No significant increases from PRE were seen in glucose concentrations for both S (5.30 ± 0.40 mmol·L−1) and P (5.50 ± 1.12 mmol·L−1). Lactate concentrations were significantly increased IP for both S (17.8 ± 5.7 mmol·L−1) and P (16.5 ± 4.7 mmol·L−1), and remained increased from PRE throughout the 30-minute recovery period, but no significant group differences were observed.
Significant 25% and 37% increases from PRE were seen in total testosterone concentration at both IP and 15P, respectively for S. A 10% increase was seen at these same time points with P, but these increases were not significantly different from PRE. In addition, no significant differences were seen between S and P at any time point. AUC analysis for total testosterone revealed no significant between-group differences. No significant differences from PRE were seen in free testosterone in either experimental group. In addition, no between-group differences were seen at any time point. Figure 5A shows the response of free testosterone to the exercise protocol. AUC analysis also failed to demonstrate any significant difference in free testosterone between exercise sessions (Figure 5B).
Plasma volumes decreased −29.1 ± 11.0% and −22.1 ± 9.8% IP with S and P, respectively. However, the difference between these groups was not significant. Average plasma volume shifts at 15P and 30P ranged from −0.3 ± 8.1% to −11.9 ± 3.7% with S and P, but no significant differences between the groups were observed. However, blood variables were not corrected for plasma volume shifts due to the importance of molar exposure at the tissue level.
The results of this study indicate that a pre-exercise S containing a combination of BCAAs, creatine monohydrate, taurine, glucuronolactone, and caffeine does enhance performance during a resistance exercise training session as reflected by an increase in the number of repetitions performed and training volume. Considering that acutely ingested BCAAs and creatine are not known to have an effect on acute exercise performance, the mechanism stimulating the enhanced training session is likely the result of the high energy compounds (e.g., taurine, glucuronolactone, and caffeine) found in the S. These compounds are typically marketed as sports energy drinks, and this study appears to be one of the first investigations to demonstrate the efficacy of these Ss during a heavy resistance exercise session.
The S used in this study was developed to enhance acute resistance training performance. The inclusion of creatine monohydrate and BCAAs in the S was to enhance muscle recovery (i.e., BCAAs) from acute exercise stress and the maintenance of high muscle creatine levels. The amount of creatine found in this S is the equivalent of a typical maintenance dose. To ensure that all subjects had maximized muscle creatine stores, subjects were required to creatine load for 1 week before the experimental sessions. Subjects continued to supplement with creatine (maintaining the loading phase regimen) until they completed both experimental sessions (within 5 days). As a result, any differences seen between experimental sessions are not considered to be influenced by the creatine content of the S.
The physiological importance of BCAAs in regards to an acute training session is limited. Although BCAAs are reported to reduce muscle soreness and muscle fatigue after resistance training exercise protocols (30), this appears to be only effective after several weeks of supplementation (24). There are no studies to date that have demonstrated acute performance improvements from BCAA supplementation during an acute resistance training session. Thus, the performance improvements seen in this study appear to be attributed to the other compounds associated with this S.
Previous studies have shown that taurine ingestion can improve endurance performance (27,35); however, the ability of taurine supplementation to enhance resistance training performance has not been examined. Although in laboratory studies using mammalian skeletal muscle, taurine has been shown to enhance force production in skinned fast-twitch fibers (3,15), these studies have not been conducted on humans. Furthermore, previous studies examining the efficacy of taurine ingestion in humans have used longer duration study protocols, and no studies appear to have been conducted focusing on the acute ingestion of taurine and its potential ergogenic benefits. This study appears to be the first to provide evidence suggesting that acute ingestion of taurine when combined with caffeine and glucuronolactone may improve resistance training performance.
The role that caffeine has in enhancing resistance training performance is not well understood. Some have suggested that caffeine can enhance force and power production through enhanced calcium release from the sarcoplasmic reticulum (26), while others have suggested that caffeine can increase catecholamine secretion (8). Although several investigations were unable to see any improvements in power performance after caffeine ingestion during a Wingate anaerobic power test (5,18), other studies have demonstrated improved isometric force production (21) and 6-second maximal cycle ergometer sprints (2) from caffeine supplementation. Recently, Beck et al. (4) demonstrated that acute caffeine ingestion resulted in significant improvements in maximal upper body strength, but no improvements in maximal lower body strength or training volume for both modes of exercise were found.
No studies appear to have examined the effect of glucuronolactone ingestion on exercise performance. However, when ingested with taurine and caffeine, the combined S has been shown to improve cognitive function, alertness, and physical performance (1). This study appears to be the first examination of a S marketed as an energy drink designed to enhance resistance training performance. The individual ingredients of this S have either not been examined or have shown inconsistent results as it relates to anaerobic exercise performance. However, the significantly greater number of repetitions performed and total volume of training for set 5 and the trend seen toward a greater number of repetitions (p = 0.08) performed and total volume of training (p = 0.09) during the workout indicate that the combination of these ingredients appears to provide an effective stimulus in improving acute resistance exercise performance. The improvement in training volume also appears to be reflected in the hormonal response to the exercise protocol. A greater anabolic hormone response (e.g., testosterone, growth hormone, and insulin) could have important implications in the repair and recovery of skeletal muscle after resistance exercise sessions and subsequently play a vital role in the muscle remodeling.
The significantly greater growth hormone response to the exercise protocol is similar to that of other studies that demonstrated the importance of training volume on growth hormone increases (17,22). Growth hormone secretion patterns have been shown to be responsive to changes in acid-base balance of muscle (14). Although lactate concentrations IP were not significantly different, the 8% difference seen between S and P IP (p = 0.07) and the 9% difference (p = 0.11) seen in the AUC analysis does suggest a trend toward a greater metabolic strain associated with the higher training volume seen with S.
The response of testosterone in this study is similar to that found in other investigations that showed that differences in training volume can influence the total testosterone response to exercise (22). However, the lack of any significant difference in total testosterone concentrations between S and P may be the result of the pre-exercise S as most studies examining the acute hormonal response to resistance exercise are conducted with subjects who initially fasted. Amino acid ingestion before exercise has been shown to attenuate the testosterone response to a resistance exercise session (7,13,19). Protein supplementation before a workout may result in a decrease in secretion rates or an increase in metabolic clearance rates (19). It has also been suggested that pre-exercise protein intake may lead to an increase in testosterone uptake by cells during exercise (32). These mechanisms may have contributed to a possible reduction in the magnitude of the total testosterone response seen during this study and perhaps also explain the free testosterone response observed during the immediate and post-exercise recovery periods.
Most studies show elevated concentrations of cortisol during an acute resistance exercise session (24). Increases in cortisol with S appear to reflect the higher training volumes seen during this training session. This is supported by other studies showing the sensitivity of cortisol to increases in training volume (28). Although no differences in cortisol concentrations were observed between S and P, it has been suggested that carbohydrate ingestion could reduce the cortisol response to exercise due to a lower demand for gluconeogenesis (23). The placebo was composed of 14.9 g of carbohydrate, which may have attenuated the cortisol response during that training session.
Insulin concentrations tend to parallel changes in blood glucose and amino acid concentrations (23). Insulin has generally been seen to decrease during an acute bout of resistance exercise (23); however, when a protein S is consumed before exercise, insulin concentrations have been shown to be increased during the post-exercise period (19). Increases in insulin concentrations seen IP with S appeared to reflect the amino acid content of the supplement.
In conclusion, the use of a pre-exercise energy S containing taurine, caffeine, and glucuronolactone consumed 10 minutes before resistance exercise appears to provide an enhanced training response that is reflected by increases in the number of repetitions performed and training volume. These changes appear to result in greater increases in growth hormone and insulin, indicating an augmented anabolic hormone response to such supplementation.
This study was supported by a grant from Champion Nutrition, Concord, CA.
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