Abstract des Autors

The purpose of this study was to find the composition shift of myosin heavy chain (MyHC) isoforms in overtraining in fast- and slow-twitch skeletal muscles and different changes in MyHC isofom composition, synthesis and turnover rate between 4-week and 6-week overtraining. Male Wistar rats were randomly assigned to 4-week and 6-week endurance training, 4-week and 6-week overtraining groups. Plantaris (Pla), extensor digitorum longus (EDL), and soleus (Sol) muscles were studied. Daily excretion of 3-methylhistidine (3-MeHis) pool as an indicator for protein degradation increased in the 4-week and 6-week overtraining group to 4.04 ± 0.21 and 4.32 ± 0.23 %/day subsequently in comparison with the control group (2.16 ± 14 %/day, p<0.001). In Pla muscle MyHC I isoform synthesis rate was 33 200 ± 2150 (after 6-week overtraining 27100 ± 1800, p<0.05), IIa 32600 ± 2100; IId 27300 ± 1890 and IIb isoform 20100 ± 1600 (after 6-week overtraining 15 500 ± 1400, p<0.05) dpm/M leucine/min. Actin synthesis rate increased in fast-twitch muscles during 4- and 6-week overtraining, and in soleus muscle during 6-week overtraining. In EDL and Sol muscle MyHC isoform composition during 6-week overtraining did not change significantly. During the 6-week overtraining the relative content of MyHC I and IIb isoforms decreased and IIa and IId isoforms increased in Pla muscle. The initial increase of MyHC IIb isoform after 4-week overtraining shows the higher stability of this isoform in comparison with MyHC I isoform in fast-twitch muscles during high volume exercise. Verf.-Referat