Training by low-frequency stimulation of tibialis anterior in spinal cord-injured men
Harrige, SDR, Andersen, JL, Hartkopp, A, Zhou, S, Biering-Sorensen, F, Sandri, C & Kjaer, M 2002, 'Training by low-frequency stimulation of tibialis anterior in spinal cord-injured men', Muscle & Nerve, vol. 25, no. 5, pp. 686-694.
The publisher's version of this article is available at http://dx.doi.org/10.1002/mus.10021
The tibialis anterior muscle of nine paraplegic men was chronically stimulated (2-6 h per day; at 10 Hz, 5 s on, 5 s off) under isometric loading conditions for 5 days per week for 4 weeks. After 4 weeks of training, muscle fatigue resistance in an electrically evoked test had increased by an average of 75% (P < .01, n = 9), but there were no changes in the relative composition of the three myosin heavy chain (MHC) isoforms. Five of the subjects continued training for an additional 5 weeks (2 h per day, 3 days per week). Although there was a tendency for twitch time to peak torque to increase after this additional period, no change occurred in relative MHC isoform content. However, in situ hybridization analysis revealed that even after 2 weeks of stimulation, there was evidence of upregulation of the mRNA for the MHC-I isoform and downregulation of the MHC-IIX isoform, a development that continued in weeks 4 and 9. This study provides evidence, at the level of gene transcription, that a fast-to-slow change in MHC isoform composition may be possible in human muscle when its usage is significantly increased.