Hydration and Physical Activity


 Nielsen B, Sjogaard G, Ugelvig J, Knudsen B, Dohlmann B.  Fluid balance in exercise dehydration and rehydration with different glucose-electrolyte drinks.  Eur J Applied Physiology 1986; 55: 318-25. 

Study Design:
Randomized Crossover Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To study the time-course of the restoration of water and electrolyte balance after exercise dehydration. 

1 of 4 different rehydration solutions given during each 2h recovery period, afterwhich physical performance was measured and compared with performance capactiy before exercise dehydration.

Inclusion Criteria:
informed consent; no others mentioned
Exclusion Criteria:
none mentioned
Description of Study Protocol:

Recruitment not mentioned


Design double-blind, randomized crossover trial


Blinding used (if applicable) double-blind randomized drink administration


Intervention (if applicable) lemon-flavored drink administration (2700 ml) during 2h recovery period:

  C-Control K Na Sucrose-S (commercially avail sports drink)
Glucose (mmol) 375 375 375 750
Sucrose (mmol) 0 0 0 345
Na (mmol) 116 116 346 35
K (mmol) 0 138 0 17
Osm (mOsm/kg) 229 323 387 465

Statistical Analysis 2-way ANOVA (Friedman's test) and paired t-test; sig level p<0.05


Data Collection Summary:

Timing of Measurements

 Pre-trial: consume 1L Water or milk evening before test session; day of testing, empty bladder; catherter inserted for blood sampling; needle biopsy taken from vastruc lateralis muscle and 1st blood sample taken.

Physical work capactiy test: submaximal and supramaximal cycle tests, load set at 50% load (which produced VO2max), worked for 6 min; load increased to 105% of VO2max and worked until exhaustion.  Body weight taken before dehydration protocol.

Dehydration procedure: cycle for 2h at 50% VO2max.  second blood sample taken during last min of exercise and 2nd biopsy taken immediately after exercise; body weight taken, urine sample collected (if possible)

Rehydration/Recovery: placed on bed. covered with blanket for 2 h; 3rd blood sample taken after 30 min (immediately before fluid intake); drank 300 ml of solution, and again q. 15 min until 9 drinks (2700 ml) had been consumed.  Blood samples taken at 10, 30, 40, 60, 90, 135 min during recovery.  Urine collected when possible, every hour, and at least at end of recovery.  3rd muscle biopsy taken w/ last blood sample, 15 min after last 300 ml had been consumed.

Physical work capacity test: repeated procedure described above.

Dependent Variables

  • body weight loss (Krogh balance)
  • PLasma vol (hgb and hct)
  • Plasma [Electrolyte] (flame emission spectrophotometer)
  • Blood glucose (Boehringer hexokinase reaction)
  • Muscle electrolyte, glycogen, glu, lactate (needle biopsies) 
  • Work performed
  • VO2max (Douglas bag method)
  • Heart rate (ECG)
  • Water and electrolyte loss
  • Urine electrolyte (see plasma e), Osm (freezing point osmometer)

Independent Variables

 Drink administered during recovery period (C, K, Na, S)

Control Variables

 Vol drink during recovery period (2700 ml);

temp controlled (30C) during 2h exercise at 50% VO2 max

Description of Actual Data Sample:


Initial N: 6 M

Attrition (final N): 6M

Age: 24 years (SEM not reported, range 18-32)

Ethnicity: not mentioned

Other relevant demographics: physically active, though not competitive


Wt: 80.6 kg (range 76-85.7); Ht: 185 cm (range, 180-195); VO2max: 4.63 l/min (range, 4.1-5.25)

Location: lab, Univerisity of Copenhagen, Denmark


Summary of Results:



Before dehydration After dehydration

After 2h rehydration:








Statistical Significance of Group Difference


18.6±0.96 16.8±1.37



 17.7±1.40  17.7±1.07

 *differed sig from C, K, S drinks, p not reported


29.8±1.39 29.2±1.60



 30.3±1.81  30.4±1.89

 *differed sig from C, K, S drinks, p not reported


48.4±2.34 46.0±2.59



 48.0±2.89  48.1±2.65


Total water loss in urine (mL) n/a n/a 555±433 224±88 445±271* 318±177 *sig different from Na, p not reported
Total Na loss in urine (mmol) n/a n/a 22±10 34±9 51±32** 32±13 **sig different from C, p not reported
Total K loss in urine (mmol) n/a n/a 28±17 26±10 56±32*** 30±1 ***sig different from C, Na, S, p not reported


Other Findings

 Mean wt loss 2.530 kg, 3.1% body weight (2.050-3.650 kg, 2.3-4.8%) during dehydration period.

Plasma vol:  decreased by 16% (9-23) after prolonged exercise; started to increase towards normal (by 7%, range 1-10%) in the 30 min interval between finishing exercise and starting to drink; after 30-45 min rehydration, was restored w/C, Na, and S drinks. 

 Plasma variables: Na, K, protein, blood glucose changes similar in 4 conditions; sig increased K during rehydration with K drink (5.4, 5.0-6.3 mmol/L) after 90 min (P not reported).  Sig incr glu after S drink (10, 9-11 mmol/L) after 60 min (p not reported).  Protein after Na drink sig lower than other 3 from 90 min (p not reported).

Muscle biopsies:  Sig incr in muscle glycogen w/Na drink (p not reported).  NS differences found between drinks or between resting and rehydration values. 

Work:  Work performed after rehydration sig lower than before dehydration (p not reported), though NS differences between 4 solutions.  NS differences between drinks in HR. 

Author Conclusion:

After exercise dehydration, plasma vol returned towards normal, even without fluid intake, due to release of water accumulated in muscles during exercise.

Largest increase in plasma volume found after a Na-rich drink, while K-rich drink produced the smallest and slowest increase in plasma volume.

Na-rich drink favored filling of the extracellular water compartment, whereas K-rich drink and Sucrose-rich drink favored intracellular water compartment.

 HR during submax test sig higher when test was performed after exercise dehydration and subsequent rest and rehydration than in test before dehydration.  This elevation was found even though plasma vol was higher than normal after rehydration period.

Work capactiy during supramax test was reduced by 20% after dehydration, even after 2h recovery.  This reduction was similar w/ and independent of the drink consumption, which may be related to decreases in muscle glycogen stores.

Funding Source:
University/Hospital: University of Coppenhagen (Denmark)
Reviewer Comments:
* See figures for time-course results.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? ???
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? ???
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes