Is this a temporary thing to gain muscle (after say, traumatic injury/surgery/illness) that you drop later and maintain via other means? Or do you sustain electrostim indefinitely as part of your normal exercise?
For quads, butt, hamstrings i do two sessions a year, 3 times a week 6 weeks each, and once a week for the remaining weeks.
This spares knees, which otherwise would hurt, for example, i would do 600 lbs on a leg press, and this puts a lot of stress on my 72 year old knees.
Equivalent electro stim puts no load at all on knees, hips.
For upper body, a couple of times a week, bodyweight plus dumbbells.