Whey Protein and Leucine Supplementation
1
Whey Protein and Leucine Supplementation
Nutrition and Exercise
The Effects of Whey Protein and Leucine Supplementation on Strength, Muscular Endurance, and Body Composition During Resistance Training
MICHELLEMIELKE1, TERRY J. HOUSH2, MOH H. MALEK3, TRAVIS W. BECK4, RICHARD J. SCHMIDT2, GLEN O. JOHNSON2, and DONA J. HOUSH5
1University of the Pacific, Stockton, California, USA2University of Nebraska-Lincoln, Lincoln, USA3 School of Medicine University of California, San DiegoLa Jolla, USA4 University of Oklahoma, Norman, USA5 University of Nebraska Medical Center, Lincoln, USA
ABSTRACT
Mielke M, Housh TJ, Malek MH, Beck TW, Schmidt RJ, Johnson GO, Housh DJ. The Effects of Whey Protein and Leucine Supplementation on Strength, Muscular Endurance, and Body Composition During Resistance Training. JEPonline 2009;12(5):39-50. The purpose of this study was to compare the effects of: 1) two sets of resistance training without supplementation; 2) one set of resistance training with whey protein plus leucine supplementation; and 3) one set of resistance training with a carbohydrate placebo on body weight (BW), strength, muscular endurance, and body composition. Untrained adult males (N=39, ageSD = 22.72.8 years) were randomly assigned to a non-supplement (NON-SUP; n=13), protein (PRO; n=13), or a carbohydrate (CHO; n=13) group and performed leg extensions and bench press (NON-SUP = 2 sets, no supplement; PRO = 1 set, protein supplement; CHO = 1 set, carbohydrate) 3 x week at 80% of 1-RM for 8 weeks. Mixed factorial ANOVAs indicated only significant (p<0.05) main effects for time for leg extension 1RM (pre = 82.5±22.4kg; post = 99.2±23.2kg), leg extension endurance (pre = 12±4 reps; post = 19±7reps), bench press 1RM (pre = 64.7±17.8kg; post = 77±20.4kg), and bench press endurance (pre = 7±2 reps; post = 13±4reps). These findings indicated that two sets of resistance training without supplementation, one set of resistance training plus whey protein and leucine supplementation, and one set of resistance training plus a carbohydrate supplement, resulted in similar strength, endurance, and body composition responses.
Key Words: Carbohydrate, Strength, Fat-free Weight.
INTRODUCTION
Resistance training has been shown to increase strength (1,2), muscular endurance (3,4), body weight (2) and hypertrophy (5,6), as well as result in favorable changes in body composition including decreases in percent body fat (%fat) and fat weight (FW), and increases in fat-free weight (FFW) (2, 7). Furthermore, the magnitude of the increases in strength and hypertrophy are related to the volume of the resistance training program (8,9). For example, recent studies have shown that an increase in the volume of resistance training from one set to two or more sets results in the recruitment of additional motor units and, therefore, greater neuromuscular adaptations, strength gains, and hypertrophy (8-11). This is especially true as the length of the training period increases (8,9).
Recreational and competitive athletes often use a protein supplement plus resistance training to increase strength, muscular endurance, and hypertrophy. Resistance training alone stimulates muscle protein metabolism, which can lead to muscle growth and strength increases (5, 6, 12). To stimulate muscle protein synthesis, however, amino acid availability is important, especially in the first few hours after exercise (13). Protein supplementation increases muscle protein synthesis without a corresponding increase in protein breakdown, which results in a net positive protein balance, thus allowing for maximal recovery, hypertrophy, and strength gains (13). “Fast” proteins, such as whey, are characterized by the rapid appearance of their amino acid constituents in the blood and have been shown to elicit strength gains and improve muscle protein balance (12). Recent studies using whey protein supplements have demonstrated improvements in muscle hypertrophy and strength (1, 3, 12) following resistance exercise.
Whey protein is a valuable source of the branched chain amino acids (BCAA) including leucine, isoleucine, and valine. Of the BCAA’s, leucine has been shown to provide the greatest stimulation of muscle protein synthesis, and prevention of muscle protein degradation (14). A recent study (1) demonstrated that 20 g whey protein plus 6.2 g leucine in conjunction with 8 weeks of unilateral (nondominant limb) leg extension resistance training elicited greater strength gains (30%) when compared to a carbohydrate placebo (22%). Although some studies have demonstrated a slight ergogenic effect from carbohydrate ingestion, most studies of protein and/or amino acid supplementation have utilized a carbohydrate placebo (1,2,15). Therefore, the purpose of this study was to compare the effects of: 1) two sets of resistance training without supplementation; 2) one set of resistance training with whey protein plus leucine supplementation; and 3) one set of resistance training with a carbohydrate placebo on body weight (BW), strength, muscular endurance, and body composition. Based on previous studies (1,2,15), it was hypothesized that: 1) there would be no difference in training induced changes in BW, strength, muscular endurance, and body composition between the group that performed two sets of resistance training without supplementation and the group that performed one set of resistance training with whey protein plus leucine supplementation; and 2) the training-induced changes in BW, strength, muscular endurance, and body composition in the group that performed two sets of resistance training without supplementation and the group that performed one set of resistance training with whey protein plus leucine supplementation would be greater than those of the group that performed one set of resistance training with a carbohydrate supplement.
METHODS
Subjects
Thirty nine adult males (age range: 19 to 28 yrs) volunteered for this study. All subjects were untrained in resistance/power exercise. Untrained was defined as not having participated in a resistance training program for at least 90 days preceding the start of the investigation. This information was elicited via the Health History Questionnaire in which subjects were asked to provide details of any type of training they currently participated in.Exclusion criteria included: 1) consumption of a medication (thyroid, hyperlipidemic, hypoglycemic, anti-hypertensive, or androgenic medications) or nutritional supplement (such as creatine, protein drinks, amino acids, or vitamin-blends) that would interfere with the results of the study; 2) participation in a resistance training program for at least 90 days preceding the start of the investigation; 3) a history of medical or surgical events that would significantly affect the study outcome including cardiovascular disease, gastrointestinal problems, metabolic, renal, hepatic, neurological or active musculoskeletal disorders; and 4) participation in another clinical trial or ingestion of an investigational product within thirty days prior to screening. The subjects were randomly assigned to 1 of 3 groups: 1) a non-supplement (NON-SUP) group (n=13, age = 22.8 2.6 yr, body weight = 80.4 15.9 kg, and height = 178.7 7.1 cm); 2) a whey protein plus leucine supplement (PRO) group (n=13, age = 23.8 2.8 yr, body weight = 79.6 18.1 kg, and height = 178.3 7.3 cm); and 3) a carbohydrate supplement (CHO) group (n=13, age = 21.5 2.5 yr, body weight = 72.4 11.6 kg, and height = 175.5 6.0 cm). All procedures were approved by the University Institutional Review Board for Human Subjects and all subjects completed a health history questionnaire and signed a written informed consent prior to any testing.
Procedures
This study used a randomized and double-blind design. There were no dietary restrictions during the course of this study, and subjects were encouraged to continue with their normal dietary habits. The design allowed for examination of the effects of adding either a whey protein plus leucine or a carbohydrate supplement to an existing diet. This is similar to the way the product would likely be used by consumers. The whey protein plus leucine and carbohydrate supplements were isocaloric to control for differences in added energy intake. All subjects participated in a resistance training program that consisted of dynamic constant external resistance (DCER) bilateral leg extension and bench press exercises performed 3 times per week for 8 weeks. Each training session was supervised by one of the investigators. In addition, although this resistance training program was the primary mode of exercise for most of the subjects, they were not restricted from performing cardiovascular exercise during the study. The subjects were, however, instructed that they should not be involved in any other weight training program outside of the study. Pre- and post-testing was conducted the week prior to and the week following the 8-week training period, respectively.
Supplement Protocol
The PRO group received 20.0 g of whey protein and 6.2 g of leucine in 8 oz of water, the CHO group received 20 g of isocaloric (to control for differences in added energy intake) maltodextrin in 8 oz of water. The subjects ingested the PRO or CHO 30 minutes prior to and immediately after each resistance training session. On non-training days, the PRO and CHO groups ingested 1 dose of the protein or carbohydrate supplement in the morning and once again in the evening. The NON-SUP group did not receive any supplement. The subjects were encouraged to continue with their normal dietary habits with the addition of the protein or carbohydrate supplement as this would be similar to the way the product would likely be used by consumers. The subjects were asked to complete a pre- and post-test 3-day food log (two weekdays and one weekend day) to ensure that there were no significant changes in macronutrient or total caloric intake.
Testing
For the determination of body composition, the subjects were instructed to avoid exercise for at least 12 hours prior to testing, and each subject indicated that he was normally hydrated and in a post-absorptive state (at least 4 hours) upon arrival at the laboratory. Body weight (BW) was determined to the nearest 0.11kg using a state certified physician’s scale. Body density was assessed from underwater weighing (UWW) with correction for residual lung volume (RV). RV was measured on land with the subject seated in the position similar to that assumed for UWW, using the oxygen dilution method of Wilmore (16). The scores (within 0.1L) from 2 or 3 trials were averaged and used as the representative RV. Underwater weight was measured in a submersion tank in which a nylon swing seat was suspended from a 10-kg Salter scale (REGO Designs & Patents, model #230). The average of the 2 or 3 highest weights from 6 to 10 trials was used as the representative underwater weight. Percent body fat (%fat) was calculated using the formula of Brozek et al. (17), with fat weight (FW) and fat-free weight (FFW) derived mathematically. Previous test-retest reliability data for UWW from our laboratory indicated that for 16 young men measured 24-72 hours apart, the ICC was R = 0.98 with an SEM of 0.9% fat.
The DCER leg extension and bench press strength were tested by determining each subject’s 1 repetition maximum (1RM) using a Body-Solid plate-loaded leg extension machine (Model CEC340; Forest Park, IL) and a standard free-weight bench (Body Power, Williamsburg, VA) with an Olympic bar, respectively. For leg extension testing, each subject sat with his torso against the backrest and was instructed to hold tightly to the handles at the sides of the device. The backrest was adjusted to align the anatomical axes of the knees with the mechanical axis of the machine. Shin pads, attached to the machine’s lever arm, were placed against the subject’s legs. The shin pads were a fixed distance from the axis of rotation of the lever arm and thus not adjustable. Positioning, however, was consistent for each subject across all tests. For bench press testing, the subjects received a lift-off from a spotter, then lowered the bar to his chest, paused briefly, and then pressed the bar to full extension of the forearms. The 1RM was determined by applying progressively heavier loads until the subject could not complete a repetition through the full range of motion (full extension of the legs and forearms). If needed, additional trials were performed with lighter loads until the 1RM was determined within 2.27 kg. The 1RM was usually determined within five trials with two minutes of rest between each trial. For the leg extension and bench press endurance testing, subjects performed as many repetitions as possible of full extension of the legs and forearms at 80% of their 1RM. At post-testing, the same procedures for leg extension and bench press testing were performed. Leg extension and bench press endurance tests were performed at 80% of the pre-test 1RM. Previous test-retest reliability data for strength testing from our laboratory indicated that for 20 young men measured 8 weeks apart, the ICC was R = 0.99 and R = 0.98 for bench press and leg extension, respectively.
Training
The subjects performed leg extension and bench press training 3 times a week for 8 weeks starting at 80% of their 1RM. Each training session for bench press and leg extensions was preceded by 2 warm-up sets. Each warm-up set consisted of 6 repetitions at 50% of the target training weight. The PRO and CHO groups performed one set of 6-8 repetitions and the NON-SUP group performed two sets of 6-8 repetitions. Two minutes of rest were allowed between sets, and when the subject was able to complete 8 repetitions, the training load was increased by 2.27 kg for the next training session.
Statistical Analyses
Body weight, %FAT, FW, FFW, 1-RM leg extension (L-1RM), leg extension endurance (L-END), 1-RM bench press (B-1RM), and bench press endurance (B-END) were analyzed with separate 3 [Group: PRO, CHO, and NON-SUP] x 2 [Time: Week 0 and 8] mixed factorial ANOVAs to determine if there were significant changes in body composition and muscle strength and endurance. The total caloric (kilocalories) and macronutrient (grams of protein, carbohydrate, and fat) intake were similarly analyzed. Group was used as a “between subjects” factor and time was used as a “within subjects” factor. An alpha level of p<0.05 was selected for all statistical comparisons. The analyses were conducted using the Statistical Package for the Social Sciences software (v.13.0, SPSS Inc., Chicago, IL). Based on the results of a previous study (1), an a priori power analysis indicated that a sample size of 39 subjects resulted in a statistical power value of 0.90 or greater for increases in L-1RM and B-1RM strength. Post-hoc power analyses for identifying group differences indicated that for the effect sizes found in the present study for B-1RM, B-END, L-1RM, and L-END, the power values equaled 0.87, 0.72, 0.99, and 0.99, respectively.
RESULTS
Body Composition
The results indicated that there were no significant (p > 0.05) training-induced changes in BW, %FAT, FW, or FFW for the NON-SUP, PRO, or CHO groups (Table 1).
Muscle Strength and Endurance
The two-way mixed factorial ANOVAs resulted in no significant (p > 0.05) group x time interactions or main effects for group, but significant (p<0.05) main effects for time for L-1RM (pre = 82.5 ± 22.4 kg; post = 99.2 ± 23.2 kg), L-END (pre = 12 ± 4 repetitions; post = 19 ± 7 repetitions), B-1RM (pre = 64.7 ± 17.8 kg; post = 77 ± 20.4 kg), and B-END (pre = 7 ± 2 repetitions; post = 13 ± 4 repetitions) (Figures 1 and 2). Table 2 shows the mean (± SD) values for strength and endurance for the PRO, CHO, and NON-SUP groups.
There were also no significant (p > 0.05) group x time interactions, main effects for group, or main effects for time for the macronutrients (i.e., grams of protein, carbohydrate, and fat) or total kilocalories consumed (Table 1).
DISCUSSION
In the current study, 1RM strength and endurance increased similarly (Table 1), over eight weeks of resistance training for all three groups (NON-SUP, PRO, and CHO). Overall L-1RM, L-END, B-1RM, and B-END increased by 20.2%, 58.3%, 14.9%, and 71.4%, respectively. These improvements, however, were not accompanied by changes in BW, %FAT, FW, or FFW for any of the groups (Table 1).
Strength
The magnitude of the strength gains made by the PRO and CHO groups were similar to those of the NON-SUP group inspite of the differences in the volume of training (1 set for the PRO and CHO groups versus 2 sets for the NON-SUP group). The ergogenic effects of the increased energy intake and/or the specific nutrients in the protein and carbohydrate supplement may have compensated for the increased volume of training by the NON-SUP group. Therefore, the current findings indicate that 1 set of resistance training, in conjunction with either whey protein and leucine or carbohydrate intake resulted in the same strength gains as 2 sets of resistance training without supplementation.
Whey protein and/or leucine supplementation, as well as carbohydrate ingestion, have previously been shown to increase net muscle protein balance following resistance exercise (6, 18). The increase observed following carbohydrate ingestion, however, was considered modest when compared to the “maximal” effect following the ingestion of amino acids (18, 19). In the present study, the effect of carbohydrate ingestion on muscular strength was equivalent to the effect of whey protein and leucine supplementation. Previous studies have examined the effects of whey protein and/or leucine supplementation separately or in combination with carbohydrate on muscular strength with inconsistent results (1,2,4,7,15,20). The variability in factors such as the quantity and ingredients of the supplements, the timing of ingestion, as well as the volume and intensity of training, and/or the initial training status of the subjects may explain some of the inconsistencies in results obtained in these studies (1,2,4,7,15,20).
For example, Coburn et al. (1) randomly assigned adult male subjects to a supplement (20 g whey protein, 6.2 g leucine), carbohydrate placebo (26.2 g maltodextrin), or control group for 8 weeks of unilateral (nondominant limb) leg extension resistance training. Even though the supplement contained similar quantities of whey protein and leucine as the current study, the protein supplemented subjects demonstrated a 30% increase in strength in the trained limb which was significantly higher than the strength increase (22%) achieved by the carbohydrate placebo group. No strength changes were observed in the control group. Similarly, Willoughby et al. (2) compared the effects of a 10 week resistance training program combined with 20 g protein (14 g whey and casein protein, 6 g free (essential and non-essential) amino acids) or 20 g dextrose placebo ingested 1hr before and after exercise on muscular strength in untrained males.