**7. The hypotheses of physical type**

The possible mechanisms of physical type capable of inducing initial structural damage to the muscular fiber, may be divided into two categories. The first includes the hypothesis of mechanical nature, whereas the second includes those induced by change of temperature. The fact that the muscular damage recognizes in an eccentric contraction its "*primum movens*", is a widely spread concept amongst many authors (Armstrong, 1984; Ebbeling and Clarkson, 1989; Stauber, 1989, Kano et al., 2008; Schache et al., 2008, Chang et al., 2009), so for this reason the mechanical theory of the fibrillary damage, underlines the substantial difference, in terms of strength production, between the eccentric and concentric and isometric contraction, whereas the theory which identifies the damage as consequence of a "temperature-dependent" mechanism is based on the hypothesis that, during an eccentric contraction, the local temper‐ ature of the muscle is higher, factor which would predispose the muscular fiber to structural and /or metabolic changes, potentially harmful.
