Botox® is Botulinum toxin. It works by temporarily paralyzing the muscles that it is injected into. It is made into precise units. It takes 3 to 7 days to become effective. It works for about 4 months.
While the muscle is inactive it loses bulk (becomes atrophic). When it recovers it gets its bulk back and gets strong again. If you add Botox® before it recovers the muscle never has a chance to bulk up again. It will continue to lose bulk and eventually will find it more difficult to recover. So, after repeated treatments it seems logical that Botox® may be able to weaken the muscle for longer and be more effective.