While this book consists of quite a bit of broscience, one should still give credit where credit is due. Arnold is a man with a naturally lanky bone structure who managed to create an extremely aesthethic physique, and beyond that one needs to realize that strength training and bodybuilding are areas where proven experience is superior to "exercise science", because these studies very often have faults.
Here are some main takeaways:
1) Training frequency. I imagined that Arnold, godfather of the gymbros, would advocate for a low-frequency brosplit, but contrary to that he instead advocates for a high frequency approach, hitting the major muscle groups three times a week, and abdominals every training session.
2) Training intensity. In a similar fashion, I thought that just a normal three sets of ten reps would be stipulated in his programs, but instead the calls for a norm of four sets of twelve to six reps with short rest in isolation exercises. Meaning that you can progress the weight as long as you hit within that rep range in each set, with short rest between sets. This is accordance with the idea that full muscle recruitment is caused either by A) having a weight close to your 1RM, or B) getting close to muscular failure. He also advocates for having heavy days in your training programme, hitting maxes on your compound lifts. This means that the distance for a synthesis in training philosophy between Arnold's bodybuilding and powerlifting isn't what certain /fit/ posters would have you believe.
3) Exercise selection. The norm in his training are large compound movements. While he isn't locked onto the idea that one needs to specifically progress the three powerlifts, he still emphasizes that the natural movements patterns (the vertical push, the horizontal pull, etc) should always be done, but that the specific exercises are according to the trainees' needs. With him being a bodybuilder, this also entails that the priority of certain movements is also subordinate to aesthethic ambitions. Thus if one has a lacking upper chest, the incline bench press takes priority to the flat bench press and dips.
4) Psychology. He puts emphasis on motivation through passion and visualization, the importance of a good training partner (often referencing Franco), and not least of all a good gym to train in. Gyms are after all something we have inherited from Ancient Greece, and it is of tremendous weight that there is a good athmosphere in the gym. It is hard to describe the motivational pain of after having trained for years in a fantastic powerlifting gym, to move to a new city and be forced to train in a sterile gym, filled with fatsos, demented old people and young women who seemingly have dressed up for a porn shoot rather than for a workout.
Of course, he also deals with posing, contest preparation and nutrition, but that is all specific to the competitor in bodybuilding and not so much the strength training enthusiast, therefore I will not comment on this.