Protein requirements and supplementation in strength sports
Daily requirements for protein are set by the amount of amino acids that is irreversibly lost in a given day. Different agencies have set requirement levels for daily protein intakes for the general population; however, the question of whether strength-trained athletes require more protein than the general population is one that is difficult to answer. At a cellular level, an increased requirement for protein in strength-trained athletes might arise due to the extra protein required to support muscle protein accretion through elevated protein synthesis. Alternatively, an increased requirement for protein may come about in this group of athletes due to increased catabolic loss of amino acids associated with strength-training activities. A review of studies that have examined the protein requirements of strength-trained athletes, using nitrogen balance methodology, has shown a modest increase in requirements in this group. At the same time, several studies have shown that strength training, consistent with the anabolic stimulus for protein synthesis it provides, actually increases the efficiency of use of protein, which reduces dietary protein requirements. Various studies have shown that strength-trained athletes habitually consume protein intakes higher than required. A positive energy balance is required for anabolism, so a requirement for "extra" protein over and above normal values also appears not to be a critical issue for competitive athletes because most would have to be in positive energy balance to compete effectively. At present there is no evidence to suggest that supplements are required for optimal muscle growth or strength gain. Strength-trained athletes should consume protein consistent with general population guidelines, or 12% to 15% of energy from protein.
Protein Requirements and Supplementation in
Stuart M. Phillips, PhD
From the Exercise Metabolism Research Group, Department of Kinesiology,
McMaster University, Hamilton, Ontario, Canada
Daily requirements for protein are set by the amount of amino acids that is irreversibly lost in a given day.
Different agencies have set requirement levels for daily protein intakes for the general population;
however, the question of whether strength-trained athletes require more protein than the general popu-
lation is one that is difﬁcult to answer. At a cellular level, an increased requirement for protein in
strength-trained athletes might arise due to the extra protein required to support muscle protein accretion
through elevated protein synthesis. Alternatively, an increased requirement for protein may come about
in this group of athletes due to increased catabolic loss of amino acids associated with strength-training
activities. A review of studies that have examined the protein requirements of strength-trained athletes,
using nitrogen balance methodology, has shown a modest increase in requirements in this group. At the
same time, several studies have shown that strength training, consistent with the anabolic stimulus for
protein synthesis it provides, actually increases the efﬁciency of use of protein, which reduces dietary
protein requirements. Various studies have shown that strength-trained athletes habitually consume
protein intakes higher than required. A positive energy balance is required for anabolism, so a requirement
for “extra” protein over and above normal values also appears not to be a critical issue for competitive
athletes because most would have to be in positive energy balance to compete effectively. At present there
is no evidence to suggest that supplements are required for optimal muscle growth or strength gain.
Strength-trained athletes should consume protein consistent with general population guidelines, or 12%
to 15% of energy from protein. Nutrition 2004;20:689–695. ©Elsevier Inc. 2004
KEY WORDS: hypertrophy, skeletal muscle, anabolism, protein turnover
Body proteins are constantly and simultaneously being made (syn-
thesized) and degraded. This constant turnover provides for a
mechanism of steady maintenance of potentially damaged and
dysfunctional proteins. In skeletal muscle, protein turnover is also
ongoing and provides the basis for skeletal muscle’s plasticity in
response to the degree of imposed high-intensity loading (resis-
tance exercise). A schematic representation of skeletal muscle
protein turnover and other muscle-speciﬁc metabolic fates of
amino acids is shown in Figure 1. The extent to which the amino
acids, liberated as a result of muscle proteolysis, are reused is
extensive. This intracellular recycling, however, is not 100% efﬁ-
cient and amino acids are lost from skeletal muscle, often in
appreciable quantities. The amino acids that are lost from skeletal
muscle have numerous fates, but generally speaking are oxidized
or converted to glucose via gluconeogenesis, with the amino
nitrogen yielding urea. Obviously, the lack of efﬁciency in reusing
amino acids from proteolysis means that we have a daily require-
ment to ingest protein.
RESISTANCE EXERCISE AND PROTEIN TURNOVER:
MECHANISMS OF HYPERTROPHY
Proteins are constantly and simultaneously being synthesized and
degraded (Figure 1). Repair of damaged proteins and remodeling
of structural proteins appears to occur as a result of a resistance
However, in human muscle, the process of
myoﬁbrillar protein turnover, at least that induced by resistance
exercise, is a relatively slow one.
This slow turnover of muscle
protein means that resistance exercise, even though it can induce
changes in muscle ﬁber type and increase ﬁber diameter, requires
a repeated exercise stimulus and a relatively prolonged period (6 to
8 wk) before an outward change in phenotype, such as a change in
ﬁber type and hypertrophy, is observed.
exercise does not induce an acute increase in protein turnover or
oxidation during exercise,
it is the postexercise period when
changes in muscle protein turnover, more speciﬁcally an increase
in muscle protein synthesis, occur; this assertion has been con-
ﬁrmed numerous times.
For an increase in ﬁber diameter to occur, there has to be synthesis
of new muscle proteins, more than 70% of which are myoﬁbrillar,
mostly actin and myosin, in nature. During the period of ﬁber
hypertrophy, there also needs to be a net positive protein balance:
muscle protein synthesis must always exceed muscle protein
breakdown. Different investigations have shown that resistance
exercise stimulates mixed muscle protein synthesis
and untrained subjects. The time course of protein synthesis after
an isolated bout of resistance exercise appears to be somewhat
S. M. Phillips received a New Investigator award from the Canadian
Institutes of Health Research. Research support from the National Science
and Engineering Research Council of Canada and the Premier’s Research
Excellence Award of Ontario is gratefully acknowledged.
Correspondence to: Stuart M. Phillips, PhD, Exercise Metabolism Re-
search Group, Department of Kinesiology, IWC AB116, McMaster Uni-
versity, 1280 Main Street W., Hamilton, ON L8S 4K1, Canada. E-mail:
0899-9007/04/$30.00Nutrition 20:689–695, 2004
©Elsevier Inc., 2004. Printed in the United States. All rights reserved. doi:10.1016/j.nut.2004.04.009
different in untrained subjects, for whom changes in the mixed
muscle protein fractional synthetic rate persist for up to 48 h
Results from cross-sectional comparisons have
shown that prolonged resistance training actually attenuates the
acute immediate response of muscle protein synthesis to an iso-
lated bout of resistance exercise,
which one might expect as a
general adaptation response to training. I and my colleagues re-
cently conﬁrmed these cross-sectional ﬁndings
by using a lon-
The implications of these ﬁndings
trained persons would likely require less protein after training to
support the maximal protein synthetic response to a given workout.
Resistance exercise stimulates an increase in the synthetic rate of
and there is a concomitant increase in the rate
of muscle protein breakdown.
The tight relation between
muscle protein synthesis and breakdown has been observed in a
number of studies in which the two variables have been measured
By using a surrogate marker of muscle myoﬁbrillar protein
degradation, urinary 3-methylhistidine, others have observed
or no change
in this variable after resistance
exercise. Why there is such disparity in the results from studies
using 3-methylhistidine as an indicator of muscle proteolysis is
likely related to the unknown contribution of gut tissue to whole-
body proteolysis, which contains signiﬁcant quantities of actin.
In studies where protein degradation has been directly measured
after resistance exercise, it has been shown consistently that resis-
tance exercise stimulates muscle protein degradation.
evidence using microdialysis has shown that 3-methylhistidine
release into the interstitium after resistance exercise also is not
and the observed lack of change in
3-methylhistidine release with hyperinsulinemia that markedly re-
duces overall amino acid release
suggest that myoﬁbrillar pro-
teins are remarkably refractory to being degraded. It is likely that
almost solely non-myoﬁbrillar proteins are being degraded and are
contributing to amino acid release after resistance exercise.
Every study that has measured muscle protein balance (synthesis
minus breakdown) after resistance exercise has found that, while
synthesis is markedly elevated (in some cases ⬎150% above
baseline levels), muscle balance is negative
until amino acids
are provided intravenously (to simulate postprandial concentra-
tions) or orally.
This feeding-induced stimulation of muscle
has been shown to be independent of insu-
and is likely reﬂective of an increased delivery of amino acids
to the muscle.
The effects of feeding and resistance exercise
are also independent and additive, due mostly to a feeding- and
exercise-induced stimulation of muscle protein synthesis (Figure
2A). Hence, it appears that feeding and resistance exercise com-
bine in the fed state to increase protein synthesis above normal
and, thus, protein balance to a greater extent than feeding or
resistance exercise alone (Figure 2B). In addition, in the fasted
state, muscle protein balance is less negative due to a stimulation
of protein synthesis.
Therefore, hypertrophy is the result of the
accumulation of successive periods of positive protein balance
after exercise when protein is consumed. A lesser contributor to
resistance exercise-induced muscle protein gains would be the
reduction in fasted negative protein balance brought about by
exercise (Figure 3).
A recent study by Bohe´ et al.
demonstrated that extracellular
rather than intracellular amino acid concentration is the controlling
parameter in stimulating muscle protein synthesis and that the
relation between the two is hyperbolic. These ﬁndings
strated a plateau in muscle protein synthesis with increasing de-
livery of amino acids, implying that consumption of larger protein
meals would stimulate muscle protein synthesis only up to a point.
Protein consumed over and above a level that stimulates protein
synthesis would result in only increased urea production. Presum-
ably, the same relation would hold true for the postexercise period.
The metabolic “machinery” responsible for muscle anabolism
within skeletal muscle does, however, have the capacity to respond
to repeated doses (3 to 6 g) of amino acids given only hours
Further, the difference in the dose of essential amino
acids given was two-fold (3 g
) and response was scaled
to dose, implying that these small protein doses do not “top out”
the synthetic response. In addition, Tipton et al.
after resistance exercise, consumption of two 15-g boluses of
essential amino acids before and 1 h after resistance exercise
elicited similar anabolic responses. Exactly which oral dosage of
protein or amino acids would elicit a plateau is not known, but the
ﬁndings of Bohe et al.
showed that synthesis does plateau; hence,
FIG. 1. Schematic of protein turnover and various metabolic fates of amino acids in skeletal muscle.
690 Phillips Nutrition Volume 20, Numbers 7/8, 2004
at some point the system would become unresponsive to increasing
amino acid delivery.
The effect of the timing of delivery of amino acids relative to
exercise has been examined acutely
and long term
resistance exercise. Insofar as timing of postexercise consumption
of protein supplements (6 g of amino acids plus 35 g of sucrose)
is concerned, it appeared to make little difference as to whether a
protein plus carbohydrate supplement was consumed1hor3h
postexercise because the same positive net protein balance resulted
at both times.
In another investigation by Tipton et al.,
exercise consumption of the same protein plus carbohydrate sup-
plement used previously
did augment muscle protein balance.
The long-term practice of pre-exercise protein consumption would,
according to these results,
result in improved gains in muscle
protein mass as a result of resistance exercise. This has not been
tested in a long-term setting.
Esmark et al.
used a long-term design to examine the inﬂu-
ence of timing of protein supplementation in supporting hypertro-
phy in elderly males. They found that delaying delivery of a
supplement by 2 h after resistance exercise and the delivery of
protein (10 g) and carbohydrate (7 g; 420 kJ total energy) do not
result in muscle hypertrophy after 12 wk of resistance training
(three sessions per week). More importantly, the 2-h delayed
supplement group had inferior strength gains versus a group that
received the same supplement immediately postexercise, in whom
muscle hypertrophy (25% increase in mean muscle ﬁber area) was
observed. These ﬁndings
are striking given the small amount of
protein (10 g) that was ingested by both groups and that a delay of
only2hiningesting that protein had such profound physiologic
effects, such as absence of hypertrophy and lesser strength gains.
Obviously, one major difference between the acute
studies was the age of the subjects. However, even in the
absence of food intake, resistance exercise has been shown to
stimulate muscle protein synthesis at 24 h
and up to 48 h
postexercise in young persons.
That fasted protein synthesis is
stimulated for so long after resistance exercise in the young
that feeding and resistance exercise synergistically add to each
FIG. 2. (A) Inﬂuences of AA consumption at rest, performance of RE, and
AA consumption after RE on muscle protein synthesis and breakdown. (B)
Net protein balance (synthesis minus breakdown) under the same condi-
tions. Data are redrawn from Biolo et al.
Values are means ⫾ standard
deviation. AA, amino acid; RE, resistance exercise.
FIG. 3. (A) Normal fed-state gains and fasted-state losses in skeletal
muscle protein balance (synthesis minus breakdown). The area under the
curve in the fed state (I) would be equivalent to the fasted loss area under
the curve (II); hence, skeletal muscle mass is maintained by feeding. (B)
Fed-state gains and fasted-state losses in skeletal muscle protein balance
with performance of resistance exercise. In this scenario, fasted-state gains
are enhanced by an amount equivalent to the stimulation of protein syn-
thesis brought about by exercise (III). In addition, fasted-state losses appear
to be less (IV) due to persistent stimulation of protein synthesis in the
Nutrition Volume 20, Numbers 7/8, 2004 691Strength Sports: Protein Turnover and Requirements
other to produce an enhanced synthetic response (Figure 2B) imply
that the elderly may have a markedly shorter synthetic response to
exercise or an insensitivity to amino acid feeding, assuming the
data of Esmark et al.
can be generalized. Alternatively, as sug-
gested by the results of Volpi et al.,
the elderly subjects studied
by Esmark et al.
may have had an age-related resistance to
insulin, which might have blunted their anabolic response to con-
sumption of an amino acid and protein supplement.
PROTEIN REQUIREMENTS IN STRENGTH-TRAINED
Resistance exercise is followed by a period lasting as long as 48 h
when rates of muscle protein synthesis are elevated above resting
The observation that protein synthesis rates are
elevated after acute bouts of resistance exercise and that infusion
or consumption of amino acids (i.e., protein) synergistically adds
to the exercise response
provide the underlying basis for
skeletal muscle growth. Observations of increases in lean body
mass and muscle hypertrophy after long-term resistance
are obviously the result of periods in which net
protein balance (synthesis minus breakdown) has been positive
; this occurs only when feeding and resistance exercise
are superimposed (Figures 2B and 3). Hence, an additional re-
quirement for protein in a group of individuals engaging in
strength training theoretically may come about due to an increased
requirement for protein to support protein synthetic gains (Figure
2B). In addition, protein needed to repair any ultrastructural dam-
age in muscle tissue occurring as a result of some eccentric
component to the activity
may lead to an increased require-
ment for dietary protein in athletes wishing to increase their lean
Studies have been conducted in which the protein
requirements of resistance-trained athletes have been directly ex-
amined and the protein requirements of these habitually exercising
persons have been determined to be greater than those of compa-
rable sedentary persons.
Despite the preceding proposed rationale for why a strength-
trained athlete might have an increased requirement for dietary
protein, in addition to experimental evidence,
there is no
consensus, at least in reviewed scientiﬁc literature, as to whether
habitual resistance exercise increases protein requirements.
The current dietary reference intakes (DRIs) set protein intake at
0.8 g · kg
, and there is no recommendation for consump
tion of extra protein with exercise.
That there is no general
concurrence on the issue of elevated dietary protein requirements
for athletes likely arises from a number of confounding issues;
more importantly, it is less than clear what the best method is when
it comes to estimating protein requirements.
It has been proposed
that there are inherent problems in conducting studies of protein
requirements in habitually active persons,
which have led to a
ﬂawed interpretation of data from studies in which the dietary
protein requirements in athletes have been found to be
Tarnopolsky et al.
conducted a study using the nitrogen
balance approach to examine the protein requirements of a group
of resistance-trained athletes and a group of sedentary controls.
Tarnopolsky et al.
previously demonstrated that an isolated bout
of resistance exercise does not increase leucine oxidation or per-
turb whole-body protein turnover. It would appear that any extra
protein required by strength-trained individuals is directed toward
muscular hypertrophy in the earlier phases of training, when mus-
cle mass is still increasing. In contrast, in highly trained power-
lifters and bodybuilders, in whom muscle mass is high but stable,
it is unlikely that their dietary protein requirements are elevated
much more than those of a sedentary person. In fact, any increase
in protein requirements for such a highly trained group of individ-
uals is likely due to an increased rate of resting protein turnover.
In support of the idea that training might induce an increase in
resting muscle protein turnover, protein requirements of highly
trained bodybuilders were found to be only 12% greater than those
of sedentary controls who had a protein requirement of 0.84 g ·
The results of this study
highlight a consistent yet
puzzling result. When consuming a protein intake (actually equiv-
alent to the habitual protein requirement of the bodybuilders) of
approximately 2.8 g · kg
, all bodybuilders were in highly
positive nitrogen balance (