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Whey Protein and Leucine Supplementation
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Journal of Exercise Physiologyonline
(JEPonline)
Volume 12 Number 5 October 2009
Managing Editor
Tommy Boone, PhD, MPH
Editor-in-Chief
Jon K. Linderman, PhD
Review Board
Todd Astorino, PhD
Julien Baker, PhD
Tommy Boone, PhD
Larry Birnbaum, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Chantal Vella, PhD
Ben Zhou, PhD
Official
Research Journal of
the American Society of
Exercise Physiologists
(ASEP)
ISSN 1097-975
Nutrition and Exercise
The Effects of Whey Protein and Leucine Supplementation on
Strength, Muscular Endurance, and Body Composition During
Resistance Training
MICHELLE MIELKE 1, TERRY J. HOUSH2, MOH H. MALEK3, TRAVIS
W. BECK 4, RICHARD J. SCHMIDT2, GLEN O. JOHNSON2, and DONA
J. HOUSH5
1
University of the Pacific, Stockton, California, USA 2University of NebraskaLincoln, Lincoln, USA3 School of Medicine University of California, San Diego
La Jolla, USA 4 University of Oklahoma, Norman, USA 5 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, ageSD = 22.72.8 years) were randomly assigned to a nonsupplement (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.
Whey Protein and Leucine Supplementation
40
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
Whey Protein and Leucine Supplementation
41
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 vitaminblends) 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 preand 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 postabsorptive 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
Whey Protein and Leucine Supplementation
42
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), 1RM 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
Whey Protein and Leucine Supplementation
43
sample size of 39 subjects resulted in a statistical power value of 0.90 or greater for increases in L1RM 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,
Table 1: Body weight, body composition, and dietary values (M ± SD), n = 39.
but significant (p<0.05)
main effects for time for
Group
Pre
Post
L-1RM (pre = 82.5 ±
22.4 kg; post = 99.2 ±
PRO (n = 13)
79.6 ± 18.1
80.2 ± 18.4
23.2 kg), L-END (pre =
Body weight (kg)
CHO (n = 13)
72.4 ± 11.5
72.5 ± 11.9
12 ± 4 repetitions; post
NON-SUP (n = 13)
80.4 ± 15.9
80.3 ± 15.8
= 19 ± 7 repetitions), BPRO
20.6 ± 7.3
21.4 ± 5.6
1RM (pre = 64.7 ± 17.8
kg; post = 77 ± 20.4 kg),
Percent fat
CHO
19.2 ± 8.5
19.9 ± 8.5
and B-END (pre = 7 ± 2
NON-SUP
21.3 ± 8.5
20.8 ± 8.3
repetitions; post = 13 ±
PRO
62.3 ± 6.7
62.6 ± 12.4
4 repetitions) (Figures 1
Fat free mass (kg)
CHO
58.0 ± 10.6
57.7 ± 7.7
and 2). Table 2 shows
the mean (± SD) values
NON-SUP
62.5 ± 8.3
62.8 ± 8.5
for
strength
and
PRO
17.3 ± 8.7
17.7 ± 8.6
endurance for the PRO,
Fat mass (kg)
CHO
14.4 ± 8.5
14.9 ± 7.1
CHO, and NON-SUP
NON-SUP
17.9 ± 11.1
17.5 ± 10.4
groups.
Total calories (kcal)
Protein (g)
Carbohydrate (g)
Fat (g)
PRO
2632.3 ± 1260.4
1987.6 ± 678.3
CHO
2494.5 ± 699.6
2156.2 ± 581.9
NON-SUP
2009.0 ± 847.2
1889.1 ± 743.0
PRO
107.9 ± 32.2
84.5 ± 21.4
CHO
93.4 ± 18.4
83.5 ± 22.4
NON-SUP
110.6 ± 27.0
85.5 ± 31.8
PRO
107.9 ± 32.2
84.5 ± 21.4
CHO
93.4 ± 18.4
83.5 ± 22.4
NON-SUP
110.6 ± 27.0
85.5 ± 31.8
PRO
95.1 ± 28.4
76.0 ± 18.6
CHO
77.5 ± 26.6
63.8 ± 17.9
NON-SUP
82.5 ± 23.4
65.4 ± 17.0
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,
There were no significant (p>0.05) changes from pre- to post-training for any
strength
and
group. PRO = supplement group; CHO = carbohydrate group; NON-SUP = non- 1RM
endurance
increased
supplement group.
similarly (Table 1), over
Whey Protein and Leucine Supplementation
44
eight weeks of resistance training for all three groups (NON-SUP, PRO, and CHO). Overall L-1RM, LEND, 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 Table 2: Strength and endurance values for bench press and leg
training (1 set for the PRO and extension (M ± SD), n = 39.
CHO groups versus 2 sets for
Group
Pre
Post
the NON-SUP group). The
ergogenic
effects
of
the
PRO (n = 13)
70.1 ± 22.6
80.1 ± 24.0*
increased energy intake and/or
CHO (n = 13)
64.7 ± 17.8
73.4 ± 18.6*
the specific nutrients in the B-1RM (kg)
NON-SUP (n = 13)
68.6 ± 18.4
77.5 ± 19.4*
protein
and
carbohydrate
PRO
7±2
14 ± 5*
supplement
may
have
compensated for the increased
CHO
6±2
13 ± 4*
B-END
(reps)
volume of training by the NONNON-SUP
7±1
13 ± 3*
SUP group. Therefore, the
PRO
80.8 ± 23.8
99.1 ± 22.5*
current findings indicate that 1
CHO
78.9 ± 16.9
94.6 ± 20.2*
set of resistance training, in
L-1RM (kg)
conjunction with either whey
NON-SUP
87.9 ± 26.3
103.8 ± 27.2*
protein
and
leucine
or
PRO
12 ± 3
20 ± 7*
carbohydrate intake resulted in
CHO
11 ± 3
17 ± 5*
the same strength gains as 2 L-END (reps)
NON-SUP
12 ± 6
18 ± 7*
sets of resistance training
without supplementation.
There were no significant (p>0.05) changes between groups. *Posttraining values were significantly greater (p<0.05) than pre-training.
Whey protein and/or leucine PRO = supplement group; CHO = carbohydrate group; NON-SUP =
supplementation, as well as non-supplement group.
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
Whey Protein and Leucine Supplementation
45
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.
120
LOAD (kg)
100
80
60
40
L-1RM
20
B-1RM
0
PRE
POST
Figure 1. Mean changes in leg extension (L-1RM) and bench
press (B-1RM) strength from pre- to post-testing averaged
across groups (SUP, PLA, and CON). The mean strength
values reflect the significant (p<0.05) main effect for time
(averaged across groups) because there was no significant
group (SUP, PLA, and CON) x time (pre- and post-testing)
interaction or main effect for group for the mixed factorial
ANOVA.
The results demonstrated that
even
though
both
groups
demonstrated significant strength
increases over time, the protein
supplemented group showed
greater improvements in bench
and leg press strength when
compared to the placebo group
(bench press (supplement vs.
placebo) = 53% vs. 23%; leg
press (supplement vs. placebo)
= 38% vs. 22%). Cribb et al. (15)
examined the effects of whey
protein (1.3 g∙kg-1∙d-1) and
creatine monohydrate [0.3 g∙kg1∙d-1 (1 week loading phase) and
0.1
g∙kg-1∙d-1
(maintenance
phase – weeks 2-11)] separately
and
in
combination
vs.
carbohydrate only (1.3 g∙kg-1∙d-1)
on strength increases following
11 weeks of resistance training
in trained males.
The groups supplementing with whey protein only or in combination with creatine exhibited greater
strength increases than the carbohydrate group. Supplementation with whey protein and/or leucine
and/or carbohydrate has not always resulted in differences in strength increases when combined with
resistance training (4, 7, 20). For example, Kerksick et al. (20) randomly assigned 36 trained males to
one of three supplement groups: whey plus casein (40 g∙d -1 of whey and 8 g∙d-1 of casein protein),
whey, branched chain amino acids, and L-glutamine (40 g∙ day-1 of whey, 3 g∙day-1 branched chain
amino acids, and 5 g∙d-1 L-glutamine), or a carbohydrate placebo (48 g∙d -1). Even though the quantity
and ingredients of the supplement differed to that of the current study, the authors found that after 10
weeks of resistance training, significant but similar increases in muscular strength (bench and leg
press 1 RM) were observed in all groups.
Similarly, Chromiak et al. (4) compared the effects of 10 weeks of resistance training with a
postexercise supplement (13 g whey protein, amino acids including 0.53 g of leucine, creatine, and
carbohydrate) or an isocaloric carbohydrate placebo (92 g of maltodextrin) in 33 trained male
subjects. Although, there were overall increases in 1 RM bench and leg press strength, there was no
significant difference between the supplement and placebo group. The similar strength gains
between the whey protein plus leucine and the carbohydrate groups observed in the current study
may be explained by the added caloric intake (7). For example, Rankin et al. (7) found that 10 weeks
of training along with either low fat chocolate milk (5 kcals∙kg-1 body weight, 0.92 g∙kg-1 carbohydrate,
0.21 g∙kg-1 protein, 0.06 g∙kg-1 fat, and natural vitamins and minerals) or a carbohydrate-electrolyte
Whey Protein and Leucine Supplementation
46
drink (5 kcals∙kg-1 body weight, 1.25g∙kg-1 carbohydrate and electrolytes) elicited similar and
significant increases in 1RM strength in 19 untrained men.
A moderate anabolic effect (decreased protein breakdown) (21) of the carbohydrate supplement
resulting in increased elevations in blood glucose, a higher glycogen synthesis rate, as well as
favorable hormonal responses (i.e. increased insulin levels and decreased cortisol levels) (22) as a
result of carbohydrate ingestion may also explain the similar strength gains between the protein
supplement and placebo groups in the current study.
# OF REPITITIONS
Muscular endurance
In the current study, muscular endurance was assessed by having subjects perform as many
repetitions as possible at 80% of their pre-test 1RM for the bench press and leg extension. Even
though the 8 weeks of training
20
did not include an endurance
18
component L-END and B-END
16
increased by 58.3% and 71.4%,
respectively. The increased
14
volume of training performed by
12
the non-supplement group (2
10
sets) may have compensated
8
for the reduced volume of
training (1 set) by the protein
6
and carbohydrate supplement
L-END
4
groups. Therefore, the current
B-END
2
findings indicate that 1 set of
0
resistance
training,
in
conjunction with whey protein
PRE
POST
and leucine or carbohydrate
intake resulted in the same Figure 2. Mean changes in leg extension (L-END) and bench press
improvement
in
muscular (B-END) muscular endurance from pre- to post-testing averaged
endurance as 2 sets of across groups (SUP, PLA, and CON). The mean muscular
resistance
training
without endurance values reflect the significant (p<0.05) main effect for
time (averaged across groups) because there was no significant
supplementation.
group (SUP, PLA, and CON) x time (pre- and post-testing)
interaction or main effect for group for the mixed factorial
ANOVA.
Few studies have examined the
effects of supplementation and
training on muscular endurance. Beck et al. (3) randomly assigned 51 untrained males to either a
supplement group (containing 5 g creatine, 26.2 g protein, and 2.2 g leucine) or placebo group
(containing 39 g carbohydrate (glucose and fructose)). After 8 weeks of resistance training, bench
press and leg extension muscular endurance (assessed in the same manner as the current study)
significantly increased in both groups. Chromiak et al. (4) recorded the number of repetitions
completed at 85% of 1RM for bench press and leg press. The pre-test and post-test comparisons for
relative muscular endurance were reported as the estimated external work [repetitions completed x
resistance (kg)] performed by 33 trained male subjects. After 10 weeks of resistance training with a
postexercise supplement (13 g whey protein, amino acids including 0.53 g of leucine, creatine, and
carbohydrate) or an isocaloric carbohydrate placebo (92 g of maltodextrin), muscular endurance on
the leg press increased significantly by 53.8%. Bench press endurance increased non-significantly by
14.4%. Kerksick et al. (20) also determined muscular endurance in 36 trained subjects by recording
the number of repetitions completed at 80% of their bench press and leg press 1RM. Relative
muscular endurance using bench press and leg press volume [repetitions completed x resistance
Whey Protein and Leucine Supplementation
47
(kg)] was estimated at pre-testing and post-testing after 10 weeks of training and supplementation
with whey plus casein (40 g∙d-1 of whey and 8 g∙d-1 of casein protein), whey, branched chain amino
acids, and L-glutamine (40 g∙ day-1 of whey, 3 g∙day-1 branched chain amino acids, and 5 g∙d-1 Lglutamine), or a carbohydrate placebo (48 g∙d-1). The results indicated that only leg press lifting
volume increased significantly by 15.6% across groups. The reason for the lack of an increase in
bench press volume in previous studies (4,20) is unknown. In both studies, the volume of training
was greater than in the current study as well as the study by Beck et al. (3).
For example, Chromiak et al. (4) used resistance exercises for the major muscle groups of the body.
The subjects trained 2 d∙wk-1 with the leg press, squats, leg curls, calf raises, leg extensions and
abdominal crunches and 2 d∙wk-1 with the bench press, shoulder press, lateral pulldown, seated row,
triceps pushdown, and biceps curl. Kerksick et al. (20) also trained subjects 2 d∙wk -1 with the leg
press, leg extensions, deadlift, lunges, lying leg curls, heel raises, and abdominal crunches and 2
d∙wk-1 with the bench press, chest flies, lateral pulldown, seated row, shoulder press, shoulder
shrugs, bicep curls, and triceps pushdown. In contrast, the subjects in the current investigation and
that of Beck et al. (3) trained 3 d∙wk-1 with bench press and leg extension exercises only. Another
difference that could potentially explain the differences in muscular endurance is the training status of
the subject. Chromiak et al. (4) and Kerksick et al. (20) used trained male subjects, whereas in the
present study and that of Beck et al. (3) untrained male subjects were used. Chromiak et al. (4) also
attributed the improvement in muscular endurance for the leg press to the corresponding increase in
muscular strength.
Future research is needed to determine the effects of protein and amino acid supplementation,
training status, and volume of training on muscular endurance.
Body Composition
In the current study, the increased volume of training associated with two sets of resistance training
(without supplementation) as well as 8 weeks of single set training (with whey protein plus leucine or
carbohydrate supplementation) had no effects on body composition. The results of previous research
of protein and amino acid supplementation, and resistance training on body composition have also
resulted in conflicting findings (1,2,7,23). The findings of the present investigation were similar to
those of Coburn et al. (1) who found no combined effect of a whey protein and leucine supplement or
a carbohydrate placebo plus unilateral resistance training for 8 weeks on BW, %FAT, FW, or FFW in
untrained males. Similarly, Antonio et al. (23) found no change in BW, FW, or FFW in untrained
females who were assigned to an essential amino acid (EAA) group or a placebo group plus 6 weeks
of resistance and aerobic training. Conversely, Willoughby et al. (2) reported significant time (Posttest>Pre-test) and group (Protein >Placebo) effects for the increases in total body mass, fat-free
mass, and thigh mass in untrained males for both a protein supplemented group [14 g whey and
casein protein, 6 g free (essential and non-essential) amino acids], and a carbohydrate placebo (20 g
dextrose) group after 10 weeks of resistance training. Rankin et al. (7) also found that mean %FAT
decreased by 8% and fat-free soft tissue (FFST) mass increased by 1.2±0.3 kg after 10 weeks of
training combined with either low fat chocolate milk or a carbohydrate-electrolyte drink in 19 untrained
men. In addition, the milk supplemented group tended to show a greater increase in FFST than the
carbohydrate group (milk vs. carbohydrate: 1.6±0.4 kg vs. 0.8±0.5 kg).
Discrepancies in the results of the various studies (2,3,7,23) may have resulted from differences in
supplementation protocol (ingredients and timing), energy content of the various supplements, and/or
variations in the training regimens (volume and length of training period).
Whey Protein and Leucine Supplementation
48
CONCLUSIONS
In summary, the findings of the current study indicated that an increased volume of training (two sets
without supplementation or placebo) or 8 weeks of single set leg extension and bench press
resistance training (with whey protein and leucine supplementation or a carbohydrate placebo) had
no effect on body composition. Increases in strength and endurance occurred across the 8 weeks,
but no differential effects were observed as a result of the supplement or placebo plus single set
training or the increased volume of training. Carbohydrate ingestion has previously been shown to
modestly increase net muscle protein balance following resistance exercise as compared to the
“maximal” (18)(p 678) effect following the ingestion of amino acids (18,19). In the present study, the
effects of carbohydrate ingestion were equivalent to the effects of whey protein plus leucine
supplementation. In addition, the effect of either the whey protein plus leucine or carbohydrate
supplementation with one set of training equaled the effects of the increased volume of training
associated with two sets of resistance exercise without supplementation.
ACKNOWLEDGEMENTS
This study was supported by General Nutrition Corporation (GNC).
Address for correspondence: Mielke M, Ph.D., Department of Sport Sciences, University of the
Pacific, Stockton, California 95211, USA. Phone: (209) 946-2209, Fax: (209) 946-3225, e-mail:
[email protected].
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