There is extensive scientific documentation regarding the efficacy of microcurrent soft tissue therapy in humans. Some documentation is provided below.
Human Microcurrent Scientific Studies
The Microlief microcurrent Controller is covered by US and International Patents including:
6,408,211; EP1294443B1; 2,410,342
After years of rigorous scientific studies, this microcurrent Controller was approved by the FDA for Over-The Counter Use in humans.
The 510(K) FDA premarket notification documents identification numbers are:
K090042 which is dated May 6, 2009, K130114 which is dated April 16, 2013, and K151995 which is dated October 5, 2016.
Here is the stated Intended Use for the device from the K-90042 document:
Indicated for temporary relief of pain associated with sore and aching muscles in the lower back due to strain from exercise or normal household and work activities
Here is the stated Intended Use for the device from the K-130114 document:
Indicated for temporary relief of pain associated with sore and aching muscles in the lower extremities (arm and/or leg) due to strain from exercise or normal household and work activities
Here is a link to a PDF file that contains scientific data regarding the microcurrent Controller that powers Microlief:
http://www.microlief.com/PDF/Clinical_Evaluation_Report.pdf