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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 27 100 +/- 1800, p < 0.05), IIa 32 600 +/- 2100; IId 27 300 +/- 1890 and IIb isoform 20 100 +/- 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.

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The aim of this study was to investigate the response of protein synthesis rate, particularly myosin heavy chain (MyHC) isoforms synthesis and the magnitude of its isoform transformation in fast-twitch plantaris muscle, to different modes of prolonged mechanical loading. Different protocols of mechanical loading were used: resistance training (RT), compensatory hypertrophy (CH) of m. plantaris after tenotomy of m. gastrocnemius and a combination of the two previous loadings (RT + CH). During the different modes of loading, plantaris muscle hypertrophy in RT group was approximately 10 %, CH approximately 40 % and CH + RT approximately 44 %. MyHC I and IID isoform synthesis rate increased in all experimental groups, as well as their relative content. MyHC IIA relative content decreased during RT and RT + CH and increased during CH. MHC IIB isoform relative content decreased in all experimental groups, but compared with CH in CH + RT MyHC IIB isoform content increased in plantaris muscle. These results demonstrate that different modes of mechanical loading resulted in the selective up- and down-regulation of MyHC isoforms in fast-twitch skeletal muscle. The synthesis rate and relative content of the two fastest isoforms of MyHC IIB and IID are regulated to different directions during mechanical loading.

Abstract:The aims of the present study were to show the distribution of individual myosin light chain (MyLC) isoforms in fast-twitch (FT) and slowtwitch (ST) muscles and between FT muscles in order to find differences between MyLC isoforms in these muscles, to identify similarities with the distribution of myosin heavy chain (MyHC) isoforms and to investigate changes in these relations during adaptation to endurance and resistance training. Male Wistar strain rats were used in this study. One-dimensional electrophoresis was used for separation of MyHC and MyLC isoforms and two-dimensional electrophoresis was used for identification of MyLC different isoforms. A difference in the relative content of MyLC isoforms between FT muscles exists only in the case of MyLC 1 slow and 2 slow isoforms. Differences in the relative content of MyHC between FT muscles are considerably larger than differences in the MyLC isoforms. MyHC and MyLC isoforms both participate in the remodelling of contractile proteins during exercise training. In conclusion: The present study shows some discrepancy between the modulation of MyHC and MyLC isoforms in muscles with different oxidative potential during adaptation to endurance and resistance training. In ST muscles, there is full agreement between the increase in the relative content of MyHC IIa isoform and MyLC 2 fast and 3 fast isoforms during resistance training without significant changes during endurance training. The ratio of MyLC 3 and MyLC 2 isoforms increases during both types of exercise training, but it is two times higher during resistance training.(Biol.Sport 26:215-234, 2009)

The purpose of this study was to find the effect of different endurance training volumes on the composition and turnover of myosin. Sixteen-week-old male rats of the Wistar strain were divided into three different volume-based training groups. Changes in myosin heavy chain (MyHC), myosin light chain (MyLC) isoforms' composition, their synthesis rate, as well as myosin binding C-protein synthesis rate, and muscle protein degradation rate were measured. In slow-twitch (ST) soleus (Sol) muscle MyHC I isoform relative content increased and MyHC IIa isoform decreased during excessive increase in the volume of endurance training (ET). In plantaris (Pla) muscle excessive increase in ET volume decreased MyHC I and IIb isoforms, and increased MyHC IIa and IId relative content. In extensor digitorum longus (EDL) muscle the relative content of MyHC IId isoform increased during ET, but excessive increase in training volume decreased it. In Pla muscle the relative content of MyLC 1 (slow) isoform decreased during ET, but excessive increase in ET volume decreased the relative content of MyLC 3 (fast) isoform in both fast-twitch (FT) muscles. Decrease in MyHC and myosin binding C-protein synthesis rate in Pla muscle had significant correlation with ET volume (r = - 0.537, p < 0.05 and r = - 0.727, p < 0.001 subsequently). MyHC I and IIb isoforms and MyLC 3 (fast) isoform in Pla muscle and MyHC IIb, IId and MyLC 3 (fast) isoforms in EDL muscle are the most sensitive to the increase in ET volume. Excessive increase in ET volume leads to a decrease in physical working capacity. The degradation of muscle protein increased during ET in all groups.