The primary objective of ingesting carbohydrates after exercise is to replenish glycogen stores for subsequent exercise bouts (1). In doing so, it increases the likelihood that further energy stores will be available more rapidly, which, in turn, may increase performance capabilities for athletes who frequently engage in sporting events and exercise (1). For example, during tournament-type events, in which a team or an individual may play 3 or 4 times within a 2- or 3-day period, or long duration endurance events, like triathlons, marathons, and road cycling, rapid glycogen resynthesis is important for successful performance.
It has been suggested that ingesting a carbohydrate and protein combination (carbohydrate-protein) after exercise may be more beneficial than carbohydrates alone for aiding muscle recovery (1–3). In support of this hypothesis, several studies have demonstrated significantly greater glycogen restoration after carbohydrate-protein was consumed postexercise vs. carbohydrates alone (15,30,33). However, these studies examined the acute recovery (up to 5 hours) after a glycogen-depleting exercise protocol. Little is known about the long-term training-related impact of regular carbohydrate-protein supplementation. According to short-term studies (25,33), post-workout consumption of carbohydrate-protein mixtures may be important for promoting muscle recovery and gains in performance during an endurance training program. For example, Roy et al. (25) demonstrated an attenuation in body weight (BW) loss, a trend toward increased positive nitrogen balance, and increased time to exhaustion (TTE) after consuming a carbohydrate-protein drink vs. a noncaloric placebo immediately after 1 hour of cycle ergometry exercise at 65% of V[Combining Dot Above]O2peak on 4 separate days. In addition, Williams et al. (33) reported greater muscle glycogen repletion rates and TTE after ingesting a carbohydrate-protein vs. carbohydrate-only drink for repeated bouts of endurance exercise in the same day. Thus, simply adding protein to a carbohydrate repletion formula may be beneficial for acute glycogen resynthesis. No previous studies, however, have compared the effects of carbohydrate-protein vs. carbohydrate-only repletion supplements on aerobic capacity, endurance performance, and body composition during an 8-week aerobic training program.
It has also been suggested that supplemental ribose, a pentose (5-carbon) sugar, may increase the body's ability to maintain and rapidly synthesize energy stores (1). Theoretically, ingesting supplemental doses of ribose may increase adenine nucleotide salvage and de novo synthesis, which would preserve the adenine nucleotide pool, increase cellular concentrations of adenosine diphosphate and adenosine triphosphate (ATP), and allow rapid restoration of cellular energy (1,5,16,18,22,27,28,35). In clinical populations, ribose has been implicated as an energy-providing supplement that may alter cardiac muscle function, reduce muscle cramping, and increase exercise tolerance (11,12,17,32,36). Therefore, adding ribose to the carbohydrate-protein repletion drink may enhance the muscle recovery and the benefits of endurance training.
Op 't Eijnde et al. (20) reported that ribose supplementation did not beneficially impact postexercise ATP resynthesis or maximal isokinetic performance of the leg extensor muscles. In addition, recent studies by Kreider et al. (17) and Bernardi and Ziegenfuss (4) have also concluded that ribose supplementation elicited no substantial ergogenic effects on anaerobic performance or metabolic markers, such as blood lactate, ammonia, glucose, or uric acid (17), during short-duration high-intensity cycling. No previous studies, however, have examined the effects of long-term ribose supplementation on aerobic capacity, endurance performance, and body composition. The purpose of this study, therefore, was to examine the effects of a carbohydrate-, ribose-, and protein-containing repletion drink vs. carbohydrates alone on aerobic capacity, endurance performance, and body composition during 8 weeks of aerobic training.
Based on the previous literature indicating that the addition of protein (1,3,15,25,30,33) may improve glycogen resynthesis and ribose (1,5,16,18,22,27,28,35) may preserve and increase the capacity for energy transfer during exercise, we hypothesized that the carbohydrate-, ribose-, and protein-containing repletion drink would augment the chronic endurance training-induced improvements in aerobic capacity and endurance performance after an 8-week period of endurance training and supplementation. Furthermore, we hypothesized that the inclusion of protein in the experimental formula may increase fat-free mass (FFM) more than carbohydrates alone (14) in cyclists.
Experimental Approach to the Problem
This was a randomized, double-blinded parallel study. All subjects participated in an exercise training program consisting of 1-hour cycle ergometry exercise (Monarch 818 E; Quinton Instruments, Seattle, WA, USA) work bouts, performed 5 times per week, for 8 weeks. In addition, each subject underwent testing at 4 time intervals (pre-training [PRE], mid-training at 3 weeks [MID3], mid-training at 6 weeks [MID6], and post-training [POST]). The first testing session (PRE) was conducted before the initiation of the training at week 0, the second testing session (MID3) was at the end of week 3, the third (MID6) was at the end of week 6, and the final testing session (POST) was conducted immediately after week 8. All 4 tests, PRE, MID3, MID6, and POST, consisted of a body composition assessment, an aerobic capacity test, and a fixed power output endurance test. Each laboratory visit was performed at approximately the same time of day (±2 hours). The PRE, MID3, and MID6 aerobic capacity test results served as an outcome measurement and a training-induced performance indicator to adjust the training intensities as the subjects' fitness levels increased. During the 8 weeks of training, the subjects rode at a power output that corresponded to 70% of their V[Combining Dot Above]O2peak. The average training power outputs for the treatment (TEST) and control (CON) groups from PRE to MID3 were (mean ± SD) 179 ± 21 W and 177 ± 25 W; MID3 to MID6 were 201 ± 23 W and 199 ± 25 W; and MID6 to POST were 217 ± 23 W and 213 ± 24 W; respectively. Independent samples t-tests indicated no significant (p > 0.05) differences between groups (TEST vs. CON) for the training power outputs. All exercise sessions were supervised by trained laboratory personnel who monitored exercise conditions to ensure that the intensity remained constant during each 1-hour work bout. Attendance at the exercise sessions averaged 89%, with no subject missing more than 5 sessions (out of a possible 40) or more than 2 consecutive sessions.
The subjects were randomly assigned to either the treatment drink (TEST; n = 15) or the control (CON; n = 17) groups. Table 1 contains the nutritional profiles and ingredients for the TEST and CON supplements. The CON drink was designed to have the same caloric content, volume, taste, and color as the TEST drink. Random samples of both the TEST and CON supplements were tested by a third-party agency (Covance Laboratories, Madison, WI, USA) to assure that the actual contents of these products were consistent with the label claims.
To avoid the confounding influence of preexercise foods, subjects were asked to refrain from any food intake for at least 2 hours before their 1-hour training sessions. To be consistent with the postexercise nutrient intake timing recommendations of Ivy et al. (15) and Williams et al. (33), subjects were asked to ingest their drink (TEST or CON) in the laboratory immediately (<10 minutes) after each training session. The subjects were instructed to allow a minimum of 1 hour after the end of their training sessions before eating a meal outside of the laboratory, which was done to avoid the potential confounding influence of other foods on glycogen resynthesis and the outcome variables in this study. To avoid investigator bias, the drinks (TEST and CON) were premixed each day by trained laboratory personnel who did not speak with subjects or administer the testing or training protocols. Both the TEST and CON drinks were mixed with 28 oz of cold water.
Other than the administration of the TEST or CON drinks, there were no dietary restrictions during the course of this study, except for the 12-hour abstention from food, alcohol, and exercise before the body composition and aerobic capacity assessments. The subjects were instructed to maintain their normal dietary habits, and they were asked to refrain from any concurrent supplemental exercise training.
Thirty-two men (mean age ± SD = 23 ± 3 years) volunteered for this study. Each subject was healthy as assessed by routine medical screening and was physically active (1–4 hours of regular exercise per week). None of the subjects reported or exhibited (a) a history of medical or surgical events that may significantly affect the study outcome, including cardiovascular disease, metabolic, renal, hepatic, or musculoskeletal disorders; (b) use of any medicine that may significantly affect the study outcome; (c) use of nutritional supplements (such as ribose, protein drinks, creatine, vitamins, etc.) in the 4 weeks before the start of the study; and (d) participation in another clinical trial or ingestion of another investigational product within 30 days before screening/enrollment. This study was approved by the Institutional Review Board for Human Subjects, and each subject signed an approved informed consent form before any testing or training. Approximately half of the sample (n = 16) were tested and trained during the fall semester (August/September to October/November), whereas the other half were tested and trained during the spring semester (January/February to March/April).
Body Composition Assessment
Body composition and aerobic capacity assessments, respectively, were performed on the same day at PRE, MID3, MID6, and POST testing. The body composition assessments always preceded the test for V[Combining Dot Above]O2peak. The subjects were instructed to avoid exercise for a minimum of 12 hours before testing, and each subject indicated that they were normally hydrated upon arrival to the laboratory. Body density (BD) was assessed from underwater weighing (UWW) with correction for residual lung volume (RV) using the oxygen dilution method of Wilmore (34). Residual lung volume was determined on land with the subject seated in a position similar to that assumed during UWW. The average of similar scores (within 0.1 L) from 2 to 3 trials was used as the representative RV. Underwater weight was measured in a submersion tank in which a nylon swing seat was suspended from a 10 kg Salter scale (model 230; REGO Designs & Patents, United Kingdom). The average of the 2 to 3 highest weights from 6 to 10 trials was used as the representative underwater weight. Percent body fat (%fat) was calculated from BD using the formula of Brozek et al. (6):
Fat-free masswas calculated from the resultant %fat values using the following equation:
Aerobic Capacity Test
A calibrated Quinton (Corval 400) electronically braked cycle ergometer (Quinton Instruments, Inc., Seattle, WA, USA) was used for all aerobic capacity and fixed power output endurance tests. Seat height was adjusted so that the subject's legs were at near full extension during each revolution, and toe clips held the subject's feet in place. Seat height was measured and recorded to maintain consistency during each laboratory visit (PRE, MID3, MID6, and POST). After a 5-minute warm-up at 30 W, the subject began pedaling at 70 rpm at a power output of 60 W. The power output was increased 30 W every 2 minutes until the subject could no longer maintain 60 rpm despite strong verbal encouragement. Expired gas samples were collected (20-second averages) and analyzed using a calibrated TrueMax 2400 metabolic measurement system (Parvo Medics, Sandy, UT, USA), whereas the subject breathed through a 2-way valve (Hans Rudolph 2700 breathing valve; Hans Rudolph, Kansas City, MO, USA). The highest recorded V[Combining Dot Above]O2 during the test was defined as V[Combining Dot Above]O2peak. Heart rate was monitored and recorded using a Polar Pacer heart rate monitor (Polar Electro, Suomi, Finland). At the end of the test, the subject continued to pedal at 30–50 W as a cool-down period until their heart rate recovered to 120 b·min−1.
Fixed Power Output Endurance Test
With 48 hours of rest after the body composition and aerobic capacity tests, each subject completed a fixed power output endurance test at PRE, MID3, MID6, and POST testing. After a 5-minute warm-up at 30 W, the subject began pedaling at 70 rpm at a power output that corresponded to 90% of the power output at V[Combining Dot Above]O2peak as determined by the first (PRE) aerobic capacity test. The average fixed power output endurance test power outputs for the treatment (TEST) and control (CON) groups were (mean ± SD) 229 ± 27 W and 228 ± 32 W, respectively, with no significant (p > 0.05) difference between groups (TEST vs. CON). The subjects were instructed to ride until they could no longer maintain a cadence of 60 rpm despite strong verbal encouragement. Time to exhaustion was recorded as the outcome measurement. Heart rate was recorded using a Polar Pacer heart rate monitor (Polar Electro, Kempele, Finland). At the end of the test, the subject continued to pedal at 30–50 W as a cool-down period until their heart rate recovered to 120 b·min−1.
Before starting this study, an average V[Combining Dot Above]O2peak of 42.8 ml·kg−1·min−1 and SD of 5.4 ml·kg−1·min−1 was used to estimate the sample size necessary to detect a 2.7 ml·kg−1·min−1 difference in V[Combining Dot Above]O2peak between TEST and CON across the 8-week duration of the study. Thirty subjects were necessary to observe a statistical power of 0.92. After data collection was complete, skewness and kurtosis statistics were calculated for normality. With the exception of leptokurtosis for TTE at MID3, MID6, and POST (2.7, 2.0, and 6.7, respectively) and slight positive skewness for TTE at POST (2.4), all skewness and kurtosis statistics were between −0.98 and 1.7.
Five separate 2-way mixed factorial analyses of variance (ANOVA) (time [PRE, MID3, MID6, and POST] × group [TEST and CON]) were used to analyze the BW, %fat, FFM, V[Combining Dot Above]O2peak, and TTE data. When appropriate, follow-up analyses included 1-way repeated-measures ANOVAs and Tukey post hoc comparisons. An alpha of p ≤ 0.05 was considered statistically significant for all comparisons.
In addition, percent change scores were calculated for each participant from PRE to MID3, PRE to MID6, and PRE to POST. These percent change scores were averaged separately for the TEST and CON groups, and 95% confidence intervals were constructed around the mean percent change scores (Figure 2). When the 95% confidence interval includes 0, the mean percent change score is no different from 0, which can be interpreted as no statistical change (p > 0.05). However, if the 95% confidence interval does not include 0, the mean percent change for that variable can be considered statistically significant (p ≤ 0.05).
Table 2 shows the mean ± SEM values for BW, %fat, FFM, V[Combining Dot Above]O2peak, and TTE for each group (CON and TEST) at each time (PRE, MID3, MID6, and POST).
The 2-way (time [PRE, MID3, MID6, and POST] × group [TEST and CON]) mixed factorial ANOVAs for BW (p = 0.570), %fat (p = 0.600), FFM (p = 0.728), V[Combining Dot Above]O2peak (p = 0.806), and TTE (p = 0.253) indicated no significant time × group interactions, no main effects for group (p > 0.05), but significant (p ≤ 0.05) main effects for time for BW, %fat, FFM, V[Combining Dot Above]O2peak, and TTE. The marginal mean values for BW (collapsed across group) decreased over time (PRE > MID6, PRE > POST, and MID3 > POST). The marginal mean values for %fat (collapsed across group) decreased over time (PRE > MID3, MID6, and POST). The marginal mean values for FFM (collapsed across group) decreased from MID3 to POST. The marginal mean values for V[Combining Dot Above]O2peak (collapsed across group) increased over time (PRE < MID3, MID6, and POST; MID3 < MID6 and POST; and MID6 < POST). The marginal mean values for TTE (collapsed across group) increased over time (PRE < MID3, MID6, and POST; and MID3 < MID6 and POST) (Figure 1).
The mean percent change scores indicated that the TEST and CON groups responded similarly from PRE to MID3, MID6, and POST for BW, V[Combining Dot Above]O2peak, and TTE (Figures 2A, D, E). Specifically, Figure 2A indicates that the percent decreases in BW were only significant (p ≤ 0.05) from PRE to POST for the TEST and CON groups. However, the percent increases in V[Combining Dot Above]O2peak (Figure 2D) and TTE (Figure 2E) were markedly similar and significant (p ≤ 0.05) at all time points for both the TEST and CON groups. In contrast, the percent change scores for the body composition variables (%fat and FFM) responded differently between the TEST and CON groups. The percent decreases in %fat were only significant (p ≤ 0.05) for the TEST group from PRE to MID3 and PRE to MID6 (Figure 2B), whereas the percent changes in FFM (Figure 2C) indicated significant increases (p ≤ 0.05) from PRE to MID3 for the TEST group. The percent changes in %fat or FFM for the CON group did not reach statistical significance (p > 0.05).
The results of this study indicated that there were no absolute mean differences (p > 0.05) between the TEST and CON supplement groups for the training-induced changes in BW, %fat, FFM, V[Combining Dot Above]O2peak, or TTE. Recent studies have suggested that postexercise nutrition is important for skeletal muscle recovery and may enhance the benefits of exercise training on performance and body composition outcomes (9,18,25). Furthermore, it has been reported that ingesting a carbohydrate-protein supplement immediately after endurance exercise may be more beneficial than carbohydrates alone for aiding acute muscle recovery and improving performance (15,30,33). However, it is possible that carbohydrates alone taken immediately after endurance training is just as effective as a carbohydrate-protein mixture for training-related improvements aerobic power and endurance performance. It is likely that relatively large amounts of carbohydrates in both groups' post-workout drinks (TEST and CON; 76 and 93 g, respectively) masked the potential benefits of the added protein, ribose, and other unique ingredients in the TEST drink during the 8-week training period. Furthermore, even though the subjects were instructed to maintain their current diet, changes in dietary habits cannot be ruled out as a confounding factor.
When the data in this study were analyzed in a different way by examining the mean percent change scores (Figure 2), the findings related to BW, V[Combining Dot Above]O2peak, and TTE were similar to the ANOVA-based models (Figures 2A, D, E). However, group-related differences in %fat and FFM emerged (Figures 2B, C). Specifically, the protein- and ribose-containing repletion drink consumed by the TEST group may have decreased %fat from PRE to MID3 and MID6 and increased FFM from PRE to MID3, whereas the carbohydrate-only repletion drink (CON) had no effect on %fat or FFM. These findings extended those of Howarth et al. (14) who showed that although the glycogen resynthesis rates were not different between conditions, the coingestion of carbohydrates and proteins after aerobic exercise acutely increased mixed muscle fractional protein synthetic rate (FSR) and whole-body net protein balance compared with an isocaloric carbohydrate-only beverage. The authors concluded that, “The higher FSR during recovery could promote muscle adaptation during recovery from acute exercise by stimulating the synthesis or repair of proteins that facilitate energy provision and force production” (p. 1401). Thus, to our knowledge, this study was the first to show that when consumed regularly after chronic aerobic training, the TEST drink (carbohydrates + proteins + ribose) may elicit improvements in body composition within the first 3–6 weeks compared with carbohydrates alone (CON), which would be consistent with the conclusions of Howarth et al. (14). However, because the ANOVA-based findings were different from the percent change scores for the body composition variables, these findings were tentative. Several studies (8,21,24,31) have discouraged the statistical analyses of percent change scores, indicating that they may not be reliable or valid (23). Therefore, although noteworthy differences emerged between the TEST and CON groups for body composition when examining the percent change scores, these findings should be interpreted with caution.
Recent studies by Tarnopolsky et al. (26) and van Hall et al. (29) have indicated that the addition of protein to a postexercise carbohydrate repletion formula did not enhance muscle recovery beyond carbohydrates alone. Williams et al. (33), however, have shown that when muscle recovery is enhanced by increased glycogen resynthesis rates, cycling performance can also be enhanced accordingly. If muscle glycogen restoration is important for increasing endurance performance, the results of this study suggested that there is little additive value of adding protein to the carbohydrate solution for improving endurance performance over the course of a training period. Therefore, the results of this study provided a practical, yet tentative, extension to the findings of Tarnopolsky et al. (26) and van Hall et al. (29) that the addition of protein to a postexercise carbohydrate recovery drink does not seem to influence the changes in BW, V[Combining Dot Above]O2peak, or TTE that occur over an 8-week training period.
Several endurance training studies have demonstrated significant changes in aerobic capacity, endurance performance, and body composition (7,10,13). For example, Hickson et al. (13) examined the effects of endurance training, 6 days per week for 10 weeks, and reported an approximately 30% increase in V[Combining Dot Above]O2peak (ml·kg−1·min−1) and a 2.5% decrease in BW. In addition, Gaesser and Rich (10) reported a 7.2% decrease in %fat and a 13.0% increase in V[Combining Dot Above]O2peak (ml·kg−1·min−1) after 9 weeks of cycling for 25 minutes per day, 3 days per week at 80–85% of V[Combining Dot Above]O2peak. Similarly, Burke and Franks (7) reported 0.3–1.1% changes in BW and 8.1–21.3% increases in V[Combining Dot Above]O2peak after 10 weeks of cycle ergometry 3 days per week at 65–85% of maximal heart rate. The results of this study demonstrated similar mean changes (collapsed across TEST and CON; Table 2) for BW (1.5% decrease), %fat (4.8% decrease), and V[Combining Dot Above]O2peak (17.4% increase) after 8 weeks of cycle ergometry at 70% V[Combining Dot Above]O2peak for 1 hour per day, 5 days per week. It is possible, therefore, that the repletion drinks (TEST and CON) in this study had little effects on training-induced changes, particularly in BW, V[Combining Dot Above]O2peak, and TTE.
A unique finding of this study, however, was the 307% increase in TTE (collapsed across TEST and CON, Table 2) observed over the 8-week training period. Hickson et al. (13) reported an approximately 120% increase in TTE after 8 weeks of endurance training. The differences between these findings may be because of methodological differences in training and testing for TTE. It is also possible, however, that the addition of the TEST and CON supplements in this study may have contributed to the larger relative increase in TTE in this study. In addition, although there were no significant interactions (p > 0.05) between the TEST and CON groups for TTE, Figure 1 illustrates the continued pattern of increase in TTE for the TEST group, but a less pronounced increase for the CON group, between the MID6 and POST testing sessions. This nonsignificant pattern toward an interaction between TEST and CON may lend support to recent studies (19,33) that have reported a greater TTE for subjects who acutely ingested a carbohydrate-protein solution compared with a carbohydrate-only drink. A longer-duration study, however, will be necessary to examine if any additional training-related benefits of a carbohydrate-protein combination vs. carbohydrates only will be beneficial for increasing TTE.
It has been suggested that supplemental ribose may aid in muscle recovery by maintaining or increasing ATP resynthesis rates after bouts of strenuous exercise (1,5,16,18,22,27,28,35). Previous studies (4,17,20), however, have reported no energy-related or performance-related benefits to ribose supplementation during exercise. The results of this study supported those of Berardi and Ziegenfuss (4), Kreider et al. (17), and Op 't Eijnde et al. (20) and indicated that the addition of protein and ribose had no additional benefits to carbohydrates alone for the training-induced changes in BW, V[Combining Dot Above]O2peak, or TTE. However, the group-related differences observed for the percent change scores in %fat and FFM (Figures 2B, C) could have been due in part to the ribose but may have been more likely caused by the protein contained in the TEST drink. Previous studies of ribose supplementation have examined 10–32 g of ribose per day (4,17,20), whereas only 2.2 g of ribose were included in the TEST formula of this study. In addition, previous studies (4,17,20) have incorporated very high-intensity anaerobic exercise to examine the effects of ribose supplementation. Therefore, higher dosages of ribose and greater exercise intensities may be necessary to elicit more substantial ergogenic effects for the training-induced changes in body composition, aerobic capacity, and endurance performance.
The results of this study indicated that there were no absolute mean differences between the TEST and CON supplement groups for the training-induced changes in BW, %fat, FFM, V[Combining Dot Above]O2peak, or TTE in men. These findings were consistent with previous studies of carbohydrate-protein (26,29) and ribose (4,5,17,20) supplements. Our findings suggested that the addition of 14 g of protein, 2.2 g of ribose, and various vitamins and minerals did not result in any measurable differences in BW, aerobic capacity, and endurance performance when compared to carbohydrates alone. However, the additional protein and ribose may have enhanced the loss of %fat and gain in FFM that occurred within the first 3–6 weeks of the 8-week training program, which was consistent with a recent study by Howarth et al. (14) showing acute increases in protein synthesis after consuming a carbohydrate and protein beverage after aerobic exercise. These results also supported the positive effects of endurance training on body composition and aerobic fitness. Therefore, based on the results of the present investigation in conjunction with previous findings (4,9,15,17–20,25,26,29,33), postexercise recovery drinks containing carbohydrates, protein, and ribose (like the TEST drink) may not affect BW or improve V[Combining Dot Above]O2peak or TTE beyond carbohydrates alone (like the CON drink); however, they may augment improvements in %fat and FFM during the early stages (3–6 weeks) of an 8-week aerobic exercise program. Future studies should incorporate greater levels of exercise intensity and volume to examine the effects of different relative combinations of carbohydrates, proteins, and ribose on the training-induced changes in body composition, aerobic capacity, and endurance performance. Furthermore, coaches and practitioners may benefit from understanding that carbohydrate-, protein-, and ribose-containing recovery drinks may not provide chronic long-term benefits in aerobic power and endurance performance, but they may be useful for improving body composition parameters—particularly in the early stages (3–6 weeks) of endurance training on a cycle ergometer.
This study was funded by a research grant from Nutricia. At the time of submission of this manuscript, J. T. Cramer was a paid consultant for Abbott Nutrition and Vital Pharmaceuticals, Inc. Within the 36 months before submission of this manuscript, J. T. Cramer had been a temporary paid consultant for Celsius, General Nutrition Corporation, Corr-Jensen Labs, and ErgoGenix. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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