Fred Hatfield's book, Hardcore Bodybuilding: A scientific Approach, described what he called an integrated training protocol.
Basically, integrated training deals with training intensities, specificity of movement, and customized rest intervals all with regard to specific and isolated muscle groups/muscle types.
Instead of a customary split where one works a specific routine every so many days, integrated training takes into account isolated muscles on the smallest scale. Daily routines are always changing - you may have worked quads and biceps on Monday. Assuming biceps will recover quickly and quads less quickly, by Wednesday integrated training may have you working biceps again, but you may not work quads until Friday. (These are just illustrations, I cannot quote advised rest intervals.) In addition, integrated training utilized periodization of intensities with each workout for a given muscle.
The idea is to assure full recovery between subsequent workouts for a given muscle, while attempting to eliminate wasted time between workouts.