Let’s put things in perspective here.
You are talking to natural pros who probably have an extensive client list with results to back them up.
In fact, a survey was cited in the introduction of the study:
“A recent survey of 127 competitive male bodybuilders found that more than two-thirds of respondents trained each muscle group only once per week (9). Moreover, none of the respondents trained a muscle group more than twice weekly and every respondent reported employing a split-body routine (9).”
But we’re looking at a study on:
“Subjects were 20 male volunteers (height = 1.76 ± 0.05 m; body mass = 78.0 ± 10.7 kg; age = 23.5 ± 2.9 years) recruited from a university population. This sample size was justified by a priori power analysis based on previous work from our lab using vastus lateralis thickness as the outcome measure with a target effect size difference of 0.6, alpha of 0.05 and power of 0.80. Subjects were well-trained; all had been resistance training a minimum of 3 days-per-week for at least 1 year, with a mean lifting experience of 4.5 ± 3.1 years. Moreover, all subjects regularly performed the barbell back squat and bench press exercises for at least 1 year prior to entering the study.”
Doing this split:
And even the author concedes one of the limitations was:
“…the novelty factor of changing programs may have unduly influenced results. During pre-study interviews, 16 of the 19 subjects reported training with a split routine on a regular basis. Although the topic has not been well studied, there is some evidence to indicate that muscular adaptations are enhanced when program variables are altered outside of traditional norms (12).”
Seriously, it’s not like no one has ever gotten big before and all our information on this subject thus far has been derived from animal models or in vitro studies.
Stuff like this normally goes into my “Who Gives a Flying Fuck” list for a good reason.