The acute effects of a multi-ingredient pre-workout supplement on resting energy expenditure and exercise performance in recreationally active females

The purpose of the current investigation was to examine the acute effects of ingesting a commercially available multi-ingredient pre-workout supplement on REE, exercise performance and select markers of clinical health in recreationally active females. The primary findings from the current study indicated that ingestion of a MIPS resulted in an acute increase in REE. These results are in accordance with previous studies that have also observed significant increases in REE following ingestion of a MIPS or caffeine containing supplement [11, 12, 22]. For example, Outlaw et al. [22] reported significant increases in REE following ingestion of a commercially available caffeine-containing supplement (340 mg of caffeine) for 3 h post ingestion. Similarly, Campbell et al. [12] reported a significant increase in REE up to three hours post ingestion of a MIPS thermogenic supplement that contained 150 mg of caffeine plus green tea extract in healthy females. However, others have reported no significant changes in metabolic activity following ingestion of thermogenic agents. As evidenced, Rashti et al. [23] did not observe a significant increase in REE following ingestion of a caffeine-containing supplement. Although, it should be noted that the subjects from the Rashti et al. study [23] were only in a 3-h post absorption state suggesting that increases in REE may only occur during a period of an extended fast (>3 h). It is likely that the increases in REE observed in the current study is a result of the caffeine contained within the product as similar increases in REE have been shown to occur following consumption of caffeine alone [11]. Caffeine acts as an adenosine antagonist, which has a regulatory influence on metabolic activity. Therefore, when caffeine binds to adenosine receptors, it likely increase acute metabolic activity such as the case in the current study. This increase in REE is likely to persist even in those who are regular caffeine users as was also seen in the current study. This is further supported by the aforementioned study done by Outlaw et al. [22] who observed the significant increase in REE at 60 min post-ingestion of a caffeine-containing supplement, even though the subjects were regular caffeine consumers and reported average caffeine intakes of approximately 200 mg per day.

Furthermore, results from the current study also indicate that MIPS ingestion does not appear to negatively influence HR in recreationally active females as HR remained stable and did not significantly increase following consumption of a MIPS compared to a PLA. This finding is consistent with other studies [3, 12] which also observed minimal changes in HR following ingestion of a MIPS. Conversely, some studies [24, 25] have reported increases in HR following consumption of a MIPS, which may be attributable to differences in the amount of caffeine consumed or the caffeine habits of the subjects.

Based upon the results of the current study, it also does not appear as though systolic blood pressure is significantly influenced by MIPS ingestion. These findings are in contrast to previous studies, which have observed significant increases in systolic blood pressure following consumption of MIPS or caffeine-containing beverages [3, 12, 25]. For example, Campbell et al. [12] reported a significant increase in both systolic and diastolic blood pressure following ingestion of a caffeine-containing thermogenic supplement in female subjects. Interestingly, a significant increase in only diastolic BP was observed in the current study. These contradictory findings may again be attributable to the differences in caffeine dosage. As stated previously, caffeine is an adenosine antagonist and therefore acts as a vasoconstrictor. This vasoconstriction can lead to an increase in systemic vascular resistance and the isolated rise seen in diastolic pressure in this study may be explained by this as vascular resistance impacts diastolic blood pressure to a greater degree than systolic pressure. A change in diastolic blood pressure of this magnitude however is rather abnormal, particularly under resting conditions and warrants further investigation. For the current investigation, the MIPS contained a blend of caffeine and various other ingredients, however, the exact amounts are unknown. Previous studies have observed changes in HR and systolic BP following ingestion of caffeine-containing beverages with dosages ranging from 230 to 495 mg, which may explain some of the inconsistencies regarding hemodynamic responses [3, 12, 24, 25]. Further, acute increases in diastolic blood pressure may be a concern for those with cardiovascular disorders. However, a recent study by Vogel et al. [5] investigated the same MIPS used in the current study and determined it to be safe for females to consume 1 or 2 servings of a MIPS daily for 28 days as evidenced by a lack of change in hematological markers or resting vitals in recreationally active females. Based on the results of the current study and those from Vogel et al. [5], it appears as though the supplement does not result in any serious adverse effects with the exception for the potential rise in diastolic blood pressure.

The current investigation observed a significant increase in upper body muscular endurance, which is in agreement with the previous findings that have investigated the acute effects of MIPS on various aspects of performance [2, 26, 27]. It can be assumed that the caffeine contained within the current MIPS likely played a significant role in the observed performance benefits, as it is one of the few ingredients with an immediate mechanism of action as described earlier and has been previously shown to improve performance [6]. It has been proposed that caffeine may positively influence muscular endurance by its direct effect on muscle anaerobic energy provision and its ability to increase muscle contractility [26]. Further, caffeine also acts as a central nervous stimulant and therefore may delay the onset of fatigue or allow individuals to better tolerate a higher training intensity ultimately allowing for a greater work capacity [24, 26]. A recent meta-analysis [6] found that caffeine ingestion appears to improve muscular endurance (overall ES = 0.28, p < 0.01) and increase maximum voluntary contraction, particularly during lower body exercises (overall ES = 0.67, p < 0.01). However, the current investigation did not observe a significant increase in lower body muscular endurance. These findings are in opposition to a prior investigation, which observed a significant increase in lower body endurance, but not upper body [24] following ingestion of a MIPS in males. These differences in performance outcomes may be explained by differences in instrumentation utilized (i.e., leg press versus the back squat) or too low of a caffeine amount to elicit a positive improvement in lower body performance. It is worth noting that other ingredients in the MIPS may also have contributed to the improvement in performance as some of them are designed to also enhance exercise performance. For example, tyrosine supplementation is purported to reduce sensations of central fatigue during strenuous exercise however the supporting evidence is not clear as previous studies have failed to detect any substantial improvements in strength, exercise capacity or anaerobic power [27, 28]. Beet-root extract is also purported to enhance exercise performance by augmenting the vasodialatory response to exercise thereby improving blood flow. There is some evidence to support its ability to improve exercise performance however, as a result of the proposed mechanism of action, it is not likely to influence the exercise modalities used in the current study in addition to the fact that prior research also suggests that multiple doses overall several days may be required in order to elicit an ergogenic benefit [2931]. Additionally, it would be expected that if adequate amounts of boot root extract were present, reductions in blood pressure would have occurred as a result of increased vasodilation and antihypertensive responses which is contradictory to the present findings. Similarly, beta-alanine supplementation has also been shown to enhance exercise performance, particularly during bouts of high-intensity exercise lasting 30–180 s. as a result of an improvement in buffering capacity. However, it is again believed that several dosages over the course of multiple weeks (~4 weeks) is required to substantiate any performance benefits [32]. Additionally, the dosage of beta-alanine required for an ergogenic benefit appears to be 4–6 g/d [32] and the MIPS used in the current study only contains 5.6 g of a proprietary blend which also contains several other ingredients. Therefore, the likelihood of there being enough beta-alanine present to elicit any acute benefit is low. Taurine is another ingredient that has been proposed to enhance anaerobic performance [33]; however, once again, a larger dose (~5 g) is likely required to substantiate any ergogenic benefit.

In the current investigation ingestion of the MIPS did not appear to influence lower body power, which is in accordance with previous findings. For example, Jagim et al. [2], also did not observe a significant improvement in lower body power following ingestion of a MIPS. However, Jagim et al. [2] did observe a significant increase in mean power during a maximal effort sprint test. Adversely, the current investigation observed a significant increase in total work during the maximal sprint following ingestion of the MIPS but not power. All other anaerobic power measurements during the maximal sprint test were not significantly different following ingestion of a MIPS compared to the PLA, which is similar to results seen in previous studies [2, 8].

A secondary aim of the current study was to examine how MIPS ingestion influences subjective markers of focus, energy, and fatigue during exercise. Based upon the results of the current investigation, it appears as though acute MIPS ingestion may positively influence feelings of focus following a bout of high-intensity exercise. The findings of the current investigation are in agreement with the observations from a previous study [15] during which subjects reported statistically greater feelings of focus and energy 10-min into running on a treadmill at 70% of ( dot{mathrm{V}} )O2max following ingestion of a MIPS. However, the current study did not observe a statistical difference in subjective feelings of energy or fatigue levels post exercise following ingestion of a MIPS compared to PLA. These findings are in opposition of Jagim et al. [2] who reported reductions of fatigue levels throughout testing following ingestion of a MIPS during a strength training protocol. This disparity between the two conditions may be more drastic due to the greater workload of a strength training protocol consisting of 5 sets of 5 repetitions with a 6th set to failure [2]. Additionally, differences in ingredient amounts, particularly caffeine, across different MIPS’s may also yield contradictory findings relating to subjective measures of fatigue and energy levels. It is likely that caffeine contained within the MIPS was primarily responsible for the observed increase in focus as previous research has observed similar findings during high-intensity exercise following consumption of caffeine-containing beverages [34, 35]. Tyrosine, which is also one of the included ingredients, has also been proposed to improve cognitive performance during exercise [36]. For example, Deijen et al. [36] observed improvements in cognitive performance during periods of physical stress in military cadets however a relatively large dose was used in the study and the supplement was ingested for a 6-day period.