Hi david_wb,
First of all I think electrical stimulation is useful only for limited cases and one of them is lower motor conditions as nerve lesion because you can stimulate the denervated muscles and prevent their atrophy untill nerve regeneration.
I always use low frequencies to stimulate denervated muscles specially the triangluar one. You can try exponential current(T current). It is useful to use pin electrode if you apply on the hand. Put it on the motor points. Start with long contraction time (300 u sec) in sever cases. Increse the intensity till you see a visible contration. Count for 30 contraction then move to another motor point. Don't increase the time because that may lead to muscle fibrosis.
Your exercises are very important too.