Hydration and Physical Activity

Study Design:
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Quality Rating:
Research Purpose:

To examine further effects of beverage volume and CHO provision on exercise capacity, thermoregulatory and metabolic response to exercise in a hot environment (30C).  Ingestion of either a dilute CES that replaced 150% fluid losses or a high-CHO CES that replaced 100% fluid losses was compared with no fluid ingestion.

Inclusion Criteria:

healthy, informed consent

Exclusion Criteria:

none mentioned.

Description of Study Protocol:


 not mentioned


 randomized crossover, 3 conditions (2 drink, 1 no-drink).

Blinding used (if applicable)

 none mentioned

Intervention (if applicable)

 3 conditions during exercise in the heat:
No drink

Drinks ingested q. 10 min

Dilute CES:2% CHO, 3.12±0.47 L (3.57 ml/kg to replace 150% fluid loss); 20 g/l glu; 67±1 mmol/l Na; 0.6±0.1 mmol/l K; 239±4 mOsmol/kg; 56±1 mmol/l Cl

Hi-CHO CES:15% CHO, 1.45±0.29L (1.79 ml/kg to replace 100% fluid loss); 20.0 g/l sucrose; 130 g/l glucose polymer; 64±2 mmol/l Na; 0.6±0.1 mmol/l K; 324±4 mOsmol/kg; 54±4 mmol/l Cl

Statistical Analysis

 Shapiro-Wilks test for normality of distribution; 2-way ANOVA w/repeated measures

Kruskal-Wallis test to determine timing of effect

t-test or Wilcoxon tests for post-hoc anaylsis to determine sig different trials

Sig level of P<0.05.

Data Collection Summary:

Timing of Measurements

 Prior to experimental sessions, familiarization trials to determine VO2max, power output, fluid losses

Experimental session followed overnight fast; emptied bladder, body mass taekn; rectal thermometer inserted, skin thermometers attached.

Sitting position for 30 min in 26.8±0.4C.  Hand immersed in hot (42C) water.  Cannula inserted for blood sampling, 2 resting samples collected.

enter climactic chamber and ingested bolus of 7.14 ml/kg of assigned drink (14C), or nodrink ; exercise session began (cycling 60-70 rpm to exhaustion).  Drinks during exercise q. 10 min.

Blood samples drawn q. 15 min and at exhaustion; Expired gass collected q. 15 min (for 2 min).

Body mass taken at end of exercise.


Dependent Variables

  • Glucose (glucose oxidase method)
  • lactate (Maughan method, 1982)
  • glycerol (boobis and Maughan method, 1983)
  • Hgb, Hct (cyanmethemooglobin method)
  • Serum FFA (enzymatic colorimetric method)
  • Sosm, Uosm (freezing point depression)
  • Selectrolytes, Uelectrolytes (flame photometry, potentiometric titration for Cl)
  • Pvol (dill and Costill)
  • Uvol
  • VO, VE, RER (Douglas bag method)
  • RPE
  • HR, skin and rectal temp
  • Body mass

Independent Variables

 Vol (3.57 vs 1.79 ml/kg) and concentration (2% or 15 CES) of Drink conditions, or no drink given during exercise.

Control Variables

 Climate (30.2±0.6C, 71±1%RH)

Drink amount and temp

Cadence of cylcing

Description of Actual Data Sample:


Initial N: N=6 M, healthy, physically active, but not highly trained.

Attrition (final N): N=6 M

Age: 27±6 y

Ethnicity: not mentioned

Other relevant demographics: none mentioned

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

70.6±5.0 kg; 178±2 cm; 1.87±0.06 m2 BSA; 4.07±0.37 l/min VO2 max

Location: Lab, Dept Biomedical Sciences, Unive Aberdeen Medical School, Foresterhill, Aberdeen, UK


Summary of Results:



no drink

2% CES


Statistical Significance of Group Difference

HR , mean (bpm)




*P<0.01 diff from 2%

Uvol (ml)

 30 (0-122)


52 (0-108)


 Other Findings

 Time to exhaustion sig different (P=0.01) between conditions, 2% conferring greatest benefit.

No differences between trials for VE, VO2, RER, rectal temp, skin temp, sweat rate; Serum and Urinary electrolytes; blood lactate; serum FFA; RPE.

Fat and CHO-oxidation: differences between trials due to exercise duration between trials:  highest CHO and fat ox with 2% CES overall.  In the 1st hour only, CHO oxidation highest for 15%CES (109±11g), lowest on no-drink (88±15 g) and intermediate for 2%CES (99±12 g).  All sig different from each other (P<0.05). 

Reduction in plasma vol on all trials between rest and 15 min sampling time; remained below resting at all ttimes on no-drink and 15%CES.  In 2%CES, Pvol gradually restored during exercise, and its reduction remained sig less than other 2 trials (P not given).

Post-ex Uvol sig (P<0.05) higher after 2%CES vs 15%CES and no-drink.

Blood glu sig different (P<0.05) between trials - 15%CES, sig elevated above resting throughout testing and sig higher at exhaustion vs other 2 trials; sig lower in no-drink.

Blood glycerol sig higher in (no P given) no-drink compared to the 15%CES at 15, 30 min, and exhaustion.

Author Conclusion:

Fluid replacement via large volume of dilute CES (2%) that replaced 156±49.5% fluid loss, or a smaller volume of more concentrated CES (15%) that replaced 101±36.8% fluid loss can onset delay of fatigue exercise in the heat compared to no fluid. 

The 2%CES resulted in the largest delay in fatigue onset indicating that fluid replacement in excess of losses with dilute CES is beneficial during exercise in the heat.  Large fluid volumes and dilute CES are most beneficial.


Funding Source:
Smithkline Beecham
Pharmaceutical/Dietary Supplement Company:
Reviewer Comments:

Small sample (N=6M).

There were no fluid controls used in this study (i.e. small vol water, large volume water).

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? ???
  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? 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? ???
  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.) ???
  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? 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? ???
  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? ???
  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? ???
  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)? 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? No
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