These findings suggest that each of these forms of CHO can serve as effective sources of CHO to ingest with PRO in and attempt to promote post-exercise anabolic responses. These recommendations are based on findings that ingestion of CHO following exercise increases insulin levels promoting glycogen restoration [ 6 — 10 ]. Additionally, increasing insulin levels following exercise optimizes an anabolic hormonal environment and can serve as a potent stimulator of PRO synthesis pathways [ 8 , 11 — 13 ].
For example, Zawadzki and associates [ 10 ] reported that adding PRO to a post-exercise CHO supplement promoted a greater increase in insulin levels and glycogen restoration. The authors suggest that this increase in insulin and growth hormone concentration may facilitate a more favorable environment for recovery than CHO alone [ 5 , 14 ].
Further, Kraemer and coworkers [ 15 ] found that ingestion of CHO and PRO two hours before, immediately following, and during three consecutive days of resistance-training increased blood glucose, insulin, growth hormone, and IGF-1 to a greater degree than a placebo. Consequently, there is considerable evidence to support recommendations that athletes should ingest CHO and PRO following exercise in order to optimize glycogen resynthesis, promote an anabolic hormonal environment, and increase PRO synthesis [ 1 — 5 ]. On the other hand, since ingestion of CHO with PRO has been reported to promote greater increases in insulin [ 9 , 28 , 30 , 31 ], it is possible that the insulin response may be maximized regardless of GI of the CHO ingested.
Moreover, ingesting different forms of CHO may have other physiological influences that may optimize recovery. Forty subjects 19 males and 21 females volunteered to participate in this study. All subjects had participated in at least one year of resistance training prior to testing and were informed of the possible risks of the investigation before giving their written and informed consent previously approved by the University of Memphis Institutional Review Board for the use of human subjects.
Prior to the start of this trial, a familiarization session was conducted to obtain one-repetition maximum 1RM for each of nine Nautilus Nautilus, Inc. Exercises included the chest press, seated row, shoulder press, lat pull, leg extension, leg curl, biceps curl, triceps extension, and leg press.
For the exercises in which 1RM was exceeded by the weights available on an individual machine, the Epley formula was used to predict 1RM based on the number of repetitions lifted at a given weight [ 33 ]. Rest periods between each 1 RM lifting attempt were not limited so that the subjects had adequate opportunity to perform to the best of their ability. The time of day was standardized within a 2-h starting time for all subjects in order to minimize potential diurnal variation in hormonal concentrations.
Upon arrival weight kg and height cm were recorded. Subjects then donated a pre-exercise baseline blood samples prior to starting the resistance-training workout. Each set of exercise was interspersed with a 2-minute rest period and research assistants monitored all sessions.
If a participant could not complete the full 10 repetitions the weight was reduced so 10 repetitions could be completed during the following set of exercise. During each set, the weight lifted and the number of repetitions performed was recorded for each subject in order to calculate total lifting volume. Following the completion of the workout, subjects returned to the laboratory and donated a post exercise blood sample.
After the post-exercise blood sample was obtained, subjects received in a double blind and randomized manner a CHO and PRO supplement containing 40 g of whey PRO with g of sucrose S , powdered honey H , or maltodextrin M. The remaining group served as a non-supplemented control group. These forms of CHO were selected because prior research in our lab demonstrated that ingesting 50 g of gel forms of these CHO's resulted in significantly different glucose and insulin profiles [ 34 ].
The supplements were similarly colored, flavored and packaged for double-blind administration by an independent food-packaging lab Paragon Labs, Torrance, CA, USA. Research assistant's blended pre-measured volumes of the powder into 16 ounces of water to form a milk shake type drink. Subjects were given as much time as needed to ingest the supplements which typically was less than 5-min. Once the subject consumed the supplement, a timer was started and blood samples were taken at 30, 60, 90, and min during recovery.
A similar time frame for collection of blood samples was employed for the control group. Subjects remained seated during the recovery period. As blood samples were collected, subjects were asked to respond to a questionnaire assessing the severity of hypoglycemia, dizziness, fatigue, headache, and stomach upset they experienced throughout the experiment. Questions were asked on a scale of 0—10 with 0 having no symptoms and 10 being most severe. Once the catheter was inserted and stabilized, a locking luer male adapter plug with an intermittent injection site was then connected to the female end of the catheter.
Once the blood samples were obtained, approximately 2—3 mL of Bacteriostatic 0. Once the line was cleared with saline, the catheter was locked to prevent clotting of blood in the line between sampling intervals.
One of the SST tubes was divided into four labeled 2. Whole blood cell counts with percent differentials were run on whole blood samples using a Coulter STKS automated analyzer using standard procedures Coulter Inc. These analyzers were calibrated daily to controls according to manufacturer's recommendations and federal guidelines for clinical diagnostic laboratories. Blood samples were assayed for each variable at all data points with the exception that creatine kinase was only measured at baseline, following exercise, and minutes following supplementation.
Frozen serum samples were assayed at the Exercise Biochemistry Lab at the University of Memphis using standardized spectrophotometric and enzymatic immunoassay procedures. Each sample was thawed only once and decoded only after all the analyses were completed. The intra-assay coefficient of variability for insulin measurements was 3. The testosterone and cortisol mean coefficient of variability was 2. Inter-assay coefficient of variability for testosterone and cortisol were Consequent to randomization procedures, total lifting volume, fasting glucose and insulin concentrations were different between groups.
Thus, covariate adjustments were made to the repeated measures analysis and AUC measures using these three variables. Demographic data for each treatment group are presented in Table 1. Body mass adjusted 1 RM for the nine exercises were: chest press 0. After adjustments were made during the exercise treatment in order to complete 3 sets of 10 repetitions per exercise, the mean percentage of maximum weight lifted during the weight training stimulus were as follows: chest press Therefore, data were analyzed by a two-way ANOVA and are presented as means for men and women combined. Figure 1 presents glucose while Figure 2 shows insulin concentrations observed during the experiment.
Plasma glucose then declined to a lower concentration i.
Glycogen resynthesis after exercise: effect of carbohydrate intake.
Glucose responses. Other areas of significance are detailed in the "Results" section. Insulin responses. No between group differences were observed at 90 and min. Glucose AUC responses.
Glycogen Supercompensation and Athletic Performance
Insulin AUC responses. Table 2 presents testosterone, cortisol and the testosterone to cortisol ratio data observed during the experiment. Likewise, no significant differences were observed among groups in testosterone, cortisol, or the ratio of testosterone to cortisol AUC values. Significant time effects were observed for each of these variables.
However, a significant interaction was observed in the ratio of BUN to creatinine. However, no differences were observed among types of supplements investigated. Table 4 shows muscle and liver enzyme levels observed during the study. Mean CK data increased from No affects were noted for lactate dehydrogenase LDH. Table 5 presents general markers of immunity evaluated in this study.
Ingestion of CHO and PRO following intense exercise has been reported to increase insulin levels, optimize glycogen resynthesis, enhance PRO synthesis, and lessen the immuno-suppressive effects of intense exercise [ 2 , 3 , 8 , 14 , 16 , 35 ]. The major findings of this study were: 1. These findings add to a growing body of literature indicating that ingestion of CHO and PRO following exercise can stimulate insulin levels and thereby anabolic processes [ 3 , 5 , 12 , 18 , 20 , 27 ]. Moreover, they extend our understanding of how different sources of CHO with differing glycemic responses influence glucose availability, insulin levels, and recovery indices.
The following provides additional insight into the results observed. This finding is of interest from a nutrient delivery and timing standpoint in that it has been suggested that athletes should ingest CHO and PRO within two hours following intense exercise in order to optimize the hormonal effects of intense exercise and recovery [ 1 , 36 ]. It has typically been thought that glucose and insulin levels increase the greatest following ingestion of a high GI form of CHO and that combining high GI carbohydrates with PRO would optimize the insulin and glucose response following exercise.
In support of this contention, glucose levels were increased to the greatest degree when ingesting honey as the source of CHO rather than sucrose or maltodextrin. As noted previously, the honey powder used in this study contained fructose These findings suggest that it may be more advantageous to ingest a mixture of CHO's with PRO following exercise in order to promote a more sustained increase in blood glucose response. However, although ingesting CHO with PRO significantly increased insulin levels in comparison to controls, no significant differences were observe among types of CHO ingested in peak insulin levels C 8.
It is also interesting to note that glucose values in the H group stayed above baseline throughout recovery while values fell below baseline in the S and M groups. Consequently, this form of CHO may help maintain glucose levels and prevent incidents of hypoglycemia that some individuals may experience when ingesting large amounts of CHO and PRO. Although we did not measure glycogen uptake at the muscle, previous research has shown that ingesting CHO with higher GI following exercise promotes a more rapid resynthesis of muscle glycogen [ 28 , 30 , 41 , 42 ].
Since co-ingesting CHO with other nutrients influences the energy density, osmolality, gastric emptying rates, and the GI of the meal [ 32 , 37 — 39 ], additional research should evaluate the effects of ingesting different forms of CHO with PRO on muscle glycogen resynthesis following intense exercise. Post-exercise ingestion of PRO and amino acids have been reported to stimulate PRO synthesis [ 3 , 12 , 16 , 19 , 26 ].
Additionally, insulin has been reported to be a potent stimulator of PRO synthesis [ 3 , 12 , 16 , 18 , 20 ]. Muscle glycogen utilization during prolonged exercise on successive days. The role of dietary carbohydrate in muscle glycogen resynthesis after strenuous running.