Depends on the human and, I suspect, the task. Also, it's hard to compare since muscles are not powered electrically, they are powered chemically. But the estimates I'm familiar with say somewhere north of 50%. Wikipedia says 25%.
Human muscle also has a bandwidth in the ~2-5 Hz range.
Human muscle also has a bandwidth in the ~2-5 Hz range.
See:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144848/