BACKGROUND: Excessive intramyocellular lipid (IMCL) accumulation is a primary cause of skeletal muscle insulin resistance, especially in older adults, and interventions that reduce IMCL contents are important to improve insulin sensitivity. Electromyostimulation (EMS)-induced changes in IMCL content in older adults remain unknown. The purpose of this study was to clarify the effects of a single bout of EMS on the IMCL content of the vastus lateralis muscle in older adults. METHODS: Twenty-two physically active, non-obese older men and women were randomly assigned to an EMS intervention group (69.0 +/- 5.2 years, n = 12) or a control group (68.4 +/- 3.5 years, n = 10). EMS was applied to the vastus lateralis (7 s on and 7 s off) for 30 min; control participants sat quietly for 30 min. IMCL content within the vastus lateralis was quantified with 1H-magnetic resonance spectroscopy (n = 7 per group). Fasting plasma glucose and insulin values were determined from blood samples collected before and after the EMS intervention. RESULTS: EMS induced a significant reduction in plasma glucose (93.1 +/- 9.6 to 89.5 +/- 9.1 mg/dL, p < 0.01), but not IMCL content (15.7 +/- 15.7 to 15.8 +/- 13.1 mmol/kg wet weight, p = 0.49) or insulin (5.4 +/- 2.4 to 4.7 +/- 2.7 micro-IU/mL, p = 0.18). In the control group, no changes in IMCL content in the vastus lateralis was observed after prolonged quiet sitting. CONCLUSION: EMS intervention for 30 min induces changes in plasma glucose, but no changes in IMCL content in older adults. TRIAL REGISTRATION: University hospital Medical Information Network (UMIN) Center ID UMIN000020126. Retrospectively registered on December 222,015. https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000023242.

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