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In spite of decades of research work on effects of physical exercise training on the
cardiac tissue, no actual consensus has been obtained on a clear view of such effects
on cardiomyocytes.
There are many reasons for this, including the followings: one is the type of ani-mals used for experiments. For evident reasons data from human are absent and the
rat, for practical reasons was the only animal used in the long list of exercise effects
publications. Furthermore, some authors have used females, others males, each of
them having a reason making sense for his choice. The problem is further compli-
cated with the characteristics of the exercise, including the fact the exercise is vol-
untary (free access to swimming or running vertical wheel) or enforced (treadmill),
and the age of the animal on which it was applied, both of them appearing to greatly
differ from one paper to another. Finally the source region of cardiomyocytes,
mainly the ventricles, also sometimes differed with discrimination between sub-
endo and sub-epicardium origin area [ 1 ] which have different electrical [ 2 ] and
mechanical [ 3 ] properties, as well as between sinus or ventricle origins.
1 Training Effects on Size, Structure and Proteins Content
of Cardiomyocytes
Nevertheless, in the following parts, we will try to highlight the main trends of the
data related to cardiomyocytes size and structure, calcium and contractile proper-
ties, and finally electrophysiological alterations induced by training as they tran-
spire from the literature. These data will be brought together in the Table 5.1 and
tentatively summarized in the Fig. 5.1.
In the following text, chronic exercise and exercise training will be used indiffer-ently and effects of acute exercise is not addressed.
1.1 Size and Structural Aspects
1.1.1 Left Ventricle Weight Increase
A majority of publications begins by reporting data related to the size, therefore the
weight, of the ventricles and in particular of the left one. Although this is not directly
related to the characteristics of cardiomyocytes, this value is necessary to get an
idea of cardiac hypertrophy, which is the most undeniable effect of chronic exercise,
and particularly of the type of hypertrophy (physiological or pathological).
While the right ventricle was more rarely measured and seems to be only slightlyhypertrophied, the left ventricle weight appeared drastically increased with chronic
exercise. Enhanced weight values were reported to range from 7 to 39% depending on
characteristics of the applied exercise and on its intensity: 7% [ 4 ], 8% [ 5 ], 12% [ 6 ], 14%
[ 7 ], 17% [ 8 ], 21% [ 9 ] or 39% [ 10 ]. Whatever was the reached weight amplitude it is
clear this mainly explains the whole heart hypertrophy induced by chronic exercise.
A. Krzesiak et al.