Some additional information from Gary Reinl of Marc Pro:
Since all
muscles contractions essentially “look” the same (the muscle contracts)
… your observation that the contractions produced by a MARC PRO unit
look the same as contractions produced by TENS unit is correct.
In fact, if you have ever been shocked by a faulty electrically wire in
your home … the contraction produced by that encounter would also
“look” the same. That said, the contraction produced
by that faulty wire (or a TENS) would not “feel” the
same. Additionally, if you continued
“shocking” yourself with that faulty wire (or a TENS)
you would eventually fatigue/damage the involved muscle. My point is
this; if you want to fatigue a muscle, MARC PRO is the wrong tool. MARC
PRO will not fatigue your muscle (instead, it will facilitate and
enhance muscle performance and recovery).