About Mechanical and Electrophysiological Properties of So-Called Slow and Fast Muscles : An investigation at the M. quadriceps femoris of marathon runners, sprinters, volleyball players and physical education students

Abstract

On the one hand, there are hints in the literature which suggest a connection between the percentage of fast-twitch muscle fibres in thigh muscles and 100 m record times, on the other hand, few out of the numerous training studies report a transformation in fiber distribution from slow-twitch to fast-twitch fibers. Most longitudinal studies rather show adaptions from fast-twitch to slow-twitch. This contrasts with numerous animal studies which provide evidence for both fiber transformation from MHCIIB via isoforms to MHCI and vice versa from MHCI to MHCIIB. A confusing situation that remains without any conclusive explanation so far. These facts provided the basis for the study at hand which aims to describe the mechanical properties of so-called slow and fast muscle fibers by examining simple voluntary contractions at different levels of demand in order to gain insight into the functional relation between specific training stimuli and fiber properties. For this purpose, 12 short-track runners, 12 volleyball players, 12 marathon runners and 12 students of the faculty of sports were submitted to tests of maximal strength, reflexes, anaerobic strength at two different levels, relaxation and aerobic strength. The anthropometric, strength and EMG data raised in the study were used as a basis for calculating 575 values. The results claim a dominant role of neuronal processes in the development of specific performance parameters of different sports. In order to link muscle innervation and morphological adaption, the Ca2+-system will be discussed. Since intracellular Ca2+ concentration can be seen as a possible trigger for MHC transformation, length and frequency of muscle innervation as well as the specific recruitment of motor units play a decisive role in the structural plasticit.On the one hand, there are hints in the literature which suggest a connection between the percentage of fast-twitch muscle fibres in thigh muscles and 100 m record times, on the other hand, few out of the numerous training studies report a transformation in fiber distribution from slow-twitch to fast-twitch fibers. Most longitudinal studies rather show adaptions from fast-twitch to slow-twitch. This contrasts with numerous animal studies which provide evidence for both fiber transformation from MHCIIB via isoforms to MHCI and vice versa from MHCI to MHCIIB. A confusing situation that remains without any conclusive explanation so far. These facts provided the basis for the study at hand which aims to describe the mechanical properties of so-called slow and fast muscle fibers by examining simple voluntary contractions at different levels of demand in order to gain insight into the functional relation between specific training stimuli and fiber properties. For this purpose, 12 short-track runners, 12 volleyball players, 12 marathon runners and 12 students of the faculty of sports were submitted to tests of maximal strength, reflexes, anaerobic strength at two different levels, relaxation and aerobic strength. The anthropometric, strength and EMG data raised in the study were used as a basis for calculating 575 values. The results claim a dominant role of neuronal processes in the development of specific performance parameters of different sports. In order to link muscle innervation and morphological adaption, the Ca2+-system will be discussed.