EAL

Hydration and Physical Activity

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the interaction between Na content and volume ingested on postexercise whole body rehydration and the restoration of cardiovascular function and fluid compartments.

Inclusion Criteria:

Capable of performing >90 min cycling at 60% VO2max; informed consent

Exclusion Criteria:

none mentioned

Description of Study Protocol:

Recruitment not mentioned

Design 2X2; randomized crossover: 4 trials, 1 week between each trial

Blinding used (if applicable) not mentioned

Intervention (if applicable) Ingestion of fluid at 100 and 150% of body mass lost w/Na at 25 and 50 mM

Statistical Analysis 3-factor (volume, Na, time) ANOVA for repeated measures. 2-way ANOVA and Newman-Keuls post-hoc test for %rehydration, fluid compartment data, Na balance. Relationships between selected DV conducted using Pearson product correlations; Sig level p<0.05.

Data Collection Summary:

Timing of Measurements

Pre-trial: measurement of VO2max; standardized food and fluid intake and exercise 24h before each test day.

4 rehydration conditions with low or high volumes (100% vs 150% of volume lost) and low or hi Na content (25 vs 50 mM), randomized couterbalanced design: LL, LH, HL, HH.

Pre-test: blood sample, urine collected, body weight obtained; rectal thermometer and heart rate monitor placed.

90 Min exercised-induced dehydration: environmebtal chamber, 35C, 55%RH; rode at 60% VO2max until 2.5% body weight lost, or until core temp reached 39C. HR, temp, CO2 rebreathing maneuvers, oxygen uptake and sweat samples obtained.

30 min transition period: immediately after exercise, normal room temp (23C, 50%RH), seated for 30 min; blood sample taken, urine collected, body weight obtained.

180 min rehydration w/1 of 4 beverages; consumed equal volumes at 30 in intervals (1/5 of total vol) after an initial drink equal to 30% of total vol. Blood samples, urine, body weight taken at 60, 120, and 180 min

20 min steady-state ride to assess recovery of cardiovascular fxn. (60% VO2max), CO2 rebreathing, HR, respiratory gases collected.

Dependent Variables

Hgb and HCt (to calc volumes)
Osm-plasma (freezing point depression)
Plasma,urine, and sweat electrolytes
ADH (RIA)

Independent Variables

Beverage consumed during rehydration: LL, LH, HL, HH

Control Variables

temp during rest and exercise; standardized intake and activity 24h pre-test. Workloads for testing; 2.5% body mass loss.

Description of Actual Data Sample:

Initial N: 10M

Attrition (final N): 10M

Age: 27.5±5.8 yr

Ethnicity: not mentioned

Other relevant demographics: moderately trained

Anthropometrics 79.6±11.9 kg; 3.88±0.47 l/min; ht not reported.

Location: Ex Phys Lab, Dept Kinesiology, Texas Christian Univ, Fort Worth, TX, USA

Summary of Results:

Variables	LL (100%:25mM)	LH (100%:50mM)	HL (150%:25mM)	HH (150%:50mM)	Statistical Significance of Group Difference
Na consumed, mM	65.6±9.8	117±19.4	95.4±17.9	179±30	p not reported

Other Findings

Level of rehydration sig greater in high vs low-vol trials (p<0.05). Restoration of plasma vol (% change) showed main effect for Na w/no interaction w/time or vol. Differences between LL and HL compared with LH and HH were present throughout rehydration (p<0.05).

Extracellular fluid and interstitial fluid vol: main effect for vol: HL and HH > LL and LH (p<0.05). Also, a sig Na-vol interaction: HL> all others (p<0.05).

Urine production: vol-by-time interaction, HL and HH> LL and LH and 2 and 3 hrs rehydration (p<0.05).

Plasma Na, Plasma Osm: main effect for time, elevation at post-ex time point for all conditions.

Urine Na: Na-by-time interaction, LH, HH> LL and HL at 2 and 3 h rehydration (p<0.05).

Na balance: main effect for Na: deficit in LH and HH< LL, HL (p<0.05).

Cardiovascular: sig time effect - decrease over time throughout dehydration, returning to normal past-rehydration.

HR: core temp increased at the end of dehydration, and again after 20 min steady-state test.

ADH incr after ex, ns diff between conditions.

Author Conclusion:

For whole body rehydration, there was no benefit in adding Na beyond 25mM, however, greater rehydration can be achieved with large volumes.

Fluid compartment restoration: interaction between Na and volume, relative to intracellular space.

Plasma vol (possibly entire extracellular space) benefits from presence of Na, however, effects of different levelsof intracellular K on fluid compartment restoration needs to be examined.

Cardiovascular restoration was complete after 3h rehydration, regardless of whether flui or Na replacement was complete; thus, there is a minimum level of fluid replacement necessary to restore cardiovascular function, particularly if accompanied by a complete plasma vol restoration.

Funding Source:

University/Hospital:

Texas Christian University Research Foundation

Reviewer Comments:

see figures in paper for time-course data.

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?	???
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?	N/A
	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)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	???
	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.)	Yes
	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?	???
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?	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)?	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