They work well for the profits of the companies marketing as "no
exercise muscles".
They have their place for professional sports people and rehab. but the
level of muscular contraction required to stimulate muscle growth would
be that of an intermittent highly intense muscular cramp.
"like doing 1000 sit-ups in your chair"
Without going too deeply into the complexities of skeletal muscles,
there are, in the most simplistic terms 2 types of muscle fibre:
White "fast twitch" - strength/power stimulated by anaerobic exercise;
Red "slow twitch" - endurance/repetitions stimulated by long bouts of
aerobic exercise.
100m sprinter V matharon runner phisique
The body changes by adaptive response and conservation of energy.
Ones muscles will decline to the point where daily (in)activity can be
maintained/sustained.
What I would say is the very best thing anyone can do for health, cure,
wellbeing etc is to change dietary habits from that of multiple meals
which maintains almost constant insulin secretion and switch to "OMAD"
(One Meal A Day) typically afternoon to evening. Effectively "fasting"
for 18+ hours every day.
Also... preferred food sources being proteins and fats which don't spike
insulin levels though sweetpotatoes, greens etc don't spike insulin either.
I have done a number of "water Only" fasts. First time for 14 days and
second time for 12 days. Energy levels go through the roof. Strength is
increased and mind is very clear! Growth hormone increases (strength
gain) and defective cells are naturally destroyed including cancer
cells, also insulin sensitivity is increased and potential reversal of
Type 1 & 2 Diabetes.
If you (we) can get past a lifetime of habitual eating and stop being a
clock controlled Pavlovs Dog, after 24 hours the hunger subsides. Water
is genuinely all you need.
I haven't managed a full 21 days yet as for me the 14 day point is where
mind and physical functioning starts to degrade but 10 days is a breeze.
Sorry for the overly long answer to a very simple question but "3 square
meals a day" is the WORST way of eating but the lifetime of conditioning
(and addiction) is very hard to break.
Simple answer... No, you will try it once and never use it again, and
any references to Bruce Lee are based on Bruce Lee tried everything.
Electro-stimulaters might have assisted muscle recovery from his intense
weight training but they didn't cause muscle growth directly.
Cheers
Pete