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Caffeine during exercise in the heat: thermoregulation and fluid-electrolyte balance.
Med Sci Sports Exerc. 2009 Jan; 41(1):164-73.MS

Abstract

PURPOSE

To investigate the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat.

METHODS

Seven endurance-trained (.VO2max = 61 +/- 8 mL.kg.min) heat-acclimated cyclists pedaled for 120 min at 63% .VO2max in a hot-dry environment (36 degrees C; 29% humidity) on six occasions: 1) without rehydration (NF); 2) rehydrating 97% of sweat losses with water (WAT); 3) rehydrating the same volume with a 6% carbohydrate-electrolytes solution (CES); or combining these treatments with the ingestion of 6 mg caffeine.kg (-1) body weight 45 min before exercise, that is, 4) C(AFF) + NF; 5) C(AFF) + WAT; and 6) C(AFF) + CES.

RESULTS

Without fluid replacement (NF and C(AFF) + NF), final rectal temperature (T(REC)) reached 39.4 +/- 0.1 degrees C, whereas it remained at 38.7 +/- 0.1 degrees C during WAT (CES and C(AFF)+ WAT; (P < 0.05). Caffeine did not alter heat production, forearm skin blood flow, or sweat rate. However, C(AFF) + CES tended to elevate T(REC) above CES alone (38.9 +/- 0.1 degrees C vs 38.6 +/- 0.1 degrees C; P = 0.07). Caffeine ingestion increased sweat losses of sodium, chloride, and potassium (approximately 14%; P < 0.05) and enlarged urine flow (28%; P < 0.05).

CONCLUSION

Caffeine ingested alone or in combination with water or a sports drink was not thermogenic or impaired heat dissipation. However, C(AFF) + CES tended to have a higher T(REC) than CES alone. Caffeine increased urine flow and sweat electrolyte excretion, but these effects are not enough to affect dehydration or blood electrolyte levels when exercising for 120 min in a hot environment.

Authors+Show Affiliations

Exercise Physiology Laboratory, Universidad de Castilla-La Mancha, Toledo, SPAIN.No affiliation info availableNo affiliation info available

Pub Type(s)

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

Language

eng

PubMed ID

19092693

Citation

Del Coso, Juan, et al. "Caffeine During Exercise in the Heat: Thermoregulation and Fluid-electrolyte Balance." Medicine and Science in Sports and Exercise, vol. 41, no. 1, 2009, pp. 164-73.
Del Coso J, Estevez E, Mora-Rodriguez R. Caffeine during exercise in the heat: thermoregulation and fluid-electrolyte balance. Med Sci Sports Exerc. 2009;41(1):164-73.
Del Coso, J., Estevez, E., & Mora-Rodriguez, R. (2009). Caffeine during exercise in the heat: thermoregulation and fluid-electrolyte balance. Medicine and Science in Sports and Exercise, 41(1), 164-73. https://doi.org/10.1249/MSS.0b013e318184f45e
Del Coso J, Estevez E, Mora-Rodriguez R. Caffeine During Exercise in the Heat: Thermoregulation and Fluid-electrolyte Balance. Med Sci Sports Exerc. 2009;41(1):164-73. PubMed PMID: 19092693.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Caffeine during exercise in the heat: thermoregulation and fluid-electrolyte balance. AU - Del Coso,Juan, AU - Estevez,Emma, AU - Mora-Rodriguez,Ricardo, PY - 2008/12/19/entrez PY - 2008/12/19/pubmed PY - 2009/5/14/medline SP - 164 EP - 73 JF - Medicine and science in sports and exercise JO - Med Sci Sports Exerc VL - 41 IS - 1 N2 - PURPOSE: To investigate the effects of caffeine ingestion on thermoregulation and fluid-electrolyte losses during prolonged exercise in the heat. METHODS: Seven endurance-trained (.VO2max = 61 +/- 8 mL.kg.min) heat-acclimated cyclists pedaled for 120 min at 63% .VO2max in a hot-dry environment (36 degrees C; 29% humidity) on six occasions: 1) without rehydration (NF); 2) rehydrating 97% of sweat losses with water (WAT); 3) rehydrating the same volume with a 6% carbohydrate-electrolytes solution (CES); or combining these treatments with the ingestion of 6 mg caffeine.kg (-1) body weight 45 min before exercise, that is, 4) C(AFF) + NF; 5) C(AFF) + WAT; and 6) C(AFF) + CES. RESULTS: Without fluid replacement (NF and C(AFF) + NF), final rectal temperature (T(REC)) reached 39.4 +/- 0.1 degrees C, whereas it remained at 38.7 +/- 0.1 degrees C during WAT (CES and C(AFF)+ WAT; (P < 0.05). Caffeine did not alter heat production, forearm skin blood flow, or sweat rate. However, C(AFF) + CES tended to elevate T(REC) above CES alone (38.9 +/- 0.1 degrees C vs 38.6 +/- 0.1 degrees C; P = 0.07). Caffeine ingestion increased sweat losses of sodium, chloride, and potassium (approximately 14%; P < 0.05) and enlarged urine flow (28%; P < 0.05). CONCLUSION: Caffeine ingested alone or in combination with water or a sports drink was not thermogenic or impaired heat dissipation. However, C(AFF) + CES tended to have a higher T(REC) than CES alone. Caffeine increased urine flow and sweat electrolyte excretion, but these effects are not enough to affect dehydration or blood electrolyte levels when exercising for 120 min in a hot environment. SN - 1530-0315 UR - https://www.unboundmedicine.com/medline/citation/19092693/Caffeine_during_exercise_in_the_heat:_thermoregulation_and_fluid_electrolyte_balance_ L2 - http://dx.doi.org/10.1249/MSS.0b013e318184f45e DB - PRIME DP - Unbound Medicine ER -