Initial hydration status, fluid balance, and psychological affect during recreational exercise in adults

Journal Title (Medline/Pubmed accepted abbreviation): Nutrition.
Year: 2011
Volume: 29
Page numbers: 897-904
doi (if applicable):

Summary of Background and Research Design

Hypothesis:The authors did not state a specific hypothesis, but stated that the two main purposes of the study were to: 1) characterize the initial hydration status of subjects prior to exercise and to describe the subjects’ subsequent exercise session and fluid balance data; 2) examine psychological responses from before to after exercise for hypohydrated vs. euhydrated subjects.

Subjects:52 physically-active fitness center members (31 male, 21 female) aged 18-55 years. Subjects were healthy nonsmokers who participated in gymnasium-based exercise at least once per week. They were not elite athletes and did not participate in prior exercise on the day of testing.

Experimental design:Observational

Treatments:No treatments were assigned.

Protocol:This was a field study in which the subjects were recruited at their personal gym at the time they wished to exercise. Immediately before the exercise session, body mass, responses to a questionnaire (Subjective Exercise Experience Scale) and a urine sample were collected. Subjects were also fitted with a heart rate monitor. Osmolality was assessed from the baseline urine sample as a marker of pre-exercise hydration status. The exercise session was unsupervised and all aspects of the workout (exercise mode, duration, and intensity) were chosen by the subject. Fluid consumption during exercise was monitored and all urine passed during exercise was collected. Body mass, questionnaire ratings and urine samples were obtained again at the end of the exercise session.

Summary of research findings:
  • Pre-exercise urine osmolality was >900 mOsm/kg in 37% of participants.
  • Fluid intake during exercise was nearly 400 mL, while sweat loss estimated at nearly 800 mL, thus subjects compensated for about 50% of the fluid loss
  • Body mass decreased by 0.62% over the course of the workout.
  • Those subjects who began exercise in a hypohydrated state reported more negative changes in psychological affect compared with those subjects who were euhydrated.

Interpretation of findings/Key practice applications:

The observation that subjects did not fully compensate for sweat losses via drinking is consistent with many other findings in the literature. It also seems reasonable that subjects already less hydrated would experience lower scores on the exercise experience questionnaire (i.e., poorer quality workout). One advantage of this study is that the subjects were allowed to exercise as they normally do, which enhances the applicability of this information to real workouts that people do in the gym. However, the lack of control of either the workout or type of beverages consumed during the workout make it difficult to draw further conclusions. For example, it is not known if there could have been differences in psychological affect between hypohydrated subjects who consumed water versus a sports drink during the exercise. The subjects’ self choice of the exercise program also allowed for considerable inter-individual variability. However, it was interesting in that even with that increased variability, a significant difference in psychological affect was still reported between hypo- and euhydration. It is possible that the differences would have been greater still with a more standardized exercise session. It is also not clear if these results would have been the same in a group of more highly trained athletes who may be better able to cope with the effects of hypohydration during a particular exercise session.
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