The use of an electronic muscle stimulator for “contitioning muscles” is quackery. Avoid it at all costs. Allow me to quote from a page called “Top Health Frauds” at:
Unproven Use of Muscle Stimulators
Muscle stimulators are a legitimate medical device approved for certain conditions–to relax muscle spasms, increase blood circulation, prevent blood clots, and rehabilitate muscle function after a stroke. But within the past few years health spas and figure salons have promoted new uses. They claim that muscle stimulators can remove wrinkles, perform face lifts, reduce breast size, and remove cellulite. Some even claim these handy little devices can reduce one’s beer belly without the aid of sit-ups! FDA considers promotion of muscle stimulators used for these conditions to be fraudulent.
And from another of QuackWatch’s pages:
The FDA considers promotion of muscle stimulators or iontophoresis devices for any type of body shaping or contouring to be fraudulent [3,4]. The most infamous of
these devices, the Relax-A-Cizor, was claimed to reduce girth by delivering electric shocks to the muscles. More than 400,000 units were sold for $200 to $400 each before
the FDA obtained an injunction in 1970 to stop its sale. At the trial, 40 witnesses testified that they had been injured while using the machine. The judge concluded that the
device could cause miscarriages and aggravate many preexisting medical conditions, including hernias, ulcers, varicose veins, and epilepsy.