Purpose: Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation settings to increase muscle mass and strength. However, the effects of NMES on muscle growth are not clear and no human studies have compared anabolic signaling between low-frequency (LF) and high-frequency (HF) NMES. The purpose of this study was to determine the skeletal muscle anabolic signaling response to an acute bout of LF- and HF-NMES.
Methods: Eleven young healthy volunteers (6 men, 5 women) received an acute bout of LF-NMES (20 Hz) and HF-NMES (60 Hz). Muscle biopsies were obtained from the vastus lateralis muscle before the first NMES treatment and 30 min after each NMES treatment. Phosphorylation of the following key anabolic signaling proteins was measured by Western blot, and proteins are expressed as a ratio of phosphorylated to total: mammalian target of rapamycin, p70-S6 kinase 1, and eukaryotic initiation factor 4E binding protein 1.
Results: Compared with pre-NMES, phosphorylation of mammalian target of rapamycin was upregulated 40.2% for LF-NMES (P = 0.018) and 68.4% for HF-NMES (P < 0.0001), and HF-NMES was 29.3% greater than LF-NMES (P = 0.026). Phosphorylation of p70-S6 kinase 1 after HF-NMES was 96.6% higher than pre-NMES (P = 0.001) and was not different between pre-NMES and LF-NMES (although it was 50.4% higher after LF-NMES) or LF- and HF-NMES (P > 0.05). There were no differences between treatment conditions for eukaryotic initiation factor 4E binding protein 1 phosphorylation (P > 0.05).
Conclusions: An acute bout of LF- and HF-NMES upregulated anabolic signaling with HF-NMES producing a greater anabolic response compared with LF-NMES, suggesting that HF stimulation may provide a stronger stimulus for processes that initiate muscle hypertrophy. In addition, the stimulation frequency parameter should be considered by clinicians in the design of optimal NMES treatment protocols.