The purpose of this study was to examine the differential effects of a complex protein beverage and an isocaloric CHO beverage on performance measures and RPE following high-intensity resistance training.
High-intensity exercise—especially high-intensity resistance training—can significantly deplete muscle glycogen. Towards the end of the 15–18 minute 2:1 work to rest HIRT workout all subjects were experiencing cardiovascular and muscular fatigue. This HIRT workout was an original protocol developed by the primary researcher. However, it was inspired by previous studies that measured performance and/ or recovery following ingestion or supplementation of treatments such as Smith et al. who utilized a 15–18 minute high-intensity cycling protocol to glycogen dilute the legs. The current design required subjects to whole-body glycogen dilute by executing compound, total body resistance and body weight exercises in a continuous, explosive pattern for two minutes. Most subjects could not reach 18 minutes (most stopped at 15 minutes) due to exhaustion; thus, implying the protocol was physically taxing and adequate to glycogen-deplete the muscles and instigate catabolic processes.
In addition, the mechanical stress associated with resistance training places eccentric loading forces on the muscle fibers during muscle contraction, which micro-tears the muscle, and this catabolic environment hosts the mechanisms that affect MPS[12, 27]. Theoretically, the consumption of macronutrients and the timing of such could affect the neuromuscular response to exercise by counteracting the negative physiological state that follows. The present investigation demonstrated that a beverage, primarily comprised of protein (approximately a 1:4 CHO to PRO ratio), provides better post-exercise replenishment for subsequent agility T-test, push-up, and sprints tests compared to an iCHO-only drink. These practical field tests were used to assess physical ability, not clinical presentations. However, the outcomes of this study can be explained by mechanisms supported in other research that utilized more invasive protocols and designs. For example, nuclear magnetic resonance spectroscopy (nMRS) is a widely used clinical tool for the observation of high-energy phosphates, such as glycogen. The technique is a minimally invasive procedure that permits in-vivo, time-dependent information to be evaluated. Ivy et al. utilized nMRS as a method to evaluate glycogen content within the vastus lateralis pre-exercise and four hours post-exercise. These findings suggested that consuming a CHO-PRO supplement compared to a CHO-only supplement may replenish muscle glycogen more effectively post-exercise. This information is transferable to the current study because carbohydrate availability and MPS are important for post-exercise recovery and subsequent performance. Replenishing muscle glycogen content after exercise is crucial to mitigate tissue damage, inflammatory markers, and upregulate the Akt/PKB pathway for MPS. The focus of the current study was to evaluate the performance and RPE differences between two products by conducting physical tests and reporting exertion. In other words, regardless of muscle glycogen content, the interest lied within the subjects’ ability to perform and which treatment provided the substrates to do so. Since glucose availability is necessary for glycogen synthesis, the objective was to indirectly determine which treatment (VPX or iCHO) provided the best substrate for glycogen synthesis, (and by conjunction recovery and repeated performance), whether it be through glucose-mediated glycogenesis or gluconeogenesis.
Macronutrient selection and recovery are indecisive topics within the sports nutrition field. Some experts back the CHO-only recovery supplement, while others stand by the 4:1 ratio of CHO to PRO, and then some advocate PRO-only. VPX Protein Rush™ falls somewhere in the middle with its proprietary mix of: calcium caseinate, milk protein isolate, whey protein concentrate, micellar casein, whey protein isolate, casein hydrolysate di- and tri-peptides, and whey protein hydrolysate di- and tri-peptides. It contains 11 g of CHO, with 6 g attributing to dietary fiber, which is a considered “non-impact” CHO because fiber does not contribute to caloric content or affect blood glucose levels and insulin response. Net protein balance and muscle accretion are essential to performance, and following physical activity, negative protein balance supersedes protein synthesis until consumption of amino acids occurs. Bovine milk protein contains approximately 80% casein and 20% whey[31, 32]. Known as the “slow-releasing” protein, casein acts as an inhibitor to whole body protein breakdown, by means of sustaining whole body leucine balance, which is the critical amino acid for MPS. However, casein is not a major contributor to new muscle accretion; rather it digests slowly to prevent the breakdown of existing muscle and preserves leucine balance. VPX also contains whey protein isolate, which is higher in quality compared to whey protein concentrate. When combined with resistance training, whey protein isolate has been shown to result in significantly greater gains in lean mass and strength compared to casein.
In regards to recovery for subsequent performance, the aim is to stunt muscle glycogen loss and catabolism while augmenting glycogen repletion and MPS, which entails replenishing lost muscle glycogen stores (which was discussed earlier), stimulating muscle recovery pathways, and reducing inflammatory and catabolic constituents. VPX possesses both glycogenic and anabolic characteristics to support the goals of recovery. Despite the small amount of CHO, the drink composition offers the qualities of fast-acting and slow-releasing proteins. Dietary protein is necessary to activate the MPS pathway, specifically mammalian target of rapamycin that signals initiation factors (p70S6K and 4EBP) responsible for activating messenger RNA translation initiation and ribosomal activity, which are rate-limiting steps for controlling protein synthesis. Catabolic factors, such as cortisol, creatine kinase, and lactate dehydrogenase, are detrimental to positive net protein balance. Neither hormone or enzyme profiles were assayed for this dissertation, but preceding investigations[13, 35] measured hormonal profiles and catabolic markers, including testosterone, cortisol, creatine kinase, and lactate dehydrogenase. The current study connects to these outcome measures because adequate and timely post-exercise replenishment is intended to reduce catabolic and inflammatory markers and improve repeated performance; thus the performance tests in this study were practical extensions of the aforementioned clinical tests.
Although the present investigation measured short-term performance effects of the beverages, the blend of proteins in VPX contains the amino acids that potentially support muscle protein synthesis, recovery, and performance compared to the iCHO. Additionally, the smaller whey hydrolysate di- and tri-peptides—which are quickly digested—have the potential to be used as gluconeogenic substrates to replenish glycogen. Especially in a depleted state, some amino acids (i.e., alanine) can be used as a substrate to manufacture glucose.
Finally, as it pertains to the primary research hypothesis—following a high-intensity resistance workout, there is a differential effect on subsequent agility T-test, push-up test, and 40-yard sprint when supplementing post-workout with VPX versus an iCHO drink. Particularly, VPX yielded a significantly larger interaction effect between the performance tests following HIRT compared to iCHO. Repeated performance is a combined series of effort (often entailing more than one exercise modality and/or skill); hence, it is important a product has collective benefits rather than just improving one measure.
Macronutrient and rate of perceived exertion
Exertion levels, or even “perceived” exertion levels, during exercise may affect performance. Very few studies have investigated the effects of PRO alone on RPE. The investigations by Backhouse et al.[36, 37] supported the supplementation of CHO to lower RPE during exercise. Kalman compared the effects of CHO-only, PRO-CHO, and PRO-only on various performance measures (i.e. resistance training), including RPE. The results did not report a significant difference in RPE between groups over time. This study reported similar findings with respect to differences between means and hypothesis testing via ANOVA—neither treatment was statistically significant towards reducing agility T-test, to-fatigue push-up, or 40-yard sprint RPE following HIRT.
Rate of perceived exertion is a subjective measurement, and studies by Utter et al.[39–42] that examined the effects of CHO on RPE observed that RPE does not correlate with the amount of total work actually performed. Subjects may have “felt” more fatigued after consuming a placebo compared to CHO, but there were no mean differences in performance between groups. Similarly, the current investigation found VPX and iCHO to be equivocal in terms of the subjects’ reported RPE; in other words, this is the first study to find that VPX provides similar exertion responses to an iCHO drink.
The ANOVA and t-test statistical results were not significant for any individual dependent variables. This could have been attributed to sample size and power (80%). The RM-MANOVA was not affected by the sample size and resulted in a meaningful and significant difference; this model reported a significant cumulative effect between the three performance tests. This outcome is likely attributed to the similarities between the tests (i.e., exercise performance variables) and their collective impact; as the variables were added into the model their compounded effects on each other became statistically apparent. Physical activity is a cumulative action often involving a combination of endurance, speed, agility, power and balance to name a few. It may be valuable to see cumulative effects than singular effects in exercise performance for athletes and exercisers who rely on more than one energy system and skill to complete a task or activity. Beyond the statistical limitations, state anxiety appeared to be a limitation for all subjects.
It is possible the subjects had apprehension leading into the second workout test. As a result, to preserve energy almost all subjects may have started slower during the first set of the second arm; therefore, subjects required verbal coaching to stay on task. Measuring pre- and post-glycogen status was not feasible for this design; however, subjects were asked to eat similar food composition before each arm. Lastly, despite each subject acting as their own control, the inclusion of an isolated control group (no treatment) would have provided an additional comparison to evaluate the effects of re-feeding versus no re-feeding. Particularly for the RPE hypothesis, which resulted in no differences between means, including an isolated control group could have provided data to support the importance of re-feeding to reduce RPE. For this particular study design, including a control group could have been unethical considering the setting and absence of medical personnel.