**28. Conclusions**

myofiber-mini MTJ " type separated by the scar. These two consecutive units contract at the same time, thanks to the fact that both are re-innerved by the same nerve (Rantanen et al., 1995). In the ECM, on a level of the place of the new MTJs, elastic and adhesive molecules are profusely expressed, whose role is to absorb the strength created by the muscular contractions (Hurmea and Kalimo, 1992; Järvinen et al., 2000). At this point of the repair process, having re-established solid terminal adhesions through these mini MTJs, the myofibers no longer need lateral adhesions of strengthening and, consequently, the strong expression of integrin decreases on a level of the lateral sarcolemma (Kääriänen et al., 2000a). The scar gradually diminishes in dimension, in such a way the stumps come close to each other and in the end the myofibers become intertwined, even though, not fully reunited (Kääriänen et al., 1998;

2000a; Vaittinen et al., 2002) (figure9 box C).

40 Muscle Injuries in Sport Medicine

(A)

(B)

(C)

**Figure 9.** At the beginning of the healing process of the injured skeletal muscle (Box A ) the expression of cellular adhesion of the integrin α7β1 molecules is enriched in the terminal part of the fibers of the damaged muscle in regen‐ eration phase, whereas only a small amount of the latter are present in the lateral profile of the myofiber. A dramatic increase in the expression of integrin α7β1 happens along the lateral aspect of the plasmatic membrane (Box B ), both in the intact part and in the part in growth phase of the injured myofibers, at the moment in which the muscular fibers in repair phase penetrate the injured tissue. In such a way, the integrin α7β1 supplies stability to the muscular fibers in growth phase which are missing in adhesion in their terminal part. The expression of the integrin α7β1 returns to nor‐ mal levels in the lateral sarcolemma (Box C) contextually to the normality of the re-distribution of the integrin α7β1 in the terminal part of the fibers in repair, when the latter form new myotendon junctions and adhere to the scar.

Today there are only a few clinical studies concerning the treatment of muscular lesions, for this reason the principles of current treatments are mainly based on experimental studies or only on empirical evidence. The experimental studies have shown that the biological basis of the processes that occur during muscle repair are identical regardless of the primary cause of the injury (contusion, elongation or tear). This emphasizes the importance of understanding the basic principles of muscle repair, which represent the essential pre-requisite for a correct approach to the treatment of muscle injuries.
