Mechanical properties of morphological different muscles interpreted as a conse- quence of neural activation patterns - implications to specific training

INTRODUCTION As we know from several studies, the fiber structure and the mechanical properties of a muscle depends on the innervation frequency, innervation time (IT) and the innervation–rest ratio (Monster et al. 1978; Hennig and Lømo 1985; Gundersen and Eken 1992). Recently Hämälainen & Pette (1996) reported that it is possible not only to transform fast contracting MHC II fibers to slow contracting MHC I fibres (for review see Pette & Staron 1997 and Gundersen 1998) but also in the opposite direction. They demonstrated the transformation of MHC I/ MHC IIA to MHC IID/X / MHC IIB fibres of the rat soleus in response to a innervation frequency of 150 Hz, an IT of 166ms and an inter-attraction interval of 15 minutes. On the other hand high portion of type II fibres in the quadriceps of fast running animals like the African cheetah or human sprinters suggests a relationship between the innervation modalities, the morphological muscle structure and the functional output (Williams et al.1997; Mero et al. 1981). The aim of this study was to compare the innervation strategies of four different sports groups to discuss them under the focus of neuromuscular plasticity.