HUMAN SKELETAL MUSCLE MYOSIN HEAVY CHAIN EXPRESSION IN RESPONSE TO STRENGTH TRAINING

Abstract

In response to physical exercise, structural, metabolic and functional changes can occur in skeletal muscle. Alteration of the myosin heavy chain (MHC) composition is one of the important mechanisms for skeletal muscle to adapt to cellular stress caused by exercise. PURPOSE: To investigate human skeletal muscle adaptation to strength training (classic vs. combination with ballistic concentric movement) in terms of myosin heavy chain isoform expression. METHODS: 24 male students (age: 25 y; height: 183 cm; body mass: 81 kg) were divided into two groups with regard to different trainings (6 weeks, 3d/w), in MAX-group (traditional strength training with maximum loads): 5 series, 3 reps (3 RM load); in COMBI-group (different external force-speed and muscle-action requirements), 1st day: 5 series, 3 reps; 2nd day: 3 series, 10 ballistic concentric-only throw movement (30%); 3rd day: 3 series, 7 reps, stretch-shorten-typed push-ups. Muscls samples were taken from m. triceps brachii before and at the end of the training using fine needle biopsy technique. MHC analysis followed SDS-PAGE with silver staining. The percentage of each MHC isoform (MHC I, IIa and IId) was calculated based on the densitometric values of the corresponding protein bands. The mRNA level of each MHC isoform was estimated by RT-PCR. RESULTS: MHC IIa increased significantly in both groups (from 48. ± 9.9% to 64.7 ± 18.6%) and there was a significant decrease of MHC I in COMBI-group (from 18.2 ± 7.0% from 9.2 ± 10.1%) whereas in MAX-group MHC IId decreased (from 33.4 ± 5.7% 19.5 ± 13.0%, P < 0.01). RT-PCR showed that MHC Ia mRNA was significantly upregulated (308 ± 109% and 160 ± 49% for MAX- and COMBI-group, respectively, P < 0.01), and the changes of mRNAs for MHC 16, IIa and IId were not statistically significant. CONCLUSION: The strength training led to an increase of MHC IIa, this increase was accompanied by a decrease of MHC IId during a traditional strength training with maximum loads, whereas the increase of MHC IIa during a strength training programme with different external force-speed and muscle-action requirements was accompanied by a decrease of MHC I. The upregulation of MHC Ia mRNA may suggest an active muscle fiber type transition and may have impact on preserving MHC I during the traditional strength training with maximum loads.