Electronic muscle stimulators have been developed to assist recovery (reanimation) of muscles, mainly of extremes (arms and legs) after a long period of bandaging.
They should be used by qualified and specially trained personnel only to expedite muscle activities after bandage removal - possibly under medical supervision.
Under no circumstances should the output AC exceed the safe value of 39Vpp at moderate currents of no more than 25mA!
(The example circuit doesn't even produce AC, but pulsing DC - if at all.)
Higher voltages and/or currents at low frequencies are generally used for torture and electrocution.
It must be a fairy tale that belly muscles "stimulated" by electric shock waves help to burn off fat!
Yet, a better and healthier way is "working" the fat off by muscle training.
You might smell like an animal after such training, but there are ways to get rid of that - I call it shower or full bath!
A good side effect of that method is increase of body power - which can be used for population policy purposes.
Boncuk