Twelve men, with resistance training experience (mean ± SD: age = 22 ± 3 years [range = 19–26 years]; height = 179 ± 7 cm; body mass = 86 ± 13 kg) were recruited for this study. The subjects were involved in a whole-body resistance training program, at least 3 times per week continuously for at least 1 year. Potential subjects who were unable to maximally back squat a weight of ≥1.5 times their body mass were excluded from participation. The mean ± SD 1RM back squat for the subjects in this study was 142 ± 34 kg (1.7 ± 0.3 × body mass). All subjects were free from musculoskeletal injuries or neuromuscular diseases and did not report any medical disorders or medicinal or supplement usage that could have affected the outcome of this study. This study was approved by the University of Kentucky's Institutional Review Board for the protection of human subjects, and all subjects completed a written health history questionnaire and informed consent document before any testing.
Body Composition Assessments
A total-body DXA scan (GE Lunar Prodigy; GE Lunar, Inc., Madison, WI, USA) scan was performed to assess total-body fat percentage (%BF) and mineral-free lean model mass (in kilograms). The subjects were instructed to remove all objects, such as jewelry or eyeglasses, and wore T-shirt and shorts containing no metal during the scanning procedure. All scans were analyzed by a single trained investigator using the Lunar software version 13.10 (GE Lunar, Inc., Madison, WI, USA).
1-Repetition Maximum Testing
All of the resistance exercises were dynamic constant external resistance (DCER) barbell movements, including 4 upper-body (flat bench press, bent-over row, incline bench press, and standing shoulder press) and 4 lower-body (back squat, deadlift, front squat, and reverse lunge) lifts. A standardized warm-up was completed before each of the 1RM tests. The warm-up began with 10 repetitions at 50%, 5 repetitions at 70%, 3 repetitions at 80%, and 1 repetition at 90% of each subject's predicted 1RM body mass. One minute of rest was provided between warm-up sets, and 2 minutes of rest was provided between the final warm-up set and the first 1RM attempt. The subjects completed up to 3 attempts to determine the 1RM (13). For all 1RM DCER strength testing, progressive loads were added until the subject could not complete a repetition through the full range of motion. Additional trials were performed with lighter loads until the 1RM was determined within 2.27 kg, which was typically achieved within 3 trials. Three minutes of rest was given between 1RM attempts.
The barbell back squat was performed on a standard free-weight rack using an Olympic barbell. The barbell was positioned above the posterior deltoids at the base of the neck. The subjects' feet were positioned shoulder-width apart, with the toes pointed slightly outward. The subjects were instructed to keep their feet on the floor and maintain a flat back, keeping the torso-to-floor angle relatively constant through the range of motion. A complete repetition was considered when the subject moved from an erect position into flexion at the knee and hip until the thighs were parallel to the floor and then returned to the original position (49). The front squat was performed in a similar manner as the back squat, with the exception that the barbell was positioned across the front of the body over the anterior deltoids near the clavicle. A clean grip or cross-armed grip was used at the subject's discretion.
The barbell deadlift was performed using free weights and a standard Olympic barbell. The subjects performed a conventional style deadlift (vs. sumo), in which their feet were approximately hip width, with toes pointed slightly outward. The subjects started the lift with flexion at the knees and hips so that the back was flat and at an approximately 60° angle to the floor. The subjects were instructed to use an alternating grip. A complete repetition was considered when the subject reached full extension at the knees and hips with the barbell and returned the barbell back to the floor in a controlled manner. “Hitching” and “back lifting” (where the lifter extends their knees before, not at the same time as, their hips) was not permitted.
The barbell reverse lunge was performed in a standard squat rack with an Olympic barbell. The subjects grasped the barbell with a closed, pronated grip. The bar was positioned above the posterior deltoids at the base of the neck. The subjects stepped backward with one, keeping the torso erect and the trailing foot planted on the floor. The subject allowed the thigh and lower leg to slowly flex until the knee was 1–2 inches above the floor and the thigh was parallel with the floor (∼2 seconds). The subjects pushed off the floor with the back leg, extending the leg and thighs, brining the back foot to the starting position. After a brief pause (∼1 second), the subject completed the same movement with the opposite leg. The 1RM was considered to be achieved only if the weight could be moved through the range of motion twice (using right and left legs as the back leg 1 time).
The flat barbell bench press was performed on a standard free-weight bench with an Olympic barbell. After receiving a liftoff from the spotter, the subjects lowered the barbell to their chest just above the nipple line, paused briefly, and then pressed the bar to full extension of the forearms. This was defined as one complete repetition. The incline bench press was performed in the same manner as the flat barbell bench press, with the exception that the bench was inclined to approximately 45°. The barbell touched the chest slightly higher than during the flat barbell bench press.
The shoulder press was performed in a standard squat rack with an Olympic barbell. The subjects used a 3-handed pronated grip to secure the barbell in their hands and lifted it from the rack. The barbell was positioned across the front of the body over the anterior deltoids near the clavicle. The subjects were instructed to take one step backward with each foot, gain their balance, and push the barbell overhead to full elbow extension. One repetition was defined as raising and lowering the bar under control. Safety pins were set within the rack, so the subject could release the weight from their grip onto the pins if needed. Additionally, one spotter was placed on each side of the barbell for safety.
The barbell bent-over row was performed from the floor with an Olympic barbell, using a closed, pronated grip. The subjects positioned their feet shoulder-width apart, with slight flexion at the knees. The torso was flexed so that it is just slightly above parallel to the floor. The movement began with the forearms fully extended and the barbell 1–2 inches from the floor. The subject pulled the bar toward the torso, keeping the back flat and slight flexion at the knees. The barbell touched the lower chest or upper abdomen and was lowered back to the starting position.
Vertical Jump Test
Vertical jump height was measured using the Vertec vertical jump device (Gill Athletics, Champaign, IL, USA). Each subject was positioned directly underneath the Vertec and instructed to jump as high as possible from a standing 2-foot position, use a countermovement, and move the highest horizontal vane with a single hand (39). Each subject performed 3 VJs with 2 minutes of rest between each trial. Vertical jump height was calculated as the difference between the highest vane of the Vertec reached and the standing reach height and expressed in centimeters. The test-retest data from our laboratory for the VJ test (n = 15) has been shown to be highly reliable (intraclass correlation [ICC] = 0.99) with no significant mean differences (mean difference = −2.36 cm; 95% confidence interval [CI] = −6.92 to 2.19 cm; p > 0.05) between test-retest values.
Isokinetic strength was assessed using a Biodex System 4 (Biodex Medical, Shirley, NY, USA). The subjects were positioned on the isokinetic dynamometer in a seated position. After several submaximal repetitions, the subjects completed 3 maximum effort concentric leg flexion and extension contractions on the dynamometer at 30°·sec−1. The peak torque (N·m) was defined as the highest of the 3 trials. The isokinetic strength testing has been shown to be highly reliable (ICC = 0.98), with no significant mean differences between test-retest values (9).
Bench Throw Test
The 1RM barbell flat bench press was determined before the bench throw test. The bench throw test was performed on a Smith machine (OSSM; Life Fitness, Chicago, IL, USA), with the subject supine on a flat bench. A weight equal to 30% of the subjects' bench press 1RM was used. The subjects were instructed to begin the movement with the arms fully extended and then lower the barbell in a rapid but controlled (without pulling or allowing the barbell to bounce off the chest) manner and then immediately move the barbell as fast as possible from the chest. The bar was released and caught by the subject, with a test administrator as the spotter. Three throws were performed, and the bench throw peak velocity was recorded by a HUMAC360 potentiometer and software (CSMi, Stoughton, MA, USA). The throw that resulted in the highest velocity (centimeter·sec−1) was used for analysis. The bench throw test from our laboratory (n = 10) has been shown to be highly reliable (ICC = 0.924) with no significant mean differences (mean difference = −4.0 cm·sec−1; 95% CI = −10.1 to 2.14 cm·sec−1; p > 0.05) between test-retest values.
The subjects performed a CP3min maximal effort protocol on mechanically braked cycle ergometer (model 894E; Monark HealthCare International, Langly, WA, USA ) with the resistance set at 4.5% of body mass (0.045 × body mass in kilograms) (6,10). Before the test, the seat height was adjusted so that the subject's legs were near full extension at the bottom of the pedal revolution. Toe cages were used to maintain pedal contact throughout the test. The subjects completed a 5-minute warm-up at 50 W at their preferred cadence (70–80 rev·min−1) followed by a 5-minute rest. The test began with unloaded cycling at the preferred cadence followed by 3 minutes of an all-out effort. The subjects were instructed to increase the pedaling cadence to 110 rev·min−1 in the last 5 seconds of the unloaded phase and then maintain the cadence as high as possible for 3 minutes. The cycle ergometer protocol was performed twice during each experimental visit, 30 minutes after ingestion of the SUP or PL (prefatigue) and 15 minutes after the bench throw test (postfatigue) (Figure 1). The CP (expressed in Watts [W]) was defined as the mean power output over the final 30 seconds of the test, and the AWC (expressed in kilojoules [kJ]) was calculated using the equation, AWC = 150 seconds (P150—CP), where P150 equals the mean power output for the first 150 seconds (10). The power outputs were recorded using the Monark Anaerobic Test software (Monark Exercise AB, Vansbro, Sweden). The test-retest reliability for the CP and AWC parameters from our laboratory (n = 13) indicated the ICC values were R = 0.91 and R = 0.79, respectively, with no significant mean differences between test and retest (CP mean difference = −0.23 W; 95% CI = −13.0 to 12.6 W; p > 0.05; AWC mean difference = 0.65 J; 95% CI = −0.74 to 2.03 J).
Resistance Exercise Protocol
After the rest period, the subjects completed a resistance exercise protocol consisting of 4 lower-body exercises (barbell back squat, deadlift, front squat, and reverse lunge) superset with 4 upper-body exercises (flat barbell bench press, bent-over row, incline press, and shoulder press). A description of the supersets and protocol are presented in Figure 2. Four sets at 75% of 1RM of each exercise were completed. Each set was performed for 10 repetitions or to volitional exhaustion. Volitional exhaustion was defined as the inability of the subject to complete a repetition through the full range of motion. Completing a repetition through 50% of the range of motion was counted as a half repetition. Three minutes of rest was provided between 1 set of an exercise and the start of the next set of that same exercise. One minute was provided between the lower-body and upper-body exercise. Water was provided ad libitum during visit 4, and the total volume consumed was recorded. The subject was asked to consume the same volume of water during visit 5. The volume of exercise was calculated for the total body (all 8 exercises listed in Figure 2A), lower body (barbell back squat, deadlift, front squat, and reverse lunge), and upper body (flat barbell bench press, bent-over row, incline press, and shoulder press), as the product of the total number of repetitions completed and the weight lifted.
The subjects were randomly assigned to ingest either the SUP or PL during visit 4 and ingested the crossover treatment for visit 5. The subjects consumed 1 scoop (1 serving = 20.9 g) of either the SUP or PL powder mixed with approximately 12 oz. of water. The SUP (MusclePharm, Inc., Denver, CO, USA) contained citrulline-malate (6 g), leucine (4 g), aspartic acid (3 g), creatine hydrochloride (2 g), beta-alanine (1.6 g), tyrosine (1.2 g), and caffeine anhydrous (350 mg). A complete list of the ingredients and the relative dose of each ingredient is provided in Table 1. The PL was flavored maltodextrin, similar in color and flavor to the SUP formulation. An investigator, who was not involved in the data collection, prepared and administered both the SUP and PL beverages for all subjects, providing double blinding of both the subjects and data collection personnel.
The subjects recorded all food and beverages consumed the day before, and the day of, the first experimental trial (visit 4). The subjects were provided a copy of the 2-day food logs and asked to consume a similar diet the day before, and the day of, the second experimental visit (visit 5). The total energy and macronutrient intake were analyzed (www.supertracker.usda.gov).
Mean differences in total-, lower-, and upper-body volume of resistance exercise for the SUP and PL were examined with separate, paired samples t-tests. In addition, mean differences in total volume between the SUP and PL were examined for each exercise (back squat, deadlift, front squat, reverse lunge, flat bench press, incline press, bent-over row, and standing overhead press) using separate, paired samples t-tests. The VJ height, bench throw velocity, and isokinetic leg extension and flexion peak torque were analyzed with separate, 1-way repeated-measures analyses of variance (ANOVAs) and least significant different paired samples t-tests. The HR and systolic and diastolic blood pressure values were examined with separate 2 (time [15 minutes after arrival and 25 minutes after ingestion]) × 2 (condition [SUP, PL]) repeated-measures ANOVAs and follow-up pairwise comparisons. The CP and AWC values were analyzed with separate 2 (time [prefatigue, postfatigue]) × 2 (condition [SUP, PL]) repeated-measures ANOVAs and follow-up pairwise comparisons. In addition, the total caloric (kilocalories) and macronutrient (grams of carbohydrate, protein, and fat) intake were analyzed with separate 2 (time [24 hours before testing, day of testing]) × 2 (condition [SUP, PL]) repeated-measures ANOVAs. An alpha level of p ≤ 0.05 was considered statistically significant for all analyses. All statistical analyses were performed with Statistical Package for the Social Sciences software (v.23.0.; IBM SPSS, Inc., Chicago, IL, USA).
The descriptive characteristics of the subjects are presented in Table 2. The HR and blood pressure analyses revealed no time × condition interactions and no main effects for time or condition for HR and systolic blood pressure. However, there was a main effect for time for diastolic blood pressure (F = 8.99; p = 0.012, pη2 = 0.45), which indicated an increase from 15 minutes after arrival (72 ± 8 mm Hg) and 25 minutes (79 ± 4 mm Hg) after ingestion of the PL or SUP but no main effect for condition (Table 3). The results of the statistical analyses for volume of exercise indicated that the total-body (SUP = 14,908 ± 3,163 kg; PL = 13,668 ± 2,731 kg) and lower-body (SUP = 8,507 ± 2,006 kg; PL = 7,493 ± 1,552 kg) volume were significantly greater (total body: t = 3.594, p = 0.004; lower body: t = 3.105, p = 0.010) for the SUP than for the PL (Figure 3). In addition, the SUP resulted in a greater total volume of exercise for 9 of the 12 subjects compared with the PL (Figure 4). There was, however, no difference (t = 1.090; p = 0.30) between the SUP (6,401 ± 1,565 kg) and PL (6,175 ± 1,565 kg) for upper-body volume of exercise (Figure 3). The volume of exercise for the back squat was greater for the SUP (2,649 ± 685 kg) than for the PL (2,286 ± 693 kg), but there were no differences between SUP and PL for any of the other exercises (deadlift, front squat, reverse lunge, flat bench press, incline press, bent-over row, and standing overhead press) (Figures 5 and 6).
The results of the statistical analyses for the power and strength performance parameters are provided in Table 4. The results of the 1-way repeated-measures ANOVA indicated significant differences among the means for the VJ height (F = 10.57; p = 0.001; pη2 = 0.49), isokinetic leg extension peak torque (F = 3.76; p = 0.04; pη2 = 0.26), and bench throw velocity (F = 3.37; p = 0.05; pη2 = 0.24). The follow-up pairwise comparisons indicated that there were significant decreases from baseline in the VJ height and isokinetic leg extension peak torque for the SUP and PL, but there were no significant differences between conditions. In addition, the bench throw velocity decreased significantly from baseline for the PL but not for the SUP. There were, however, no significant differences among the 3 time points (baseline, PL, SUP) for the isokinetic leg flexion peak torque values (F = 2.16; p = 0.14; pη2 = 0.16).
The results of the 2 × 2 repeated-measures ANOVA for CP indicated no time × condition interaction (F = 2.35; p = 0.15; pη2 = 0.18), and there were no main effects for time (F = 4.52; p = 0.06; pη2 = 0.29) or condition (F = 2.97; p = 0.11; pη2 = 0.21) (Table 5). The results of the 2 × 2 repeated-measures ANOVA for AWC indicated no time × condition interaction (F = 2.84; p = 0.12; pη2 = 0.21) and no main effects for condition (F = 0.19; p = 0.68; pη2 = 0.02); however, there was a main effect for time (F = 9.04; p = 0.01; pη2 = 0.45). The follow-up pairwise comparison indicated that AWC significantly decreased from prefatigue (15.6 ± 2.8 J) to postfatigue (13.9 ± 3.5 J) (Table 5). There were no significant differences in total caloric intake or macronutrients consumed 24 hours before, and the day of, the experimental protocol for the SUP and PL conditions.
The primary purpose of this study was to examine the effects of a multi-ingredient preworkout supplement on the total volume of resistance exercise. The current findings indicated a 9% increase in the total-body volume of exercise and a 14% increase in lower-body volume of exercise for the SUP compared with the PL, with no effect on exercise volume for the upper body between the SUP and PL. The resistance training protocol in this study included 8 separate exercises, divided into 4 supersets of a lower-body and an upper-body exercise. When each exercise was examined separately, the volume was only greater for the SUP than for the PL for the back squat (∼16%) (Figures 5 and 6). The back squat was superset with the bench press and was the first exercise performed in the resistance training protocol, 45 minutes after supplementation. A number of recent studies have examined the effects of preworkout supplements containing similar ingredients to the SUP in this study (22,23,27,31). When performed in isolation, an increase in lower-body (22,23) and upper-body (27) exercise volume has previously been reported after acute ingestion of a multi-ingredient preworkout supplement. Preworkout supplementation has also been reported to have no effect on exercise volume for the bench press or leg press preformed at 70% of the 1RM to failure (31). This study was unique in the inclusion of 4 supersets of multiple resistance exercises (4 lower body and 4 upper body), a common practice by individuals who perform whole-body resistance training programs. The increases in the volume of exercise after multi-ingredient preworkout supplementation were likely related to the acute effects caffeine and its role as an adenosine receptor antagonist (14,15,18,40). Caffeine has been shown to decrease the ratings for perceived exertion (14) and increase subjective ratings of task motivation (34), focus (23), and energy (23). The caffeine contained in the SUP in this study resulted in a mean relative dose of 4.2 ± 0.6 mg·kg−1, which was higher than the relative dose (∼3.5 mg·kg−1) in preworkout supplements previously reported (22,23,27,31) to be effective for improving exercise volume or cognitive performance. The increased exercise volume observed in the present study may also be attributed to the acute ingestion of 6 g of citrulline-malate in SUP, which can increase the vasodilatory response (44,45) and improve muscular efficiency (17), whereas ingestion of amino acids, leucine and tyrosin, and huperzine A have enhanced cognitive function and focus during exercise (26,48,51). It is possible that these ingredients (caffeine, citrulline-malate, amino acids, and huperzine A) worked synergistically to increase exercise volume by increasing blood flow and the removal of metabolic by-products and improving focus and decreasing perceptions of fatigue. Thus, the current findings suggested that the multi-ingredient preworkout was most effective for increasing exercise volume within the first 45 minutes of supplementation and for exercise involving large muscle groups of the lower body.
A secondary purpose of this study was to examine the effect of the SUP on strength and power performance following a high volume resistance training session. In contrast to previous studies (5,36,46) that have shown acute increases in performance of lower-body parameters (i.e., muscular strength and power) after preworkout or caffeine supplementation, there were similar decreases in the lower-body power (VJ), quadriceps strength (isokinetic leg extension peak torque), and anaerobic cycle ergometry performance (AWC) for the SUP and PL after the resistance exercise. These findings, however, indicated that the increased lower-body volume of exercise performed for the SUP did not result in greater lower-body power and quadriceps strength performance decrements compared with the PL. Thus, although the SUP did not improve subsequent lower-body strength and power performance after an exhaustive resistance exercise protocol, it is possible the multi-ingredient preworkout supplement examined in this study could increase lower-body volume of exercise without altering subsequent performance to a greater extent than a lower volume exercise program. In addition, the upper-body power (i.e., bench throw test) was maintained for the SUP but not for the PL. These findings suggested that the upper body did not demonstrate the same level of fatigue as the lower body for the SUP. In addition, there was no decrease in leg flexor strength for either the SUP or PL, which indicated that the protocol was not fatiguing for the hamstrings muscle group. One limitation of the present study, however, was the ∼20-minute delay between the completion of the final resistance exercise and the measurement of lower-body strength. This delay may have allowed some recovery of muscular strength. Taken together, these findings suggested that the current protocol demonstrated the greatest fatigue and potential effect for the SUP for the quadriceps muscle group.
In summary, the preworkout supplement examined in this study resulted in a 9% increase in the total-body volume of exercise and a 14% increase in lower-body volume of exercise for the SUP compared with the PL, with no effect on exercise volume for the upper body between the SUP and PL. These findings suggested that the SUP was most effective for increasing exercise volume within the first 45 minutes of supplementation and for exercise involving large muscle groups of the lower body. The increased lower-body volume for the SUP did not result in greater lower-body strength and power performance decrements after exhaustive exercise, when compared with the PL. In addition, the upper-body power was maintained in the SUP after the exhaustive exercise. Taken together, these findings suggested the potential for the SUP to increase resistance exercise volume, without greater impairment in performance, when compared with a PL.
The multi-ingredient preworkout supplement examined in this study was effective for increasing the total volume of resistance exercise, primarily related to increases in lower-body volume of exercise. Although volume is an important aspect of resistance training adaptations (38), the 9–14% differences in exercise volume between SUP and PL may not be large enough to elicit greater adaptions for the SUP than for the PL. It is possible that the acute increases in exercise volume for the SUP observed in this study may translate into greater strength and performance adaptations if the effects of the supplement are maintained with a chronic dosing strategy (i.e., before each training session for >4 weeks). Future studies should examine the effects of the preworkout supplement used in this study on resistance exercise volume and performance adaptations with chronic (i.e., > 4 weeks) supplementation to determine if increases in exercise volume are maintained and translate into greater adaptations. In addition, there is some evidence (30) that 4 and 8 weeks of preworkout supplementation before resistance training may improve 1RM strength and cognitive function to a greater degree, compared with a placebo. It was suggested (30) that these adaptations were the result of longer-term supplementation of ingredients such as beta-alanine and creatine nitrate contained in the preworkout supplement. Many of the ingredients in the SUP do not have acute effects, but they may have implication for strength and power performance parameters after longer-term dosing strategies (>4 weeks). For example, longer-term (∼4 weeks) dosing strategies for creatine and beta-alanine have been shown to result in increases in energy stores (i.e., phosphocreatine) (24) and intramuscular buffering capacity (i.e., increased levels of carnosine) (12,20,21), respectively. These adaptations have been shown to increase strength and power (8,9,11,25) and augment the effects of caffeine by delaying neuromuscular fatigue (12,41,42), allowing a greater number of repetitions to be completed via mechanisms other than adenosine receptor antagonism. The supplement in this study, however, contained only 2 g of creatine hydrochloride, which is reported to be less effective at increasing intramuscular phosphocreatine levels than creatine monohydrate, and the dosage was lower than typically recommended (5 g·d−1 for 30 days or 20 g·d−1 for 5–7 days) (7). In addition, the amount of beta-alanine in the SUP in this study was less than previously shown (47) to be effective at increasing intramuscular carnosine levels (3–6 g·d−1 for 2–4 weeks). Thus, it is unclear if the amount of creatine and beta-alanine contained in this study would be sufficient to increase intramuscular phosphocreatine and carnosine levels. In addition, future studies should measure intramuscular levels of phosphocreatine and carnosine after chronic supplementation to determine if the lower doses of creatine and beta-alanine (2 g and 1.6 g, respectively) result in increased energy stores and intramuscular buffering capacity, which have the potential to effect strength and performance adaptations.
The supplement examined in this study was provided by MusclePharm, Inc. (MusclePharm, Denver, CO), and the placebo was provided by True Nutrition (True Nutrition, Vista, CA).
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Keywords:Copyright © 2018 by the National Strength & Conditioning Association.
ergogenic aid; training volume; caffeine