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European Journal of Applied Physiology
Published in: European Journal of Applied Physiology 12/2015

01-12-2015 | Original Article

Dietary nitrate reduces the O2 cost of desert marching but elevates the rise in core temperature

Authors: Matthew Kuennen, Lisa Jansen, Trevor Gillum, Jorge Granados, Weston Castillo, Ahmad Nabiyar, Kevin Christmas

Published in: European Journal of Applied Physiology | Issue 12/2015

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Abstract

Purpose

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).

Conclusion

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.
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Metadata
Title
Dietary nitrate reduces the O2 cost of desert marching but elevates the rise in core temperature
Authors
Matthew Kuennen
Lisa Jansen
Trevor Gillum
Jorge Granados
Weston Castillo
Ahmad Nabiyar
Kevin Christmas
Publication date
01-12-2015
Publisher
Springer Berlin Heidelberg
Published in
European Journal of Applied Physiology / Issue 12/2015
Print ISSN: 1439-6319
Electronic ISSN: 1439-6327
DOI
https://doi.org/10.1007/s00421-015-3255-0

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