-h period with access to heated shelter when not working. Adventure sporting events (e.g., Iditarod Trail Invitational, 6633 Ultra), can take place over multiple days under extreme environmental conditions where participants self-select their exercise intensity These military and sporting scenarios often have multiple exacerbating physiological stressors, including very high energy expenditures and energy deficits [15]. This cumulative exposure to cold and other stressors may increase susceptibility to cold injuries [16], but the impact of multiple days of sub-freezing cold exposure during field training on cardiovascular and thermal strain during high deficits are not well described
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