During resistance training, it is well documented that muscle glycogen stores can become significantly decreased (4,17,20,24,25). Generally, acute resistance training bouts result in a 24-40% reduction in muscle glycogen stores depending on the duration, intensity, and overall workload encountered during the training bout (4,19,20,24,25). The amount of glycogen utilized during a resistance training bout seems to be related to the overall workload and intensity of the bout. Research by Robergs et al. (20) has indicated that the amount of work accomplished significantly affects the amount of glycogenolysis, whereas the intensity of the exercise bout significantly affects the rate of glycogenolysis during an acute resistance training bout. In their study, Robergs et al. (20) report that twice as much work must be performed using a 35% one repetition maximum (1RM) intensity to equal the amount of glycogenolysis that occurs during resistance training performed at 70% 1RM. Additionally, although equal workloads resulted in equal amounts of glycogenolysis, the 70% 1RM intensity significantly increased the rate of muscle glycogenolysis. Based on these data, higher intensities of resistance training also have the potential to significantly affect muscle glycogen stores.
Because many athletes perform resistance training bouts with intensities in the 70-85% range (22,23) and accomplish significant workloads, the rate and amount of glycogenolysis poses a potential impediment to training performance and/or adaptations. The deleterious effects of decreased muscle glycogen stores may be manifested as increases in muscular weakness (27), decreases in maximal isometric strength (11), and decreases in maximal isokinetic force production capabilities (14). Therefore, any methods that attenuate or augment muscle glycogen stores may result in an ergogenic effect that may be manifested as a maintenance or enhancement of resistance training performance.
The use of CHO supplements to attenuate muscle glycogen losses (4) and augment performance during acute resistance training bouts (7,8,15) has received some attention in the scientific literature. Generally, the studies that have suggested an ergogenic benefit with CHO supplementation during resistance training have used high-volume, low- to moderate-intensity (<70% of 1RM) bouts of exercise that have lasted longer than 55 minutes (7,8,15). Haff et al. (5) suggested that the duration and the volume or total workload of the resistance training bout plays a significant role in the amount of glycogenolysis that occurs in response to the training session. The overall workload or length of the training session seems to play a significantly role in determining the ergogenic effectiveness of the CHO supplement. It seems that an increased reduction in muscle glycogen and a greater reliance on exogenous blood glucose is directly related to the duration of the activity or the overall workload accomplished.
Because higher intensity resistance training bouts are commonly performed by athletes (22,23) and have the potential to affect the rate and amount of muscle glycogenolysis (20), CHO supplements may also be warranted. This may be particularly important in light of the direct relationship between the rates of glycogenolysis and exercise intensity (20,25).
Therefore, based on the current body of scientific literature, it seems that the implementation of a CHO supplementation regimen may offset the decrease in muscle glycogenolysis, which could result in improvements in markers of resistance training performance. To the authors' knowledge, no published studies have examined the performance and physiological effects of a CHO supplementation regimen on resistance training performed at intensities greater than 70% 1RM. Therefore, the purpose of this investigation was to determine whether supplemental CHO ingestion could enhance resistance training performance during an acute resistance training bout at an intensity of 85% 1RM. Based on the work of Robergs et al. (20) and Haff et al. (9), it was hypothesized that the use of a CHO supplement would increase performance of an acute training bout performed at an intensity of 85% of 1RM.
Experimental Approach to the Problem
Subjects reported to Human Performance Laboratory at the same time of day for each of the three testing sessions. Each testing session was separated by 7 days. The first testing session was used to determine subjects' biometric data and to establish a 1RM back squat. This session was also used as a familiarization session for the testing protocol. Subjects were then assigned a treatment session of either a CHO beverage or placebo (PLC). Treatments were administered in a randomized counterbalanced, double-blind protocol, with each subject receiving one of the treatments on each testing session. Subjects participated in this protocol on their second and third visits to the laboratory. For the 3 days before the second and third visits, subjects were required to eat from an eating list to maintain pre-exercise glycogen levels (4). During each of these two visits, subjects consumed either a CHO or PLC beverage before and during the resistance training protocol. The research design is outlined in Figure 1.
Eight healthy resistance-trained men participated in this investigation, which was approved by the Human Subjects Research Committee at Midwestern State University. All subjects were required to have been participating in a resistance training program for a minimum of 6 months and had a 1RM back squat that was a minimum of 150% of body mass. All subjects read and signed an informed consent and completed a health history questionnaire in accordance with the Human Subjects Review Committee at Midwestern State University. Descriptive characteristics for the subjects are presented in Table 1.
Preliminary testing consisted of the measurement of height (cm), body mass (kg), body composition, and 1RM parallel squat. All preliminary testing was conducted 1 week before the first testing session. Height was measured on a Model 400 Healthometer physician's stadiometer (Continental Scale Corp., Bridgeview, IL). Body mass was measured on an electric weight scale (Befour Inc., Saukville, WI). Height and body mass measurements were recorded to the nearest 0.01 cm and 0.01 kg, respectively. Body composition was evaluated using a seven-site skinfold method (13). A standardized testing protocol was used to determine the 1RM parallel squat (21). The maximal weight lifted was recorded as the subject's 1RM. The bottom position of the squat was determined when the tops of the thighs were parallel to the floor (8).
Pretreatment Dietary Controls
For 3 days before the data collection, subjects recorded their food intake and ate a recommended diet that was designed to supply approximately 55% carbohydrates, 20% protein, and 25% fat (8). The diet intervention used in the present study was chosen based on the fact that it has been used in other CHO supplementation studies (7,8), and a recent study has reported that a self-selected 55% carbohydrate diet results in impairments in strength power performance when compared with a diet higher (80%) in carbohydrates (10). Subjects were instructed to refrain from caffeine and alcohol during these 3 days. To ensure that the 3-day dietary recalls were accurate, each subject was given a standardized 3-day dietary journal in which to record food intake, method of food preparation, and the time of day that the food was consumed. Additionally, each subject received detailed descriptions on methods of measuring and recording dietary intake in the journal. The 3-day dietary recall before the first testing session was used as a menu for the three days before the second testing session. Before each testing session, the subjects were questioned about their diet recall and compliance to pretesting guidelines. If a subject indicated that he was noncompliant, the testing session was rescheduled or the subject was dropped from the study. Dietary analyses for total calories and carbohydrates were performed using Food Processor Plus for Windows version 6.05 (ESHA Research, Salem, OR). Food Processor Plus for Windows was chosen because previous research has stated that it has a low percentage (0.3%) of missing information (16).
Subjects were instructed to arrive at the testing site in a 3-hour fasted state (4). On arrival, subjects were fitted with a heart rate monitor (Polar Electro Inc., Woodbury, NY) and rested in a seated position for 10 minutes to minimize metabolic activity. A pre-exercise 10-ml blood sample (PRE) was then collected from an antecubital vein by a trained phlebotomist.
Subjects then began the designated workout protocol, outlined in Table 2, which was based on the individual subject's predetermined 1RM. Each set was performed for five repetitions, with an 8-second per repetition cadence, coupled with 3 minutes of rest in a seated position between sets. Subjects performed the sets of five repetitions with the target weight until they could no longer squat to parallel, failed to complete a repetition every 8 seconds, could no longer continue the protocol because of exhaustion, or voluntarily terminated the session. Ratings of perceived exertion (RPE) were collected immediately after and before each set (2,3). Immediately after the testing session, a 10-mL blood sample (IP) was taken from an antecubital vein. Subjects were then sequestered in the laboratory for 1 hour where they refrained from physical activity and were only permitted to consume water. At the completion of the 1-hour recovery period, a final 10-mL blood sample was collected (1 Hr-POST).
During each testing session, subjects ingested either a CHO supplement (20% Gatorade® solution, The Gatorade Co., Chicago, IL.) or a non-caloric PLC beverage that was identical in taste, texture, color, and volume. Immediately before exercise, subjects consumed either the CHO supplement (0.3g·kg·bodymass−1) or the PLC supplement. Subjects then consumed either a CHO supplement (0.3g·kg·bodymass−1) or PLC after every other successful set of five repetitions, beginning at the completion of warm-up set 2, and continuing until the testing session was terminated. The CHO supplementation regimen was based on previous research that involved CHO supplementation and resistance training (8).
Total number of sets, repetitions, and total work were analyzed to determine performance during the testing sessions. Sets were counted as the total number of completed sets of five repetitions. Repetitions were determined by the total number successfully completed to muscular failure. Vertical displacements of the barbell were measured with the use of a V-Scope weightlifting analysis system (Lipman Inc., Israel), then combined with a work prediction equation (18) to determine the total work performed during each testing session.
Blood samples were used in the determination of hematocrit (Hct), lactate (La) concentration, blood glucose (BG) concentration, and free fatty acid (FFA) concentration. Whole blood was frozen at -80°C and later analyzed for BG and La using a Yellow Springs Model 2700 Select Biochemistry Analyzer (YSI, Yellow Springs, OH). The remaining blood was centrifuged at 2750g at 4°C for 30 minutes (IEC Centra MP4, Needham Heights, MA). The serum was later analyzed for FFA concentrations using a nonesterified fatty acid (NEFA) in vitro enzymatic colorimetric method (Wako Chemicals GmbH, Neuss, Germany). Fluctuations in plasma volume were calculated from the Hct (26) and used to correct the BG, La, and FFA measurements. All blood samples were analyzed in duplicate and averaged for analyses. Coefficient of variance (CV) and intraclass correlations (ICC) for La, BG, and FFA were as follows: La ICC = 0.999, CV < 3.0%; BG ICC = 0.994, CV < 2.9%; FFA ICC = 0.933, CV < 4.0%.
A 2 × 3 repeated measures analysis of variance (ANOVA) was used in the examination of BG, La, and FFA with significance set at p ≤ 0.05. When significant F values were determined, paired comparisons were coupled with a Holms sequential Bonferroni procedure (12) to control for type I errors and to determine where differences existed. Total sets, total repetitions, and total work were analyzed with paired t-tests, with significance set at p ≤ 0.05. Three-day dietary recalls for each subject were analyzed using paired t-tests with significance set at p ≤ 0.05. The observed statistical power of the dependant variables ranged from 0.05 to 1.00. All data are reported as means ± standard deviation. All statistical analyses were performed with the use of SPSS 12.1 (Chicago, IL).
For the 3 days before each testing session, a standard diet was followed. Dietary intake for all subjects before the CHO and PLC trials was not statistically different between treatments for total calories (CHO 3428.8 ± 1092.3 kcal, PLC 3443.0 ± 1098.2 kcal), CHO (CHO 410.7 ± 137.87 g, PLC 415.7 ± 143.6 g), protein (CHO 162.3 ± 47.8 g, PLC 158.9 ± 44.5 g), or fat (CHO 126.5 ± 49.5 g, PLC 127.6 ± 50.5 g).
Resistance Training Performance
Table 3 presents the performance measures for both the CHO and PLC treatments. No statistically significant differences were noted between the CHO and PLC treatments when examining the number of repetitions (p = 0.88, η2 = 0.004), number of sets (p = 1.00, η2 = 0.000), total work (p = 0.83, η2 = 0.008), volume load (p = 0.78, η2 = 0.012), and duration of exercise (p = 0.70, η2 = 0.023).
Blood Glucose Response
There were no statistically significant differences in BG levels between the CHO and PLC treatments at the PRE (p = 0.52, η2 = 0.06) and 1Hr-Post measurements (p = 0.52, η2 = 0.06). However, BG was significantly elevated in the CHO treatment when compared with the PLC at the IP testing measurement (p ≤ 0.01, η2 = 0.86).
BG was significantly elevated IP in the CHO treatment session compared with PRE (p = 0.03, η2 = 0.50). Conversely, the BG level was significantly decreased (p ≤ 0.01, η2 = 0.72) at the 1 Hr-Post measurement when compared to the IP measurement. No significant differences existed in the CHO group from PRE to 1 Hr-POST.
There was a significant decrease in BG at the 1 Hr-POST measurement in the PLC group (p = 0.02, η2 = 0.59) compared with PRE. There were no significant differences (p = 0.36, η2 = 0.12) in BG between the PRE and IP measurement periods. A complete summary of all BG results is presented in Table 4.
There was no significant difference between the La response to the CHO and PLC treatments at the PRE (p = 0.46, η2 = 0.08) and IP (p = 0.08, η2 = 0.38) measurements. However, the CHO treatment elicited a significantly (p = 0.04, η2 = 0.48) increased La concentration compared with the PLC treatment at the 1 Hr-POST measurement. A summary of the La responses to the CHO and PLC treatments is presented in Table 4.
There was a significant change in the La response in both CHO and PLC treatments from PRE to IP (CHO p ≤ 0.01, η2 = 0.91; PLC p ≤ 0.01, η2 = 0.84) and from IP to 1 Hr-POST (CHO p ≤ 0.01, η2 = 0.88; PLC p ≤ 0.01, η2 = 0.86). In the PLC treatment group, a significant difference existed from PRE to 1 Hr-POST (p ≤ 0.01, η2 = 0.68).
Free Fatty Acids Response
There were no significant differences between FFA concentrations in response to the CHO and PLC treatments. However, there was a trend for the FFA concentration at the 1 Hr-Post measurement to be significantly higher in the PLC treatment group (p = 0.07, η2 = 0.39).
The FFA was significantly lower at 1 Hr-POST when compared with PRE in the CHO treatment (p ≤ 0.01, η2 = 0.65) and the PLC treatment (p ≤ 0.01, η2 = 0.65). No significant differences existed between IP and 1 Hr-POST measurement in the CHO or PLC treatments (Table 4).
Rating of Perceived Exertion
The RPE for each resistance training bout is presented in Table 5. No significant differences existed between CHO and PLC treatments for any measurement period There were significant differences in time effect between the CHO and PLC treatments between Warm-up and Target (p ≤ 0.01, η2 = 0.96), Warm-up and END (p ≤ 0.01, η2 = 0.99), and Target and END (p ≤ 0.01, η2 = 0.82)..
Heart Rate Response
There were no statistically significant differences noted between the CHO and PLC treatments when examining the heart rate responses to the resistance training bout.
The primary finding of the present investigation is that the use of a CHO supplementation regimen does not enhance acute resistance training performance when an intensity of 85% 1RM is reached during back squats performed to volitional failure. These findings were unexpected, as several investigations presented in the scientific literature have suggested that CHO supplementation during acute resistance training bouts elicits an ergogenic effect (6,7,15).
The ergogenic effects of CHO supplementation regimens are most commonly linked to the amount of glycogenolysis that occurs during acute resistance training bouts (5-7). Acute resistance training bouts are associated with a 25-40% decreases in muscle glycogen stores depending on the duration, intensity, and overall workload accomplished during the training bout (4,19,20,24,25). Robergs et al. (20) reported that an acute bout of resistance training performed at 70% 1RM resulted in a significantly greater rate of muscle glyogenolysis compared with a 35% 1RM bout. To accomplish the same total amount of glycogenolysis in the 35% group as the 70% group, twice as many repetitions needed to be performed. These data suggest that higher intensity bouts of resistance training have the potential to increase the rate of glycogenolysis and stimulate substantial amounts of glycogenolysis if the overall workload is high.
Although muscle glycogen was not measured in the present investigation, it may be hypothesized that significant muscle glycogenolysis should have occurred. In a previous study, Haff et al. (4) reported a significant 19.2% decrease in response to a resistance training bout that resulted in 298.4 ± 39.8 J of work. The resistance training bout utilized in the present investigation resulted in 29.9 ± 22.3 kJ and 28.6 ± 19.5 kJ of work in the CHO and PLC groups, respectively. Because the current resistance training bout resulted in a larger overall workload, it is likely that a greater overall glycogenolytic effect may have occurred. Additionally, it is likely that the greater intensity encountered in the present investigation resulted in an increased rate of glycogenolysis, thus suggesting that the inclusion of a CHO supplementation regimen should have resulted in an ergogenic effect that would be manifested as maintenance of or improvement in resistance training performance.
The lack of an ergogenic effect noted in the present study is in contrast to several investigations presented in the scientific literature (6,7,15). This divergence with the scientific literature may have occurred as a result of several factors that are significantly different in the present investigation. Generally, the studies that have reported improvements in resistance training performance with CHO supplementation have utilized protocols with intensities less than 85% 1RM, durations of exercise longer than 55 minutes, and large workloads (5).
In the study by Haff et al. (8), the resistance training bout was performed with an intensity of 55% 1RM, and CHO supplements resulted in significant improvements in performance. This lower intensity of exercise resulted in a workload of 335.9 ± 88.7 kJ in the CHO group and 223.6 ± 46.6 kJ in the placebo group, which was much larger than the workload (CHO 29.7 ± 22.3 kJ, PLC 28.5 ± 3.0 kJ) accomplished in the present study. Additionally, the duration of the present study (CHO 29.7 ± 3.6 min, PLC 28.5 ± 3.0 min) was significantly less than the duration achieved (CHO 77.7 ± 19.4 min, PLC 46.0 ± 8.9 min) in the study by Haff et al. (8).
When examining the study by Lambert et al. (15), increases in the repetitions and sets were noted with the use of a CHO supplementation regimen and an exercise protocol that used an intensity of 70% 1RM. No work data were presented, but the number of repetitions (CHO 149.0 ± 16.0, PLC 129.0 ± 12.0) were similar to those accomplished (CHO 198.7 ± 46.8, PLC 131.0 ± 27.2) in the study by Haff et al. (8). In the present study, many fewer repetitions were accomplished (CHO 20.4 ± 14.9, PLC 19.7 ± 13.1) compared with the studies by Lambert et al. (15) and Haff et al. (8). Additionally, the duration of the exercise bout reported by Lambert et al. (15) was approximately 56 minutes, which was substantially longer than the current investigation (CHO 29.7 ± 3.6 minutes, PLC 28.5 ± 3.0 minutes).
In the study by Haff et al. (7), CHO supplements resulted in increases in total work (CHO 41.1 ± 3.9 kJ, PLC: 38.1 ± 3.9 kJ) during isokinetic leg exercise while the duration of the exercise bout was held constant at 57 minutes. The workload (CHO 29.7 ± 22.3 kJ, PLC 28.5 ± 3.0 kJ) and duration of exercise (CHO 29.7 ± 3.6 minutes, PLC 28.5 ± 3.0 minutes) in the present study was markedly less than that in the study by Haff et al. (7).
Taken collectively, the studies by Lambert et al. (15) and Haff et al. (7,8) suggest that relatively high workloads that last for a longer duration are necessary to elicit a large enough glycogenolytic effect to allow CHO supplements to be an effective ergogenic aid. In the present study, a CHO supplementation regimen did not result in a significant increase in any performance markers. It is possible that the intensity of the acute resistance training bout did not allow the subjects to perform enough work or exercise for long enough to induce a significant glycogenolytic effect and thus increase the need for CHO as a fuel substrate (5). However, it is likely that muscle glycogen stores were significantly affected even though few sets were completed in the present study, but it is unlikely that this was the major cause of the fatigue experienced during the training bout.
Because CHO supply was not a limiting factor in the acute resistance training bout, other factors most likely resulted in the fatigue stimulated by the protocol. MacDougall et al. (17) suggested that it is unlikely that ATP and PCr are limiting factors in an acute resistance training bout performed with 80% 1RM to volitional failure. In their study, MacDougall et al. (17) reported that three sets of biceps curls performed at 80% 1RM does not significantly affect ATP concentration and significantly decreases PCr. Although muscle biopsies were not collected during this investigation, it is likely that decreases in PCr may partially explain the development of fatigue during the present investigation.
In the present study, a significant seven- to eightfold increase in blood La concentration was noted IP compared with PRE La concentration in both the CHO and PLC treatment groups. It is likely that the 3 minutes of recovery between sets was not long enough to result in the clearance of muscle La (1). MacDougall et al. (17) suggest that increases in muscle La and H+ partially explain the fatigue that occurs in response to high-intensity resistance training bouts performed to volitional failure. Based on these results, it is likely that the increases in blood La partially explain the cause of fatigue in the present investigation.
In conclusion, the primary finding of the present investigation is that the ingestion of CHO supplements before and during an acute resistance training bout performed for sets of five repetitions with 85% 1RM to volitional failure does not elicit an ergogenic effect. It is likely that CHO supplements are not needed for bouts of resistance training that do not induce a large workload or require a long duration. Although it is very likely that muscle glycogen stores are affected by high-intensity, shorter-duration resistance training bouts, it seems that other factors, such as decreases in PCr and increases in La, have a greater impact on the fatigue accumulated in response to the training bout.
These data suggest that the consumption of a CHO supplement before and during a resistance training bout that requires athletes to perform exercises with an intensity of 85% 1RM does not result in improved performance. Therefore, when considering the use of CHO supplements, the strength and conditioning professional or strength/power athlete may receive the most benefit from the supplement when it is consumed before and during high-volume resistance training such as that seen during a traditional hypertrophy phase of training or when multiple training sessions are performed during 1 day (4,6).
However, it is important to note that, based on previous literature, a high-intensity resistance training session can result in a significant glycogenolytic effect. If several days of high-intensity resistance training are coupled with inadequate dietary carbohydrate consumption, muscle glycogen stores may be negatively affected, which could result in a performance decrement (9). One countermeasure that may be useful in ensuring the maintenance of muscle glycogen stores by strength/power athletes could be the consumption of CHO supplements during high-intensity training (4). It is, however, important to note that further research is needed to understand the ergogenic roles of CHO supplementation during various types of resistance training bouts.
The current research project was supported by a Midwestern State University College of Health and Human Services research grant and donations from The Gatorade Sports Science Institute.
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