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Hydration

Hydration and Physical Activity

Citation:

Kenefick RW, Maresh CM, Armstrong LE, Riebe D, Echegaray ME, Castellani JW.  Rehydration with fluid of varying tonicities: effects on fluid regulatory hormones and exercise performance in the heat.  J Appl Physiol 2007; 102: 1899-1905. 

PubMed ID: 17317877
 
Study Design:
Experimental; within-subjects
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine the effects of hypovolemia and [Na] on fluid-regulatory hormone responses to exercise in the heat, subsequent to exercise-induced hypohydration.
Inclusion Criteria:
unacclimatized to heat, informed consent; no others mentioned
Exclusion Criteria:
none mentioned
Description of Study Protocol:

Recruitment not mentioned

 

Design randomized, within-subject experimental design; 4 conditions (1 per test day), each test day separated by 14 d

 

Blinding used (if applicable) not mentioned

 

Intervention (if applicable): 4 conditions given during rehydration:  0.9% IV; 0.45% IV; 0.45% Oral; no Rehydration fluid (NF)

 

Statistical Analysis 4X3 (treatment X time) repeated measures ANOVA to compare differences among trials.  Newman-Keuls post-hoc analysis to determine significant differences within and between conditions.  Significance level P<0.05.  Power analysis was conducted to justify N=8 subjects.

 

Data Collection Summary:

Timing of Measurements

Preliminary testing: VO2max determined (treadmill running test); hydrostatic weighing w/measurement of residual lung volume via N-washout method; instructed to drink 450 ml water evening before testing, and 450 ml morning of testing.

Testing:  3 treatments, randomly assigned during rehydration period: 0.9% IV, 0.45% IV, 0.45% oral, No rehydration fluid (NF)

Each Test  consisting of 3 stages:

Pre-test: Urine sample, Usg(via refractometer) and Posm measured; Usg 1.023±0.006 and Posm <286±3 mosm/kg H2O used to verify adequate hydration status.  Subjects fitted with HR monitor, thermistor (rectal temp), and teflon catheter (blood sampling). Entered Environmental chamber (33C), stood quietly, blood sample taken, consumed standardized breakfast.

1)180-190 min Exercise-induced dehydration: 33.0 ± 0.1C, 47.6±0.5% RH to reduce body weight by 4% - alternating stationary cycling (117±9W) with treadmill walking (1.6±0.1 m/s; 5±1% grade) at a 25-to-5 min exercise to rest ratio.  Body weight measured during each rest interval ; urine collected throughout testing; blood sample taken at end of dehy protocol.

2)45 min Rehydration: 25.5±0.2C, recumbent position, received 1 of 3 treatments over 45 min, 0.56 ml/kg/min IV infusion rate.  Stood for  55 min (equilibration).

3)90 min Moderate exercise in heat: re-entered environmental chamber (35.9±0.1C, 46.6±2% RH, 2.3 m/s airflow), standing for 20 min; blood sample taken; consumed 1 g/kg carbohydrate (candy) and 100 ml water.  Performend 90 min bout of treadmill walking, 3-5% grade at 50% VO2max.  Blood sample taken at end of test.

Dependent Variables

  • HR & Rectal temp (every 15 min)
  • O2 consumption (every 30 min, MedGraphics system)
  • Blood measures (pre-dehy, post-dehy, pre-ex/post-rehy, post-ex): 
  • Hgb (cyanomethemoglobin method), Hct (micorcapillary technique)
  • Posm (freezing point depression)
  • Pna, Una (ion-sensitive electrodes)
  • P [AVP, ALD] (radioimmunoassay kit)
  • Percent change Pvol (Dill & Costill method)

Independent Variables

 Rehydration treatment (0.45% IV, 0.45% oral, 0.9% IV, NF)

Control Variables

 Climate control during all testing stages; standardized fluid and food intake during testing; hydration status; rehydration fluid intake/administration

Description of Actual Data Sample:

 

Initial N: 8M, unacclimatized to heat

Attrition (final N): 8 M

Age: 22.1±0.8 years

Ethnicity: not mentioned

Other relevant demographics: none mentioned

Anthropometrics 179.6±1.5 cm; 73.6±2.4 kg; 57.9±1.6 ml/kg/min VO2max; 7.7±0.9% body fat.

Location: Lab, Department of Kinesiology, University of Connecticut, Storrs, CT

 

Summary of Results:

 

Variables

 0.45% IV

 0.45% Oral

 0.9% IV  NF

Statistical Significance of Group Difference

Dehy % VO2max (ml/kg/min)

51±2

50±2

 50±3 51±2 

 ns

Exercise time (min)

 190±12

 182±8

 179±12  180±10

 ns

Post-dehy Uvol (l)

 0.34±0.12

 0.40±0.10

 0.44±0.11  0.48±0.09

 ns

Post-Rehy Uvol (l)  0.06±0.02  0.08±0.02  0.08±0.02  0.08±0.02 ns
Post-Dehy %weight loss  4.4±0.07  5.1±0.1  4.5±0.07  4.6±0.07 ns
Post-Rehy % weight loss  2.1±0.10  2.3±0.1  2.1±0.10 4.6±0.04* *P<0.05, sig different from 0.45% IV, 0.45% Oral, 0.9% IV
Pre-Dehy body wt (kg) 75±2 74.3±2.6 74±3 74±3 ns
Pre-Dehy; Post-Dehy          
Plasma AVP (pg/ml)  5.5±0.8; 20.0±1.9*  5.8±0.9; 22.0±2.0*  3.8±0.8; 15.4±1.9*  4.9±1.2; 18.4±1.9*  *P<0.05 (difference from Pre-Dehy value)
Plasma ALD (pg/ml)  410±69; 1351±226*  277±71; 996±269*  386±66; 1148±139*  248±62; 1054±147*  *P<0.05
Posm (mosm/kg H2O)  284±2; 294±2*  282±2; 296±2*  282±1; 294±2*  286±1; 296±1*  *P<0.05
Pna (meq/l)  146±0.4;153±1.0*  145±1; 151±1  145±1; 151±1*  146±0.4; 151±1*  *P<0.05
Uvol (ml) n/a; 300±10 n/a; 500±10 n/a; 400±10  n/a; 500±10  n/a
Uosm (mosm/kg H2O)  499±117; 607±108  487±76; 655±97  403±101; 555±133  432±94; 617±113 ns
Una (meq/l)  61±9; 44±6 75±14; 24.5±9*   64±23; 63±7  58±12; 52±6  *P<0.05
Usg  1.015±0.003 1.017±0.003   1.014±0.003  1.010±0.002 ns
Pre-Ex; Post-Ex          
Exercise time (min) 77±5 84±2 76±6 58±8*,** *P<0.05 diff from 0.45 and 0.9%IVs; **P<0.05 diff from 0.45% oral; ^P<0.05 diff from pre-ex value
Temp (rectal, C) 37.5±0.1; 39.1±0.1^ 37.4±0.1; 39.1±0.2^ 37.5±0.1; 38.9±0.2^ 37.8±0.1*; 39.3±0.1^  
Temp (skin, C) 31.0±0.2; 35.4±0.2^ 31.1.±0.1; 35.5±0.1^ 31.1.±0.2; 35.5±0.2^ 31.8±0.1*, **; 35.6±0.1^  
HR (bpm) 102±5; 158±61^ 93±4; 158±5^ 97±4; 152±61^ 113±2*; 162±31^  
Body weight 73.2±2.3; 71.8±2.3 72.7±2.7; 71.4±2.7 73.2±2.7; 71.8±2.7 71.4±2.3*; 70±2.3*,**,^  

 

Other Findings

 Pre-Dehy plasma AVP, ALD Osm, and Na, as well as urine Osm and Na not significantly different among treatments.  Post-Dehy, these values were elevated above pre-dehy values, but not sig diferent among treatments.

 4-5%exercise-induced hyhpohydration caused subjects to become hyperosmotic, hypovolemic, and elevated circulaing AVP, ALD.  Following partial rehydration, there were no overall differences in %change in Pvol or Pna, Pos, AVP, ALD among treatments.  No greater fluid restoration with 0.9% compared with 0.45% IV, nor was there greater fluid restoration associated with IV versus oral treatment.  No cardiovascular, thermoregulatory or performance advantages during  subsequent exercise in the heat associated with either a particular solution or administration route.

Author Conclusion:
Rehydration solution with 0.9% IV saline did elevate PNa, Osm, and [AVP] above levels observed following 0.45% IV solution.  However, while rehydrating with fluid containing Na has been shown to result in greater restoration of Pvol versus water, in this study it appears that the greater tonicity of the 0.9% fluid did not result in greater restoration of Pvol, enhanced heat tolerance, or diminished physiological strain during subsequent exercise in the heat compared to 0.45% saline fluid. 
Funding Source:
Government: US Army
University/Hospital: University of Connecticut, U of Rhode Island, University of Puerto Rico
Reviewer Comments:

homogeneous population; small sample, though have reported power analysis was done.

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
  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
  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
  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
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? 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
  1.1. 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? Yes
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
  2.1. 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
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? 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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
  3. Were study groups comparable? Yes
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
  3.1. 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
  3.2. 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
  3.3. 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? 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? Yes
  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
  3.5. 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")? Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
  4. Was method of handling withdrawals described? 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
  4.1. 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
  4.2. 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
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. 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
  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. 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? ???
  5.1. 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.) ???
  5.2. 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
  5.3. 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
  5.4. 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
  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. 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
  6.1. 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
  6.2. 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
  6.3. 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
  6.4. 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
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments 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
  6.7. 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
  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. 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
  7.1. 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
  7.2. 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
  7.3. 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
  7.4. 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
  7.5. 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
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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
  8.4. 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
  8.5. 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? ???
  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? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? 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. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes