The rate at which muscle glycogen is degraded depends primarily upon the intensity and duration of physical activity. During high-intensity intermittent exercise, and throughout prolonged endurance training, muscle glycogen is broken down to produce the adenosine triphosphate (ATP) required for muscle contraction.
Critically low levels of muscle glycogen can expedite the onset of fatigue and drastically decrease exercise intensity. As a result, it has been consistently demonstrated that consuming a carbohydrate-rich meal in the hours prior to endurance exercise can benefit performance.
Considering the significant glycogen depletion observed with prolonged endurance-based activity, it makes sense to prioritize carbohydrate consumption during and prior to exercise to ensure maximal glycogen reserves and thus, prevent potential performance decrements.
In a study by Koopman et al., subjects completed eight sets of ten reps for both the leg extension and horizontal leg press. Each exercise was performed at 75% of 1RM with two-minute rest intervals between sets. The training session took approximately 45 minutes to complete. At the end of the intervention, it was found that muscle glycogen content in the vastus lateralis muscle was depleted by 33.7 ± 7%.
Despite evidence for only a modest amount of glycogen depletion during high-volume resistance training, it is often recommended to consume a large bolus of carbohydrate before a resistance exercise session.
The rationale for this seems to be largely adopted from research on endurance and field sports, but there is some direct data on the topic available. For instance, low muscle glycogen status has been shown to limit the muscles’ ability to contract with high force and lead to significantly fewer reps performed over multiple sets of squats.
From the plethora of data available, pre-exercise glycogen content significantly affects resistance training quality and adaptation. As such, adequate restoration of muscle glycogen from day to day is required to sustain the capacity for consistent and progressive high-intensity activity.
With that being said, this does not indicate that consuming a large portion of carbohydrates before resistance exercise is necessary to optimize performance. It simply suggests a sufficient level of glycogen prior to exercise is a prerequisite for a productive session.
The question then remains, does consuming carbohydrates pre-workout to “top off” muscle glycogen stores boost resistance exercise performance? Let’s see what science has to say on the matter.
The Benefits of Pre-Workout Carbohydrate Consumption: Physiological?
In this study, the researchers examined the effect of a typical high-carbohydrate breakfast meal on subsequent resistance exercise performance. The subjects featured in this experiment were resistance-trained men who also habitually consumed breakfast.
The same exercise intervention was completed on two separate occasions to test the effects of the pre-workout meal. Subjects performed four sets of squat and bench press at 90% of their 10RM to failure.
Subjects arrived at the laboratory after an overnight fast and consumed either water only or a high-carbohydrate breakfast providing 1.5 g/kg body mass of carbohydrate two hours prior to the training session.
At the end of the trial, it was shown that total reps completed for the back squat were 15% lower during the water only condition, equating to a reduction of ten reps over four sets. The number of reps performed was significantly lower on sets one and two, with no significant differences between sets three and four.
For the bench press, the water only condition resulted in a 6% decrease in performance, equating to a reduction of three reps over four sets. Similar to squats, the number of reps completed were lower on sets one and two, with no significant differences between sets three and four.
On the surface, this study appears to be a win for pre-workout carbohydrate intake, but there is a major limitation of this trial – it does not account for the placebo effect. The subjects utilized in this study were habitual breakfast consumers. As a result of their consistent dietary patterns, we can’t be sure whether improved performance following the high-carbohydrate meal was achieved through a physiological or psychological effect.
The placebo effect is very real and current research suggests it can exert a moderate effect on performance (like the sort of moderate effect that can get you a few extra reps across four sets of squat and bench press). Since these were habitual breakfast consumers, the participants might have created an association between consuming a pre-workout meal and having a productive training session. Otherwise stated, when you remove their pre-workout meal, these individuals might convince themselves that they are bound for suboptimal performance.
To tease out these nuances, we would need an experiment that utilized both a high-carbohydrate and a placebo condition. With this design, the subjects wouldn’t know whether or not the item they consumed contained a significant amount of energy. Fortunately, a few trials with these specifications have been recently conducted.
The Benefits of Pre-Workout Carbohydrate Consumption: Mainly Psychological
In this trial, resistance-trained men with a 1RM back squat of at least 150% of body mass completed two interventions in a randomized, double-blind fashion.
Immediately before and during a resistance exercise session, subjects consumed either a carbohydrate supplement containing 0.3 g/kg body mass of carbohydrate (CHO) or a non-caloric placebo. For three days before each testing session, subjects recorded their food intake and ate a recommended diet that was designed to supply approximately 55% of energy from carbohydrates.
The exercise intervention utilized the back squat and was quite unique, so rather than trying to summarize it, I’ll provide a quote of exactly how the authors described it. “Each set was performed for five reps, with an eight second per rep cadence, coupled with three minutes of rest in a seated position between sets. Subjects performed the sets of five reps with the target weight until they could no longer squat to parallel, failed to complete a rep every eight seconds, or could no longer continue the protocol because of exhaustion, or voluntarily terminated the session.”
In the three days before each testing session, dietary intake was not statistically different for total calories or carbohydrates. In the CHO condition, carbohydrate intake was 410.7 ± 137.87 g. In the placebo condition, carbohydrate intake was 415.7 ± 143.6 g. The results of the testing session showed no significant differences for total reps or sets performed between interventions.
Total reps performed in the CHO and placebo intervention was 20.4 ± 14.9 and 19.7 ± 13.1, respectively. For total sets completed, the CHO intervention resulted in 3.5 ± 3.2 sets, while 3.5 ± 2.7 sets were completed in the placebo intervention.
From these findings (or lack thereof), we see no significant differences in performance when consuming a carbohydrate-rich or non-caloric placebo beverage prior to and during a resistance exercise session.
This is evidence of a potential placebo effect with the caveat of adequate glycogen stores prior to starting exercise. Based on the evidence provided by the three-day food journals, the subjects were consuming an ample amount of carbohydrates leading up to the testing sessions. As a result, glycogen stores were at adequate levels to maximize performance and thus, there was no physiological benefit to consuming carbohydrates prior to exercise.
In a more recent study utilizing a randomized, double-blind design, the effects of carbohydrate supplementation 30 minutes before resistance training on exercise performance and muscle glycogen were examined. Two days prior to each of the three testing sessions, subjects collected a food diary.
At the testing sessions, participants consumed either maltodextrin at a dose of 2 g/kg body mass, or a flavored, non-caloric placebo.The exercise intervention featured four sets of reps to volitional fatigue with 70% 1RM on the leg press. A rest interval of 45 seconds was utilized between sets.
The results displayed similar total carbohydrate intake between conditions, with 2.8 ± 1.18 g/kg and 2.7 ±1.11 g/kg, in the carbohydrate and placebo interventions, respectively. For performance, no statistically significant differences were found between interventions. Total reps completed for the placebo condition was 53.8 ± 7.8. For the carbohydrate condition, 51.8± 6.9 reps were completed.
The authors surmised that the lack of effect found for the carbohydrate supplement could be attributed to adequate glycogen stores at baseline (meaning total carbohydrate intake was sufficient in the days preceding the test), negating any benefit from additional carbohydrates before the brief testing session.
In the third study we’ll be putting under the microscope, resistance-trained men, who were also habitual breakfast consumers, were randomized to three separate trials in a crossover design. Subjects consumed a breakfast two hours before a bout of resistance exercise featuring four sets to failure at 90% of 10RM for the back squat and bench press. All sets were separated by three minutes of rest.
Prior to the testing session, subjects consumed either water only, a low-energy viscous breakfast providing 2.4 g of carbohydrates and 5.4 g of fiber (placebo), or a low-energy viscous breakfast plus ~119 g of carbohydrates (CHO).
In the end, the researchers found that, compared to water, total reps performed for the back squat were greater in the placebo and CHO conditions, with no significant differences between placebo and CHO. Similar findings were recorded for the bench press.
In combination, the findings of these three experiments suggest that a pre-workout meal including a large bolus of carbohydrates likely influences resistance exercise performance via a psychological (placebo) rather than physiological effect.
To add, this finding is under the context of sufficient total daily carbohydrate consumption. If muscle glycogen is not restored following an exercise session, consuming carbohydrate in the meal prior to the following workout is probably beneficial.
Another important point to consider when analyzing these studies is the amount of work being performed. Despite each of these trials featuring an exhaustive protocol (maximum reps to failure over multiple sets), the total amount of work could be considered relatively low in comparison to training for other sports. Across the aforementioned studies, anywhere from four to eight sets were performed during the exercise intervention.
With this in mind, it’s possible that pre-workout carbohydrate consumption did not show an effect because the amount of training volume performed wasn’t enough to result in severe glycogen depletion during the intervention. This could explain the contrasting results between these trials and endurance exercise research.
As exercise duration increases, there is a greater decrease in muscle glycogen and greater reliance on plasma glucose as a fuel source. As a result, having some glucose floating around in the blood from a pre-workout meal will positively influence performance during prolonged exercise. With short-duration exercise (≤ 45 minutes), it is likely that muscle glycogen is the primary fuel source. For this reason, a sufficient level of muscle glycogen prior to a resistance training session is sufficient to facilitate maximal performance, and a large bolus of carbohydrate pre-workout will not provide further benefit.
In alignment with current sports nutrition guidelines, it is recommended that athletes consume carbohydrates in the 1-4 hours before exercise when the duration is longer than 60 minutes. Furthermore, there is little evidence to suggest pre/intra-workout carbohydrates will enhance performance for exercise lasting less than 45 minutes.
Do the above findings mean you shouldn’t consume carbohydrates pre-workout? No, but if you’re a bodybuilder, and not an endurance or field sport athlete, carbohydrate timing likely has little impact on performance.
In comparison to long-duration endurance activity, glycogen depletion during a resistance exercise session is quite trivial. In addition, muscle glycogen depletion is local, or specific to the muscle being worked, and most physique oriented trainees give at least 48 hours of recovery before training a muscle again.
For bodybuilders who perform twice-daily training, or follow very-high-volume high-frequency routines, pre/intra-workout carbohydrate may be useful, but this likely isn’t the case for most trainees.
If the former does not apply to you and you traditionally consume a pre-workout meal, it’s likely worthwhile to continue doing so. Whether the effect is physiological or psychological, if ingesting a pre-workout meal featuring a large bolus of carbohydrates produces an improvement in performance, then the practice is justified.
For others who are confident that they will not fall victim to the placebo effect, it might be valuable to know that you can shift your pre-workout carbohydrates to a more preferable window of time without negatively affecting your resistance-exercise performance.
To summarize, with appropriate total daily carbohydrate intake and rest between training bouts, it appears that glycogen stores will be at a level sufficient to facilitate maximal performance during resistance exercise. For these reasons, strength and physique athletes should primarily be concerned with total carbohydrate intake rather than timing, and current evidence recommends a carbohydrate intake of ≥ 3-5 g/kg body mass for bodybuilders.