I have done old style circuit, not Firm.
I agree with
@Cafelattee --- You have been spot on explaining the difference.
Old style circuit focused on light weight, endless repetition. They did work in terms of burning calories/Loosing weight!
That type of circuit purpose was to work in aerobic zone of 60-70% max as an overall figure confirmed by HR monitor
The type of muscle mainly worked and recruited is slow twitch --- Mainly recruited during long distance running/Marathon.
New style circuit also known as Metabolic is different, the anaerobic zone start from 75-90% max. Professional
athletes push themselves harder
. Fast twitch muscle fiber are recruited, Example sprinting. These are the type of fibers mainly
recruited during muscle building. That said we need to recruit both type, depending on the goal we want to achieve.
should it be for Earn-living purpose, health or purely for aesthetic.
Anaerobic short burst training protocol is the most friendly to muscle building/Anabolism.It does do the job of burning
fat, improving metabolism --- thus Metabolic name, improving cardiovascular ability etc....
That said, the Overall main focus has changed since the old style circuit came out. People are more aware IMO of the fact that it
is much more HARDER to maintain and keep off all those pound/kilos lost during tough strict diet! That is when embracing
anaerobic short burst and anabolism/muscle building makes the difference!
A better metabolism help keeping those layers off in long term!! Patience is the key!!!! There is no shortcut!