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1.2 Training Effects on Contractile Proteins Content
The contractile proteins, like myosin and actin present inside the cardiomyocytes play
a key role in the contraction mechanism. Indeed, they are responsible for contraction
and relaxation of the cell following the displacement of tropomyosin by troponin in
the presence of calcium. Given the improvement in contractility observed following
physical training, numerous studies have emerged in order to bring out a possible link
between the expression of contractile proteins and the effects of chronic exercise.
1.2.1 Myosin Heavy Chain Protein: Increase in the α/βMHC Ratio
Myosin Heavy Chain protein (MHC), is the major contractile protein in the heart.
The vertebrate myocardium presents two isoforms of these protein, α-MHC and
β-MHC. The latter is predominant in the human heart but the first is thought to pre-
dominate in adult heart rat. These two proteins have an important role in the con-
tractile properties of cardiomyocytes. Changes in either of the α- or β-MHC proteins
can be directly linked with cardiac contractility properties change.
Effects of exercise training at the level of expression of these two contractileproteins diverge according to the studies. As previously noted, the observed differ-
ences may be due to several training-related parameters such as type of exercise and
duration or study model such as age and sex of the animals and other parameters.
A number of studies using swimming training protocol, in healthy rats, have sug-gested that exercise training induces an increase in α-MHC expression [ 19 , 20 ]. A
high intensity swimming training also allows to increase α-MHC expression by 1.2
fold and the synthesis of the protein by 8.5 fold compared to the control group [ 21 ].
Others studies showed an increased in α-MHC isoform expression in rats trained by
running, during 10 weeks, ranging from 30 to 75% [ 22 , 23 ]. Moreover, in the latter
paper, authors reported a 75% increase in the α-MHC expression of the gene and a
60% increase of the protein expression following only 1 weeks of running exercises.
All these studies suggest that adaptations of contractile elements like MHC proteins
seems to be an early event and sustained during cardiac growth as training contin-
ued. Nevertheless, some studies, using running as a training protocol during
11 weeks [ 24 , 25 ] or resistance exercises during 5 weeks [ 26 ], have found no evi-
dence for a change in α-MHC expression. Results related to the level of α-MHC
expression continue to be controversial.
On another side, a number of studies using treadmill or resistance training,showed a decrease in β-MHC expression. A halving of the expression of this protein
has been described following chronic aerobic exercise in rat myocytes isolated from
the endocardium and epicardium [ 27 ] or after 5 weeks of resistance training [ 26 ].
However, another study using running as a training modality, suggested no change
in the gene or protein expression of β-MHC [ 23 ].
Even if some results remained divergent in absolute values, the increase ofα-MHC expression and the decrease of β-MHC expression observed in some of
A. Krzesiak et al.