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Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect.

Abstract

INTRODUCTION

Authorities advise individuals to refrain from caffeine intake before or during exercise, especially when performed in the heat, due to potential fluid-electrolyte imbalances that exaggerate physiological strain. Yet, military personnel are often deployed to hot environments and must perform under sleep-deprived conditions where caffeine would be an ideal intervention strategy to enhance physical and cognitive performance.

PURPOSE

To assess the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT).

METHODS

Subjects were 59 active, college-aged males (mean +/- SE 21.6 +/- 0.4 yr, 177.9 +/- 0.8 cm, 75.4 +/- 1.0 kg, 11.1 +/- 0.7% body fat) who were randomized and stratified by age, bodyweight, and body composition into three groups. All subjects equilibrated caffeine intake at 3 mg x kg(-1) x d(-1) for days 1-6. On days 7-12, they consumed a treatment dose of either 0 (G0), 3 (G3), or 6 (G6) mg x kg(-1) x d(-1). Fluid-electrolyte and physiological measures were made on day 12, 1 h after caffeine intake, during the EHT (90 min walking, 1.56 m x s(-1), 5% grade; dry bulb temperature, 37.7 +/- 0.1 degree C; relative humidity, 56.3 -1.5%).

RESULTS

There were no between-group differences (p > 0.05) in plasma, urinary, thermoregulatory, cardiovascular, and perceptual variables across time (pre- vs. post-EHT), although some of these variables increased significantly over time (p < 0.05). EHT time was significantly greater in G3 (86 +/- 2.0 min) vs. GO (75 +/- 3.3 min, p < 0.05).

DISCUSSION

Acute caffeine ingestion, in chronically consuming subjects (3 and 6 mg x kg(-1) x d(-1)) did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during EHT when compared with G0.

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  • Authors+Show Affiliations

    ,

    The University of Connecticut, Human Performance Laboratory and Department of Kinesiology, Storrs, CT, USA. mroti@wsc.ma.edu

    , , , , , ,

    Source

    MeSH

    Adult
    Analysis of Variance
    Body Temperature Regulation
    Caffeine
    Double-Blind Method
    Exercise
    Heat Stress Disorders
    Hot Temperature
    Humans
    Male
    Military Personnel
    Physical Endurance
    Water-Electrolyte Balance

    Pub Type(s)

    Journal Article
    Randomized Controlled Trial
    Research Support, Non-U.S. Gov't

    Language

    eng

    PubMed ID

    16491580

    Citation

    Roti, Melissa W., et al. "Thermoregulatory Responses to Exercise in the Heat: Chronic Caffeine Intake Has No Effect." Aviation, Space, and Environmental Medicine, vol. 77, no. 2, 2006, pp. 124-9.
    Roti MW, Casa DJ, Pumerantz AC, et al. Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect. Aviat Space Environ Med. 2006;77(2):124-9.
    Roti, M. W., Casa, D. J., Pumerantz, A. C., Watson, G., Judelson, D. A., Dias, J. C., ... Armstrong, L. E. (2006). Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect. Aviation, Space, and Environmental Medicine, 77(2), pp. 124-9.
    Roti MW, et al. Thermoregulatory Responses to Exercise in the Heat: Chronic Caffeine Intake Has No Effect. Aviat Space Environ Med. 2006;77(2):124-9. PubMed PMID: 16491580.
    * Article titles in AMA citation format should be in sentence-case
    TY - JOUR T1 - Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect. AU - Roti,Melissa W, AU - Casa,Douglas J, AU - Pumerantz,Amy C, AU - Watson,Greig, AU - Judelson,Daniel A, AU - Dias,Joao C, AU - Ruffin,Katherine, AU - Armstrong,Lawrence E, PY - 2006/2/24/pubmed PY - 2006/5/4/medline PY - 2006/2/24/entrez SP - 124 EP - 9 JF - Aviation, space, and environmental medicine JO - Aviat Space Environ Med VL - 77 IS - 2 N2 - INTRODUCTION: Authorities advise individuals to refrain from caffeine intake before or during exercise, especially when performed in the heat, due to potential fluid-electrolyte imbalances that exaggerate physiological strain. Yet, military personnel are often deployed to hot environments and must perform under sleep-deprived conditions where caffeine would be an ideal intervention strategy to enhance physical and cognitive performance. PURPOSE: To assess the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT). METHODS: Subjects were 59 active, college-aged males (mean +/- SE 21.6 +/- 0.4 yr, 177.9 +/- 0.8 cm, 75.4 +/- 1.0 kg, 11.1 +/- 0.7% body fat) who were randomized and stratified by age, bodyweight, and body composition into three groups. All subjects equilibrated caffeine intake at 3 mg x kg(-1) x d(-1) for days 1-6. On days 7-12, they consumed a treatment dose of either 0 (G0), 3 (G3), or 6 (G6) mg x kg(-1) x d(-1). Fluid-electrolyte and physiological measures were made on day 12, 1 h after caffeine intake, during the EHT (90 min walking, 1.56 m x s(-1), 5% grade; dry bulb temperature, 37.7 +/- 0.1 degree C; relative humidity, 56.3 -1.5%). RESULTS: There were no between-group differences (p > 0.05) in plasma, urinary, thermoregulatory, cardiovascular, and perceptual variables across time (pre- vs. post-EHT), although some of these variables increased significantly over time (p < 0.05). EHT time was significantly greater in G3 (86 +/- 2.0 min) vs. GO (75 +/- 3.3 min, p < 0.05). DISCUSSION: Acute caffeine ingestion, in chronically consuming subjects (3 and 6 mg x kg(-1) x d(-1)) did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during EHT when compared with G0. SN - 0095-6562 UR - https://www.unboundmedicine.com/medline/citation/16491580/Thermoregulatory_responses_to_exercise_in_the_heat:_chronic_caffeine_intake_has_no_effect_ L2 - https://www.ingentaconnect.com/openurl?genre=article&amp;issn=0095-6562&amp;volume=77&amp;issue=2&amp;spage=124&amp;aulast=Roti DB - PRIME DP - Unbound Medicine ER -