Was reading a book that referenced this, so posting for discussion.
Human Performance Laboratory, Ball State University, Muncie, IN.
NSCA Conference Abstract (2000)
It showed that adding isolated weight training exercises to compound movements added nothing.
The researchers compared the effects of a weight training program on 5RM strength and arm circumference and divided the subjects into two groups. Group 1 performed four compound upper body exercises, while Group 2 used the same program but included biceps curls and triceps extensions.
The results showed that both groups significantly increased strength and arm size
However, the addition of direct arm training to group two produced no additional effect on strength or arm circumference after 10 weeks of training.
The additional localized training did not result in anything that the bigger compound exercises didn't provide.
Let me present a hypothetical example:
Twin brothers eating the same diet, working at the same job. Three times a week for the next 52 weeks, both brothers undertake a progressive resistance-training program, each adding weight, sets, or reps in a logical manner over the whole year. One difference: the first brother does deadlifts only. The second brother does arm curls only.