Post-Exercise Muscle Glycogen and Performance45Journal of Exercise PhysiologyOfficial Journal of The AmericanSociety of Exercise Physiologists (ASEP)ISSN 1097-9751An International Electronic JournalVolume 4 Number 1 January 2001Exercise NutritionCARBOHYDRATE-PROTEIN DRINK IMPROVES TIME TO EXHAUSTION AFTERRECOVERY FROM ENDURANCE EXERCISE.ERIC S. NILES, TONY LACHOWETZ, JOHN GARFI, WILLIAM SULLIVAN, JOHN C. SMITH, BRIAN P.LEYH, AND SAMUEL A. HEADLEY.Allied Health Sciences Center, Springfield College, Springfield, MAABSTRACTERIC S. NILES, TONY LACHOWETZ, JOHN GARFI, WILLIAM SULLIVAN, JOHN C. SMITH, BRIAN P.LEYH, AND SAMUEL A. HEADLEY. Carbohydrate-Protein Drink Improves Time to Exhaustion AfterRecovery from Endurance Exercise. JEPonline, 2001 4(1):45-52. Ten endurance trained males were studiedto investigate the ergogenic effects of isocaloric carbohydrate (CHO, 152.7 g) and carbohydrate-protein (CHOPRO, 112 g CHO with 40.7 g PRO) drinks ingested after a glycogen lowering diet and exercise bout.Treatments were administered in a double-blind and counterbalanced fashion. After a glycogen lowering dietand run, two dosages of a drink were administered with a 60 min interval between dosages. The CHO-PRO trialresulted in higher serum insulin levels (60.84 vs 30.1 mU/ml) 90 min into recovery than the CHO only trail(p 0.05). Furthermore, the time to run to exhaustion was longer during the CHO-PRO trial (540.7 91.56 sec)than the CHO only trial (446.1 97.09 sec, p 0.05). In conclusion, a CHO-PRO drink following glycogendepleting exercise may facilitate a greater rate of muscle glycogen resynthesis than a CHO only beverage,hasten the recovery process, and improve exercise endurance during a second bout of exercise performed on thesame day.Key words: Serum Insulin, Anaerobic Threshold, Ergogenic.
Post-Exercise Muscle Glycogen and Performance46INTRODUCTIONPre-exercise intramuscular glycogen levels determine the time to exhaustion during endurance events ofmoderate intensity (1,2). If endurance athletes are required to complete multiple events within the same day, itwould be to their advantage to adopt practices designed to hasten the resynthesis of intramuscular glycogen.Fallowfield and Williams (3) demonstrated that by increasing the daily consumption of carbohydrate (CHO) to8.8 g/kg body wt, restoration of intramuscular glycogen stores occurred within 22.5 hr following a bout ofcarbohydrate depleting endurance exercise. Ivy et al. (4) found that following endurance exercise subjectsachieved rapid glycogen repletion after consuming CHO immediately as opposed to waiting several hours postexercise. Blom et al. (5) studied varying dosages and types of simple sugars on post-exercise glycogen synthesisand found no significant difference in glycogen synthesis after either a 0.7 or a 1.4 g/kg body wt dosage ofglucose.Though CHO is definitely of prime importance to the endurance athlete, proteins (PRO) are now considered tobe of greater importance than previously thought. For example, Nuttall et al. (6) reported that a PRO dose incombination with glucose elicited a higher insulin release than seen with either glucose or PRO alone and thisresulted in the lowering of plasma glucose levels in a group of type 2 diabetics. In addition, Zawadzki et al. (7)studied nine male cyclists to determine if the ingestion of both CHO and PRO (CHO-PRO) after prolongedexercise would result in a higher insulin response compared to the ingestion of CHO alone. In addition, musclebiopsies were performed to quantify the rate of muscle glycogen resynthesis. The rate of glycogen storageduring the CHO-PRO treatment was found to be 38% higher than during the trial in which only CHO wasconsumed. However, the results of this study have been questioned since the CHO-PRO combination providedthe athletes with 43% more energy than the CHO only trial (8). Furthermore, there was no assessment ofsubsequent exercise performance following the ingestion of the two different beverages.The present study was designed to compare the effects of a CHO-PRO drink versus an isocaloric drinkcontaining only CHO on the recovery process following CHO depleting exercise. It was hypothesized thatduring the CHO-PRO trial, there would be a greater insulin release and a greater run time to exhaustion thanduring the CHO trial.METHODSSubjectsTen male runners ranging in age from 24-34 years, with a minimum peak oxygen uptake (VO2peak) of 50mL/kg/min and a percentage body fat below 15%, volunteered to participate in this study. All subjects gavetheir informed consent to participate in this study which was approved by the Institutional Review Board of theCollege.Research DesignThis was a repeated measures, double-blind and counter-balanced study. To avoid systematic order effects,subjects were randomly assigned to the various treatment conditions (CHO vs. CHO-PRO).Testing ProceduresPreliminary testsAll subjects had their VO2peak determined via open circuit spirometry using a SensorMedics metabolic cart,(Model 2900, Yorba Linda, CA). A standard running protocol was used (9). Tests were terminated when at leasttwo of the following criteria were met: a plateau in oxygen uptake with increasing work rate, a peak heart ratewithin 10 beats of the age predicted maximum, and an RER 1.15 (10).
Post-Exercise Muscle Glycogen and Performance47During the test of VO2peak, blood samples were collected (via capillary puncture from a finger) at baseline andduring the last 30 s of each stage. All samples were analyzed by a 1500 YSI lactate analyzer (Yellow SpringsInstruments, Yellow Springs, OH) which was calibrated according to manufacturer’s guidelines. The individualanaerobic threshold (IAT) was determined by using the log-log transformation as described by Beaver,Wasserman, and Whipp (11).Practice runWithin a week following the VO2peak test, a practice treadmill run was performed. This was done to familiarizethe subjects with the protocol that they would use during the performance run. Once the IAT was achieved, thecorresponding VO2 (IATVO2) was determined and a value corresponding to 10% above the IATVO2 was thencalculated and served as the target VO2 value which the subject used during the final performance running test.This intensity was chosen to help ensure the predominant use of glycogen as a fuel.Diet manipulationTo facilitate a reduction of intramuscular glycogen, subjects were instructed to follow a prescribed diet over a48 hr period prior to the exercise tests. The exchange system was used to plan all of the diets. Diet recordingsheets and exchange lists were issued to all subjects. All recorded diet logs were analyzed for the following:total calories, FAT, CHO, and PRO contents using Nutritionist III (N-Squared Computing, Salem, OR). Thegoal during this period was to have the subjects consume CHO, PRO, and fats in the following respectiveproportions 48 hrs prior to the test: 40, 40, and 20 %. Twenty-four hours prior to the test the subjects aimed toachieved a diet containing 35% CHO, 45% PRO and 20% FAT.Pre-testing exercise recordSubjects were instructed to record the duration and intensity of exercise sessions during the 48 hrs prior to thetreatment sessions. Seven subjects ran on the days prior to testing and were instructed to keep their heart ratesbelow 70% of their age-predicted maximum values. Three subjects did not exercise the day prior to testing. Allsubjects then replicated the same exercise or rest prior to the second treatment session.Treatment sessionsEach subject came to the laboratory after a 12-hr overnight fast, and proceeded to have height, weight, andskinfold measures taken. Skinfold sites consisted of the abdomen, supra iliac, triceps, and thigh (12). Theglycogen depletion run was then administered. During the depletion run, subjects were given a total of 1 L ofwater administered in 200 mL volumes with the first drink given immediately prior to the start of exercise andthe remainder given at approximately 12 min intervals. The room temperature was 24 C during all sessions.The exercise intensity was set in accordance with Muoio et al. (13) at 80 % of VO2peak for the first 30 min ofthe run. The intensity was then dropped to 70-75% of VO2peak for the remainder of the run. Gas analysis wastaken for the first 10-12 min until a steady state VO2 was attained, after which the mask was removed forsubject comfort. At 30 min the mask was attached to monitor the drop in intensity. The mask was left on for 5-7min until VO2 values leveled, after which the mask was removed for the remainder of the run.A finger stick blood sample to determine plasma glucose levels was obtained at 40 min into the run andimmediately analyzed. A Reflotron glucose analyzer (Boehringer Mannheim, Germany) was used forimmediate glucose values. During the first treatment session, the depletion run lasted 45 min for all subjects.During the second treatment session, the run was terminated when the plasma glucose levels were within 5mg/100 mL of the first session. Approximately one week later, during the second depletion run the meanrunning time was 50.35 0.23 min. Those subjects running longer than 45 min during the second testing sessionhad a blood sample taken at 2.5 min intervals throughout the subsequent 5-10 minutes until glucose values werewithin the desired range, at which time the run was terminated.Supplementation PeriodFollowing the depletion run, the subject was given the appropriate supplement drink for that session. Each drinkcontained the following nutrients: the CHO-PRO drink contained 112.0 g of dextrose and maltodextrin, and40.7 g of protein consisting of milk and whey protein isolate mixture. The CHO drink contained 152.7 g ofCHO in the same ratio of dextrose and maltodextrin.
Post-Exercise Muscle Glycogen and Performance48Sixty min after the initial dosage, another serving of the same supplement was administered. To avoid any errorin lactose contribution to caloric count, all supplements were ingested with water. The volume of each dosagetotaled 600 mL. Two subjects had difficulty in ingesting the second dosage on both treatment days. Therefore asample of 31.0 mL of the mixed drink was eliminated for these two subjects. The final test during thetreatment session was a running performance test.Blood collection and analysisDuring the recovery period after the depletion run, blood was drawn via venipuncture, at the following two timeperiods: immediately after the depletion run (0 min), prior to receiving the first drink, and at the 90 min markwhich was 30 min after the second ingestion of the drink. These time periods were chosen from the findings ofZawadzki et al. (7) who demonstrated that with a similar supplement as the product in the current, insulinpeaked at roughly 30 min after the second dosage.Blood samples of 8.3 mL were collected, left at room temp for 5 min, and then refrigerated for 30 min beforecentrifugation at 1500 rev/min for 10 min. The serum was removed and transferred to separate tubes and frozenat –20 C for later analysis of insulin and glucose. Serum insulin assays were performed using an automatedenzyme immunoassay method (Boehringer Mannheim ES300, Roche/Boehringer-Mannheim, Indianapolis, IN).Intra- and inter-assay coefficients of variation were 4.8 and 5.8 % respectively at 10 ng/dL, and 4.4 % at 60ng/dL. Serum glucose was measured using a standard (glucose oxidase) automated laboratory method (Hitach911, Roche/Boehringer-Mannhelm, Indianapolis, IN).Running performance test (post-treatment)The purpose of the running test was to determine whether the CHO- PRO drink allowed subjects to run longerat the VO2 corresponding to 10 % above the IAT. The work rate at the IAT is suggested to be a good indicatorof the racing potential for a distance runner (14).A warm-up period of 5 minutes was allowed, as was the case with the VO2peak test, after which the treadmillspeed and grade were increased to bring the oxygen consumption values into the desired range. The timing ofthe performance run clock started when the VO2 corresponding to 10 % above the IAT was reached. Apart fromthe 5 min warm-up, 2 min were allowed for this process to occur. A range of 3 % was allowed due to difficultyin maintaining steady state oxygen consumption. The criterion for termination of the current test was theduration (min) when subjects voluntarily stopped. Verbal encouragement was given of equal measure for allsubjects under both treatment sessions. The test was then terminated and a cool-down period was initiated forseveral minutes.Statistical AnalysisTo determine if significant differences existed between group means across time at 0, and 90 min post exercisefor the two blood values (insulin, and glucose), two 2 x 2 (drinks vs. time) factorial repeated measuresANOVA’s were computed. Any significant interaction was then followed by a dependent t-test to show wherethe difference was located. To determine if any significant mean difference existed between the run time toexhaustion trials, a paired t-test was computed. All data were analyzed using the SPSS Statistical Package forthe Social Sciences (15). The alpha level was 0.05, and data are presented as Mean SD.RESULTSTen endurance trained subjects completed this study. Their physical characteristics are presented in Table 1.The subjects who participated in this study were young (age, 27 2.5 years), aerobically trained (VO2peak,59 5.5 ml/kg/min) and lean (body fat, 10.2 4.4 %). As shown in Table 2, their dietary intake was similarduring the 48 hours prior to each testing session.
Post-Exercise Muscle Glycogen and Performance49InsulinA significant interaction between drink and time with respect to serum insulin levels was found (p 0.007).Using a repeated measures t-test, no significant difference was found (p 0.955) in insulin values at baseline.However, at 90 minutes, the insulin levels were higher in the CHO-PRO than CHO trial (p 0.015) (Figure 1).Insulin (mU/mL)T