Histochemical and mechanomyographical evaluation of the adaptive potential of human biceps femoris muscle

Abstract

The goal of this study was to estimate the ability of biceps femoris (BF) muscle, a hamstring muscle crucial for biarticulate movement, to adapt to changed functional demands. For this purpose and due to ethical reasons, in a group of healthy sedentary men and of 15 sprinters, a non-invasive mechanomyography (MMG) method was used to measure the muscle twitch contraction times (Tc). These correlate with the proportions of slow and fast fibers in the muscle. To further elucidate the data obtained by MMG method and to obtain reference data for the muscle, the fiber type proportions in autoptic samples of BF in sedentary young men were determined according to histochemical reaction for myofibrillar adenosine triphosphatase (mATPase). With MMG we indirectly demonstrated that biceps femoris muscle has a strong potential to transform into a faster contracting muscle after sprint training, since the average Tc in sprinters was much lower (19.5 ± 2.3 ms) than in the sedentary group (30.25 ± 3.5 ms). The results of the histochemical analysis of BF muscle also imply a high adapting potential of this muscle. Beside type 1, 2a and 2× (2b) fibers a relatively high proportion of intermediate type 2c fibers (5.7% ± 0.7), which co-expressed MyHC-1 and -2a, was found. Therefore, type 2c might represent a potential pool of fibers, capable of transformation either to slow type 1 or to fast type 2a in order to tune the functional response of BF muscle according to the actual functional demands of the organism. © 2007 Springer.