Creatine monohydrate supplementation has been shown to increase the intramuscular total creatine (TCr) and phosphocreatine (PCr) pools (∼10-20%) in humans (12,13). An elevated intramuscular PCr may permit enhanced temporal buffering of ADP during high-intensity muscular contractions (5,9), a reduction in neuromuscular fatigue (31), and thus allow for an increase in the total number of contractions performed during strength training (8,37). Given that one of the most potent stimuli for increasing protein synthesis in skeletal muscle is muscle contraction (21), a greater number of contractions over a period of time may result in a greater cumulative stimulus for protein synthesis and an increased net muscle protein retention.
It has been consistently observed that an effect of acute creatine ingestion (∼20 g·d−1 × 5–10 d) is an increase of between 1 and 2 kg in fat-free mass (FFM) (8,20,37). Most of the increase is likely to be net water retention (12,13); however, in the long-term, intracellular water retention, resulting in cell swelling, could have positive effects upon net protein retention (3). There is also in vitro evidence that creatine can increase myosin specific protein synthesis (14,15,38) and increase satellite cell mitotic activity during muscle hypertrophy in a rat tenotomy model (7). Over a period of time, an increase in myosin synthesis (assuming no changes in protein breakdown) could promote an increase in skeletal muscle protein.
It has been consistently reported that dietary supplementation with creatine monohydrate during a period of strength training enhanced muscle mass and strength gains (8,17,18,34,36). Each of these studies concluded that the increase in FFM and strength was greater for the creatine-supplemented group as compared with those who received placebo (8,17,18,34,36). However, in most cases, the creatine-supplemented group was not compared with a group who received an isoenergetic and isonitrogenous “placebo”(8,17,34,36). One study compared a combined creatine, carbohydrate, and protein supplement with one containing an isonitrogenous, but not isoenergetic, supplement containing protein and carbohydrate, and concluded that the FFM gains during weight training were greater for the creatine containing supplement (18).
The choice of the timing of nutrient delivery is also an important consideration, for we and others have found that the provision of glucose and amino acids in the postexercise period enhanced aspects of protein metabolism that could have significant effects upon FFM and strength gains (26,33). Therefore, we chose an isoenergetic and isonitrogenous “placebo” and provided both supplements in the immediate postexercise period to simulate the dietary practices emerging from the results of studies showing a more positive protein balance when nutrients are consumed at that time (25,32).
We hypothesized, a priori, that isoenergetic and isonitrogenous creatine-glucose and protein-glucose supplements, consumed in the immediate postexercise period, would be equivalent in their capacity to enhance the strength and FFM gains after an 8-wk period of supervised strength training.
Twenty-three young, healthy, male volunteers were recruited to participate in the study. Written informed consent was obtained from each participant, and the study was approved by the McMaster University Ethics Committee. None of the participants were performing regular physical activity (< 2× per week) at the start of the study and had not done so for the preceding 6 months. Before, and after, participation in the 8-wk exercise training program (see below), all subjects completed 4-d diet records (analyzed using Nutritionist V, First Data Bank, San Bruno, CA) to develop a dietary checklist for each of the testing sessions and to ensure that no subjects were vegans. The physical and dietary characteristics of the subjects are presented in Table 1.
The participants were randomized using a double-blind design to receive a commercially available supplement containing creatine monohydrate and glucose (N = 12; ∼ 308 kcal (assuming no energy from creatine) = 10-g creatine monohydrate; 75-g dextrose; 2-g taurine; 250-mg ascorbic acid; 300-μg chromium picolinate; 200-mg α-lipoic acid; 100-mg phosphorus; 150-mg potassium; 60-mg sodium; 70-mg magnesium, and 20-mg calcium [CR-CHO] (CELL-Tech®)), or protein and glucose (N = 11; ∼ 340 kcal = 10-g caseinate; 75-g dextrose [PRO-CHO]) after each exercise training session under direct supervision of a research assistant (Table 2). The supplements had identical grape flavoring and were mixed into cold water and consumed within 30 min of exercise completion. The research assistant who supervised each session mixed up the drinks and ensured that each drink was consumed within 5 min. Because of the direct supervision, compliance was 100% with supplement consumption on five of the six exercise days. On one of the six exercise days, the drink was mixed the night before and kept refrigerated and was to be consumed within 30 min of exercise completion on the semisupervised day (see below). Compliance was reported to be 100% by the subjects on this day.
After the first testing session, there were a total of three subjects in the CR-CHO and one subject in the CR-CHO group who dropped out of the study during the training period for various personal reasons. Thus, there were a total of 8 participants who completed all aspects of the training/testing in the PRO-CHO group and 11 who completed all aspects of the training/testing in the CR-CHO group. Each subject completed 8 wk of supervised whole body split-routine weight training, 1 h·d−1, 6 d·wk−1, and completed pre- and post-testing as described below.
Pre- and post-testing.
Pre- and post-testing were each conducted over an 8-d period. Before pretesting, each subject completed three familiarization sessions under supervision. Strength testing (one repetition maximal strength (1RM)) was conducted over a 3-d period (days 1-3) for each of 16 exercises. The legs were tested on the first day (leg press, leg curl, leg extensions, standing calf raises), followed by chest and back exercises (machine bench press, latissimus pull-down, vertical bench press, seated narrow low row, machine chest fly, seated machine wide-grip row), and, finally, shoulder and arm exercises (seated machine shoulder press, standing cable lateral raise, seated triceps machine extension, seated biceps curl (preacher), standing triceps extension (press-down) with angled bar, standing biceps curl with cambered bar). Subjects initially performed a warm-up set of 12 repetitions at approximately 50% of their estimated 1RM, and a second preparatory set of three repetitions at approximately 85% of estimated 1RM. The first set was the first attempt at the predicted 1RM. A successful lift was judged being through the full range of motion of the exercise and was performed with proper technique as assessed by an investigator. There was a 2-min rest period between each successive attempt of a new 1RM. If a subject could not lift the initial 1RM, the weight was reduced accordingly and a 2-min rest period was provided before the next 1RM attempt.
After the strength testing (day 4), subjects performed strength and fatigue testing of the knee-extensors using an isokinetic dynamometer (Biodex Medical Systems; System 3, Shirley, NY). Low-velocity (45°·s−1) and high-velocity (240°·s−1) isokinetic torque were both assessed. The subject’s leg was strapped into the unit with Velcro® belts across the leg, chest, and lap, and leg length, seat height, seat-back position, and seat position were recorded for subsequent testing. Subjects performed one warm-up at each velocity, and the second trial was recorded as their peak power at the given velocity. After a 3-min rest period, a fatigue test was performed consisting of 3 sets of 10 contractions at 180°·s−1 with a 2-min rest period between each set. Isokinetic strength/fatigue testing and 1RM strength testing were performed pretraining, in the 5th week of training and posttraining. Test-retest (2-5 d between sessions) coefficients of variation for isokinetic strength were 2.4% (45°·s−1) and 3.4% (240°·s−1), and for 1RM testing ranged from 0.8 to 5.3%.
For the next 3 days (days 5–7), subjects followed a customized (isoenergetic and isonitrogenous with habitual intake), flesh-free, checklist diet, performed no exercise, and on day 8 an individual prepackaged diet was provided. The day before biochemical testing (day 7), a 24-h urine sample was collected, and in the evening body composition (total body mass (TBM)), fat-free mass (FFM), and whole body fat (body fat %)) were measured by dual energy x-ray absorptiometry (DEXA; Model QDR-1000/W, Hologic Inc., Waltham, MA) as previously described (20). The scans were completed before and after supplementation at the same time of the evening and 4 h after a defined light snack (250 kcal, 60% carbohydrate). Whole body scans were performed from head to toe in the single beam mode, and bone mineral content (BMC), fat, and lean mass were calculated using custom software (V 5.56, Hologic Inc.). FFM was taken as BMC + lean. All subjects were scanned with their hands pronated at their sides and feet between 25 and 30 cm apart. The same investigator completed all of the testing and recorded the subject position on the first trial to ensure similar positioning for the subsequent trial. In a previous reproducibility experiment, using the identical machine and with the same operator training program, it was found that the coefficient of variation (CV) was 1.6, 1.4, and 1.8%, for whole body BMC, lean mass, and fat mass, respectively, in 21 young female subjects (20.9 ± 1.6 yr) tested between 1 and 2 wk apart (6). From these data, it was calculated that a sample size of 11 was sufficient to detect a change in whole body lean mass of 2.0%(6). Given that most acute creatine loading studies demonstrated increases in mass of about 2.0–2.5%(5,8,20), we concluded a priori that the power was adequate to avoid a type II statistical error in the current study.
On day 8, the subjects arrived at the laboratory after consuming 50% of their daily energy and nitrogen intake provided as a prepackaged diet and performing no exercise. A plastic catheter (20 Ga) was inserted into the antecubital vein, and a blood sample was collected for plasma (heparin) and serum (untreated) analysis of metabolites and enzymes as outlined below. The serum sample was allowed to clot, and the plasma sample blood was immediately centrifuged at 1200 rpm and the plasma/serum were stored at −50°C until subsequent analysis (see below). Subjects then performed unilateral leg model weight exercise such that one leg was exercised while the other remained in a resting state. The dominant leg was exercised using 2 × 10 repetitions of leg press at 80% of 1RM and 6 × 10 repetitions of leg extension at 80% of 1RM. Each set was recorded and if the subject was unable to complete 10 repetitions, the posttesting protocol was modified to match the pretesting protocol. Subjects were also infused with tracer doses of 2H5-phenylalanine for 6 h after the exercise session for analysis of protein turnover (data not reported in this study). The subjects had a muscle biopsy of the vastus lateralis taken 2 h after the exercise session from the nonexercised (rested) leg using a suction modification. The sample was immediately blotted and trimmed of any connective tissue if required. One sample was quenched and stored in liquid nitrogen one min after the sample was taken (29) for subsequent analysis of phosphocreatine and creatine as previously described (32). A second sample was mounted in optimal cutting temperature (OCT) embedding medium that was prechilled in isopentane cooled in liquid nitrogen, snap frozen, and stored at −80°C until subsequent analysis (see below).
After the pretraining testing session, subjects began a 6-d·wk−1 split-routine/straight set training program lasting 8 wk (see below). Three workouts were designed and performed twice per week (2 d of each of the 3 exercise types described above (legs, chest and back, shoulder and arms)). All training sessions from Monday to Friday were monitored by one of two of the investigators (NY, CB) to ensure correct technique and compliance to the workout intensity. Saturday training sessions were performed without direct supervision; however, there was an independent person verifying attendance at the training center via a sign-in system. The order of the workouts was staggered to prevent the same workout from falling on a Saturday each week.
The program design utilized only machine exercises (Badger Magnum, Milwaukee, WI) to ensure safety and to reduce the “learning curve” required by the subjects for performance of the exercises. The exercise intensity was initiated as approximately 80% of the predetermined 1 RM for each exercise. In subsequent exercise sessions, the load was adjusted to cause muscular failure within 6–12 repetitions. The load was constantly adjusted between training sessions to remain within the desired range of repetitions and intensity.
The first three training sessions of week 1 were performed for only 1 set of each exercise at the prescribed intensity. The final three training sessions of week 1 were performed for 2 sets of each exercise, and in weeks 2–8 there were 3 sets performed for each exercise. Every set was performed to the point of muscular failure (fatigue). Training logs were kept to record the volume and intensity of each workout. Subjects were instructed not to engage in any new additional exercise programs but were encouraged to continue with their previous activity levels. All subjects performed 48 workouts with the exception of one person in each of the groups who only completed 47 workouts between the pre- and post-testing sessions.
Plasma samples were analyzed for aspartate aminotransferase (AST) (intra-assay CV = 9.1%), urea nitrogen (intra-assay CV = 6.3%), and creatinine (intra-assay CV = 7.7%) by using kit assays (nos. 505, 640, and 555-A, respectively, Sigma, St. Louis, MO). Creatine kinase activity (CK) was determined in serum using a kit assay (no. DG147, Sigma) (intra-assay CV = 6.1%). Urine was analyzed using the above creatinine (intra-assay CV = 7.2%) and urea (intra-assay CV = 5.4%) kits with appropriate dilutions for urine analyses.
Muscle samples frozen in liquid nitrogen were lyophilized, powdered, and extracted in 0.5 M perchloric acid/1 mM EDTA and neutralized using 2 M KHCO3 as previously described (32). The extracts were analyzed for ATP, PCr, and creatine by using an enzymatic method that has recently been described in detail by our group (32). We found unusually low ATP and low PCr concentrations in about 50% of the samples. It was subsequently discovered that some of the samples had been left on a counter for up to 30 min during a move of the laboratory. Thus, the ATP and PCr values were of no use, and we shall only report the total creatine values (given that partial thawing would increase free creatine, decrease PCr, yet would not alter the total creatine concentration due to the stoichiometry of the creatine kinase reaction). The intra-assay CV was 3.7% for total creatine.
The OCT embedded biopsy samples were serially sectioned (7 μm thick) on a cryostat microtome (Micron International, Walldorf, Germany) with sample and cabinet temperatures at −20°C. Samples were stained for myosin ATPase activity after preincubation at a pH of 4.3, 4.6, and 10.1 using established methods (4), with pre- and post-training cross-sectional samples assayed simultaneously. A total of 150–500 fibers were available for analysis from each subject. Fiber analyses were performed using image analysis software (Image Pro Plus, Media Cybernetics, Silver Springs, MD) interfaced with a microscope (Olympus BX60, Melville, NY) and a digital camera (SPOT Diagnostics Instruments, Inc., Sterling Heights, MI). We used a custom MACRO program written within the image analysis software to automatically calculate individual fiber areas and to determine the percentage of each fiber type. From this program, we determined the total number and area of type I and II fibers at pH 4.3 and 10.1, respectively. The program also allowed for the determination of the type I fibers at pH 4.6, yet individual identification of the IIA and IIB fibers had to be thresholded by the operator for each slide. When the analysis of % total fiber area and mean fiber area were tested for reproducibility, the intra-assay CVs were 1.5% and 2.6%, respectively. When two serial sections of the same muscle biopsy were tested for day to day reproducibility of % total fiber area, and mean area of fibers the interassay CVs were 2.4% and 1.3%, respectively .
All data were analyzed using analysis of variance (ANOVA) with a two-way split-plot design (between factor = CR-CHO/PRO-CHO; within factor = PRE/POST training). Where appropriate, Tukey post hoc analysis was employed to make pair-wise comparisons. Any power calculations were performed using between-group comparisons with a two-tailed test, α = 0.05 and β = 0.20; N/group = [(Zα + Zβ)·SD/D]2, where Z = Z-score, SD = standard deviation of the differences between the groups, and D = mean difference between the groups. Statistical significance was considered to be at level P < 0.05. Statistical analysis was performed using a computerized statistical package (Statistica 5.1, Statsoft, Tulsa, OH).
There were no differences between the groups in habitual energy intake or the percentage of major macronutrients. Energy, carbohydrate, and protein intake increased for the PRO-CHO group during the study as compared with their habitual intake (P < 0.05); however, during the 2-month trial, there were no differences between the groups in terms of their habitual energy, protein, fat, and carbohydrate intake (Table 3).
There was a significant increase in total body mass for both groups; however, the increase for the CR-CHO group was greater (5.4%) as compared with the PRO-CHO group (2.4%) (P < 0.05 for interaction). Both groups increased FFM as a result of the training program (P < 0.05), and there was a trend toward an interaction between treatment and training (P = 0.11, two-tailed; 0.055, one-tailed). A post hoc sample size calculation revealed that 13 subjects/group would have been required to detect a significant interaction between supplement and training for FFM (see Statistics section). Fat mass was reduced for the PRO-CHO group only after training (P < 0.05 for interaction). The percentage of body fat was reduced similarly for both groups after training (P < 0.05). A summary of the results is found in Table 4.
There were no differences in muscle total creatine concentration between the groups before training; however, the CR-CHO group had a higher total creatine concentration after the training period as compared with PRO-CHO (P < 0.05) (Table 5). There were no between-group differences in the percentage area or mean area for each of the major fiber types between the groups before training. after the training program, there were large increases in fiber areas of all fiber types that were similar for both groups (P < 0.01). The data analysis was identical for each of the three major fiber types; however, thresholding of the fiber density was difficult for three of the Cr-CHO and two of the PRO-CHO subjects at pH 4.6, and a full data set was available for the total type I and II fibers.
There were no between-group differences in baseline 1RM strength for any of the 16 exercises listed in Table 2. There were significant increases in 1RM strength for each of the exercises from pretesting to that at 4 wk and 8 wk (post) (P < 0.01). There were no treatment effects on the rate of increase in strength for any of the 16 exercises (Table 6). In addition, there were significant and similar increases for both groups in isokinetic torque of the knee extensors at both slow (45°·s−1) and fast (240°·s−1) contraction speeds from baseline to 4 wk and from 4 wk to 8 wk of training (P < 0.05). The fatigue index (F.I. = % [maximum −minimum]) was similar for both groups before and after training across all three sets (Table 7).
Plasma and urine analyses.
Plasma AST activity increased similarly for both groups after training but was still within the normal range for age (P < 0.05). Serum CK activity decreased similarly for both groups after training (P < 0.05). There were no treatment or training effects upon blood urea nitrogen concentration. Plasma creatinine concentration was higher for the CR-CHO group after training but unchanged in the PRO-CHO group (P < 0.05 for interaction). Twenty-four-hour urinary creatinine and urea N excretion were not affected by either training or treatment (Table 8).
Two of the male subjects experienced a transient, mild sense of abdominal discomfort on the CR-CHO trial, and one reported a similar effect with the PRO-CHO trial.
The main finding in the current study was that the strength increases after 8 wk of strength training were identical for subjects who consumed a creatine/glucose supplement (CR-CHO) as for those who consumed an isoenergetic and isonitrogenous protein/glucose supplement (PRO-CHO) postexercise. In spite of the similar increases in strength, the increases in total body mass were higher for the CR-CHO as compared with PRO-CHO group.
There have been four studies that have found greater increases in strength for subjects who consumed creatine as compared with a placebo during strength exercise training (8,17,34,36). Differences in initial training status cannot explain the differences as one study examined previously untrained subjects (34), whereas the other studies used either moderately trained (8,36), or highly trained athletes (17). We specifically chose subjects who were untrained because strength and lean mass increases would be expected to be greater (1,19) as compared with already well-trained athletes (8), and therefore a differential treatment effect would be magnified. Clearly, the strength increases in specific weight exercises ranging from 14 to 40% in the current study were significant, identical between groups and among the highest increases reported to date for this duration of training (2,19,28). Gender differences in the response to creatine also cannot explain the different outcome in our study as compared with the four previously mentioned, for three studies had exclusively male (8,17,36), whereas the other used exclusively female (34) subjects. Finally, a type II statistical error (small sample size) is not a likely explanation for the increases in strength that were observed, because these were greater for the CR-CHO group in seven of the exercises, greater for the PRO-CHO group in six of the exercises, and identical for three of the testing exercises. Therefore, the lack of a difference in strength increase between the two treatment groups in our study is likely due to the fact that strength training on either supplement resulted in similar strength gains. In addition to the lack of a treatment effect on the increases in movement specific strength, we also did not find an effect of treatment upon the increases in isokinetic knee extension strength. Furthermore, we did not find any differences in the fatigue index with repetitive knee extension isokinetic movements. This latter finding supports the results of a previous study that did not find an effect of creatine supplementation upon PCr resynthesis (35). Alternatively, our lack of between-group fatigue resistance in the isokinetic trials could indicate a lack of statistical power due to the fact that only a subgroup of individuals may show enhanced PCr resynthesis after supplementation (10).
Another interesting observation was that similar increases in strength occurred in spite of the higher concentration of total creatine in the CR-CHO group as compared with the PRO-CHO group. This did show that the treatment was effective in increasing the total creatine content. It could be argued that although total creatine content was increased, we were not able to show an increase in phosphocreatine, due to technical reasons described above. However, in the training study performed by Volek and colleagues (36), neither the total nor phospho-creatine concentration in skeletal muscle were higher at 12 wk for those who were supplemented with creatine, yet they demonstrated that both performance and FFM increases were greater for CR versus placebo.
One of the reasons that may explain the differing results between our study and previous work (8,17,34,36) is that the dietary interventions in these studies were not designed to provide similar energy contents. For example, in these studies the “placebo” was either cellulose (36), maltodextrin (34), or glucose (8). In another study, the placebo and creatine supplements each contained 99 g of glucose, 3 g of taurine, and ∼ 1.1 g each of sodium and potassium phosphate with the creatine group also getting an additional 15.75 g of CM (17). One study compared several different nutritional supplements (maltodextrin 190 g·d−1 (PL); 290 g carbohydrate·d−1 + 60 g protein·d−1 (GF); and 64 g carbohydrate/d + 67 g protein·d−1 + 20 g creatine·d−1 (+ taurine and glutamine)(P)) during 28 d of resistance training in young men (18). They concluded that GF and P were superior in terms of total mass accretion compared with PL and that P was superior in terms of FFM accretion (18). Unfortunately, the energy content between the supplements in the latter study varied substantially (18), which limited the interpretation regarding an effect of energy and/or composition. In the current study, we compared supplements with nearly identical amounts of energy, with creatine and casein protein hydrolysate being the major difference between the groups. In the CR-CHO group, there were also some minor compounds present (i.e., taurine), which, in the amounts found, have not been shown to have a direct influence upon the outcome variables examined in the current study. For example, taurine (present in the highest quantity in our study) was present in higher concentrations in the supplements used in one study (17) where the effects of creatine and training upon FFM and strength were similar to the three other studies in which the supplements did not contain taurine (8,34,36). Furthermore, the timing of ingestion of the supplement with respect to the training sessions has not been optimized in the latter studies (8,17,34,36). We have shown that immediate postexercise glucose supplements can reduce myofibrillar protein breakdown (26) and enhance muscle glycogen resynthesis (25), and others have shown that amino acid (33) and amino acid-glucose (24) supplements can enhance net protein balance, after strength exercise. It is also advantageous to consume creatine with glucose in the postexercise period because insulin (30) and muscle contraction (12) can stimulate creatine uptake into skeletal muscle. For these reasons, and because most athletes consume some nutrition and/or supplement during or after exercise, we chose to compare a creatine/carbohydrate supplement to a protein/carbohydrate supplement provided in the immediate postexercise period.
A finding that also supports our observation of no differences in strength gains between the two supplements was the finding of identical increases in muscle fiber diameter in the current study. An earlier study found that a creatine-supplemented group had greater increases in fiber diameter after training as compared with a group who consumed a placebo (36). Careful examination of the data revealed that the diameter of the muscle fibers were 21.9% smaller (range 12.6–27%) for the creatine as compared with placebo supplemented group at baseline before training and that after training there was no difference in the fiber areas (36). Our findings do show that after strength training there were no differences in muscle fiber area between persons who consumed creatine and carbohydrates as compared with those who consumed protein and carbohydrates and that when initial fiber areas are similar, the increase as a result of training is similar for either CR-CHO or PRO-CHO.
A somewhat surprising finding was that although the increase in strength and muscle fiber areas were identical between the groups, the total mass for the CR-CHO group was greater than for the PRO-CHO group. Although there was a trend toward a greater increase in fat-free mass for the CR-CHO group, this was not statistically significant (P = 0.11). The maintenance of fat mass for the CR-CHO group and the significant decrease in fat for the PRO-CHO group can explain 37.5% of the difference between the groups in total mass. If we assume that the trend for an increase in FFM (paralleling the increase in total mass) is true, then there are two hypotheses to explain this phenomenon. First, the increase is due to higher total body water content. If creatine does function as an osmolyte and draws water into the cell (13), then the increase in weight could be total body water. We did show a higher total muscle creatine content for those who supplemented with creatine, which, in combination with the fact that most of the body’s total creatine is found in skeletal muscle (11,12), would fit the hypothesis presented. Although an increase in muscle cell diameter would be expected with an increase in myofibrillar water, the absolute difference between the groups in lean mass accretion was 1.4 kg, and, assuming that a 75-kg male has 30 kg of muscle mass, this amounts to a 4.7% increase in muscle water mass (assuming that all the water is intracellular), and the resultant area changes may not be detectable with histochemical techniques. Alternatively, but not to the mutual exclusivity of the aforementioned hypothesis, there could be a greater increase in total creatine, hence, an increase in volume of nonskeletal muscle tissues. The locus of this is unclear as creatine transporters are found predominantly in skeletal muscle, heart, kidney, and brain (11), although creatine transporter mRNA is also found in liver (27) and intestine (16). From a practical standpoint for the athlete, it may be that those who participate in sports where a high strength:lean mass ratio is important (i.e., wrestling, jumping) should consider the PRO-CHO postexercise nutrition, whereas those in which a high absolute mass is required (i.e., American football) could consider a creatine-carbohydrate supplement (ignoring, for sake of argument, any potential ethical issues in sport).
Finally, we found that the creatine-carbohydrate and protein-carbohydrate supplements were well tolerated by the subjects with only minor abdominal discomfort reported in two and one subject(s), respectively. From a biochemical standpoint, we found a small but significant increase in aspartate amino transferase activity for both groups after exercise, with the values still being in the normal range. Creatine kinase activity was slightly lower after exercise training with no effect of supplementation, which was consistent with an earlier report by our group after acute creatine monohydrate supplementation (20). Plasma creatinine concentration did increase to a greater extent for the creatine-supplemented group after training, which was identical to the findings of another study using highly trained football players (17). As we and others have demonstrated, an increase in creatinine in the plasma represents an increase in the rate of appearance of creatinine to the nephron and creatinine clearance is unchanged after acute (20,22) and long-term (23) creatine supplementation.
In summary, we have shown that the provision of protein-carbohydrate supplements in the postexercise period results in similar increases in strength and muscle fiber area as compared with a creatine-carbohydrate supplement after a period of strength training. The increases in total mass were greater for the creatine-carbohydrate supplement. Both supplements were well tolerated. There may be sport-specific supplement recommendations from these results.
This research was supported by MuscleTech Research and Development and Hamilton Health Sciences Department of Rehabilitation. Thanks to John Stein for help during data collection.
Address for correspondence: Dr. M. Tarnopolsky, Dept. of Neurology, Rm. 4U4, McMaster University Medical Center, 1200 Main St. W., Hamilton, Ontario, Canada, L8N 3Z5; E-mail: tarnopol@ mcmaster.ca.
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Keywords:© 2001 Lippincott Williams & Wilkins, Inc.
ERGOGENIC AIDS; MUSCLE FIBER AREA; LEAN MASS; NUTRITIONAL SUPPLEMENT