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Hydration

Hydration and Physical Activity

Citation:

 Fallowfield JL, Williams C, Singh R.  The influence of ingesting a carbohydrate-electrolyte beverage during 4 hours of recovery on subsequent endurance capacity, Int J Sport Nutrition 1995; 5: 285-299.

PubMed ID: 8605516
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine the influence of ingesting either a carbohydrate-electrolyte solution (CE) or a placebo during 4h recovery, on rehydration and subsequent exercise capacity.
Inclusion Criteria:
Informed consent; provided details on running ability, medical history
Exclusion Criteria:
None mentioned
Description of Study Protocol:

Recruitment Not mentioned

 

Design RCT: subjects divided into matched groups according to ht, age, wt, VO2max, VEmax; within each matched pair, subjects were randomly assigned to control (P) or CE.

 

Blinding used (if applicable) Not mentioned, but assumed

 

Intervention (if applicable) Assignment to 1 of 2 treatments during recovery: Placebo (orange-flavored, sweetened water, 15.5±0.8 g CHO) or CE (noncarbonated, isotonic sports drink, 2.9% sucrose, 2.7% maltodextrin, 1.3% orange fruit, 52mg/100 ml Na, 14 mg/100 ml K, 6 mg/100ml Ca, 1 mg/100ml Mg) beverages.  Equal vol of each solution for each group consumed immediately post-R1 and 2 h later. 

 

Statistical Analysis Performance times compared by ANCOVA;

Changes in plasma FFA, glycerol, ammonia, Na, K; serum insulin; changes in body wt, plasma vol within each trial (Student's t-test for paired data).  Differences in these variables (independent t-test). 

Changes in capillary blood glucose, blood lactate, RER, HR, RPE, CRS, Temperatures (2-way ANOVA with repeated measures and Tukey post-hoc). 

Significance at P<0.05.

 

Data Collection Summary:

Timing of Measurements

Pre-testing: 7d prior to start of study, subjects kept food intake diaries, nutritional content determined, and control diets providing same amts E and nutrient intake were prescribed for 48h prior to testing.  VO2max determined, blood lactate obtained during treadmill running.  Venous and capillary samples obtained. 

Testing: 2 runs performed, separated by 4 h recovery.  Run1 in the AM after 10h fast - emptied bladders, body weight obtained; HR and temp recorded before warm-up, at start of R1 & R2, and every 5 min suring exercise.  Capillary samples taken at 30 and 60 min of each run.  5 min warm-up at 60% VO2max; then run at 70% VO2max; run for 90 min or until volitional fatigue.  Expired gases collected over 60s, q. 15 min.

Recovery: 4 hr; ingested CE or P solutions immediately following R1 and again 2h later.

Post-testing: venous and capillary samples taken end of each run. 

 

Dependent Variables

  • Performance times
  • Changes in: plasma FFA, glycerol, ammonia;  Na & K (Flame photometry)
  • Changes in: Serum insulin (radioimmunassay)
  • Changes in Body wt, plasma vol (Dill & Costill method)
  • Changes in capillary blood glucose, lactate, RER (calculated from VE, VO2, VCO2 gas analyses - Douglas bag --> gas meters), HR (ECG); RPE, CRS (scales); temperature (skin probes)
  • Hgb (cyanmethemoglobin method)

Independent Variables

 Assignement to P or CE beverage.

Control Variables

 Diet 48h prior to testing; lab temp during testing (20C); treadmill running at 70% VO2max

Description of Actual Data Sample:

 

Initial N: 12 M, 4 F, trained

Attrition (final N):

Age: P group: 27.9±1.9; CE group: 26.1±1.3 yrs

Ethnicity: Not mentioned

Other relevant demographics: Run distances between 40-100 km/week

Anthropometrics

  ht (cm) wt (kg) VO2max (ml/kg/min)
P 173.9±2.5 68.8±3.4 57.6±2.1
CE 174.3±2.4 68.8±4.6 59.5±1.7

Location: lab

 

Summary of Results:

Running Speeds and Relative Exercise Intensities at Blood Lactate Concentrations of 2 mmol/L-1 and 4 mmol/L-1 of Treatment (CHO) Group and Control (P) (mean±SEM); Running Times and Carbohydrate oxidation at R1 and R2

Variables

Treatment Group (CE)

 

Control group(P)

 

Statistical Significance of Group Difference

Running speed (m/s) at

Blood Lactate 2 mmol/L

4 mmol/L

 

 

3.57±0.25

4.65±0.15

 

 

3.71±0.21

4.56±0.18

 not reported

VO2max (%)

Blood Lactate:

2 mmol/L

4 mmol/L

 

 

68.3±4.1

85.1±3.1

 

 

67.3±2.8

86.3±1.3

 not reported

Run Times (min)

R1

R2

 

87.5±2.5

62.0±6.2*

 

86.3±3.8

39.8±6.1

 

ns

*P<0.05

CHO oxidation (%)

R1

R2

 

47*

44*

 

41

32

 

*P<0.05

 

Other Findings

Blood glucose maintained in normal range during R1, both groups, serum Insulin decreased by 50%.  Blood lactate increased w/onset of exercise; normal levels were restored in both groups during recovery, though concentrations were elevated in the CHO group vs P group (P<0.05).  No differences between groups for blood lactate during R2.

Plasma FFA and plasma glycerol increased (p<0.01) during R1 in both groups.  Plasma glycerol remained elevated in P following recovery (P<0.01), while FFA increased by 15% (p<0.01).  Pre-R2 concentrations were elevated in p group (p<0.05).   In CHO group, pre-R2 concentrations did not differ from pre-R1 after 4h recovery. 

Absolute concentrations of ammonia same in both groups at end of exercise, despite differences in running performance between the 2 groups.

Plasma Na ns differences between groups during R1; plasma K sig increased by 19% both groups (P P<0.01; CHO p<0.05).  NS differences from pre-R1 to 4hr post-recovery.

No differences in water ingestion during R1 between 2 groups.  Plasma vol decre during R1, but restored during recovery.  NS differences between groups in HR. 

Sclaes:  RPE and CRS higher in both groups during R2 vs R1 (p<0.01); higher ratings in P vs CHO group after 15 min of R2, and rest of R2 (RPE, p<0.05; CRS p<0.01).

Neither group restored pre-R1 body weight following 4h recovery (p<0.05).  Est rehydration 65.9±6.3% in P and 62.6±7.3% in CHO (ns).  Temp profile similar during R1 and R2; pre-R1 temp restored during P trial recovery, but remained elevated at start of R2 in CHO (p<0.05).

 

Author Conclusion:

Ingesting 1g CHO/kg body wt at 2h intervals following prolonged, constant-pace running improved endurance capacity 4h later. 

Provision of 6.9% CE solution facilitated rehydration as effectively as non-CHO Placebo solution. 

Failure to maintain adequate CHO availability rather than failure to adequately rehydrate appeared to hasten onset of fatigue during a further bout of exercise.

Funding Source:
University/Hospital: Loughborough University, London Hospital Medical College
Reviewer Comments:
Ingesting 1g CHO/kg BW every 2 hours of a 4h recovery period following prolonged running improved endurance capacity during a subsequent running bout (post-recovery).
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? 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? 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? 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? 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
  3.6. 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.) ???
  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? N/A
  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? N/A
  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