In the past decade, there has been an increased emphasis on the timing of ingesting specific nutrients. This concept has become known as nutrient timing. Simply stated, nutrient timing is focused on “when to eat” and not solely on “what to eat.” In the scientific literature, nutrient timing has been studied under various modes of exercise, including running (49,50), cycling (21,27), and resistance training (12,45,48). This article will discuss aspects of nutrient timing in relation to resistance exercise, with an emphasis on the macronutrients, particularly carbohydrate and protein.
Scientific studies investigating nutrient timing and its applications to resistance exercise have focused on the following 4 outcomes:
* Enhancing performance in individual resistance exercise training bouts
* Enhancement of recovery after a resistance exercise bout
* Enhancement of net protein balance after a resistance exercise bout
* Enhancing adaptations (muscular strength and hypertrophy) resulting from a resistance training program over several weeks or months of training.
In relation to each of these outcomes, nearly all the scientific studies involving nutrient timing and resistance exercise have investigated carbohydrate and protein supplementation. In contrast, few (if any) studies have investigated the effects of the timing of dietary fat intake around the resistance exercise bout. The reason for this is that resistance training is an anaerobic activity, relying on the phosphagen system and carbohydrate oxidation for ATP production (26). In addition, resistance training also increases protein synthesis, and it has been demonstrated that high-quality protein intake enhances the protein synthesis response to an acute bout of resistance exercise. Dietary fat is not relied upon for energy to fuel a resistance exercise bout nor has its ingestion been shown to amplify the anabolic response resulting from an acute bout of resistance exercise. In light of this, the discussion of nutrient timing and its effects on resistance training performance will center on carbohydrate and protein/amino acid ingestion. Table 1 highlights the effectiveness that appropriately timed carbohydrate and protein/amino acid ingestion has on each of the outcomes described above.
ENHANCING PERFORMANCE IN INDIVIDUAL RESISTANCE EXERCISE TRAINING BOUTS
Because of the fact that resistance training relies heavily on carbohydrates as an energy source, it has been hypothesized that ingesting carbohydrates before and/or during a resistance training bout will increase the total amount of work that may be performed during the workout (17,23,24). The rationale is based on the fact that skeletal muscle glycogen is depleted during resistance exercise, and as it is depleted, the intensity and subsequently the total work volume (measured by the amount of weight lifted × repetitions performed) are compromised.
Research has demonstrated that resistance exercise does deplete skeletal muscle glycogen (Figure 1) (26,31,44). Despite this depletion of skeletal muscle glycogen, the majority of studies in which supplemental carbohydrate was ingested before a resistance training bout did not report improvements in resistance training performance (15,23,24). In the limited studies that reported a performance-enhancing effect of pre-exercise carbohydrate supplementation (16), it should be noted that the resistance training workouts were not of a practical nature (i.e., 16 sets of lower-body resistance exercise conducted on an isokinetic dynamometer) and did not resemble workouts that are conducted in a typical athletic strength and conditioning program.
As compared with carbohydrates and fats, proteins (amino acids) are not heavily oxidized for energy during exercise. Of the approximate 20 amino acids, only 3 are oxidized for energy during exercise— the branched-chain amino acids (BCAAs—leucine, isoleucine, and valine). Even though the BCAAs are oxidized for energy, they are oxidized at levels far below carbohydrates and fats (22). In a study published in abstract form (9), researchers gave BCAAs to male subjects at a dose of 40 mg/kg of body mass 30 minutes before and then another 40 mg/kg of body mass immediately before an acute bout of lower-body resistance exercise (totaling 80 mg of BCAAs per kilogram of body mass). The resistance exercise consisted of 4 sets of leg press followed by 4 sets of knee extension at 80% 1 repetition maximum (1RM) to failure. The authors reported that the BCAAs had no effect on resistance exercise performance. Because of their limited role in oxidation during exercise and their inability to improve acute resistance exercise performance, amino acids should not be ingested before a resistance exercise bout, with the belief that they will improve the performance of the subsequent workout.
CARBOHYDRATE AND PROTEIN SUPPLEMENTATION
Individual resistance exercise workouts are not enhanced with carbohydrate or protein supplementation alone. A study conducted at the University of Texas under the direction of Ivy sought to investigate the effects of pre-workout carbohydrate plus protein supplementation on resistance exercise performance (2). Participants included non–resistance-trained male subjects who completed 3 sets of 8 repetitions to volitional fatigue in 7 different exercises targeting the upper and lower body. In terms of supplementation, either an electrolyte and artificial sweetener solution (placebo) or a carbohydrate plus protein beverage (in a 4:1 ratio of carbohydrate to protein) was ingested according to the following schedule:
* 30 minutes before exercise: 26 g of carbs plus 6.5 g of whey protein or a placebo
* Immediately before exercise: 13 g of carbs plus 3.2 g of whey protein or a placebo.
In total, 39 g of carbohydrates and approximately 10 g of whey protein were ingested within 30 minutes before the initiation of the workout in the supplemental group. Resistance exercise performance was measured by assessing the total amount of weight lifted on the third and final set completed to volitional fatigue on each of the 7 exercises. There were no significant differences between the carbohydrate plus protein group (534 ± 19 kg) and the placebo group (556 ± 22 kg) in terms of total weight lifted during the third and final set of each exercise (2).
In summary, it appears that ingesting carbohydrate alone, protein/amino acids alone, or carbohydrate plus protein before resistance exercise does not improve the performance of the resistance exercise workout in terms of total amount of weight lifted during the workout. In contrast, there are favorable outcomes resulting from carbohydrate and protein supplementation in terms of enhancing adaptations over time and on recovery. Both of these aspects are discussed below.
RECOVERY AFTER A RESISTANCE EXERCISE BOUT
CARBOHYDRATE AND MUSCLE GLYCOGEN RESYNTHESIS
Skeletal muscle glycogen is depleted during a resistance exercise workout. In fact, a single resistance training session can reduce skeletal muscle glycogen stores from 24 to 40%, depending on the duration, intensity, and overall work accomplished during the session (42). Although not all studies agree (29), if skeletal muscle glycogen is depleted and not purposefully replenished, a subsequent resistance exercise workout will be compromised (17,25). Hence, carbohydrate ingestion for the purpose of either preventing or replenishing skeletal muscle glycogen allows for optimal resistance exercise performance in a subsequent bout.
To demonstrate this point, Haff et al. (17) investigated the effects of carbohydrate supplementation on multiple sets of resistance training exercise during the second training session on a given training day. In this randomized, counterbalanced double-blind study, 6 resistance trained men completed 2 identical resistance exercise sessions separated by a week. The exercise consisted of a morning and an afternoon resistance exercise session and included a 4-hour recovery period between the 2 sessions. The morning session was designed to deplete skeletal muscle glycogen in the lower body. The afternoon session consisted of sets of squats performed to exhaustion at an intensity of 55% of 1RM at a rate of 1 repetition every 6 seconds. Subjects were allowed a 3-minute rest between each set with the goal of completing as many sets of 10 repetitions as possible. An inability to complete a set of 10 repetitions at the correct cadence signaled the end of the workout.
During the morning resistance training session, subjects ingested a 20% glucose-maltodextrin solution at a dose of 1.2 g/kg of body weight per hour or a calorie-free placebo. After the morning session and during the 4-hour recovery period, subjects ingested the carbohydrate solution at 1, 2, 3, and 4 hours post-workout. The amount of carbohydrate ingested was at a rate of 0.38 g/kg of body weight per hour. During the afternoon workouts, it was reported that a significantly greater number of sets and repetitions were performed during the carbohydrate treatment (carbohydrate group completed about 18 sets and 199 repetitions as compared with 11 sets and 131 repetitions in the placebo group). Total work performed was also greater in the carbohydrate group, but it did not reach statistical significance (17).
In a related finding, Leveritt and Abernethy (25) instructed non–resistance-trained subjects to deplete skeletal muscle glycogen by engaging in aerobic exercise followed by 2 days of a carbohydrate-restricted diet. The carbohydrate restriction program caused a significant reduction in the number of squat repetitions performed as compared with a control group that did not induce depleted skeletal muscle glycogen.
Based on these 2 studies (17,25), it appears that replenishing skeletal muscle glycogen after exercise is important to maximize resistance training performance in a subsequent workout. However, if the repetition ranges used in a resistance exercise workout target the depletion of the phosphagen system (3–5RM, a repetition range advocated for maximum strength gains), then the extent to which glycogen depletion would occur would be reduced. Because of the limited number of scientific studies conducted in this area, more research is needed to either confirm or challenge the findings of these studies (17,25).
Studies investigating the optimal amounts of carbohydrate to be ingested after resistance exercise are limited. Table 2 summarizes the research in which specific amounts of carbohydrate were ingested after resistance exercise and its impact on skeletal muscle glycogen resynthesis. Given that 1 g/kg/h was as effective as 1.5 g/kg/h, it can be concluded that 1 g/kg/h is sufficient for resynthesizing skeletal muscle glycogen after resistance exercise to levels reaching 90% of pre-exercise values. After this dosing schedule, a 180-pound individual would ingest about 82 g of carbohydrate immediately after and then again 1 hour after their resistance exercise workout (totaling ∼165 g of carbohydrates within an hour after completing the resistance exercise workout).
CARBOHYDRATE PLUS PROTEIN AND MUSCLE GLYCOGEN RESYNTHESIS
Roy and Tarnopolsky (38) wanted to determine if adding protein to a carbohydrate beverage after resistance exercise would maximize the rate of skeletal muscle glycogen resynthesis after resistance exercise (as compared with carbohydrate ingestion alone). In this study, each resistance-trained male subject was given one of the following beverages immediately and 1 hour after resistance exercise:
* Carbohydrate at a rate of 1 g/kg of bodyweight
* Isocaloric carbohydrate-protein-fat (66% CHO, 23% Pro, and 11% fat)
* Noncaloric placebo.
At 4 hours post-exercise when skeletal muscle glycogen levels were reassessed, the carbohydrate-only group resynthesized glycogen levels to approximately 89% of pre-exercise levels. Similarly, the carbohydrate-protein-fat group also observed glycogen levels that were 89% of pre-exercise levels (the noncaloric placebo group had glycogen levels at approximately 72% of pre-exercise levels at 4 hours post-exercise). These results imply that ingesting 0.67 g of carbohydrate per kilogram of body mass when combined with protein and fat is just as effective as 1 g of carbohydrate alone per kilogram of body mass in replenishing skeletal muscle glycogen (38).
Another interesting aspect of this study is the inclusion of fat calories in the post-exercise beverage. It has often been suggested that adding fat to the post-workout recovery beverage should be avoided because of its potential to slow down the digestion and absorption of ingested carbohydrate (which may suppress the rate of skeletal muscle glycogen resynthesis). The finding of this study (38) indicates that adding fat to the post-workout carbohydrate-protein beverage does not negatively alter the rate of skeletal muscle glycogen resynthesis. In further support of this position, when subjects were given a post-endurance workout beverage containing carbohydrate, protein, and fat (even up to 45% of the calories being derived from fat), it was reported that the added fat content did not alter muscle glycogen resynthesis or glucose tolerance the next day (14).
PROTEIN/AMINO ACIDS AND MUSCLE DAMAGE
In addition to replenishing skeletal muscle glycogen, optimal recovery also includes reducing muscle soreness and suppressing muscle damage after a workout. In this context, BCAAs and protein ingestion have been reported to favorably impact both of these variables.
Surprisingly, a small amount of protein taken immediately after physical activity has been found to be very effective. During a 54-day basic training period in U.S. marine recruits (13), only 10 g of protein (taken with 8 g of carbohydrate and 3 g of fat) was superior to placebo and control groups (containing no protein). Specifically, the protein-containing supplement was taken immediately after exercise and resulted in an average of 33% fewer total medical visits, 28% fewer visits because of bacterial/viral infections, and 37% fewer visits because of muscle/joint problems as compared with the non–protein-containing placebo and control groups. In addition, muscle soreness was measured during the basic training period and on the last day of the training program. The protein group reported significantly improved muscle soreness scores in comparison with the control and placebo groups. Results from this study indicate that post-exercise protein supplementation has significant potential to positively impact health and muscle soreness during prolonged intense exercise training (13).
Resistance exercise induces muscle soreness and actual skeletal muscle damage (32,35). A main objective of optimizing recovery after resistance exercise is to reduce muscle soreness referred to as DOMS (delayed-onset muscle soreness) and to suppress skeletal muscle damage. Interestingly, BCAA supplementation has been reported to improve both of these aspects of recovery—DOMS and muscle damage.
In relation to DOMS, BCAA supplementation reduces the muscle soreness that surfaces in the hours and days after eccentrically based (20) and high-volume resistance exercise (41). In terms of dosage, non-resistance-trained subjects in the first study ingested 100 mg/kg before resistance exercise (41). In the other study, non-resistance trained subjects ingested 100 mg/kg at four different time points (totaling 400 mg/kg over the course of an entire day) (20). In both studies, the approximate ratio of the BCAAs (leucine:isoleucine:valine) ingested was 2:1:1 (50% leucine, 25% isoleucine, and 25% valine).
To further develop this point, Sharp and Pearson (40) gave a BCAA supplement to resistance-trained male subjects and evaluated its effectiveness over a 4-week period. Specifically, subjects consumed a BCAA supplement for 3 weeks before commencing a fourth week of BCAA supplementation with concomitant high-intensity total-body resistance training. Participants ingested 42 mg/kg of BCAAs per day (divided into 2 doses—one in the morning and another in the evening equating to 21 mg/kg per dose). Skeletal muscle damage was measured by serum creatine kinase levels, which was measured before and after supplementation, then again after 2 and 4 days of training. Serum creatine kinase levels were significantly lower in the BCAA group during and after resistance training (as compared with a placebo group).
Recovery from a bout of resistance exercise includes replenishing skeletal muscle glycogen, reducing muscle soreness, and attenuating serum markers of muscle damage. Ingesting a carbohydrate-protein beverage after resistance exercise will replenish skeletal muscle glycogen. Also, BCAA supplementation taken in conjunction with resistance exercise has been shown to enhance recovery by suppressing both muscle soreness and damage.
NET PROTEIN BALANCE
Maximizing the anabolic response to a resistance exercise bout is the central focus of nutrient timing. Maximizing the anabolic response leads to increases in both skeletal muscle hypertrophy and strength. Skeletal muscle hypertrophy can be summarized by the status of net protein balance. Net protein balance is equal to muscle protein synthesis minus muscle protein breakdown. For skeletal muscle hypertrophy to occur, the net protein balance must be positive (synthesis must exceed breakdown). There are 3 scenarios in which net protein balance can be changed to a positive net protein balance:
1. Increase protein synthesis
2. Decrease protein breakdown
3. A combination of increasing protein synthesis and decreasing protein breakdown.
At rest, in the absence of an exercise stimulus and nutrient intake, the net protein balance is negative (4,10,33). An acute bout of resistance exercise increases muscle protein synthesis above baseline values, but it also increases the rate of protein degradation (6,34). Even though net protein balance is improved after resistance exercise, if nutrients (i.e., protein) are not ingested, net protein balance does not improve to the point of becoming positive (equating to an anabolic environment) (Figure 2).
Ingesting carbohydrate alone after resistance exercise improves net protein balance, but the improvement is minor and delayed compared with the ingestion of amino acids (7). The small improvement observed in net protein balance resulting from carbohydrate ingestion is primarily because of a decrease in muscle protein breakdown (3,7,39), with little to no improvement in muscle protein synthesis. The improvement observed in the rate of muscle protein breakdown is likely because of the insulin response that is associated with the carbohydrate ingestion (6,7). In terms of dosage, Roy et al. (39) observed that 1 g/kg of carbohydrate supplementation ingested immediately and 1 hour after resistance exercise can decrease myofibrillar protein breakdown and urinary urea excretion, resulting in a more positive net protein balance.
In contrast to the effects of carbohydrate ingestion, essential amino acid ingestion after resistance exercise has been shown to significantly improve protein synthesis to the point of inducing a positive net protein balance (5,8,28,47). Whole-protein sources (including whey, casein, and soy protein sources), when ingested either before (45) or after (37,43,46) an acute bout of resistance exercise, also significantly improve net protein balance by increasing rates of protein synthesis. In one of these investigations (43), it was reported that whey protein was superior to soy and casein in its ability to increase protein synthesis (approximately 22 g of each type of protein was ingested after resistance exercise). Surprisingly, even though soy is lower in quality than casein, they found that of the 3 protein sources, casein resulted in the lowest net response in protein synthesis. The authors suggested that this was a factor of the slow rate of digestion induced by casein. Therefore, after resistance exercise, it may be ideal to select a protein source high in BCAA content (whey) that is also fast digesting in nature.
After a bout of resistance exercise, what is the optimal amount of protein that will maximally stimulate muscle protein synthesis? Until recently, this question was not addressed. Research conducted at McMaster University sought to answer this question by giving male subjects (with at least 4 months of resistance training experience) 5 different amounts of protein in a randomized crossover design (30). Immediately after a lower-body resistance exercise bout, the subjects consumed drinks containing 0, 5, 10, 20, or 40 g of whole egg protein. After consuming the whole egg protein supplement, protein synthesis was measured for the next 4 hours. Mean mixed muscle protein synthesis was maximally stimulated with 20 g of whole egg protein (meaning that ingesting 40 g of protein offered no additional benefit than 20 g of protein in terms of maximizing protein synthesis rates). In terms of relative dosage, this amount of protein was equivalent to 0.23 g of whole egg protein per kilogram of body mass. It is important to note, however, that this research relates to a relatively rapid digesting protein source and may not apply to slower digesting proteins, such as casein. However, based on previous data discussed, we emphasize the need to consume a rapidly digesting source of protein after exercise.
Not surprisingly, when carbohydrate and protein are ingested together after resistance exercise, a significant increase in muscle protein synthesis is observed (28,36). In fact, when essential amino acids and carbohydrate are ingested together after resistance exercise, the improvements in muscle protein synthesis are greater as compared with when essential amino acids or carbohydrate are ingested alone (28). A review of the literature indicates that a positive net protein balance is maximized from ingesting both protein/essential amino acids and carbohydrate. It appears that protein/essential amino acids maximize protein synthesis (19) and carbohydrates suppress protein breakdown.
ENHANCING ADAPTATIONS AFTER SEVERAL WEEKS OR MONTHS OF RESISTANCE TRAINING
It is often assumed that maximizing the anabolic response to each and every resistance exercise workout by attaining a positive net protein balance leads to an increase in strength and lean body mass over a period of several weeks to several months. However, caution must be taken when making this assumption based on acute studies because it is a theoretical prediction and not a guaranteed outcome. As a result, the best way to draw conclusions about the combined effects of nutrient ingestion in conjunction with chronic resistance training (i.e., weeks to months) is to focus on those specific studies that actually examined changes in strength and lean body mass. This is not to say that acute studies are unimportant. In fact, they are vital in gaining a more in-depth knowledge of how muscle responds on a cellular level. However, it could be argued that investigations examining chronic resistance training may actually be more beneficial to the strength and conditioning practitioner who needs to confidently disseminate long-term benefits of resistance training to their clients/athletes.
Two studies using nutrient timing principles have compared the effects of carbohydrate and protein supplementation (immediately after resistance exercise) on strength and hypertrophy adaptations in conjunction with a resistance training program (1,3). Unfortunately, both these investigations used healthy, non–resistance-trained male subjects instead of resistance-trained male subjects.
Anderson et al. (1) compared the effect of 14 weeks of resistance training combined with timed ingestion of isoenergetic protein versus carbohydrate supplementation on muscle fiber hypertrophy and mechanical muscle performance. Supplementation was administered before and immediately after each resistance training bout, and the subjects were instructed to not ingest anything else except water for 2 hours before and 2 hours after the workout. Supplements were also ingested in the morning on nontraining days. One serving of the supplements consisted of 25 g of protein (16.6 g of whey protein, 2.8 g of casein, 2.8 g of egg white protein, and 2.8 g of glutamine) or 25 g of maltodextrin carbohydrate. In total, 50 g of protein (which was about half of the day's total protein intake) or 50 g of carbohydrate was ingested in the minutes before and after the workout.
Skeletal muscle hypertrophy was measured by changes in cross-sectional areas of the vastus lateralis. After 14 weeks of resistance training, only the protein group showed muscle fiber hypertrophy with an 18% increase in type I and a 26% increase in type II muscle fibers. In contrast, no significant change occurred in the carbohydrate group. Greater muscle performance (assessed with an isokinetic dynamometer at both slow and fast speeds) was observed in the protein group as compared with the carbohydrate group, but the differences did not reach statistical significance (1). Several other studies have also demonstrated that protein supplementation is superior to carbohydrate supplementation alone in terms of lean muscle mass (11,18) and muscular strength (11) in conjunction with a resistance training program in non–resistance-trained male subjects.
Bird et al. (3) not only compared carbohydrates alone and essential amino acid supplementation alone but also incorporated a group that supplemented with carbohydrate and essential amino acids. In this study, 32 non–resistance-trained male subjects completed 2 whole-body resistance exercise sessions per week for 12 weeks. As soon as the workouts began, subjects began ingesting one of the following 4 beverages (after each set) until they were completely consumed before the end of the workout.
* 40 g of carbohydrate (approximately 0.5 g CHO per kilogram of body mass)
* 6 g of essential amino acids
* 40 g of carbohydrate + 6 g of essential amino acids (CHO-EAA)
* Noncaloric placebo.
Fat-free mass, muscle fiber cross-sectional area, and 3-methylhistidine excretion (a measure of muscle protein breakdown) were determined pretraining and posttraining. Fat-free mass significantly improved for all groups (including the placebo group), but only the CHO-EAA group (9 pounds) demonstrated significantly greater gains in fat-free mass as compared with the placebo (4 pounds). Similarly, all groups significantly improved Type IIb muscle fiber cross-sectional area over the course of the 12-week training program. However, only the CHO-EAA group (20% increase) and the essential amino acid group (18% increase) resulted in significant improvements as compared with the placebo group (7% increase).
Muscle protein breakdown (as measured by urinary 3-methylhistidine) was measured before and 48 hours after the last training session of the program. For clarification, the higher the 3-methylhistidine values after exercise, the greater the skeletal muscle protein breakdown. The essential amino acid group (∼5% decrease) and carbohydrate group (13% decrease) showed no significant change in 3-methylhistidine excretion. Conversely, the CHO-EAA group significantly decreased 3-methylhistidine (∼26% decrease), suggesting an additive effect of carbohydrate and essential amino acids and their ability to suppress skeletal muscle protein breakdown (3).
Taken together, these studies (1,3) demonstrate that timed protein/essential amino acid ingestion is superior to carbohydrate ingestion in terms of improving lean body mass and muscular strength. However, combined ingestion of carbohydrate and protein/essential amino acid is superior to protein/essential amino acid ingestion alone in regards to improving fat-free mass and suppressing skeletal muscle protein breakdown.
Adhering to the principles of nutrient timing while engaging in a resistance training program will maximize the adaptive response to the stimulus provided by the exercise program. Specifically, timed ingestion of protein/essential amino acids and carbohydrate will replenish skeletal muscle glycogen, reduce muscle soreness and rates of protein degradation, induce a positive net protein balance, and amplify strength and lean muscle mass gains beyond what would be realized from a resistance training program alone.
Currently, there is not a consensus on the amounts of protein/essential amino acids and carbohydrate that is needed to maximize these gains. Based on the available literature, 1 g/kg/h of carbohydrate (taken immediately after and then again 1 hour later) will effectively restore depleted skeletal muscle glycogen and decrease protein degradation. In regards to protein, around 20–25 g of high-quality fast-digesting protein taken immediately after resistance exercise appears to maximize protein synthesis, reduce muscle soreness, and increase skeletal muscle hypertrophy. On a scale that is relative to bodyweight, 0.25 g of high-quality fast-digesting protein per kilogram of bodyweight would likely supply adequate amounts of the essential amino acids needed to realize the aforementioned benefits. The research supporting these recommendations has accumulated over the past 10–15 years, and there is a great deal of appreciation that is because of those researchers who have contributed to the advancement of the science of nutrient timing. Looking forward, research is needed to investigate the effects of nutrient timing using resistance-trained individuals who are participating in a longer term (several months) resistance training program.
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