Hydration and Physical Activity


Robinson TA, Hawley JA, Palmer GS, Wilson GR, Gray DA, Noakes TD, Dennis SC.  Water ingestion does not improve 1-h cycling performance in moderate ambient temperatures, Eur J Appl Physiol 1995; 71: 153-60.

PubMed ID: 7588683
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 examine whether attempts to replace the large fluid losses during intense exercise might improve performance in ambient temperatures of 20C. 

Inclusion Criteria:

endurance-trained, male cyclist; regularly rode >90 min/d, 4-6 d/wk; no others mentioned.

Exclusion Criteria:

none mentioned.

Description of Study Protocol:


 not mentioned.


 randomized crossover, 2 conditions.

Blinding used (if applicable)

 not mentioned.

Intervention (if applicable)

 2 conditions:

beverage: instructed to drink 629±22 ml water at start of warm-up, and the rest in 5 equal aliquots at 0, 10, 20, 30, 40 min during 60 min performance ride. 

no beverage.

Statistical Analysis

 2-way ANOVA for repeated measures; Scheffe post-hoc test; paired Student's t-test; sig level of P<0.05.

Data Collection Summary:

Timing of Measurements

 Prior to test sessions:

VO2 max determined; fluid losses and sweat rate calculated during 1h cycle in environmental chamber (20C, 60%RH).

Test sessions:  3 h after standardized breakfast, 350 ml water consumed2 h prior to testing; emptied bladder, body mass recorded; cannula inserted for blood sampling pre- and during (5, 20, 40 min), and after exercise.  Gastric contents aspirated after exercise. 

During 60 min performance ride, subjects rode their own cycles in envronmental chamber (20C, 60%RH), resistance of a 65 kg cyclist (power calibration conducted based on 300W).


Dependent Variables

  • cycling speed, distance, power output (monitored and calculated continuously)
  • HR
  • Rectal and skin temp (10 min intervals)
  • RPE
  • Gastric contents
  • Hct, Hgb (Cyanomethemoglobin method)
  • Pvol (via Hgb, hct)
  • serum Na, K, Osm (electrode; freezing point depression)
  • PLasma ADH, angiotensin II (radio-immunoassays)

Independent Variables

 beverage or no beverage during exercise. 

Control Variables

 Beverage vol and ingestion rate; temp/RH during exercise; all subjects euhydrated at start of testing.

Description of Actual Data Sample:


Initial N: N=8 M, endurance-trained cyclists.

Attrition (final N): N=8M

Age: see table below

Ethnicity: not mentioned

Other relevant demographics: none mentioned.

Anthropometrics (e.g., were groups same or different on important measures)

Age (yr) 25.3±1.4
Ht (m) 1.82±0.02
Wt (kg) 78.2±2.4
VO2peak (l/min) 5.17±0.31
PPO (W) 433±27
HR (bpm) 183±3


lab, Bioenergetics of Exercise Research Unit of the Medical Research Council and Univ of Cape Town Medical Observatory, South Africa.


Summary of Results:



No beverage


Statistical Significance of Group Difference

 Volume ingested (l)




 Residual gastric vol (l)




 Vol urinated (l)




 Volume retained (l)    1.02±0.12  
 Loss of bodt mass (kg/h) 1.78±0.15  0.73±0.12**  **P<0.0001 
 Sweat rate (l/h)  1.78±0.15 1.74±0.10  NS 


Other Findings

 All subjects euhydrated before start of exercise.  No sig differences in RPE, temperature, change in Pvol, serum K, ADH, Angiotensin II between 2 conditions. 

During beverage trial, ratings of abdominal fullness rose, and were consistently higher than no-beverage conditions (no P given).   Serum Na decreased sig (P<0.005) in beverage trial (from 140.3±0.6 to 138.6±0.5) after 20 min, and remained 2-3 matom/l lower than the no-beverage trial until the end of the ride.  Serum Osm decreased from initial to final sig (P<0.054) vs no-beverage trial, from 294±1.7 to 290±1.9 mosm/l. 

Distance covered and exercise intensity (respectively) in the 1-h ride in the beverage condition (42.32±0.58 km; 293±2.6 W) was sig decreased (P<0.05) vs the no-beverage condition (43.05±0.68 km; 303±2.7 W). 

Author Conclusion:

Drinking fluid to replace 100% of sweat losses during exercise at high intensity and short duration may not be advisable or practical in moderate ambient temperatures. 

Maximal retention of about 1.0l of ingested fluid had no measurable physiological benefit, and produced an uncomfortable stomach fullness and a decrease in performence. 

Funding Source:
University/Hospital: University of Cape Town (South Africa)
Reviewer Comments:
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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  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? ???
3. Were study groups comparable? N/A
  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? N/A
  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? N/A
  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? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  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? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) N/A
  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? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  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? N/A
  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? No
  10.2. Was the study free from apparent conflict of interest? Yes