Hydration and Physical Activity
Millard-Stafford ML, Sparling PB, Rosskopf LB, DiCicarlo LJ. Carbohydrate-electrolyte replacement improves distance running performance in the heat, Med Sci Sports Exer 1992; 24(8): 934-40.PubMed ID: 1406180
To evaluate the effects of a 7%CES (versus water) on physiological responses, hydration status, exercise performance in male distance runners during simulated outdoor 40-km road race under warm, humid conditions.
training >65 km/week; completion of 32-km training run in previous month; use of programmed drinking during run training; informed consent.
Recruitment not mentioned
randomized, double-blind crossover study in field setting; 2 conditions assigned in counter-balanced fashion.
Blinding used (if applicable)
Double-blind, randomized assignment of drink conditions.
Intervention (if applicable)
During 40-km run, given 1 of 2 drink conditions: water or 7% CES (250 ml/5 km, which was equivalent to dose of 0.75 l/h)
ANOVA with repeated measures; Student's t-test for dependent samples; sig level of P<0.05.
Timing of Measurements
Instructed to consume typical pre-competition diet for 3d prior to 1st trial, and replicate this for the 2nd trial; no exercise during the 24h prior to trial.
Day of trial, consumed water, but no solid food; 30 min prior to run, consumed 400 ml of either 7%CES or water. Trial conducted outdoors in summer (25C-32C, 82%-62%RH change across test sessions from beginning to end of trial). Temp between trials was not significant.
Trial: 5Km loop completed 8x for distance of 40 km. 2-4 runners tested during each session. 250 ml of drink administered every 5 km, RPE, temp, and HR recorded; break at 20 km for blood sample, weight.
At end of trial, drink beverage ad libitum during 30 min recovery period.
- RER and VO2 (Douglas bag method)
- body weight
- Sweat rate (net change in body weight, corrected for fluid)
- Core temp
- Glucose, total pro, BUN
- Electrolytes and Hgb (reflectance spectrometry)
- Plasma lactate (analyzer)
- Posm (freezing point depression)
- Pvol (from hgb, hct)
7%CES: 5% glu, 2% fructose, 9.7 mmol/l Na and Cl; 5 mmol/l K.
drink volume and timing, timing of measurments; distance of run
Initial N: N=8M
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)
|Training distance (km/wk)||86.6±19.2|
|Best marathon time (min)||156.4±17.4|
Outdoors; Atlanta, GA (summer season)
Total duration of run (water; CES)
Statistical Significance of Group Difference
Fluid intake (l/hr)
Body weight loss (%)
NS between trials
|Sweat rate (l/h)||1.8||NS|
Urine output (kg)
|Run time, first 35 km (min)||149±4.2; 149.9±5.0||NS|
|Performance during last 5 km (min)||24.4±1.5; 21.9±1.0*||*P<0.03 CES vs water|
No differences between the 2 drink trials for serum electrolytes, blood lactate, total pro, BUN, Osm, %change Pvol, RER, HR, RPE, blood pressure.
Blood glucose sig higher (P<0.01) throughout 40K and recovery during CES vs water.
%VO2max sig higher (P<0.05) at 5K when consuming water (70.4%) vs CES (66.6%)
7% CES is similar to water as a fluid replacement drink interms of thermoregulation, maintenance of phsiological function, hydration status. However, the 7% CES increased blood glucose and had a significant regogenic effect on prolonged running, and thus may confer a benefit to highly-trained marathoners competing in the heat.
Quality Criteria Checklist: Primary Research
|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|
|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?||N/A|
|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?||Yes|
|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?||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?||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.)||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?||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?||N/A|
|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?||N/A|
|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)?||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|