STRENGTH TRAINING INDUCES UPREGULATION OF MHC I ALPHA MRNA IN HUMAN SKELETAL MUSCLE

Abstract

Myosin heavy chain (MHC) Iα, a cardiac-like isoform of MHC, has been proven to be expressed in skeletal muscle in animals and is regarded as an intermediate between MHC Iα and MHC IIa. Studies on animals show that MHC Iα is expressed during muscle fiber transition, however, no study dealing with this issue in human skeletal muscle in terms of muscular adaptation to training has been reported. PURPOSE To investigate the expression of MHC Iα at mRNA level in human skeletal muscle in response to strength training with different strategies. METHODS 24 male subjects (mean, age:25 y; height:183 cm; body mass:81 kg) were divided into two groups with regard to the 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. Total RNA was extracted from the muscle samples and Oligo primed synthesis of cDNA was performed using MuLV reverse transcriptase. MHC Iα mRNA level was determined using real-time quantitative PCR with relation to internal reference (HPRT). RESULTS Strength training led to a significant increase in 1RM in both groups (5.6 kg for MAX-group and 5.0 kg for COMBI-group, respectively), but the combined strength training had an additional improvement on maximum movement velocity (0.1 m/s, p < 0.05). MHC Iα mRNA was significantly upregulated (308 ± 109% and 160 ± 49% for MAX- and COMBI-group, respectively, p < 0.01). CONCLUSION It can be demonstrated that an upregulation of MHC Iα mRNA could be induced in human skeletal muscle in response to training, and MHC Iα mRNA level can be affected by different training patterns. MHC Iα upregulation may suggest an active muscle fiber type transition.