Composition and Turnover of Contractile Proteins in Volume-Overtrained Skeletal Muscle

Abstract

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.

High‐Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle

“…Compared to the Co group, the Tr group exhibited a significant (P < 0.05) decrease in pure fiber IIA and IID CSA in the plantaris DR portion; there was also a tendency for pure fiber I and IIB CSA to decrease in this portion (P ¼ 0.08 and P ¼ 0.09, respectively). Our results are consistent with several studies which show a predominance of catabolic condition (Seene et al, 1999;Petibois et al, 2000;Seene et al, 2004) in situations with a persistent combination of excessive overload plus inadequate recovery (Jamurtas et al, 2000;Fatouros et al, 2006). Although the molecular events that underlie our findings remain unknown, these observations raise questions as to what signals and cellular conditions initiate muscle mass changes during overtraining conditions.…”

“…These authors reported that overtraining syndrome in skeletal muscle may decrease capillarization impairing oxygen exchange between capillaries and muscle tissue which contributes to exercise intolerance. In this sense, considering that muscle fiber type is also classified according to the type of energy metabolism used (glycolytic or oxidative; Gunawan et al, 2007), our results together with those of Seene et al (2004), suggest that overtraining situations can result in a decrease in muscle oxidative capacity.…”

“…This might indicate that the activity patterns of fiber Types I and IIA (MHCI and MHCIIa isoforms), more frequent in plantaris DR portion, which have relatively high oxidative potential, possibly were more susceptible to oxidative damage by reactive oxygen species during high volume exercise in rats plantaris muscle. In addition, Seene et al (2004) also observed an increase of fast MHC isoforms after 6 weeks of endurance overtraining. These authors reported that overtraining syndrome in skeletal muscle may decrease capillarization impairing oxygen exchange between capillaries and muscle tissue which contributes to exercise intolerance.…”

“…This increased requirement for amino acids during hypermetabolism is partly satisfied by an augmentation of muscle proteolysis, the major storage pool of amino acids, and by a concomitant reduction in muscle anabolism (Smith, 1999). In addition, Seene et al (2004) showed that during overtraining condition, degradation increased and a decreased muscle protein synthesis rate lead to a decrease in muscle mass, particularly in fast twitch muscles. These authors also observed in rat fast twitch muscles during overtraining, that the DNA content per muscle decreased due to a loss of myonuclei consequent to muscle atrophy (Seene et al, 2004).…”

“…In addition, Seene et al (2004) showed that during overtraining condition, degradation increased and a decreased muscle protein synthesis rate lead to a decrease in muscle mass, particularly in fast twitch muscles. These authors also observed in rat fast twitch muscles during overtraining, that the DNA content per muscle decreased due to a loss of myonuclei consequent to muscle atrophy (Seene et al, 2004). Collectively, the results of these studies suggest that during conditions of overtraining an increase in the catabolism/anabolism ratio could lead to muscle fiber atrophy.…”