Effect of acute transcranial magnetic stimulation on intracellular signalling in human skeletal muscle.

Objective: To investigate the potential of an acute bout of transcranial magnetic stimulation to induce anabolic signalling. Design: Experimental intervention on healthy subjects. Subjects: Ten healthy subjects, 5 women and 5 men (mean age 32 years; standard deviation (SD) 4). Methods: Transcranial magnetic stimulation, resulting in contraction of the quadriceps muscles, was applied at a frequency of 10 Hz for 10 s followed by 20 s of rest, repeated 40 times over 20 min. Electromyography and force data were collected for all transcranial magnetic stimulation sequences. Muscle biopsies were obtained from the vastus lateralis muscle before and 1 and 3 h after stimulation for evaluation of the molecular response of the muscle. Results: The described stimulation decreased phosphorylation of AKT at Thr308 (1 h: -29%, 3 h: -38%; p<0.05) and mTOR phosphorylation at Ser2448 (1 h: -10%; ns, 3 h: -21%; p < 0.05), both in the anabolic pathway. Phosphorylation of AMPK, ACC and ULK1 were not affected. c-MYC gene expression was unchanged following transcranial magnetic stimulation, but rDNA transcription decreased (1 h: -28%, 3 h: -19%; p<0.05). PGC1 alpha-exlb mRNA increased (1 h: 2.3-fold, 3 h: 2.6-fold; p<0.05), which also correlated with vastus lateralis electromyography activity, while other PGC-1 alpha variants were unchanged. Conclusion: Acute transcranial magnetic stimulation of skeletal muscle in weight-bearing healthy individuals did not induce anabolic signalling, but some signs of impaired muscle anabolism were detected. Therefore, these results do not support the use of acute transcranial magnetic stimulation in preventing muscle wasting.