Logan, H. M., Heigenhauser, G. J., Jones, G. L., & Spriet, L. L. (2010). The effects of hypohydration on exercise skeletal muscle metabolism in males. Presentation 861 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

This study investigated the metabolic responses to 120 minutes of cycling as male cyclists (N = 9) became progressively hypohydrated or maintained body mass by replacing sweat losses. Ss cycled at ~ 67 % VO2peak (23ºC, 33% RH) with blood samples taken at rest and every 20 minutes and muscle biopsies taken at 0, 40, 80, and 120 minutes.

Ss were hydrated prior to each. Ss lost 0.8% body mass after 40 minutes, 1.8% after 80 minutes, and 2.7% after 120 minutes of cycling in the hypohydrated trial. Mean respiratory exchange ratio over 120 minutes was the same for both trials and there was no difference from 0-40, 40-80, or 80-120 minutes between trials. Blood lactate was significantly higher in the hypohydrated trial from 20 minutes onward. Blood glucose and plasma free-fatty acids were not significantly different between trials. Muscle creatine and adenosine tri-phosphate significantly changed in both trials with no significant trial effect. There was no significant difference in muscle glycogen use between trials. Muscle lactate was significantly higher at 120 minutes in the hypohydrated trial.

Implication. In the final 40 minutes of the two-hour cycle in a hypohydrated condition, Ss were between 1.8 and 2.7% hypohydrated. Whole body carbohydrate oxidation and skeletal muscle glycogen use were not significantly affected by mild hypohydration.

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