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Researched
and Composed by
Jacob Wilson, BSc. (Hons), MSc. CSCS
Address correspondence to:
jwilson@abcbodybuilding.com
Journal of HYPERPLASIA
Research 6(3):
Published August 3, 2006
Abstract
Three critical stimuli for protein balance include leucine concentrations,
insulin, and various exercise stimuli. The following paper will analyze the
interaction between exercise and leucine concentrations. In particular the
paper attempts to distinguish between catabolic or exercising conditions which
lower muscle tissue compared to those which increase muscle tissue. It is
demonstrated that leucine levels may differentiate between these conditions,
followed by recommendations on how to maximize muscle tissue growth and hinder
muscle tissue loss.
Introduction
Bodybuilder’s goals are directed towards maximizing muscular hypertrophy. In
parts one of this series the general role of leucine as a modulator of protein
balance was discussed, while in part two its effects and interaction with
insulin were analyzed. Generally the findings of these papers suggest that
leucine is the primary regulator of meal induced protein synthesis, while
insulin appears to be the primary regulator of protein degradation.
When analyzing the effects of leucine on protein synthesis it is found that
protein synthesis increases from 30 minutes to 2 hours following ingestion of a
leucine containing meal, followed by a return to baseline. Therefore its
effects are transient, causing the bodybuilder to opt for a high frequency of
feeding periods. In contrast external resistance training changes protein
synthesis for up to 72 hours.
The
interaction of exercise with leucine is a complex situation. As a brief
overview:
1. Resistance training is associated with little change in protein synthesis
during exercise, with an increase in protein synthesis for up to 72 hours
following training.
However, because protein degradation is increased, overall net protein balance
is negative unless a protein containing meal is consumed (Biolo et al, 1997).
2. Endurance exercise is associated with a depression of protein synthesis
during and after exercise that is proportional to the duration and intensity of
the exercise session (Norten et al., 2003).
The
differences between the two appear to be related to plasma leucine
concentrations. For example Durham et al. (2004) had participants perform 8
sets of 10 repetitions at 75 % of their 1-RM on the leg press, followed by 8
sets of 8 repetitions on the leg extension at 80 % of their 1-RM. No
significant changes in plasma leucine concentrations were found. In contrast
Durham et al. (1996) found that participants performing 90 minutes of cycling
had significant decreases in plasma leucine levels.
Norten et al. (2003) modeled the endurance bout and had rats perform an
exhaustive long duration treadmill run. After the run was completed the rats
had a 25 % decrease in protein synthesis. Following the bout of exercise the
animals were given either a glucose and sucrose drink, a complete meal
containing protein, or a leucine alone. Results found that the CHO condition
did not recover protein synthesis, while both the meal, and leucine alone did.
Therefore differences in resistance exercise and endurance exercise appear to be
related to plasma (or intracellular) leucine concentrations.
Mechanisms of Action
As
stated in article one of this series immediate changes in protein synthesis are
regulated at the level of translation initiation, or the beginning stage of
protein synthesis. Translation initiation is comprised of assembling the mRNA
which contains instructions for said protein to a ribosome molecule. A family
of proteins known as initiation factors is responsible for regulating this
process. Further, the cell can increase its capacity for protein synthesis by
activating ribosomal protein S6, which specifically enhances the production of
ribosomal proteins, initiation, and elongation factors. It appears that the
Mamallian Target of Rapymysium (mTOR) is the machinery responsible for both up
regulating initiation factors, and enhancing the cells capacity for protein
synthesis.
Evidence suggests that by hindering mTOR the effects of leucine, insulin,
exercise, and growth factors such as IGF-1 are hindered. Therefore mTOR acts as
an integrating center for signals which regulate protein synthesis.
mTOR
is also sensitive to the energy status of the cell, and it is this process which
is critical for the reader to grasp. Muscle cells contain a protein kinase
known as AMP activated protein kinase. ATP is our body’s main energy source.
ATP can be broken down into ADP, and finally AMP. When this occurs the energy
released is used to power muscular contraction (see Wilson and Wilson, 2004 for
a review). AMP activated protein kinase is increased in activity when AMP
levels increase. This is because increased AMP levels indicate lower energy
status in the cell. Continual long term contractile activity associated with
endurance activity maximally stimulates AMPK. AMPK is able to inhibit mTOR
through downstream events.
During resistance training exercise leucine levels are maintained and it appears
that these maintained concentrations are able to counter the effects of AMPK.
However, during endurance training when leucine levels lower, AMPK is not
hindered from inhibiting mTORs actions, and protein synthesis lowers until
leucine is provided.
Supplementing with Leucine Prior to
Exercise
Often
it is stated that individuals should not perform long duration cardiovascular
sessions because they can be highly catabolic in nature. Further,
cardiovascular training on an empty stomach in the morning serves as a double
edged sword. Both long duration cardiovascular training and morning training
are associated with a higher reliance on fat metabolism due to depletion of the
body’s energy reserves. The negative aspect is that the catabolism of muscle
tissue is also high during this time period (see Wilson and Wilson, 2005 for an
in depth review). The research question that needs to be asked is why is this
the case. Evidence presented above suggests that it may be due to a depletion
of plasma leucine levels. This is based on the finding that the negative
protein balance seen after an overnight fast, and during and after endurance
exercise is reversed when leucine is administered. Therefore it may be that
athletes can perform longer duration endurance training sessions, as well as
cardiovascular training in the morning if they consume a large dose of essential
amino acids prior to the training session.
Summary and Conclusions
mTOR
appears to be the regulating center for stimuli which effect protein synthesis.
Exercise increases protein synthesis most likely due to increased blood flow and
amino acid delivery during and after training. Further high intensity
resistance exercise is associated with increases in insulin like growth factor
and growth hormone, which are potent regulators of protein synthesis. Evidence
also suggests that they are mTOR dependent (see Wilson, 2005 for a review).
Resistance exercise is associated with little change in protein synthesis during
training, and an increase in protein synthesis following training. However
protein balance remains negative unless a leucine rich meal is administered
after. It should be noted however, that because protein degradation increases
during exercise, protein balance during this time is typically negative. Tipton
et al. (2001) found that an EAA supplement prior to exercise caused a positive
protein balance. Therefore athletes should consume an EAA or protein supplement
prior to and after resistance exercise.
Endurance exercise is associated with a decrease in protein synthesis during
exercise, and this appears to be linked to lowered leucine levels. Evidence
suggests that lowered energy levels in the cell stimulate AMPK which inhibits
mTOR. When leucine levels are low, AMPK is not antagonized, and protein
synthesis plummets. If athletes consume leucine along with other EAAs prior to
long duration endurance exercise and possibly in the morning they can maximally
stimulate fat metabolism, while sparing muscle tissue.
References
Biolo G, Tipton KD, Klein S, Wolfe RR. An abundant
supply of amino acids enhances the metabolic effect of exercise on muscle
protein
synthesis. Am J Physiol. 1997;273:E122–9.
Paul GL,
Rokusek JT, Dykstra GL, Boileau RA, Layman DK. Oat, wheat or corn cereal
ingestion before exercise alters metabolism in humans. J Nutr. 1996;126:1372–81.
Durham WJ,
Miller SL, Yeckel CW, Chinkes DL, Tipton KD, Rasmussen BB, Wolfe RR. Leg glucose
and
protein metabolism during an acute bout of resistance exercise
in humans. J Appl Physiol. 2004;97:1379–86.
Norton LE,
Layman DK. Leucine regulates translation initiation of protein synthesis in
skeletal muscle after exercise. J Nutr. 2006 Feb;136(2):533S-537S.
Wilson, J.
and G.J. Wilson. (2004)
Energetic Transference
Occurring in the Biosphere Part II. The Journal of HYPERplasia Research. 4:
http://www.abcbodybuilding.com/energetic2.php
Wilson, J.
and G.J. Wilson.
2005 Direct Comparisons of Fuel use during Low,
Moderate, and High Intensity Exercises . The Journal of HYPERplasia
Research. 5:
http://www.abcbodybuilding.com/Nutrientpartitioningpart4.php
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