Share this article on:

Impact of Four Weeks of a Multi-Ingredient Performance Supplement on Muscular Strength, Body Composition, and Anabolic Hormones in Resistance-Trained Young Men

Kreipke, Vince C.1,2; Allman, Brittany R.1,2; Kinsey, Amber W.1,2; Moffatt, Robert J.1,2; Hickner, Robert C.2,3,4; Ormsbee, Michael J.1,2,3

Journal of Strength and Conditioning Research: December 2015 - Volume 29 - Issue 12 - p 3453–3465
doi: 10.1519/JSC.0000000000000995
Original Research

Kreipke, VC, Allman, BR, Kinsey, AW, Moffatt, RJ, Hickner, RC, and Ormsbee, MJ. Impact of four weeks of a multi-ingredient performance supplement on muscular strength, body composition, and anabolic hormones in resistance-trained young men. J Strength Cond Res 29(12): 3453–3465, 2015—Although multi-ingredient performance supplements (MIPS) have increased in popularity because of their array of ergogenic ingredients, their efficacy and safety remain in question. The objective of this study was to determine the impact of supplementation with T+ (SUP; Onnit Labs, Austin, TX, USA), an MIPS containing long jack root, beta-alanine, and branched-chain amino acids, and other proprietary blends, on strength, body composition, and hormones in young resistance-trained men. Subjects were randomized to consume either T+ (SUP; n = 14; age, 21 ± 3 years; body fat, 18.3 ± 4.7%) or an isocaloric placebo (PL; n = 13; age, 21 ± 3 years; body fat, 21.5 ± 6.2%) for 4 weeks. Both groups underwent a progressive, 4-week high-intensity resistance training protocol. Before and after the training protocol, mood state, body composition, blood hormones (also collected at midpoint), and maximal strength were measured. SUP had significantly greater increases in bench press (SUP, 102 ± 16 kg to 108 ± 16 kg vs. PL, 96 ± 22 kg to 101 ± 22 kg; p < 0.001) and total weight lifted (SUP, 379 ± 59 kg to 413 ± 60 kg vs. PL, 376 ± 70 kg to 400 ± 75 kg; p < 0.001) compared with PL. Additionally, deadlift strength relative to total body mass (calculated as weight lifted/body mass; kg:kg) (2.08 ± 0.18 to 2.23 ± 0.16; p = 0.036) and lean mass (2.55 ± 0.19 to 2.72 ± 0.16; p = 0.021) increased significantly in SUP but not PL (2.02 ± 0.30 to 2.15 ± 0.36 and 2.56 ± 0.31 to 2.70 ± 0.36, respectively). No other significant differences were detected between groups for the remaining variables. Supplementing with SUP enhanced resistance training adaptations independent of hormonal status, and thus SUP use may warrant inclusion into peri-workout nutrition regimens. This study was registered with clinicaltrials.gov (identifier: NCT01971723).

1Department of Nutrition, Food and Exercise Sciences, Florida State University, Tallahassee, Florida;

2Institute of Sports Sciences and Medicine, Florida State University, Tallahassee, Florida;

3Discipline of Biokinetics, Exercise and Leisure Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa; and

4Department of Kinesiology, Human Performance Lab, East Carolina University, Greenville, North Carolina

Address correspondence to Michael J. Ormsbee, mormsbee@fsu.edu.

Back to Top | Article Outline

Introduction

With increased access to the most current forms of training and nutrition knowledge, and the increased stringency of substance-banning agencies, more athletes are resorting to new nonbanned methods that will give them an advantage over their competition (16). As such, nutritional ergogenic aids are increasingly used by athletes and some data supports improved strength and power performance when combined with resistance training (36). Use of these ergogenic aids, including multi-ingredient performance supplements (MIPS), has increased by 64% in young athletes since 2010 (16). Although the specific composition of MIPS varies, the primary ingredients frequently include creatine monohydrate, caffeine, beta-alanine (BA), and branched-chain amino acids (BCAAs) (36). Both individually (15,37 15,37) and in combination (along with the addition of other ingredients such as caffeine and leucine) (41), BA and creatine monohydrate are known to elicit muscle strength increases when combined with a resistance training program in trained (15) and untrained (41) individuals.

Common MIPS blends consist of BA, BCAAs, caffeine, and creatine, which have been shown to improve strength and power, however are not ubiquitously present in all MIPS. Beta-alanine is a nonessential amino acid that increases intramuscular carnosine levels (25) and subsequently buffers the decrease in pH associated with hydrogen ion accumulation in working muscles. This action delays the onset of fatigue, promoting increased time to exhaustion (43). With these acute effects, it can be postulated that the quality of training per session could be improved, which could ultimately lead to enhanced adaptions to training. The BCAAs (leucine, isoleucine, and valine) are energy substrates, precursors for amino acid and protein production (8), and are known to increase muscle force recovery (10) and protein synthesis in skeletal muscle (23). It has been suggested that daily supplementation with as little as 5 g of BCAAs can aid in the reduction of exercise-induced muscle damage (42). Although not including all BCAAs, it has further been reported that 12 weeks of resistance training in combination with as little as 4 g of leucine alone promotes significant strength increases in untrained men compared with consuming nothing (19). Lastly, caffeine and creatine are known to increase power output and volume of training in athletes and strength-trained populations (7,17,45,49 7,17,45,49 7,17,45,49 7,17,45,49).

Multi-ingredient performance supplements are marketed for their purported ability to improve alertness, attenuated fatigue, and increase the anabolic environment and hormonal milieu. Long jack root (Eurycoma longifolia), one of the potential additional ingredients in MIPS, is purported to directly influence anabolic hormones, because it may increase serum testosterone concentrations. Indeed, studies in rats (31,52 31,52) and humans (9,11 9,11) have shown that long jack root ingestion significantly increases serum testosterone levels by roughly 150 and 37%, respectively. Tambi et al. (47) reported that 4 weeks of supplementation with long jack root extract increased serum testosterone concentrations (pre, 5.61 ± 1.52 nM vs. post, 8.31 ± 2.47 nM) in men experiencing late-onset hypogonadism, determined by both the Ageing Males Symptoms Rating Scale and serum testosterone levels below 6 nM. It is suggested that long jack root may augment anabolic processes by both increasing testosterone levels and reducing estrogen production. Reduced estrogen production elicits increases in endogenous testosterone production through modulation of the hypothalamic-pituitary-gonadal axis and subsequent luteinizing hormone and follicle-stimulating hormone release (31). However, these mechanisms have not been fully elucidated. Although the existing evidence is scant, it is, nevertheless, intriguing that elevations in testosterone have been reported with long jack root supplementation. An increase in testosterone has also been linked to increases in muscular power and strength (5). However, the influence of long jack root on testosterone and performance in eugonadal resistance-trained young men has not been studied despite its theoretical basis for use in this population. The addition of long jack root to “traditional” MIPS may further enhance the positive outcomes that have been reported (36,41 36,41).

Further, resistance training–induced strength gains may be mediated by anabolic hormones such as testosterone, which is produced mainly in the testes of men and has a key role in androgenic, anabolic, and anticatabolic physiological processes. These processes include growth of muscle, increased muscular strength, and the prevention of muscle protein breakdown through inhibition of the catabolic hormone, cortisol (44). When combined with resistance training, the addition of MIPS is purported to elicit changes in hormone concentrations, which may lead to greater increases in the aforementioned adaptations.

Individually, the aforementioned ingredients have been reported to mediate one or more of the following: (a) increases in serum testosterone levels (9,11 9,11), (b) enhancements of muscle size (43), and/or (c) enhancements of muscular strength (19). However, the combined effects of these ingredients have not been investigated despite the increasing popularity of MIPS. Moreover, the safety of many MIPS has not been extensively studied. Therefore, the purpose of this study was to examine the effects of an MIPS, called T+ (SUP), which contains long jack root, BA, and BCAAs, along with other proprietary blends (Table 1), vs. a maltodextrin placebo (PL), in combination with a 4-week resistance training program on mood state, body composition, hormone concentrations, cardiometabolic blood markers, and maximal muscular strength in collegiate resistance-trained men. It is hypothesized that consumption of SUP in combination with resistance training will elicit greater strength increases than resistance training alone. Further, it is anticipated that consumption of SUP will increase serum testosterone levels and lower serum estrogen levels, have a negligible effect on mood state, and no significant effect on cardiometabolic blood markers, compared with PL.

Table 1

Table 1

Back to Top | Article Outline

Methods

Experimental Approach to the Problem

This study was designed to investigate the effects of a commercially packaged MIPS on strength performance, body composition, hormone concentrations, and blood lipid profiles when combined with high-intensity strength-focused resistance training. As such, this study used a 4-week progressive resistance training and supplementation protocol in a stratified, randomized double-blind placebo-controlled design (Figure 1). Each week consisted of 4 strength training sessions, with a focus on improving strength in the 3 powerlifting competition lifts (squat, bench, and deadlift).

Figure 1

Figure 1

Back to Top | Article Outline

Subjects

Thirty-two resistance-trained young men (≥1 year training in the 3 main powerlifting competition movements: squat, bench, and deadlift; age range 21 ± 3 years) volunteered to participate in this study. Subjects were recruited from Florida State University and the city of Tallahassee. Subjects were excluded if they had pre-existing musculoskeletal disorders or injuries, existing cardiovascular diseases, or if they were currently using performance supplements (with the exception of whey protein, casein protein, multivitamin, or caffeine). A 3-week washout period was required before participation for those taking supplements other than protein, a multivitamin, and caffeine. All procedures were approved by the Florida State University Human Subjects Institutional Review Board in accordance with the Helsinki Declaration, and all subjects gave written informed consent and completed a medical history questionnaire.

Back to Top | Article Outline

Procedures

After an 8-hour fast, subjects reported to the Human Performance and Sports Nutrition Laboratory in the morning (07:00–10:00 hours) on 3 occasions: baseline (for mood state questionnaires, body composition, blood sample collection, and cardiovascular measures), midpoint (for blood sample collection), and posttesting (to repeat all baseline measures).

Back to Top | Article Outline

Questionnaires

Mood state was assessed through the Profile of Mood States (POMS) questionnaire, which quantitatively analyzes tension, depression, anger, vigor, fatigue, and confusion based on responses to 65 mood descriptors recalled over the previous 7 days (34). Subjects completed the questionnaires before the blood draws at baseline and posttraining time points, after resting for 5 minutes in a quiet laboratory setting.

Back to Top | Article Outline

Anthropometrics and Body Composition

Measurements of height (SECA, Hamburg, Germany) and weight (Detecto, Brooklyn, NY, USA) were recorded without shoes and with minimal clothing to the nearest 0.1 cm and 0.1 kg, respectively. Body composition was measured using dual-energy x-ray absorptiometry (DXA, model DPX-IQ; GE Medical Systems, Madison, WI, USA) with subjects lying in the supine position according to the manufacturer's instructions. The coefficient of variation for measures of fat-free mass and fat mass (FM) on this specific DXA scanner was 1.9 and 1.5%, respectively, based on 3 repeated measures of 10 physically active young men.

Back to Top | Article Outline

Blood Pressure

Systolic (SBP) and diastolic (DBP) blood pressures were measured in the supine position using an automated sphygmomanometer (Omron HEM-907XL, Bannockburn, IL, USA) immediately after the DXA scan, having rested for at least 10 minutes.

Back to Top | Article Outline

Blood Sampling and Analysis

Fasted venous blood samples (20 ml) were collected from an antecubital vein. Samples collected in EDTA were then centrifuged (IECCL3R Multispeed Centrifuge; Thermo Electron Corp., Needham Heights, MA, USA) for 15 minutes at 3,500 rpm at 4° C, with the resultant supernatant aliquoted into two 1,000 μl and six 500 μl aliquots stored at −80° C until analysis. Whole blood was subsequently analyzed for total cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein, insulin, and glucose (Cholestech LDX, Hayward, CA, USA). Insulin-like growth factor-I, creatine kinase, total testosterone, free testosterone, bioavailable testosterone, estradiol, cortisol, sex hormone–binding globulin, and dihydrotestosterone were measured from the blood serum samples. Twenty-microliter aliquots of serum were placed into a microcuvette panel and subsequently analyzed for total cholesterol, triglycerides, high-density lipoproteins, low-density lipoproteins, insulin, glucose, total testosterone, estradiol, cortisol, and sex hormone–binding globulin (Access Immunoassay System; Beckman Coulter, Brea, CA, USA). Insulin-like growth factor-I, creatine kinase, free testosterone, bioavailable testosterone, and dihydrotestosterone were measured using commercially available ELISA kits (VWR International, Radnor, PA, USA).

Back to Top | Article Outline

Dietary Analysis

Three-day food records (2 weekdays and 1 weekend day) were completed before and after the 4-week intervention. Subjects were asked to maintain their normal dietary intake for the duration of the study. Dietary analysis (The Food Processor SQL; ESHA Research, Salem, OR, USA) was performed by the same research technician for all subjects.

Back to Top | Article Outline

Strength Testing

All strength testing was directly monitored by a certified strength and conditioning specialist. Subjects were instructed to report to the laboratory in the fed state. Subjects were also asked to mimic the same diet on both testing days. One repetition maximum (1RM) strength tests for the squat, bench press, and deadlift occurred on the same day, no less than 48 hours before the first day of training and 72–96 hours after the last day of training. One repetition maximum was defined as the most weight lifted one time through the full range of motion using proper form, according to the National Strength and Conditioning Association guidelines (3). Before each lift, subjects followed a warm-up specific to the respective lift at 50, 75, 85, and 90% 1RM for 5, 3, 1 and 1 repetitions, respectively. Each warm-up set was separated by 3 minutes of rest while each maximal attempt was separated by 7 minutes of rest. Baseline 1RM weight was selected based on previous lifting experience of each respective subject, whereas posttesting warm-up percentages were based on baseline testing 1RM. Subjects were given the option to use their own weightlifting equipment, such as shoes, belts, and wrist wraps. However, any gear used was also used during training and for posttesting. A designated researcher gave a verbal “start” and “rack” command to indicate the beginning and completion of the movement. Lifting techniques followed the USA Powerlifting (USAPL) rules (53) and were accepted if all requirements were followed. According to the USAPL rules, (a) a successful squat required the crease between the hip and abdomen to be lower than the top of the knee cap, (b) proper execution of the bench required the feet to remain on the floor while hips, shoulders, and head remained flat on the bench, and (c) during the deadlift, the bar was not permitted to rest on the thighs. Music was prohibited during testing sessions; however, verbal encouragement by research personnel and other subjects was consistent.

Back to Top | Article Outline

Exercise Training

Subjects were closely supervised by a certified strength and conditioning specialist for all training and trained 4 days per week for 4 weeks (Table 2). Subjects trained as a group in the evening (17:00–20:00 hours). To ensure compliance, subjects were also allowed to train at 07:00 and 14:00 hours in extenuating circumstances (i.e., class or work schedule) and were allowed to miss 3 lifting sessions at most per the 4-week training period. The program selected was a progressive, strength-oriented powerlifting regimen constructed by a certified strength and conditioning specialist. This specific program has not been used in any other study, because of the required specificity of progressing trained power athletes. Before each workout, subjects were permitted to perform their own warm-up to ensure that they were mentally and physically prepared for the training session; however, individual warm-ups were kept constant throughout all training and testing. Each lifting session was composed of a primary lift and an auxiliary lift, selected to ensure a more balanced training program. On “day 1,” the primary lift was deadlift while the auxiliary lift was squats. On “day 2,” the primary lift was military press and the auxiliary lift was pull-ups. “day 3” consisted of back squats as the primary lift and Romanian deadlift as the auxiliary lift. Finally, bench press was the primary lift and bent-over rows were the auxiliary lift for “day 4.” The final set of each exercise was performed as a “plus” set, whereby the subject completed the maximal amount of repetitions to volitional fatigue (Table 2). This allowed subjects to increase repetition volume while working toward exhaustion. The extra repetitions were recorded by a researcher to account for volume of all tested lifts. Music was permitted during training, and all subjects received consistent verbal encouragement by researchers and other subjects. Each lifting session lasted approximately 1 hour.

Table 2

Table 2

Back to Top | Article Outline

Supplementation Protocol

After baseline 1RM testing, all subjects were stratified by the sum of the total weight lifted (squat + bench + deadlift = total weight lifted) and randomly assigned to one of the 2 groups that consumed either SUP (n = 16; T+; Onnit labs) or an isocaloric flavor-matched PL (n = 16; maltodextrin; Onnit labs). The contents of the respective supplements are detailed in Table 1. Supplements were provided in single-serving bags (Ziploc, Racine, WI) and were consumed 20 minutes before and 2 hours after the end of each training session. To ensure compliance, ingestion of supplements before training was monitored by researchers, whereas ingestion of supplements 2 hours posttraining was monitored through returned empty serving bags. Both groups followed dosing recommendations relative to body mass, set by the manufacturer: ≥93.2 kg consumed 14 g pretraining and 14 g posttraining, <93.2 to >75 kg consumed 14 g pretraining and 7 g posttraining, and ≤75 kg consumed 14 g pretraining and 0 g posttraining with 10–20 ounces of water. On nontraining days, subjects consumed their respective pretraining and posttraining doses at breakfast and lunch. Compliance on nontraining days was assessed by the return of the empty supplement packages to the researchers. The acceptable compliance margin was ≥80% for supplementation. SUP was the third party tested for anabolic steroids from ChromaDex (Irving, CA, USA; report number: CDXA-ATR-5839-00).

Back to Top | Article Outline

Statistical Analyses

JMP software (Cary, NC, USA) was used for all statistical analysis. Dietary records, POMS scores, body composition, and relative strength were compared using 2-tailed t-tests. Hormone and blood profile analysis and absolute strength measures were completed using 2-way analysis of variances (ANOVAs) to measure main effects of time and group × time for the 3 time points (pre, mid, post). All ANOVAs were confirmed with a Tukey's post hoc analysis. Statistical significance was set at p ≤ 0.05. Based on an a priori study (32) and an anticipated mean difference in strength performance measures of 82 kg, power analysis indicated that 6 subjects per group would be required to yield a power of 0.8 with a significance level of p ≤ 0.05. However, because there was a larger than expected variability in maximal strength, 30 participants were recruited for this study to ensure that small changes could be detected in all of the measured variables and to account for subject attrition.

Back to Top | Article Outline

Results

Subjects and Compliance

There were no differences in subject baseline characteristics (Table 3). Of the 32 subjects who volunteered, 5 subjects (SUP: n = 2; PL: n = 3) were withdrawn from the study for the following reasons: injuries suffered outside training (n = 3) and not meeting the 80% compliance requirements by missing over 3 lifting sessions (n = 2). Their data were excluded in the analysis.

Table 3

Table 3

Back to Top | Article Outline

Mood State Questionnaires

No group × time interactions were observed for the POMS variables. However, there was a main effect of time for anger (p ≤ 0.05), as both groups increased (SUP: pre, 5.7 ± 4.8 to post, 9.3 ± 6.0 vs. PL: 7.0 ± 4.1 to 9.2 ± 4.5).

Back to Top | Article Outline

Body Composition

There was a significant main effect of time for decrease in FM and percent body fat (p ≤ 0.05) and increased lean (p < 0.001) and total body mass (p ≤ 0.05) (Table 4). There were no group × time interactions.

Table 4

Table 4

Back to Top | Article Outline

Blood Analysis

A significant main effect of time was observed for free testosterone, bioavailable testosterone, percent free testosterone, and percent bioavailable testosterone (Table 5), as each variable decreased. There was also a decrease in sex hormone–binding globulin (p = 0.0009). There were no significant changes within or between pre-, mid-, and post-testing for cortisol, insulin, estrogen, total testosterone, free testosterone, creatine kinase, dihydrotestosterone, insulin-like growth factor-I, sex hormone–binding globulin, bioavailable testosterone, percent free testosterone, or percent bioavailable testosterone (Table 5). In addition, there were no significant changes in glucose, cholesterol, or triglycerides (Table 6). No group × time effects were observed for any of the variables (Tables 5 and 6).

Table 5

Table 5

Table 6

Table 6

Back to Top | Article Outline

Strength Measures

There was a significant main effect of time for 1RM absolute strength in bench press, squat, deadlift, and total weight lifted (Table 7). However, SUP had significantly greater increases in bench press 1RM strength (SUP, 102 ± 16 kg to 108 ± 16 kg vs. PL, 96 ± 22 kg to 101 ± 22 kg; p < 0.001), total weight lifted (SUP, 379 ± 59 kg to 413 ± 60 kg vs. PL, 376 ± 70 kg to 400 ± 75 kg; p < 0.001), and percent change in total weight lifted (SUP, 9 ± 3% vs. PL, 7 ± 4%, p < 0.041) (Table 7). No group × time differences were observed in deadlift or squat 1RM absolute strength. However, deadlift strength relative to total body mass (calculated as weight lifted/body mass; kg:kg) (2.08 ± 0.18 to 2.23 ± 0.16; p = 0.036) and lean mass (calculated as weight lifted/lean mass; kg:kg) (2.55 ± 0.19 to 2.72 ± 0.16; p = 0.021) increased significantly in SUP but not in PL (2.02 ± 0.30 to 2.15 ± 0.36 and 2.56 ± 0.31 to 2.70 ± 0.36, respectively). In addition, total weight lifted (3 combined lifts) relative to total body mass showed a trend toward increasing in SUP but not PL (SUP, 5.01 ± 0.48 to 5.36 ± 0.41, p = 0.053 vs. PL, 4.82 ± 0.69 to 5.11 ± 0.73, p = 0.363). Total weight lifted relative to lean mass approached significance (SUP, 6.14 ± 0.53 to 6.54 ± 0.47, p = 0.052 vs. PL, 6.15 ± 0.76 to 6.44 ± 0.84, p = 0.418) (Figure 2). Lastly, SUP exhibited a greater percent change in total weight lifted (8.86 ± 2.80%) compared with PL (6.50 ± 3.81%) (p = 0.041). There were no additional differences in percent change (Table 4).

Table 7

Table 7

Figure 2

Figure 2

Back to Top | Article Outline

Training Volume Measures

At the completion of training, SUP exhibited a significantly greater total training volume (set1 + set2 + set3) in auxiliary squats on “day 1” (33 ± 3 repetitions vs. 32 ± 5 repetitions; p = 0.04). Additionally, SUP exhibited significantly higher volume of total squats (primary plus auxiliary lifts) per week (61 ± 7 repetitions per week vs. 56 ± 11 repetitions per week; p = 0.02). Further, SUP performed more total repetitions per week for all squat, deadlift, and bench press movements compared with PL (SUP, 120 ± 19 repetitions per week vs. PL, 111 ± 21 repetitions per week; p = 0.006) over the course of the 4-week training program.

Back to Top | Article Outline

Dietary Analysis

Dietary analysis is depicted in Table 8. Total energy intake was not different between groups (SUP: pre, 3,371 ± 1,391 kcal and post, 3,614 ± 1,926 kcal; PL: pre, 3,146 ± 975 kcal and post, 3,301 ± 1,635 kcal; p = 0.89). A significant group × time effect was reported for percent protein intake (p ≤ 0.05), with greater pretraining percent protein intake in PL (29.8 ± 5.5 g) compared with pre- and post-training percent protein intake in SUP (24.1 ± 6.4 g and 25.2 ± 8.9 g, respectively). There was also a significant main effect of time for percent carbohydrate intake (p < 0.001), likely because of the changes (albeit insignificant) in caloric intake. No other statistically significant changes among or between groups were measured.

Table 8

Table 8

Back to Top | Article Outline

Discussion

This study was an investigation into the effects of SUP ingestion in conjunction with a 4-week resistance training program on mood state, body composition, blood hormone and cardiometabolic blood markers, and muscular strength changes in young resistance-trained men. The primary finding of this study was that addition of SUP to the progressive resistance training program resulted in greater increases in strength as measured by bench press and total weight lifted compared with ingestion of PL; however, no differences in circulating anabolic hormones or body composition were reported between the 2 groups.

Strength measures increased with 4 weeks of SUP ingestion in conjunction with a progressive resistance training program. Similarly, Shelmadine et al. (41) reported significant improvements in bench press (8.82% with MIPS, compared with 0.73% with PL) after 4 weeks of resistance training and supplementation with an MIPS (whey protein, caffeine, arginine, leucine, creatine monohydrate, BA, and BCAAs) vs. PL in recreationally-active, non–resistance-trained young men. Conversely, although Ormsbee et al. (36) reported no significant differences in strength changes between groups when young resistance-trained men were supplemented with an MIPS (whey protein, casein protein, BCAA, creatine, BA, caffeine) in conjunction with a periodized resistance training program for 6 weeks, there was a significant increase in peak anaerobic power in the MIPS group (pre 933 ± 173 W vs. post 1,119 ± 184 W, p = 0.002) while PL remained unchanged. Although these findings concerning the benefits of an MIPS on strength and anaerobic performance have been replicated by other studies (40,41 40,41), findings are not unanimous. Indeed, other studies have reported no strength enhancements with ingestion of MIPS with varied composition in subjects with varying resistance training statuses (36,40,41 36,40,41 36,40,41). The inconsistency of results is likely a result of the compositional differences between MIPS, as each product contains different ingredients and quantities. Additionally, although this study showed significant increases in deadlift strength measures relative to total body weight (BW) and lean mass, there is little research regarding the effects of MIPS on increasing relative strength measures. Despite this scarcity of evidence, 8–12 weeks of resistance training alone has been shown to increase back squat, bench press, lateral pull-down, and dumbbell shoulder press strength measures relative to BW in healthy men (24). This study showed no increases in relative strength for PL, suggesting that the addition of an SUP helped to augment typical deadlift strength increases compared with resistance training alone. Furthermore, little is known about the additive or synergistic effects that supportive ingredients (such as the aforementioned) may exert when combined. As such, it is problematic to directly compare the results of this study with previous studies examining other MIPS. Nevertheless, the current results suggest that the ingredients in SUP are effective in enhancing both absolute and relative strength measures in young resistance-trained men, and there still remains to be only a small body of evidence to support the efficacy or synergy of the combined ingredients.

The mechanisms for increases in strength measures in this study were assessed by analyzing changes in the anabolic and catabolic hormone milieu. Many of the ingredients in SUP have been demonstrated to increase endogenous testosterone, such as long jack root (32), red clover (20), nettle root (35), and velvet bean (2). Even so, interestingly, total and free testosterone levels did not increase with the addition of SUP compared with PL in this study. No reported increases in testosterone with the addition of an MIPS to a resistance training program are confirmed in a study by Ormsbee et al. (36), who used the same population supplemented with an MIPS containing some of the same ingredients (BCAA, BA), as well as many additional ingredients (whey protein, casein protein, creatine, BA, caffeine) in combination with a resistance training program for 6 weeks.

However, the testosterone-boosting properties of many MIPS or the individual ingredients in MIPS may be more apparent in hypogonadal individuals who likely have a higher capacity to experience supplementation- and exercise-induced increases in endogenous testosterone levels (9), compared with eugonadal men. Tambi et al. reported a testosterone-boosting effect in elderly hypogonadal men supplemented with 4 weeks of 200 mg·d−1 of long jack root (9), which is similar to the 250 mg·d−1 dose used in this study. Additionally, when active male seniors were supplemented with 400 mg·d−1 of long jack root for 5 weeks, total testosterone, free testosterone, and the testosterone:cortisol ratio significantly increased (13). Many other supplements are known to improve testosterone levels in hypogonadal men (48) and animal models (35,46 35,46), and not in young men (14,36,38 14,36,38 14,36,38). This study used healthy, resistance-trained young men with testosterone levels ranging from 344 to 710 ng·dl−1, falling within the normal range of testosterone levels in young men (300–1,000 ng·dl−1) (21). Thus, changes in testosterone stemming from the current MIPS were likely less pronounced in this population compared with the potential testosterone-boosting effects in hypogonadal populations. Also important to mention is that total and free testosterone levels did not remain constant, rather they were found to significantly decrease in both groups (Table 5). This finding was not expected, because testosterone levels typically increase with the addition of a resistance training protocol (29). There were no significant changes in any other hormones measured in this study. For example, contrary to decreased estrogen levels in rats provided with 25 mg·kg−1 BW of long jack root (32), serum estrogen concentrations did not decrease in this study, suggesting that downstream alteration of the hypothalamic-pituitary-gonadal axis did not occur. In addition, 5-alpha-reductase (enzyme-catalyzing dihydrotestosterone production from testosterone) and aromatase (enzyme-catalyzing estrogen production from testosterone) are inhibited in male rats injected with 20 μl of stinging nettle root (also present in SUP) (12). Both of these changes would certainly mediate increases in endogenous testosterone levels; however, this study reported no such findings. Cortisol levels also remained constant throughout the training and supplementation protocol, which is supported by the literature (29). Kraemer et al. (29) reported that, independent of supplementation, 10 weeks of heavy resistance training significantly lowered cortisol levels in aged men with no differences in young men. Quite similar to increases in testosterone, increases in the overall anabolic hormonal milieu and decreases in catabolic hormonal milieu seem to only be present in hypogonadal aged men and animal models, and not in eugonadal young men. Therefore, the mechanism for strength enhancements in this study with SUP does not appear to be hormone-dependent.

With SUP, bench press and total weight lifted improved despite insignificant changes in lean mass. Conversely, although Hamzah and Yusof (11) reported strength increases (1RM) with a 5-week hypertrophy training program in physically active (cycling) young men supplemented with 100 mg·d−1 of long jack soluble extract compared with a placebo, these changes were indeed accompanied by significant increases in lean mass only in the long jack root supplemented group. Differences in findings are likely due to methodology used, as this study used a resistance training regimen, an MIPS containing long jack root as only one of the supportive ingredients, and resistance-trained men, whereas Hamzah and Yusuf used a hypertrophy training program, pure long jack root, and aerobically trained cyclists. Lack of changes in lean body mass may also suggest that reported strength changes were mediated by training-induced neural adaptions commonly associated with acute resistance training (39) (used in this study), rather than hypertrophic growth commonly associated with chronic resistance training (28). However, there is no documented evidence of the effects of herbal supplementation on neural adaptations to exercise.

Further, the greater training volume in the SUP group may have also provoked the greater changes in strength. Beta-alanine, present in the current MIPS, has been shown to attenuate fatigue and consequently increase training volume in bench press when compared with a placebo in collegiate football players (15). It should also be noted that this study reported a trend for greater volume in the entire training session (15). Moreover, BA has been shown to increase amounts of total work performed at high sprint intensities (43). Thus, it may be concluded that greater strength increases were mediated by the significant increases in volume with SUP.

The currently tested supplement contained multiple active ingredients in addition to long jack root. These additional ingredients include but are not limited to BA, BCAAs, and velvet bean. It may be postulated that these other active ingredients explain the testosterone-independent improvements in strength with SUP. Beta-alanine supplementation is known to improve muscular strength in 4.0 g·d−1 doses provided over 8 weeks (26). On average, the SUP used in this study supplied 1.5 g·d−1 of BA for 4 weeks. Because strength was significantly increased, this may confirm that the doses of BA in SUP suffice for young resistance-trained men, at least in combination with other ingredients in the current formulation. Leucine, one of the BCAAs, taken in 4 g·d−1 doses provided over 12 weeks in combination with a resistance training program was shown to increase strength compared with a lactose PL in untrained men (19). The range of daily BCAA consumption in the SUP was 2.5–5.0 g·d−1 (average, 3.75 g) of BCAAs, falling just short of the recommendations. Importantly, these findings suggest that lower doses may provide similar results in muscular strength outcomes. Velvet bean supplemented in 706 mg per serving doses as part of an MIPS, which did not contain the ergogenic aids of BA, BCAA, caffeine, or creatine, combined with 8 weeks of resistance training did not elicit significant increases in muscular strength in young resistance-trained men (51). However, in the present study, the 500–1,000 mg·d−1 dose of velvet bean in SUP combined with 4 weeks of resistance training in the present study produced positive results. These contrasting findings with velvet bean supplementation as part of an MIPS was likely due to the presence or lack of BA, BCAA, caffeine, and creatine. Therefore, the respective amounts of potential ergogenic ingredients in SUP are likely sufficient to produce testosterone-independent improvements in strength.

The tested supplement did not seem to influence the well-documented resistance training–induced improvements in body composition in humans (1,27,48,50 1,27,48,50 1,27,48,50 1,27,48,50). It is difficult to make effective comparisons of the potential synergistic effects of the combination of resistance training and individual ingredients, as most studies that examine the effects of individual ingredients do not include resistance training. Although not combined with resistance training, decreases in body fat associated with supplementation of long jack root are equivocal, as there is evidence to support (11), and refute (18) these outcomes. Importantly, the aforementioned studies involving long jack root supplementation were performed in rats, rather than human models, and used pure long jack root, rather than long jack root as part of an MIPS. Therefore, findings are difficult to compare. Likewise, some of the other ingredients in SUP have been reported to enhance body composition. Specifically, resveratrol is known to reduce adipose tissue mass by inhibiting differentiation of preadipocytes and stimulating both lipolysis and adipocyte apoptosis (4). Research has shown that 30 mg·kg−1·d−1 (2.1 g for a 70-kg man) for 6 weeks reduces white adipose, mesenteric, and subcutaneous fat depots in rats fed with a hypercaloric diet (33). In this study, there were only 20 mg of resveratrol per serving of SUP, likely only modestly contributing to the minimal changes in body composition. Additionally, subjects in this study consumed a eucaloric diet. Acute BCAA ingestion of 100 mg·kg−1 BW (7,000 mg BCAA for a 70-kg man) beneficially affects protein metabolism (indicative of preservation of lean body mass) in trained male cyclists (6). However, this study supplied 2,500 mg·d−1 of BCAA for 4 weeks and found no significant changes in lean body mass. Therefore, although empirically many of the ingredients in SUP are known to improve body composition, ingredient doses in the current MIPS were likely too low to elicit body composition changes, at least when paired with a strength training program.

The tested supplement did not alter lipoprotein profiles, triglyceride levels, blood lipids, or glucose levels in this study, reflecting results of previous studies using MIPS (40,41 40,41). Likewise, SUP did not influence blood pressure. Thus, there seems to be no negative effects on markers of cardiometabolic disease risk in the group studied. Also noteworthy is that SUP does not seem to elicit negative side effects. With SUP, 2 subjects reported acne, one reported paresthesia (sensation of tingling, burning, or numbness), which is typical with BA supplementation (30), and 2 reported increased libido. There were no reports of any side effects in the PL group. These reported side effects are mild compared with other MIPS side effects, such as dizziness, feelings of nausea, headache, rapid heart rate, shortness of breath, and nervousness that have been reported (41).

Regarding psychological profile, there were no differences in POMS ratings between the 2 groups. There was, however, a significant increase in anger in both groups, indicating resistance training alone may increase anger. The increase in hostility rating could not be accounted for by changes in testosterone profile, as there is no relationship between the mood states and serum testosterone concentrations. The change for both groups may be due to the high intensity of the training in this study, as there were no significant changes in some POMS variables (fatigue and vigor) with 12 weeks of moderate-intensity hypertrophy training in combination with protein supplementation in a previous study using healthy young men (22). However, in that study, hypertrophy resistance training alone (without protein supplementation) decreased POMS vigor (22). Therefore, many of the ingredients (i.e., amino acids) in SUP may attenuate the decrease in some POMS variables in recovery; however, there is a limited body of evidence to suggest the association of increased anger and resistance training, as in this study.

There were several limitations in this study. Foremost, amounts of individual ingredients in SUP are standardized and therefore are unable to be individualized or altered. Additionally, because dosing was dependent on mass of the subject, subjects consumed differing amounts of ingredients with only modest changes in outcome measures, and thus there may have been differences in outcome measures with post hoc analysis between weight groups. However, the group sizes were too small to make substantial assessments. Likewise, the varying ingredients and dosages of MIPS make effective comparisons extremely difficult, as that would entail analysis of an extremely large number of studies. Furthermore, although comparisons were only made with MIPS containing at least 1 ingredient similar to the supplement used in this study, it is clear that the differences between compositions likely affect the outcome measures. Much of the aforementioned research supports much higher doses of individual ingredients to promote changes in anabolic hormone levels, performance, and body composition. Therefore, the very low amount of certain ingredients in SUP was likely too small to initiate measureable physiological changes. Despite the lack of hormonal changes, SUP did elicit strength performance enhancements that could have been due to the previously discussed other active ingredients in SUP, or the combination thereof. Inconsistent evidence of the benefits of the combination of MIPS supplementation and strength training is often primarily due to the type of training being administered. This study used a low-volume high-intensity training program, whereas many other studies have administered high-volume moderate-intensity training or no training. Despite observing strength changes over the course of training, the 4-week training period may have been too short to elicit significant changes in both hormonal and body composition measures. In addition, the volume of the nontested lifts (i.e., shoulder press) was not calculated and may have influenced the differences in strength increases. However, there may be other potential mechanisms that lead to strength increases such as neuromuscular adaptations, which this study did not analyze. Body composition effects due to the length of the protocol may be a factor as well. Although the current data show that short-term resistance training (with or without ergogenic aids) in previously resistance-trained individuals positively affects body composition, long-term resistance training (10 weeks) in young men with no previous resistance training experience does not seem to affect body composition or body fat (29). These findings may be due to the intensity of the protocols used in other studies, as the intensity of exercise was lower in the individuals with no previous resistance training experience compared with this study in young resistance-trained men.

In conclusion, 4 weeks of supplementation with SUP in conjunction with a resistance training program improved 1RM strength performance in young resistance-trained men; however, these changes were not mediated by changes in the anabolic or catabolic hormonal milieu. SUP did not negatively influence cardiometabolic markers in the individuals studied, and it may cause only minimal side effects.

Back to Top | Article Outline

Practical Applications

This study furthers our understanding of commercially packaged MIPS. Considering the lack of pronounced changes in the anabolic or catabolic hormonal milieu, coaches and athletes may consider supplementation with the SUP in conjunction with a powerlifting-oriented resistance training program as a safe way to enhance strength, which may warrant its use as a peri-workout nutritional supplement.

Back to Top | Article Outline

Acknowledgments

The authors thank the assistance of all students and subjects who took part in this study. The authors also specifically thank Gabriel S. Dubis, Charles J. Tanner, and Will Hyder for laboratory guidance and assistance. This study was supported by a grant from Onnit Labs to MJO.

Back to Top | Article Outline

References

1. Abe T, DeHoyos D, Pollock ML, Garzarella L. Time course for strength and muscle thickness changes following upper and lower body resistance training in men and women. Eur J Appl Physiol 81: 174–180, 2000.
2. Ahmad MK, Mahdi AA, Shukla KK, Islam N, Jaiswar SP, Ahmad S. Effect of Mucuna pruriens on semen profile and biochemical parameters in seminal plasma of infertile men. Fertil Steril 90: 627–635, 2008.
3. Baechle E, Roger W, Thomas R. Essentials of Strength Training and Conditioning. Leeds, United Kingdom: Human Kinetics, 2008.
4. Baile CA, Yang J-Y, Rayalam S, Hartzell DL, Lai CY, Andersen C, Della-Fera MA. Effect of resveratrol on fat mobilization. Ann N Y Acad Sci 1215: 40–47, 2011.
5. Bhasin S, Woodhouse L, Casaburi R, Singh AB, Bhasin D, Berman N, Chen X, Yarasheski KE, Magliano L, Dzekov C, Dzekov J, Bross R, Phillips J, Sinha-Hikim I, Shen R, Storer TW. Testosterone dose-response relationships in healthy young men. Am J Physiol Endocrinol Metab 281: E1172–E1181, 2001.
6. Blomstrand E, Saltin B. BCAA intake affects protein metabolism in muscle after but not during exercise in humans. Am J Physiol Endocrinol Metab 281: E365–E374, 2001.
7. Chilibeck PD, Magnus C, Anderson M. Effect of in-season creatine supplementation on body composition and performance in rugby union football players. Appl Physiol Nutr Metab 32: 1052–1057, 2007.
8. Ferrando AA, Williams BD, Stuart CA, Lane HW, Wolfe RR. Oral branched-chain amino acids decrease whole-body proteolysis. JPEN J Parenter Enteral Nutr 19: 47–54, 1995.
9. George A, Henkel R. Phytoandrogenic properties of Eurycoma longifolia as natural alternative to testosterone replacement therapy. Andrologia 46: 708–721, 2014.
10. Goldstein L, Newsholme A. The formation of alanine from amino acids in diaphragm muscle of the rat. Biochem J 154: 555–558, 1976.
11. Hamzah S, Yusof A. The ergogenic effects of Eurycoma longifolia Jack: A pilot study. Br J Sports Med 37: 464–470, 2003.
12. Hartmann RW, Mark M, Soldati F. Inhibition of 5 α-reductase and aromatase by PHL-00801 (Prostatonin), a combination of PY102 (Pygeum africanum) and UR102 (Urtica dioica) extracts. Phytomedicine 3: 121–128, 1996.
13. Henkel RR, Wang R, Bassett SH, Chen T, Liu N, Zhu Y, Tambi MI. Tongkat Ali as a potential herbal supplement for physically active male and female seniors–a pilot study. Phyther Res 28: 544–550, 2014.
14. Hoffman J, Ratamess N, Ross R, Shanklin M, Kang J, Faigenbaum A. Effect of a pre-exercise energy supplement on the acute hormonal response to resistance exercise. J Strength Cond Res 22: 874–882, 2008.
15. Hoffman JR, Ratamess NA, Faigenbaum AD, Ross R, Kang J, Stout JR, Wise JA. Short-duration beta-alanine supplementation increases training volume and reduces subjective feelings of fatigue in college football players. Nutr Res 28: 31–35, 2008.
16. Hoyte C, Albert D, Heard K. The use of energy drinks, dietary supplements, and prescription medications by United States college students to enhance athletic performance. J Community Health 38: 575–580, 2013.
17. Hudson GM, Green JM, Bishop PA, Richardson MT. Effects of caffeine and aspirin on light resistance training performance, perceived exertion, and pain perception. J Strength Cond Res 22: 1950–1957, 2008.
18. Ismail SB, Wan Mohammad WMZ, George A, Nik Hussain NH, Musthapa Kamal ZM, Liske E. Randomized clinical trial on the use of PHYSTA freeze-dried water extract of Eurycoma longifolia for the improvement of quality of life and sexual well-being in men. Evid Based Complement Alternat Med 2012: 249–268, 2012.
19. Ispoglou T, King RFGJ, Polman RCJ, Zanker C. Daily L-leucine supplementation in novice trainees during a 12-week weight training program. Int J Sports Physiol Perform 6: 38–50, 2011.
20. Jarred RA, McPherson SJ, Jones MEE, Simpson ER, Risbridger GP. Anti-androgenic action by red clover-derived dietary isoflavones reduces non-malignant prostate enlargement in aromatase knockout (ArKo) mice. Prostate 56: 54–64, 2003.
21. Javorsky B, Aron D, Findling J, Tyrrell J. Greenspan's Basic & Clinical Endocrinology (9th ed.). New York, NY: McGraw Hill, 2011.
22. Kalman D, Feldman S, Martinez M, Krieger DR, Tallon MJ. Effect of protein source and resistance training on body composition and sex hormones. J Int Soc Sports Nutr 4: 4, 2007.
23. Karlsson HKR, Nilsson PA, Nilsson J, Chibalin A, Zierath JR, Blomstrand E. Branched-chain amino acids increase p70S6k phosphorylation in human skeletal muscle after resistance exercise. Am J Physiol Endocrinol Metab 287: E1–E7, 2004.
24. Kell RT. The influence of periodized resistance training on strength changes in men and women. J Strength Cond Res 25: 735–744, 2011. Available at: http://journals.lww.com/nsca-jscr/Abstract/2011/03000/The_Influence_of_Periodized_Resistance_Training_on.22.aspx. Accessed January 30, 2015.
25. Kendrick IP, Kim HJ, Harris RC, Kim CK, Dang VH, Lam TQ, Bui TT, Wise JA. The effect of 4 weeks beta-alanine supplementation and isokinetic training on carnosine concentrations in type I and II human skeletal muscle fibres. Eur J Appl Physiol 106: 131–138, 2009.
26. Kern B, Robinson T. Effects of beta-alanine supplementation on performance and body composition in collegiate wrestlers and football players. Int Soc Sport Nutr 6: 1804–1815, 2011. Available at: http://journals.lww.com/nsca-jscr/pages/articleviewer.aspx?year=2011&issue=07000&article=00005&type=abstract. Accessed July 25, 2014.
27. Kosek DJ, Kim JS, Petrella JK, Cross JM, Bamman MM. Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults. J Appl Physiol (1985) 101: 531–544, 2006.
28. Kraemer WJ, Fleck SJ, Evans WJ. Strength and power training: Physiological mechanisms of adaptation. Exerc Sport Sci Rev 24: 363–397, 1996.
29. Kraemer WJ, Hakkinen K, Newton RU, Nindl BC, Volek JS, McCormick M, Gotshalk LA, Gordon SE, Fleck SJ, Campbell WW, Putukian M, Evans WJ. Effects of heavy-resistance training on hormonal response patterns in younger vs. older men. J Appl Physiol (1985) 87: 982–992, 1999.
30. Liu Q, Sikand P, Ma C, Tang Z, Han L, Li Z, Sun S, LaMotte RH, Dong X. Mechanisms of itch evoked by β-alanine. J Neurosci 32: 14532–14537, 2012.
31. Low BS, Choi SB, Abdul Wahab H, Das PK, Chan K-L. Eurycomanone, the major quassinoid in Eurycoma longifolia root extract increases spermatogenesis by inhibiting the activity of phosphodiesterase and aromatase in steroidogenesis. J Ethnopharmacol 149: 201–207, 2013.
32. Low BS, Das PK, Chan KL. Standardized quassinoid-rich Eurycoma longifolia extract improved spermatogenesis and fertility in male rats via the hypothalamic-pituitary-gonadal axis. J Ethnopharmacol 145: 706–714, 2013.
33. Macarulla MT, Alberdi G, Gómez S, Tueros I, Bald C, Rodríguez VM, Martínez JA, Portillo MP. Effects of different doses of resveratrol on body fat and serum parameters in rats fed a hypercaloric diet. J Physiol Biochem 65: 369–376, 2009.
34. McNair D, Lorr M, Droppleman L. Manual for the Profile of Mood States. San Diego, CA: Educational and Industrial Testing Services, 1971.
35. Nahata A, Dixit VK. Ameliorative effects of stinging nettle (Urtica dioica) on testosterone-induced prostatic hyperplasia in rats. Andrologia 44: 396–409, 2012.
36. Ormsbee MJ, Mandler WK, Thomas DD, Ward EG, Kinsey AW, Simonavice E, Panton LB, Kim JS. The effects of six weeks of supplementation with multi-ingredient performance supplements and resistance training on anabolic hormones, body composition, strength, and power in resistance-trained men. J Int Soc Sports Nutr 9: 49, 2012.
37. Rawson ES, Volek JS. Effects of creatine supplementation and resistance training on muscle strength and weightlifting performance. J Strength Cond Res 17: 822–831, 2003.
38. Rogerson S, Riches CJ, Jennings C, Weatherby RP, Meir RA, Marshall-Gradisnik SM. The effect of five weeks of Tribulus terrestris supplementation on muscle strength and body composition during preseason training in elite rugby league players. J Strength Cond Res 21: 348–353, 2007.
39. Sale DG. Neural adaptation to resistance training. Med Sci Sports Exerc 20: 135–145, 1988.
40. Schmitz S, Hofheins J, Lemieux R. Nine weeks of supplementation with a multi-nutrient product augments gains in lean mass, strength, and muscular performance in resistance trained men. J Int Soc Sports Nutr 7: 1–9, 2010.
41. Shelmadine B, Cooke M, Buford T, Hudson G, Redd L, Leutholtz B, Willoughby DS. Effects of 28 days of resistance exercise and consuming a commercially available pre-workout supplement, NO-Shotgun(R), on body composition, muscle strength and mass, markers of satellite cell activation, and clinical safety markers in males. J Int Soc Sports Nutr 6: 1–13, 2009.
42. Shimomura Y, Murakami T, Nakai N, Nagasaki M, Harris RA. Exercise promotes BCAA catabolism: Effects of BCAA supplementation on skeletal muscle during exercise. J Nutr 134: 1583–1587, 2004.
43. Smith AE, Walter AA, Graef JL, Kendall KL, Moon JR, Lockwood CM, Fukuda DH, Beck TW, Cramer JT, Stout JR. Effects of beta-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial. J Int Soc Sports Nutr 6: 1–9, 2009.
44. Snyder PJ. Goodman & Gilman's the Pharmacological Basis of Therapeutics. New York: McGraw-Hill Education/Medical. 12th ed. 2011.
45. Stuart GR, Hopkins WG, Cook C, Cairns SP. Multiple effects of caffeine on simulated high-intensity team-sport performance. [Online]. Med Sci Sports Exerc 37: 1998–2005, 2005. Available at: http://www.ncbi.nlm.nih.gov/pubmed/16286872. Accessed February 11, 2015.
46. Tajul Ariff AS, Soelaiman IN, Pramanik J, Shuid AN. Effects of Eurycoma longifolia on testosterone level and bone structure in an aged orchidectomised rat model. Evid Based Complement Alternat Med 2012: 1–7, 2012.
47. Tambi M, Imran MK, Henkel RR. Standardised water-soluble extract of Eurycoma longifolia, Tongkat ali, as testosterone booster for managing men with late-onset hypogonadism? Andrologia 44: 226–230, 2012.
48. Tanimoto M, Sanada K, Yamamoto K, Kawano H, Gando Y, Tabata I, Ishii N, Miyachi M. Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men. J Strength Cond Res 6: 1926–1938, 2008.
49. Volek J, Kraemer W, Bush J, Boetes M, Incledon T, Clark K, Lynch J. Creatine supplementation enhances muscular performance during high-intensity resistance exercise. J Am Diet Assoc 97: 765–770, 1997.
50. Welle S, Thornton C, Statt M. Myofibrillar protein synthesis in young and old human subjects after three months of resistance training. Am J Physiol Endocrinol Metab 268: 422–427, 1995.
51. Wilborn C, Kerksick C, Campbell B, Taylor L, Marcello B, Rasmussen C, Greenwood M, Almada A, Kreider R. Effects of zinc magnesium aspartate (ZMA) on training adaptations and markers of anabolism and catabolism. J Int Soc Sports Nutr 1: 12–20, 2004.
52. Zanoli P, Zavatti M, Montanari C, Baraldi M. Influence of Eurycoma longifolia on the copulatory activity of sexually sluggish and impotent male rats. J Ethnopharmacol 126: 308–313, 2009.
53. USAPL Rulebook 2013. International Powerlifting Federation Technical Rule Book. 1–54: 2013.
Keywords:

long jack root; testosterone; resistance training; powerlifting

Copyright © 2015 by the National Strength & Conditioning Association.