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Thermoregulatory responses to constant versus variable-intensity exercise in the heat.

Abstract

PURPOSE

To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 m x s(-1) airflow).

METHODS

In a random order, seven endurance-trained, heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials.

RESULTS

Net metabolic heat production was not different between trials (394 +/- 12 vs 408+/- 11 W x m(-2) for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W x m(-2)), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats x min(-1)) were all higher for VAR than for CON (P < 0.05). During VAR, averaged forearm skin blood flow (S(K)BF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L x h(-1)) and dehydration (2.8 +/- 0.1% vs 2.5 +/- 0.2%) were higher than during CON (P < 0.05). Final blood lactate during VAR was higher than during CON (3.5+/- 0.4 vs 2.1 +/- 0.3 mmol x L(-1); P < 0.05).

CONCLUSION

Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovascular (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimize physiological stress.

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  • Authors+Show Affiliations

    ,

    University of Castilla-La Mancha, Exercise Physiology Laboratory at Toledo, Spain. Ricardo.Mora@uclm.es

    ,

    Source

    MeSH

    Adult
    Bicycling
    Body Temperature Regulation
    Dehydration
    Exercise
    Hot Temperature
    Humans
    Male
    Monitoring, Physiologic
    Physical Exertion
    Skin
    Young Adult

    Pub Type(s)

    Journal Article

    Language

    eng

    PubMed ID

    18845968

    Citation

    Mora-Rodriguez, Ricardo, et al. "Thermoregulatory Responses to Constant Versus Variable-intensity Exercise in the Heat." Medicine and Science in Sports and Exercise, vol. 40, no. 11, 2008, pp. 1945-52.
    Mora-Rodriguez R, Del Coso J, Estevez E. Thermoregulatory responses to constant versus variable-intensity exercise in the heat. Med Sci Sports Exerc. 2008;40(11):1945-52.
    Mora-Rodriguez, R., Del Coso, J., & Estevez, E. (2008). Thermoregulatory responses to constant versus variable-intensity exercise in the heat. Medicine and Science in Sports and Exercise, 40(11), pp. 1945-52. doi:10.1249/MSS.0b013e31817f9843.
    Mora-Rodriguez R, Del Coso J, Estevez E. Thermoregulatory Responses to Constant Versus Variable-intensity Exercise in the Heat. Med Sci Sports Exerc. 2008;40(11):1945-52. PubMed PMID: 18845968.
    * Article titles in AMA citation format should be in sentence-case
    TY - JOUR T1 - Thermoregulatory responses to constant versus variable-intensity exercise in the heat. AU - Mora-Rodriguez,Ricardo, AU - Del Coso,Juan, AU - Estevez,Emma, PY - 2008/10/11/pubmed PY - 2009/7/7/medline PY - 2008/10/11/entrez SP - 1945 EP - 52 JF - Medicine and science in sports and exercise JO - Med Sci Sports Exerc VL - 40 IS - 11 N2 - PURPOSE: To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 m x s(-1) airflow). METHODS: In a random order, seven endurance-trained, heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials. RESULTS: Net metabolic heat production was not different between trials (394 +/- 12 vs 408+/- 11 W x m(-2) for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W x m(-2)), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats x min(-1)) were all higher for VAR than for CON (P < 0.05). During VAR, averaged forearm skin blood flow (S(K)BF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L x h(-1)) and dehydration (2.8 +/- 0.1% vs 2.5 +/- 0.2%) were higher than during CON (P < 0.05). Final blood lactate during VAR was higher than during CON (3.5+/- 0.4 vs 2.1 +/- 0.3 mmol x L(-1); P < 0.05). CONCLUSION: Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovascular (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimize physiological stress. SN - 1530-0315 UR - https://www.unboundmedicine.com/medline/citation/18845968/Thermoregulatory_responses_to_constant_versus_variable_intensity_exercise_in_the_heat_ L2 - http://Insights.ovid.com/pubmed?pmid=18845968 DB - PRIME DP - Unbound Medicine ER -