The first thing to realize is that the idea of “muscle confusion” isn’t based on science. It has been proposed as a plausible explanation for possibly unreliable results reported in some studies, but it’s not really an accepted concept. The phrase was coined by George Hackenschmidt, who described his system for training multiple muscle groups at once during each rep of an exercise—a technique known as “muscle splitting.” Hackenschmidt believed this potentially confusing arrangement could help improve muscular development and prevent injury. However, the idea has fallen out of favor because researchers have suggested that other factors may be more responsible for inconsistencies in results seen in various studies. One potential culprit is the basic design or setup of many studies used to test hypotheses about muscle growth. For example, in most situations where there is a control group and an experimental group (as with a study comparing compound vs isolation exercises), all subjects perform both types of exercise through the same exact protocols and relative intensities. If these variables are controlled carefully enough, they can minimize differences between groups that might otherwise appear due to chance; however, such controls are generally unavailable in most current research projects due to practical reasons (such as shortage of time). There aren’t well-designed scientific studies looking specifically at whether varying splits/rep ranges etc can actually influence gains beyond what occurs naturally over time.