Wikipedia article about power rack mentions a long article by Peary Rader in IronMan magazine popularizing the use of power rack. I tried to find the article online with not success. I decided to find it and bought IronMan magazine vol. 23, no. 6 from 1964 on eBay. About a week later it was delivered to my mailbox. I will retell you its content with some comments so as not to violate copyright of the IronMan magazine, which still exists today.
The article is called “Power Rack Training For Maximum Muscular Development”.
Peary Rader says that the magazine mentioned the power rack 10-15 and even twenty years prior to this article, which is right post WW2 period. It was not always called the power rack, but was essentially the same tool. The limited motion range exercises were criticized to make one muscle bound, which was proven not to be the case. Rader was optimistic about the use of power rack for muscle development.
When the magazine found the effectiveness of isometric training one of the readers of the magazine Frank Spellman made an accidental discovery. While working on isometric program with heavy weights on a wooden rack broke partitions between holes on the posts . This way the slots were created and Frank can up with an idea to load a barbell and make short movements within created slots. Frank soon realized that training with the limited motion range was the best he ever tried and made a great progress performing this training. That was the end of the isometric training for Frank.
Many weightlifters followed the system invented by Frank and it was announced the system of the year by the IronMan magazine. They called these exercises Isometronic as a combination of isometric and isotonic – movement and pulling against immovable resistance.
Many athletes who followed Frank’s program gained muscle mass rapidly, and they were able to keep their weight gain to muscles by following healthy lean diet. One of the prominent followers of power rack regimen who achieved remarkable results was Norbert Shemansky. After a few years of power rack workouts his weight went up from 200 to 265 lbs with the height of 5’11”.
Another follower of isometronic training was Lou Riecke, who was originally an isometric athlete but realized the benefits of limited movement exercises and won a physique title, even though he primarily trained for lifting.