The Effects of Neuromuscular Electrical Stimulation on Anabolic Signaling in Older Adults
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Neuromuscular electrical stimulation (NMES) generates involuntary muscle contraction and may be a safe and effective alternative for voluntary resistance training. However, further research needs to be done to fully understand the effects of NMES on muscle strength, self-efficacy for activities of daily living (ADL’s), and on anabolic signaling. PURPOSE: The purpose of this study was to investigate the effects of a 12 session, 4-week neuromuscular electrical stimulation (NMES) intervention in healthy, older adults. The outcomes investigated were anabolic signaling, strength, and self-efficacy of daily activities. METHODS: Participants (n = 11; NMES = 8, Sham = 3) consisted of healthy, older adults (mean age: 71.7 ± 7.2 years). Participants performed maximal voluntary contractions (MVC) using the quadriceps on an isokinetic dynamometer, a 5RSTS test, and completed a survey about their self-efficacy for ADL’s pre-post-Intervention. Day 1 and Day 12 of the intervention consisted of a muscle biopsy pre-NMES, 30 min post-NMES, and 120 min post-NMES. The participants were randomly placed in a treatment group (NMES) or Sham group. The participants were treated with exact same protocol except the Sham group did not receive stimulation. The NMES was administered 3 times a week for 4-weeks (12 sessions) at 60 Hz for 40 minutes on each leg. RESULTS: Phosphorylated S6K1( p = 0.020) and phosphorylated mTOR (p = 0.009) had a significant main effect for time (S6K1 Day 1: Pre-NMES 0.65 ± 0.17, Post-30min 0.98 ± 0.17, Post-120min 1.01 ± 0.19; Post-Intervention: Day 12: PreNMES 0.63 ± 0.17, Post-30min 1.25 ± 0.17, Post-120min 0.89 ± 0.21) (mTOR Day 1: Pre-NMES 0.46 ± 0.13, Post-30min 1.01 ± 0.13, Post-120min 0.92 ± 0.14; Day 12: PreNMES 0.49 ± 0.13, Post-30min 0.74 ± 0.14, Post-120min 0.48 ± 0.16) and the post hoc revealed Post-30 min was significantly upregulated when compared to Pre-NMES for both proteins (S6K1 p = 0.017, mTOR p = 0.007). There was no main effect or interaction for phosphorylated 4E-BP1, MVC, or 5RSTS. The intervention-by-group interaction for ADL Self-efficacy had a medium effect size (η2 = 0.197). CONCLUSION: The findings of this study suggest that a 4-week session of NMES upregulates signaling proteins of the mTORC1 pathway (p-mTOR and p-S6K1) 30 minutes after stimulation. Even though there was no significant difference in MVC or 5RST, there was a medium effect size for self-efficacy ADLs for this preliminary data set. Therefore, further research with more subjects is warranted in order to better understand the effects of this 4-week NMES intervention in older adults.