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Variability in muscle adaptation to electrical stimulation.
M A Minetto1, A Botter, O Bottinelli
1Department of Internal Medicine, Division of Endocrinology, Diabetology and -Metabolism, Molinette Hospital, University of Turin, Turin, Italy. marco.minetto@unito.it
International Journal of Sports Medicine
|January 9, 2013
Summary
Neuromuscular electrical stimulation (NMES) alters myosin heavy chain (MHC) phenotypes and increases muscle force and conduction velocity. However, MHC distribution does not correlate with muscle fibre conduction velocity (MFCV).
Area of Science:
- Muscle physiology
- Neuromuscular electrical stimulation research
- Skeletal muscle plasticity
Background:
- Skeletal muscle adaptations to training involve changes in myosin heavy chain (MHC) composition.
- Muscle fibre conduction velocity (MFCV) is an electrophysiological measure influenced by muscle fibre characteristics.
Purpose of the Study:
- To investigate myosin heavy chain (MHC) phenotype plasticity after neuromuscular electrical stimulation (NMES).
- To assess the correlation between MHC isoform distribution and muscle fibre conduction velocity (MFCV).
Main Methods:
- 14 men underwent 24 sessions of quadriceps NMES.
- Vastus lateralis muscle biopsies and neuromuscular tests were performed pre- and post-training.
- Myosin heavy chain (MHC) isoform distribution and muscle fibre conduction velocity (MFCV) were analyzed.
Main Results:
- NMES significantly increased quadriceps maximal force, vastus lateralis thickness, and MFCV in both vastus lateralis and medialis.
- A wide spectrum of MHC isoform adaptations was observed, including fast-to-slow transitions and shifts toward MHC-2A and MHC-2X.
- No significant correlation was found between MHC-2 relative content and vastus lateralis MFCV post-training.
Conclusions:
- NMES induces significant adaptations in MHC composition, muscle force, thickness, and MFCV.
- MHC isoform distribution is not correlated with MFCV, suggesting MFCV cannot estimate fibre type proportions.
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