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Hydration

Hydration and Physical Activity

Citation:

Millard-Stafford ML, Sparling PB, Rosskopf LB, Snow TK. Should carbohydrate concentration of a sports drink be less than 8% during exercise in the heat? Int J Sports Nutr Exerc Metab. 2005; 15 (2): 117-130.

PubMed ID: 16089271

Study Design:

Randomized crossover trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To determine if commercially available 6% sucrose-glucose and 8% fructose-glucose-maltodextrin carbohydrate-electrolyte drinks would differentially affect physiological responses, relative fluid uptake and run performance, compared to water placebo in the heat.

Inclusion Criteria:

Highly-trained male distance runners
Aged less than 40 years
Training of 110km per week for the last three months with no anticipated change in training throughout the duration of the study
Use of programmed drinking during training
Completion of a 32-kilometer training run in the month before the study.

Exclusion Criteria:

Excluded if not included above.

Description of Study Protocol:

Recruitment: Methods not specified; all were from the Georgia Tech cross-country team
Design: Randomized crossover trial
Blinding used: Double-blind.

Intervention

Subjects ran 32km while ingesting a placebo, 6% or 8% carbohydrate-electrolyte solutions
At 15km, a 250ml drink labeled with deuterium oxide was ingested
Trial was separated by 14 days
400ml consumed 15 minutes before the run and 250ml was consumed every five km.

Statistical Analysis

A two-way ANOVA with repeated measures was used to determine differences between trials
ANCOVA was utilized on run performance data to account for different heat indices on different testing days.

Data Collection Summary:

Timing of Measurements

Heart rate, ratings of perceived exertion and core temperature were measured throughout the run
Respiratory gases collected at five, 15, 21 and 27km
Blood samples were obtained before exercise, at selected intervals during exercise (not mentioned) and immediately after exercise.

Dependent Variables

Heart rate was measured using telemetry
Core temperature was measured with a telethermometer
RPE was measured with a Borg scale
Respiratory gases were collected using a Douglas bag
Blood samples were analyzed for serum glucose, electrolytes, hemoglobin, lactate, hematocrit.

Independent Variables

Placebo, 6% or 8% carbohydrate-electrolyte solutions.

Control Variables

Runners were asked to follow a standard-normal mixed diet (55% CHO, 15% protein, 30% fat) and to duplicate training for three days prior to testing.

Description of Actual Data Sample:

Initial N: 10 men
Attrition (final N): 10
Age: Mean, 23.7±3.6 years
Ethnicity: Not mentioned
Location: Georgia.

Summary of Results:

Other Findings

Environmental conditions were not similar on all testing days
Blood glucose and respiratory exchange ratio were significantly higher for the 6% and 8% carbohydrate-electrolyte drinks, compared to placebo (P<0.05)
There were no significant effects of the treatments on relative change in plasma volume, plasma osmolality or serum electrolytes
Rectal temperature at 32km was higher for the 8% compared to placebo, but similar to the 6% solution
Deuterium oxide accumulation was not different among trials
Run performance was 8.5% faster for the 8% carbohydrate-electrolyte solution (1,062±31 seconds, P<0.05), compared to placebo (1,154±56 seconds) and tended to be faster (7%) for the 6% carbohydrate-electrolyte solution (1,078±33 seconds). There were no differences in performance between the two carbohydrate-electrolyte solutions.

Author Conclusion:

Congruent with ACSM guidelines, we observed an 8% CHO sports drink (containing 3.3% fructose) is clearly within the range for optimal CHO content and can enhance performance during competitive distance running in the heat
No meaningful differences were observed in the relative fluid uptake or other measures reflecting the state of hydration between 6% and 8% commercially available sports drinks during running
Moreover, these data suggest that among acclimatized distance runners, CHO availability (vs. achieving a similar peak core temperature) limits prolonged running performance in the heat.

Funding Source:

Industry:

Coca-Cola

Food Company:

Reviewer Comments:

Authors note the possibility of Type II errors resulting from uncontrolled environmental conditions.

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?		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?	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?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	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?	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?		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?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		???
	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?	N/A
	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?	Yes
	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?	???
	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?	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?	Yes
	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