Dietary nitrate reduces the O2 cost of desert marching but elevates the rise in core temperature.
OBJECTIVE
Dietary nitrate (NO3 (-)) supplementation reduces the O2 cost of fixed-workload tasks performed in temperate environments but has not been examined in the heat. If this effect were retained it could reduce heatstroke risk in military personnel that are deployed for desert combat.


METHODS
Nine men completed three 45 min loaded battle marches at a standard cadence (4.83 km h(-1)/1.5 % grade) while wearing full combat gear [BDU, boots, body armor (8 kg), NBC suit] and carrying a loaded rucksack (16 kg). The 1st March (FAM) commenced in a temperate environment. The 2nd and 3rd commenced in simulated dry desert conditions (41 °C/20 % RH) and required subjects to ingest the beetroot juice equivalent of 8.4 mmol NO3 (-) (BRJ) or a NO3 (-) depleted placebo (PLA) for 6 days prior. VO2, VCO2, V E, core (T re), skin (T sk), and mean body (T b) temperatures, HR, and physiological strain index (PSI) were measured continuously. Thermal sensation, generalized discomfort, and perceived exertion (RPE) were measured at 5 min intervals. Heat storage (HS) was calculated. Blood markers of gastrointestinal permeability (TNF, Il-6, HO-1) were measured before and after exercise.


RESULTS
VO2 in BRJ was lower than PLA from 1 to 12; 16 to 26; and 29 to 45 min of exercise (p < 0.05). VCO2 in BRJ was lower than PLA from 1 to 12 min (p < 0.05). V E in BRJ was lower than PLA from 1 to 20 min of exercise (p < 0.05). T re and T b in BRJ exceeded PLA from 16 to 45 min (p < 0.05). TNF, Il-6, and HO-1 were reduced in BRJ (p < 0.05) while HR, PSI, Tsk, and HS were not altered (p > 0.05). Thermal sensation, generalized discomfort, and RPE were elevated in BRJ from 40 to 45, 25 to 45, and 10 to 45 min, respectively (p < 0.01).


CONCLUSIONS
Metabolic efficiency was improved in BRJ. Paradoxically, body temperatures rose more. This was not due to gut permeability. Therefore, we speculate that based on elimination of other possibilities, blood redistribution from skin to skeletal muscle may have contributed to impaired heat exchange.
Department of Exercise Science, Norcross Graduate School 249F, High Point University, High Point, NC, 27268, USA. mkuennen@highpoint.edu.|Department of Sports and Exercise Sciences, West Texas A&M University, Canyon, TX, USA. mkuennen@highpoint.edu.
Matthew
M
Kuennen
Department of Sports and Exercise Sciences, West Texas A&M University, Canyon, TX, USA.
Lisa
L
Jansen
Department of Kinesiology, California Baptist University, Riverside, CA, USA.
Trevor
T
Gillum
Department of Sports and Exercise Sciences, West Texas A&M University, Canyon, TX, USA.
Jorge
J
Granados
Department of Sports and Exercise Sciences, West Texas A&M University, Canyon, TX, USA.
Weston
W
Castillo
General Electric Power and Water, Research Division, Boulder, CO, USA.
Ahmad
A
Nabiyar
Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, TX, USA.
Kevin
K
Christmas
D000328:Adult; D001831:Body Temperature / Q000187:drug effects*; D003889:Desert Climate / Q000009:adverse effects*; D019587:Dietary Supplements; D015444:Exercise; D018883:Heat Stroke / Q000517:prevention & control*; D006801:Humans; D008297:Male; D008889:Military Personnel; D009566:Nitrates / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D010100:Oxygen / Q000378:metabolism*
D009566:Nitrates; D010100:Oxygen
Dietary nitrate; Exertional heat stroke; Hyperthermia; Military work; Nutritional countermeasure