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Arnold was always been known for chest development and if you look at his right upper chest(1975 B&W Mr. Olympia photo below) you can see a strong separation between the clavicular portion of the pectoralis major and the sternal rest-of-the-pecs. Even so, prior to 1980, Schwarzenegger didn’t seem to train his upper(clavicular) pecs as much as the lower(sternal) portions, as evidenced by his massive lower pec development. If you look at the picture below of Frank Zane you can see that the upper an outer portions of his pecs are more developed and the lower portion gets lost in shadow. Zane purposely concentrated on the upper and outer portions of the chest to create a strong delt/pec tie-in which makes the chest appear more angular and broader. Regular flat bench presses create more rounded pecs like you see on Arnold, Sergio Oliva, and Lou Ferrigno. However, for the 1980 Mr Olympia, Arnold seemed to concentrate more on upper pecs. If you look at the picture of Schwarzenegger/Mentzer(directly below) or further below in the 1980 color photograph, you will notice that Arnold’s pec/delt tie-ins were super strong and even though he still had a massive lower chest, he wasn’t as lower chest dominant as in the past.