Hydration and Physical Activity

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the hydration capabilities of three commercially-available sports drinks and water using deuterium dilution under conditions of rest and exercise. 

Inclusion Criteria:

between 18-35 yrs of age; healthy; informed consent.

Exclusion Criteria:

none mentioned

Description of Study Protocol:

Recruitment through newspaper, radio, TV ads; word-of mouth.


Design 2 separate studies conducted (rest and exercise); randomized crossover studies (4 conditions each).


Blinding used (if applicable) not mentioned.


Intervention (if applicable)

 4 different beverage conditions administered during rest and exercise (2 separate studies);  given 300 ml of test beverage (temp: 6C), along with capsules containing 99% 2H2O to acheive a dose of 0.05 g/kg body weight:


5%CES (glucose): 89kj (21 kcal)/100 ml; 1 mmol/100 ml Na; 0.6 mmol/100 ml K; 0.1 mmol/100 ml Mg

6.7%CES (glucose, fructose, sucrose, maltodextrin): 121 kJ (29 kcal)/100 ml; 1.8 mmol/100 ml Na; 0.3 mmol/100 ml

8% CES (maltodextrin, sucrose): 134 kj (32 kcal)/100 ml; 1 mmol/100ml Na; <1.0 mmol/100 ml K

Statistical Analysis

 Mathematical model to describe kinestics of hydration:

t1: calc time at which absoprtion rate of drink was maximum;

t2: when rate of absoprtion returned to 0;

t 1/2: when 50% was absorbed;

max rate of absorption;

%drink absorbed when rate was maximum.

ANOVA to compare rest and exercise separately.

Data Collection Summary:

Timing of Measurements

 4 hr fast prior to testing; body weight recorded; height measured

Saliva sample  to determine basal levels of 2H; then comsumes 300 ml test beverage (temp 6C) with capsules of 99% 2H2O equivalent to does of 0.05 g/kg body weight; drink and 2H2O consumed as quickly as possible.  Allowed to chew gum to enhance salivation.

Rest trial: saliva samples provided at 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 min after ingestion, seated position.

Exercise trial: completed PAR-Q prior to testing; Maximum HR calculated (220-age); 55% max HR calculated (~35% VO2max).  HR monitor fitted, waled on treadmill at high grade and speed to reach 55% HR max as quickly as possible (3-5 min);  grade and speed lowered and monitored while subjects were dosed with drink and 2H2O.  Walked on treadmill for 1h, maintaining HR at 55% HR max; saliva samples collected at 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 min after ingestion

Dependent Variables

  • Deuterium in saliva (isotope ratio mass spectometry)

Independent Variables

 Drink conditions (see above description)

Control Variables

 Drink temp (6C); work load (55% HR max); drink volume (300 ml); exercise time (60 min); saliva sample collection

Description of Actual Data Sample:


Initial N:

Rest group: N=21 (M, F not reported for initial)

Exercise group: N=19 (M, F not reported for initial)

Attrition (final N):

Rest group: N=18 (10 F, 8 M)

Exercise group: N=16 (6 F, 10 M)

Age: see table below

Ethnicity: not mentioned

Other relevant demographics: non mentioned.

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

Subject Characteristics
  Rest (N=18) Exercise (N=16)
Age (yr) 26.1±5.2 26.4±4.6
Ht (cm) 169.2±11.2 175.7±6.9
Wt (kg) 72.8±14.1 73.7±10.9

Location: Lab, Royal Childern's Hospital, Brisbane, Australia


Summary of Results:



Rest Group        (water; 5% CES; 6.7%CES, 8% CES)

Significance between Conditions at Rest

Exercise group (water; 5% CES; 6.7%CES; 8%CES)

Significance between conditions during exercise

 t1 (min)

 19.3±0.8; 14.6±0.9*; 15.6±0.8*; 14.3±0.7*

*Sig different from water (P not given)

 19.8±1.3; 14.2±1.2*; 14.3±1.2*; 13.4±1.0*

 *Sig different from water (P not given)

 t2 (min)

 26.8±2.1;26.0±1.6; 23.8±1.4; 28.9±2.2


 41.2±5.2; 41.1±5.8; 40.7±6.3; 49.0±9.6


 t 1/2 (min)

 15.9±0.7;  13.7±0.5*; 13.4±0.4*; 14.4±0.7

*Sig different from water (P not given)

 20.3±1.6; 17.7±1.8; 17.7±1.6; 19.7±2.6


Max absorption rate (g/min)  0.080±0.004; 0.082±0.005; 0.088±0.004; 0.076±0.006 NS  0.056±0.004; 0.057±0.005; 0.064±0.008; 0.055±0.005  NS
Amt drink absorbed at t1 (%)  76.4±4.0; 60.7±5.4; 69.6±4.9; 54.1±4.4* *Sig differeant from water (P not given)  53.8±4.3; 39.2±4.3; 47.3±6.6; 38.6±5.4  NS


Other Findings

Rest group:  more water was absorbed than the CES, though the water took longer to reach its maximum absoprtion rate.

Exercise group: no sig differences for parameters invesitgated during exercise (those parameters not mentioned in methods).  Maximum rate of absorption was attained more quickly with CES vs water. 

Cannont compare Exercise and Rest groups due to between-subjects design between rest and exercise (vs within-subjects design).

Author Conclusion:

CES do not enhance the absoprtion of water either at rest or during exercise at 55%HRmax, when total absoprtion time is taken into account. 

Funding Source:
University/Hospital: Leeds University
Reviewer Comments:

no P-values given; poor design (cannot compare rest and exercise groups directly because same subjects not used for the 2 conditions); exercise intensity/workload (55%HRmax/35%VO2max) may not have been enough to see effect; hydration status of subjects not described.

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? ???
  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? ???
  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? 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? ???
  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? ???
  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? N/A
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? ???
  7.2. Were nutrition measures appropriate to question and outcomes of concern? ???
  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? No
  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? No
  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)? No
  8.6. Was clinical significance as well as statistical significance reported? No
  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