Treat specific numbers like “90% of muscle fibers” as marketing, not science. Those figures come from manufacturers, not independent peer-reviewed research, and there isn’t solid published evidence pinning EMS to an exact activation percentage.

What’s true: EMS does recruit muscle differently from voluntary exercise, and it can engage a lot of muscle at once — part of why it’s time-efficient and why 20 minutes can leave you tired. That’s a real, useful effect.

What’s not established: precise, impressive-sounding percentages. If a brand leans hard on a number like that, read it as a marketing claim. The honest case for EMS rests on the strength and muscle outcomes in the trials, which are good enough on their own.