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To assess whether ingesting carbohydrate-electrolyte solution (CES) during recovery from exercise in the heat (35C, 40%RH) influences endurance capacity 4 hours later. 

Healthy, informed/written consent; no others mentioned

None mentioned

Recruitment not mentioned

 

Design

CES and placebo treatments during 4h recovery period, administered in double-blind, crossover design.  Exercise trials (90 min treadmill running, or until fatigue, whichever reached first) in environmental chamber (35C, 40% RH).

 

Blinding used (if applicable): Double-blinded

 

Intervention (if applicable)

 CES  (commercially-available sports drink, 6.9%CHO, 24mmol 1^-1 Na, 2.6 mmol 1^-1 K, 1mmol 1^-1 Cl) and placebo (flavored sweetened water) treatments during 4h recovery period

Statistical Analysis

 Comparisons made after establishing normality (Anderson-Darling Goodness of Fit test). 

Performance times, rate of change of tempertaure and HR were tested for treatment X run interaction, and data obtained over time tested for treat X time interaction(2-way ANOVA for repeated measures). 

Sig interactions subjected to Tukey post-hoc analyses to identify differences between means. 

Total volumes fluid consumed, Urine vol and body mass changes analyzed (Student's paired t-test);

Sig level at p<0.05.

Timing of Measurements

Pre-exercise: Standard breakfast; void bladder, body mass obtained; venous and capillary samples taken

T1: Treadmill running at 60% VO2 max for 90 min or until volitional fatigue; temp and HR recorded, along with expired gas every 60 sec.  RPE and RPTD every 15 min.

Recovery: 3 equal feedings (equivalent to 100% weight loss) of treatment solution (CES or P) at 0, 1, 2 hr.  after 3 h, void bladder, body mass recorded; bolus dose of treatment solution given to remaining fluid deficit (140% of body mass loss).  Capillary samples taken every 60 min throughout recovery.  Urine collected throughout recovery.  Voided bladder at end of recovery. 

T2: procedures from pre-exercise and T1 repeated; venous and capillary samples, body mass obtained at end of trial.

Dependent Variables

• Temp and HR (arual thermometer, ECG)
• VO2, VCO2, VE (expired gases -- infrared and dry gas meters) ---> calculate RER
• Body mass (scale)
• Hgb, packed cell vol, plasma vol
• Urine vol
• Rating of perceived exertion (RPE) and thermal discomfort (RPTD) (scales)

 

Independent Variables: CES or Placebo treatment during recovery period

 

Control Variables: temp and RH of environmental chamber (35C, 40%RH); standard breakfast before testing; running at 60% VO2max

 

 

Initial N: 13 trained M

Attrition (final N): 13

Age: 32.4±1.4 yr

Ethnicity: not mentioned

Other relevant demographics:

Anthropometrics: 178.2±1.4 cm; 79.4±2.8 kg; 16.5±1.0% body fat

Location: Laboratory, Institute Naval Medicine, Alverstoke, Gosport, Hampshire, UK

 

 

 

Variables	T1 CES P	Recovery CES P	T2 CES P	Statistical Significance of Group Difference
Run times (min)	74.8±4.6** 72.5±5.2**		60.9±5.5* 44.9±3.0	*r=0.93, p<0.01, ces vs p *p<0.01 T1 vs T2
Pre-Exercise body mass (kg)	78.82±2.88 78.42±2.90
Post-exercise body mass	77.39±2.91 77.11±2.92	78.88±2.87 78.42±2.91	77.79±2.88 77.34±2.95	ns
Fluid intake (g)	757±50 728±50	2006±176 1830±165	615±57 452±35	ns
Sweat loss (g)	2167±156 2035±152		1705±187 1525±127	ns
Sweat rate (g/min)	29.2±2.1 28.6±1.8		29.1±3.5 33.8±1.8*	*p<0.05, p vs ces
Urine production (g)		515±69 527±89		ns
Net fluid balance (g)	-1433±126 -1307±118	58±26 -4±68	-1032±170 -1077±148	ns

 

 

Other Findings

 Metabolic Measurements:  progressive increase in VO2 over time during each exercise period, and in both conditions (p<0.01).  Nature of E-metabolism did not differ between 2 treatments during T1, but RER values were higher at all time points during T2 of CES vs P (P<0.01). 

Blood Measurements:  plasma vol reduced after T1 and T2, compared to pre-exercise and recovery (respectively) in both conditions (p<0.01).  No differences between CES and P in magnitude of calculated decrease in plasma vol.  No differences in blood glucose between CES and P, or throughout T1.  During recovery, blood glucose increased after 60 min (p<0.01), 120 min (p<0.01) and 180 min (p<0.05) of the CES vs P.  Moderately severe hypoglycemic response seen after 30 min and at end of T2 during CES vs P (p<0.01).  Blood lactate increased from resting after 30 min of exercise during both trials - no differences in magnitude of increase.  No differences in blood lactate between CES and P at any time point during T2.

Thermal & Subjective Responses:  NS treatment effects on Temp, HR, RPE, RPTD during T1.  HR incr at end of T1 (P<0.01); Increases in Temp, RPE, RPTD (all p<0.01) during T1.  HR and temp greater after 30 min exercise during T2 of P vs CES trial (P<0.05). Rate of HR increase per hour of exercise lower during T2 in CES vs P (P<0.01).  RPE and RPTD higher after T2 during P vs CES (P<0.01 and p<0.05, respectively)

Ingesting a CES in sufficient quantities to replace body mass loss following prolonged, constant pace running in a warm environment improves endurance capacity 4 hours later. 

6.9% CES facilitated rehydration as effectively as the flavored, sweetened water solution. 

Provided that adequate hydration status is maintained, inclusion of CHO and electrolytes within a rehydration solution will delay onset of fatigue during subsequent bout of prolonged submaximal running in a warm environment.

Government:

Ministry of Defense (UK)

Including CHO and electrolytes within rehydration/recovery period after exercise will delay onset of fatigue during a subsequent bout of prolonged activity.