Page 116 - JSOM Summer 2019

Navy SEALS), DS consumption is even higher, with about heat acclimation protocol increased gastrointestinal barrier
80% of these groups reporting use. Certain DSs including permeability (increasing endotoxicity), reduced the expression
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ephedra, caffeine, green tea extracts, and capsaicin increase of heat shock proteins, and exercise core temperature was not
resting metabolic rate and are thus considered “thermo- reduced over the 7 days. Three days of 500mg/day curcumin
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genic.” 90,91 They have been hypothesized to exacerbate heat supplementation (generally promoted for antioxidant and
stress, but studies are generally sparse. Case studies suggested anti-inflammatory effects) improved gastrointestinal barrier
that ephedra may have been associated with aggravating EHS function and reduced overall core temperature in nonacclima-
in hot enviroments. 92,93 Ephedra was banned by the US Food tized individuals during 60 minutes of treadmill running in
and Drug Administration in 2004, in the wake of numerous the heat (99°F, 25% RH). Current data suggest that gluta-
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adverse effects (primarily cardiovascular) associated with its mine and curcumin may reduce gastrointestinal permeability
use, but synephrine, another compound with similar chemi- and curcumin may improve thermoregulation during exercise
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cal structure, is still on the market. in the heat, but more investigation under a wider variety of
conditions are needed before these can be recommended for
The few studies that have examined the effect of acute inges- these purposes.
tion of various dosages of caffeine (3–6mg/kg body weight) on
core temperature in the heat (86–95°F) are equivocal. Some Conclusion
studies showing a core temperature elevation (compared with
a placebo), 96,97 but others do not. 98,99 EHS is a relatively rare event, but as shown by data from the
Falmouth Road Race (Table 1) the incidence can be relatively
Beetroot juice has a high concentration of nitrates (NO ) that high if individual are intensely active, especially under condi-
–
3
convert to nitrogen compounds (i.e., NO , NO). Studies have tions of high ambient temperature and humidity. Symptoms
–
2
generally shown that beetroot juice improves the utilization and signs are mental dysfunction combined with a core tem-
of oxygen in skeletal muscle and reduce the energy cost of perature (measured rectally) near 40°C (104°F). The goal of
exercise. This could lower thermogenesis during physical treatment is to lower the temperatures as rapidly as possible,
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activity in the heat, but results from two studies are not clear. preferentially with a whole body water bath. In the field, wa-
One study in which participants consumed beetroot juice or a ter baths may not be available, and in this case it may be nec-
placebo for 6 days before 45 minutes of walking on a treadmill essary to use cold packs or towels soaked in ice water over as
with a load in the heat (106°F, 20% RH) showed a more rapid much of the body as possible or to splash large quantities of
rise in core temperature after consuming the beetroot juice, water over the body with fanning. The victim should be trans-
despite a 6% reduction in energy cost. On the other hand, ported to more definitive care after cooling, but cooling should
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3 days consumption of beetroot juice or a placebo before 60 continue while transporting. Prevention involves proper accli-
minutes of cycling in a hot environment (91°F, 49% RH) mation to heat, understanding the thermal environment, ap-
showed effects on core temperature and energy cost did not preciating work/rest cycles, proper hydration during activity,
differ between the two conditions. Current evidence does and considering DSs that may influence thermoregulation.
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not support the use of beetroot to assist in thermoregulation. Proper attention to these factors should considerably reduce
the incidence of EHS.
Other DSs including glutamine, quercetin, and curcumin have
been examined for effects on gastrointestinal permeability Disclaimer
and core temperature during exercise in the heat. However, The views expressed in this presentation are those of the au-
more research is needed because for each DS tested there is thors and do not necessarily reflect the official policy of the
only one investigation and these were conducted under very Department of Defense, Department of the Army, US Army
specific conditions (e.g., dosages, temperature, exercise inten- Medical Department or the US government. The use of trade-
sity). A single, acute ingestion of 0.9g/kg body weight of the mark names does not imply endorsement by the US Army but is
amino acid glutamine was found to reduced gastrointestinal intended only to assist in the identification of a specific product.
permeability and plasma endotoxins during 60 minutes of
treadmill running (70% VO max) in the heat (86°F and 12– References
2
20% RH). Two g/day of quercetin (a DS promoted for its 1. Climate change impacts in the United States: the third national cli-
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antioxidant and anti-inflammatory effects in cell cultures and mate assessment https://doi.org/10.7930/J0Z31WJ2. Accessed 30
animal models) consumed each day during a 7-day exercising January 2019.
TABLE 4 Work/Rest Ratios and Fluid Replacement Guidelines for Hot Weather Training 82
Easy Work Moderate Work Hard Work
Work/Rest Water Intake Work/Rest Water Intake Work/Rest Water Intake
Heat Level WBGT (°F) (min) (qt/h) (min) (qt/h) (min) (qt/h)
1 78–82 No limit 0.50 No Limit 0.75 40/20 0.75
2 82–85 No limit 0.50 50/10 0.75 30/30 1.00
3 85–88 No limit 0.75 40/20 0.75 30/30 1.00
4 88–90 No limit 0.75 30/30 0.75 20/40 1.00
5 >90 50/10 1.00 20/40 1.00 10/50 1.00
WBGT, wet blub globe temperature.
Easy work examples: weapons maintenance, walking 2.5 miles/h with ≤30 lb, drill and ceremony, manual of arms, marksmanship training.
Moderate work examples: walking 3.5 miles/h with ≤40 lb, calisthenics, low/high crawl, defensive position construction, field assaults, patrolling.
Hard work examples: walking 3.5 miles/h with >40 lb load, walking in loose sand at 2.5 miles/h with load.

114 | JSOM Volume 19, Edition 2 / Summer 2019