Superimposed electromyostimulation (SEMS) training involves artificially activating the muscle while performing voluntary contractions during a resistance exercise protocol. This style of exercise training has been used in the rehabilitation setting as a compliment to voluntary resistance training (24,35). Also, SEMS is used to increase muscle strength and to accelerate hypertrophy after immobilization-induced atrophy (e.g., casting during an injury) (35,41). The SEMS training programs are also being used by healthy individuals (13,14) and competitive athletes (38) to enhance muscle strength and physical performance during sport-specific skills (7,10,18). This modality of training has been shown to enhance muscle strength more so than just normal strength training alone (26,27).
In particular, it has been reported that electromyostimulation of the quadriceps muscle results in greater increases in muscle strength (4), thereby potentially augmenting anaerobic sport performance (10,39,40,42). The SEMS enhanced the physical performance of elite and subelite healthy athletes in sporting activities such as tennis (39), basketball (40), volleyball (42), swimming (46), rugby (1), track and field (54), and ice hockey (10). The increased physical performance may be attributed to an augmented muscle activation of pattern (16), thus causing increased force production and anaerobic performance (52).
Conversely, acute application of SEMS has been shown to result in increased fatigue of the working muscle (9,30,51,56). This rapid onset of fatigue during work bouts may be attributed to increased fiber activation patterns (16). In both SEMS and anaerobic training, high levels of adenosine triphosphate (ATP) hydrolysis are required by the active muscles to sustain force output. Originally, it was speculated that this energy demand was met exclusively by the ATP–phosphocreatine system; however, studies have reported that significant glycolytic activity does occur in people performing resistance exercise (20,47,50). These studies suggest that decreases in endogenous glycogen stores coupled with hypoglycemia may lead to a reduction in force output during periods of prolonged resistance exercise.
In this regard, an exogenous supply of glucose may delay fatigue (25,43) by lessening the dependency on endogenous muscle glycogen (2,55). The reduced reliance on endogenous muscle glycogen has been found to occur during resistance exercise (19,20), and thus, the consumption of an exogenous carbohydrate supplement before and during an exercise session may attenuate muscle glycogen depletion. However, the literature has yielded conflicting results regarding the ergogenic impact of carbohydrate ingestion during resistance exercise. In 4 studies, the authors reported increases in the amount of work performed during resistance exercise sessions in subjects supplemented with carbohydrates (20,23,36,53). However, these findings are in contrast to those of another study that reported no augmentation in performance measures after carbohydrate supplementation (34). These disparate results may be because of differences in exercise intensity, exercise duration, participant selection criteria, or central nervous system factors (i.e., psychological factors and emotions).
Therefore, the aim of this study was to investigate the effects of supplemental carbohydrate ingestion on blood parameters and total force output during SEMS of the quadriceps muscle in elite weightlifters. We hypothesized that carbohydrate ingestion before and during an isometric resistance exercise protocol coupled with SEMS would lead to greater blood glucose availability, consequently resulting in an increased performance.
This study was conducted in parallel with the prior mentioned publication by Wax et al. (53). This second article uses data from the same experiment but reports the effects of supplemental carbohydrate ingestion during an SEMS resistance exercise protocol on plasma glucose, nonesterified fatty acids, glycerol, and the sum of the total force produced during the submaximal phase, rather than its effects on blood lactate, time to exhaustion, and periodic maximal force output.
Experimental Approach to the Problem
This study was designed as a randomized counterbalanced, double-blind experiment. The protocol employed in this study was based on a prior study (53), which tested the efficacy of carbohydrate (CHO) ingestion on time to exhaustion in a SEMS resistance exercise protocol. The subjects reported to the laboratory 3 times (i.e., visit 1, visit 2, and visit 3) at the same time of the day. Visit 1 was used to obtain anthropometric data and to familiarize the subjects with the experimental techniques. During visit 2, half of the subjects chosen at random consumed a CHO solution, and the other half consumed a placebo (PL) solution before and during the exercise protocol. On visit 3, the subjects consumed the other solution, and the same exercise protocol was performed. There was a 7-day period between visit 1 and visit 2, and between visit 2 and visit 3.
Six apparently healthy male volunteers (age: 29 ± 4 years old, height: 1.79 ± 0.09 m, weight: 102 ± 21 kg, and body fat: 14 ± 9% ) with a minimum of 5 years of continuous competitive bodybuilding and power lifting experience participated in this study. A sample size analysis was performed a priori for force output (primary dependent measure) and showed that for this repeated measures experimental design 6 participants were required to achieve a power of 0.80. All the subjects were national level competitors in their perspective power lifting and bodybuilding sports. The subjects had no lower extremity musculoskeletal injuries in the previous 6 months and were free (self-reported) of any anabolic steroid use for a year before the experimental sessions. This study was reviewed and approved by the Institutional Review Board, and all the subjects completed a health history questionnaire and signed an informed consent before initiation of data collection.
During the CHO condition, the subjects consumed a loading dose of a 10% carbohydrate solution (Carboplex, Unipro Inc., Atlanta, GA, USA) at 1 g of carbohydrate·per kilogram of body mass. The subjects also consumed the same solution at a dose of 0.17 g of carbohydrate per kilogram of body mass before the exercise protocol started and thereafter at 6-minute intervals until the completion of the exercise protocol. Prior data indicate that this concentration of carbohydrate clears from the stomach at a rate comparable with that of water, while maintaining a high rate of carbohydrate availability to the muscle (45). In addition, the carbohydrate intake timing was based on data showing that this amount of carbohydrate increases resistance exercise performance during lower body muscle contractions (36,53). During the PL condition, the subjects consumed a solution that contained saccharin and aspartame that was similar in taste, texture, color, and volume to the carbohydrate solution.
This session was used to determine subjects' anthropometric data. Also, the subjects were instructed to refrain from strenuous leg exercise and caffeine and alcohol intake for 48 hours before each of the following 2 visits. Furthermore, the subjects were asked to maintain a log of their dietary intake 3 days before visit 2 and were instructed to duplicate the nutritional intake before visit 3. In addition, the subjects performed a mock submaximal session to familiarize themselves with the experimental procedures and equipment.
Visits 2 and 3
The subjects reported to the laboratory at the same time of the day for visit 2 and visit 3, after an overnight fast during the morning hours. Upon arrival, the subjects were questioned about their compliance in regard to their activity level and submitted their nutritional journal to a trained evaluator. If a subject failed to meet the pretesting guidelines required for participation in that day's protocol, the session was rescheduled. All the subjects complied with the pretesting criteria and completed their scheduled sessions.
After the evaluator's clearance regarding compliance to the pretesting guidelines, the subjects consumed their assigned solution (CHO or PL; minute 0). Next, electrodes (10.16 × 10.16 cm) were securely placed on the subjects transversely to the proximal (10 cm below the groin) and as close as possible to the motor point of the vastus medialis and vastus lateralis muscles on subjects' perceived dominant leg. The subjects were then seated with the dominant knee secured to a 300-lb load cell strain gauge (Transducer Techniques, Temecula, CA, USA) at an angle between 85 and 90° just above the malleoli. This position mimics a typical seated leg extension model used in training facilities. A restraint was placed around the pelvic region to maintain quadriceps muscle length and to prevent substantial use of hip flexors during exercise protocol.
To determine maximal voluntary force output, the subjects performed an isometric maximal voluntary contraction without SEMS by using their dominant leg (preexercise—minute 10). The subjects performed a series of three, 3-second maximal voluntary contractions. Force output was amplified (Model SGA-6, Advanced Mechanical Technology, Inc., Watertown, MA, USA) by using the signal sent via the load cell and the signal was recorded at 1,000 Hz using DataPac 2000 (Run Technologies, Laguna Hills, CA, USA). Each subject rested between each maximal voluntary contraction for a duration of 90 seconds. The greatest force held for 1 second was deemed to be the maximal voluntary contraction. After determination of maximal voluntary contraction, the subjects underwent transcutaneous muscle stimulation to obtain a level of stimulation they could comfortably tolerate without discomfort (preexercise—minute 20). The quadriceps muscle was stimulated using a transcutaneous electronic muscle stimulator (Dynapulse 8, Health Group, Vista, CA, USA) and pulse waves of 60 Hz lasting 100 microseconds were used. Stimulation intensity was determined by the pain tolerance of each subject. The maximal tolerated intensity varied between 70 and 110 mA. The level of stimulation and electrode placement remained constant for each subject throughout the study, and this stimulation was used to apply SEMS during isometric maximal voluntary contractions. This assured minimal variability in fiber recruitment during each session. No subject reported any serious discomfort during the experiment.
The subjects had a set target force of 50% of their predetermined maximal voluntary contraction and began the exercise protocol (minute 30) by performing repeated isometric contractions. Additionally, visual feedback was provided to the subjects marked on a storage oscilloscope. The subjects generated a continuous pattern of 20-second contractions without SEMS followed by a 40-second rest period (duty cycle 0.20). During the last 3 seconds of the first 20-second voluntary isometric contraction, and thereafter at 5-minute intervals, SEMS was applied during a maximal voluntary contraction in a concomitant manner.
The exercise protocol continued until failure. Failure in this investigation was defined as the inability of a subject to sustain 50% target force output for 5 consecutive seconds. After failure, the subjects remained seated for 5 minutes, and this time point was defined as recovery. Total force output was defined the sum of the force produced during the 50% maximal voluntary contractions for the duration of the exercise protocol. These procedures are summarized in Figure 1.
Blood samples were obtained at minute 10 (pre), within 15 seconds of failure, and 5 minutes after failure (recovery). All blood samples were obtained using a 20-G Teflon cannula placed in a superficial antecubital vein by a registered nurse. The cannula was maintained patent using an isotonic saline solution (with 10% heparin solution) placed in a 3-way stopcock with a male Luer lock adapter. Blood samples for nonesterified fatty acids and glycerol analyses were collected in serum-separator tubes, and blood samples for glucose, hematocrit, and hemoglobin analyses were collected in tubes containing ethylenediaminetetraacetic acid.
Plasma glucose concentration was measured by the hexokinase method as described by Barthelmai and Czok (3), and later modified by Konig et al. (31). Nonesterified fatty acids were determined by in vitro enzymatic colorimetric method (Wako Pure Chemical Industries, Dallas, TX, USA). Glycerol levels were determined by using the modified methods published by McGowan et al. (44). Hematocrit and hemoglobin values (Sigma Diagnostics, St. Louis, MO, USA) were used to determine plasma volume shifts (15) and values for glucose, nonesterified fatty acids, and glycerol were corrected for these shifts changes. Intraassay variance was <5% for all assays.
Total force output data were analyzed using repeated measures t-test. Glucose, nonesterified fatty acids, and glycerol data were analyzed by using a 2 (condition; PL or CHO) × 3 (time; pre, failure, recovery) repeated measures analysis of variance (ANOVA). When the ANOVA was found to be significant, pairwise comparisons were made using repeated measures t-test to deduce differences between groups. All statistical analyses were performed by using analyzed using PASW Statistics 20 (SPSS, Inc., Chicago, IL, USA). Data are reported as mean ± SD.
Dietary intake analysis showed no differences for carbohydrate, protein, fat, or total kilocalories consumed for CHO or PL (p > 0.05).
Total force output (newtons) was significantly increased (p < 0.05) in CHO compared with that of PL. It is important to note that all 6 subjects had a higher total force output when they consumed the carbohydrate solution compared with placebo solution (Figure 2). The correlation coefficient of average measures was 0.85 (p < 0.05).
The average measure of intraclass correlation coefficient of plasma glucose was 0.91 (p < 0.05). A 2-way repeated measures ANOVA indicated a significant interaction effect (p < 0.05) for plasma glucose. The subjects who ingested CHO had significantly higher (p < 0.05) plasma glucose at all 3 time points (pre, failure, recovery) compared with PL subjects (Figure 3). Furthermore, in CHO subjects, plasma glucose was significantly higher (p < 0.05) at recovery compared with failure and pre, and at failure, plasma glucose was statistically higher (p < 0.05) compared with pre. In regard to PL, we observed a significant increase (p < 0.05) in plasma glucose at failure and recovery compared with pre. However, unlike CHO subjects, plasma glucose during the PL condition was not statistically different (p > 0.05) at recovery compared with failure.
The results for serum nonesterified fatty acids and glycerol are presented in Figures 4 and 5, respectively. The average measure of intraclass correlation coefficient of serum nonesterified fatty acids was 0.93 (p < 0.05). Although PL subjects had numerically higher serum nonesterified fatty acids compared with CHO, no statistical differences (p > 0.05) were detected. Also, our data did not show any statistical differences (p > 0.05) for serum glycerol. The average measure of intraclass correlation coefficient of serum glycerol was 0.67 (p < 0.05).
In this study, it was hypothesized that carbohydrate ingestion before and during resistance exercise coupled with SEMS would lead to greater blood glucose availability and higher total force output. Our results clearly indicate that the subjects who consumed the carbohydrate solution generated a greater overall force output during the exercise protocol compared with placebo ingestion. Further, the data also show that plasma glucose remained at significantly higher levels when the subjects consumed the carbohydrate solution compared with when they consumed the placebo solution. The data also show that nonesterified fatty acids and glycerol levels were not altered by the resistance exercise protocol used in this study after either placebo or carbohydrate supplementation.
In this study, an SEMS resistance exercise protocol was used to investigate the potential ergogenic benefits of carbohydrate supplementation during this type of activity. Previous studies have shown increased muscular force generation and anaerobic performance with the application of SEMS in conjunction with voluntary isometric muscle contractions compared with voluntary contractions alone (6,16,49,52). Despite this increase in performance, a single bout of SEMS of the quadriceps muscle—as used in this study—has been reported to induce significant muscle fatigue (∼20% torque loss) and soreness (56). However, these studies did not investigate the possible additional benefits of carbohydrate supplementation on the work performed in conjunction with SEMS. Our study used both of these experimental paradigms, and our main findings are that carbohydrate supplementation provided further ergogenic effect to SEMS.
The increase in force output indicates that resistance exercise performance is affected by decreased muscle glycogen stores and increased blood glucose availability (21). In response to intense bouts of exercise, the body is primarily in a catabolic state. Many of the stress hormones are elevated and important fuel stores (e.g., muscle glycogen) decrease (28). For the body to recover and training adaptations to occur, this process must be mitigated. The supplementation of carbohydrate before, during, and immediately after intense bouts of exercise has been shown to be beneficial during cardiovascular endurance exercises (17,29,37), resistance exercises (20,22,23,34,36), and to a limited extent in electromyostimulation training (53). Exogenous carbohydrate supplementation can inhibit the release of catabolic stress hormones (33), suppress protein catabolism (8), and augment muscle glycogen stores by increasing insulin concentrations (11), resulting in elevated growth hormone levels (32,48), which fosters the creation of an anabolic environment (21). This increase in growth hormone resulting from carbohydrate-induced insulin spikes have been reported to last 5–6 hours postexercise (11). The enhancement of this anabolic state may increase muscular strength and decrease recovery time.
In this regard, the findings from our study are in agreement with the findings of Haff et al. (20,23), and Lambert et al. (36) who reported that carbohydrate supplementation increased muscular performance. Our previous results (53) revealed that the total time to exhaustion and mean force production were significantly higher in the carbohydrate treatment than in placebo treatment when performing SEMS concurrently with isometric leg contractions. This ergogenic effect may be explained by several factors. Specifically, SEMS training concurrently with voluntary isometric exercise results in greater fiber use, thus resulting in greater depletion of muscle glycogen stores. Researchers have postulated that intermittent carbohydrate ingestion during intense resistance exercise would mitigate this glycolytic effect occurring in the muscle by providing an exogenous source of glucose. Because most forms of resistance exercise have intermittent characteristics, carbohydrate ingestion may foster an internal environment within the exercising muscle that augments performance (22). This may be attributed to decreased reliance on muscle glycogen (2,5,20,55) by way of continued delivery of exogenous glucose to the working muscle (12,22,36).
Despite claims that carbohydrate supplementation can augment performance during resistance exercise, the literature has not consistently supported this assertion. This may be related to the nature of subjects selected (i.e., untrained, novice, recreational lifter, trained lifter) and the various resistance exercise paradigms used (21) or the timing of the ingestion of carbohydrate ingestion combined with the length of the resistance exercise session (12,36). It is reasonable to suggest that carbohydrate supplementation before and during resistance exercise may increase plasma glucose availability and improve performance thereby delaying the onset of muscular fatigue. Therefore, the potential ergogenic effects of carbohydrate ingestion would be clearer if trained subjects performed highly intense exercise bouts of high work volumes.
The primary findings of this study reveal that carbohydrate ingestion before and intermittently during an SEMS session of isometric leg contractions at 50% 1 repetition maximum to failure mitigates fatigue factors by providing exogenous glucose to the exercising muscle, eliciting an ergogenic effect by augmenting submaximal force output. Furthermore, the results suggest that practitioners and athletes may find that carbohydrate supplementation above that of their normal food intake may provide ergogenic benefits when ingested before and during high-volume resistance training as performed during muscular endurance and hypertrophy phases of traditional periodization training programs. Consequently, despite these positive findings, there are limitations to our study such as limited number of subjects, homogeneity of subjects used, specific training condition (isometric SEMS of dominant quadriceps muscle), and heterogeneity in individual response to SEMS. Therefore, further investigations are warranted to elucidate the ergogenic benefits of carbohydrate supplementation with various types of resistance training bouts.
No grant support was used to perform this study. The results of this study do not constitute endorsement of any products by the authors or National Strength and Conditioning Association.
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