arnold worked very much from anecdotally correlating what he did to what he saw in results and thruogh what limited info they had at the time..
so when he did more work at less intensity but more volume he noticed he got leaner- this is purely just because he was burning more energy and not working much outside of the aerobic zone..
of course he was right, but it wasnt really any secret as athletes had been doing this for years and it certainly wasnt anything to do with the specific rep scheme or actual workload..so in that respect his association of the cause and effect was incorrect...it wasnt the higher reps and more sets that caused it directly..it was the time spent doing more activity in the fat burning zone- 60-80% of max heart rate.
he couldve achieved the same if hed stuck to heavy, low rep sets and long rests and then did some cardio on the side.
