896
Koopman et al.
intake, net muscle protein balance will remain nega-
adaptive response. Factors that play an important
tive. Consequently, athletes need to ingest carbohy-
role in the regulation of muscle cell size are: muscle
drate and protein following exercise to attain a posi-
cell stretch,
[14,15]
increases in intracellular calci-
tive protein balance and, as such, to improve the
um,
[14]
as well as exercise-induced increases in lo-
adaptive response to exercise.
cally produced and circulating growth factors such
The interaction between exercise and nutrition is
as insulin-like growth factor-1 (IGF-1)
[16]
and mus-
not only important for athletes, but also of important
cle growth factor (MGF).
[17,18]
An acute bout of
clinical relevance in the elderly. As such, the Ameri-
resistance exercise has been shown to activate tran-
can College of Sports Medicine currently recom-
scription factors such as Myo-D and myogenin,
[19]
mends resistance-type exercise training as an impor-
and increases the rate of messenger RNA (mRNA)
tant component of an overall fitness programme.
[2]
formation encoding for myosin heavy chain
This is particularly important in the elderly where
(MHC).
[19,20]
Interestingly, changes in the rate of
the loss of muscle mass and strength are prominent
protein synthesis occur before changes in mRNA
deficits. Exercise interventions combined with spe-
accumulation.
[21]
Therefore, acute activation of
cific nutritional intervention provide an effective
muscle protein synthesis must be controlled by post-
strategy to counteract or reduce the loss of muscle
transcriptional mechanisms.
[22]
The post-transcrip-
mass generally associated with chronic metabolic
tional regulation of protein synthesis involves
disease and aging. This article discusses the effects
mRNA translation initiation, elongation, termina-
of exercise and nutrition on muscle protein metabo-
tion and post-translational modification. The initia-
lism in both the young and elderly.
tion of mRNA translation is thought to be most
important for the overall control of muscle protein
1. Resistance Exercise
synthesis.
[23]
Muscle hypertrophy can only occur when muscle
Resistance exercise or strength training involves
protein synthesis is exceeding protein breakdown
a relatively small number of muscle contractions
for a prolonged period of time. As such, it is the
against a heavy load.
[3]
It has been shown that this
balance between muscle protein synthesis and
type of exercise acutely increases whole-body insu-
breakdown that determines net muscle protein ac-
lin sensitivity,
[4]
which can partly be attributed to a
cretion.
[6]
Resistance-type exercise can effectively
reduction in the muscle glycogen stores.
[5]
However,
stimulate muscle protein synthesis.
[24-27]
A single
the most apparent adaptation to resistance exercise
session of resistance exercise accelerates muscle
is the increase in muscle strength and mass, or
protein synthesis rates within 24 hours.
[27]
Acceler-
muscle hypertrophy. However, it generally takes
ated protein synthesis rates have been reported to
weeks to months before these changes become ap-
last for 2448 hours.
[24,25,27]
The increase in muscle
parent.
[6]
The prolonged time course for hypertrophy
protein synthesis rate or fractional synthetic rate is
is a reflection of the slow turnover rate of muscle
largely attributed to an increase in myofibrillar (i.e.
proteins, i.e. about 1% per day for contractile pro-
MHC and actin) protein synthesis rates. The latter is
teins.
[7-9]
supported by the observation that MHC synthesis
The primary determinant of skeletal muscle hy-
rates are increased after a single resistance exercise
pertrophy following resistance training is the exter-
session.
[28-30]
Interestingly, muscle protein break-
nal load that is applied. Several animal models have
down is also stimulated following resistance exer-
shown that increased loading results in an increased
cise, albeit to a lesser extent than protein synthesis.
muscle mass and protein content per muscle.
[10-12]
The net result is an improved net muscle-protein
Increased loading amplifies muscle protein synthe-
balance that persists up to 48 hours.
[27]
However, net
sis and breakdown and this training-induced eleva-
muscle protein balance remains negative in the ab-
tion in muscle protein turnover leads to a more rapid
sence of nutrient intake, indicating that muscle tis-
protein remodelling
[13]
and, therefore, allows a faster
©
2007 Adis Data Information BV. All rights reserved.
Sports Med 2007; 37 (10)
Study 