Hydration

HYD: Before Continuous Endurance Exercise (2007)

• Assessment
  What fluid and electrolytes are needed before continuous endurance physical activity/exercise of 1-4 hours in duration in adults (19 years or older) to maintain hydration?

  • Conclusion

    Limited research suggests that consuming ~10ml/kg of a high Na⁺ containing beverage (~164mEq Na⁺/L) prior to physical activity that is 1-4 hours in duration may enhance maintenance of core body temperature in moderately to highly trained males (age 23-46 years).  Based on two studies, high Na⁺ beverages do not maintain plasma osmolality.  Hyperhydration with water may significantly increase total body water (TBW) thereby lowering plasma osmolality. Limited research is available to evaluate the effectiveness of K⁺ in beverages consumed before exercise, relevant to hydration maintenance. Care must be taken when applying these conclusions beyond the limited populations studied. Research is needed to determine fluid and electrolyte needs in:

    • women
    • pregnant and/or lactating women
    • athletes older than 46 years.

    The comparison between carbohydrate-electrolyte solutions (CES) and non-CES beverages effect on performance was not evaluated in this question. Further research is needed to evaluate optimal fluid and electrolyte intake prior to physical activity/exercise that is 1-4 hours in duration in adults. 

    * See Conversion Table for information on converting mmol to mEq and mg and % CHO to grams.

     

     

  • Grade: III
    • Grade I means there is Good/Strong evidence supporting the statement;
    • Grade II is Fair;
    • Grade III is Limited/Weak;
    • Grade IV is Expert Opinion Only;
    • Grade V is Not Assignable.
    • High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
    • Moderate (B) means we are moderately confident in the effect estimate;
    • Low (C) means our confidence in the effect estimate is limited;
    • Very Low (D) means we have very little confidence in the effect estimate.
    • Ungraded means a grade is not assignable.
  • Evidence Summary: What fluid and electrolytes are needed before continuous endurance physical activity/exercise of 1-4 hours in duration in adults (19 years or older) to maintain hydration?
    • Detail
    • Quality Rating Summary
      For a summary of the Quality Rating results, click here.
    • Worksheets
      • Greenleaf JE, Jackson R, Geelen G, Keil LC, Hinghofer-Szalkay H, Whittam JH. Plasma Volume Expansion with Oral Fluids in Hypohydrated Mean at Rest and During Exercise.  Aviation, Space, and Environmental Medicine, 1998 69(9):837-844.
      • Latzka WA, Sawka MN, Montain SJ, Skrinar GS, Fielding RA, Matott RP, Pandolf KB. Hyperhydration: thermoregulatory effects during compensable exercise-heat stress. Journal of Applied Physiology, 83(3):860-866, 1997.
      • Sims ST, vanVliet L, Cotter JD Rehrer NJ.  Sodium Loading Aids Fluid Balance and Reduces Physiological Strain of Trained Men Exercising in the Heat.  Med Sci Sports Exerc, 2007 Jan;39(1):123-30.
  • Search Plan and Results: HYD: Fluid/Electrolyte Needs Before Physical Activity/Exercise 2007