I would love others to add to this as I am attempting to make an ambitious thread: document the history and advancement of training methods for middle and long distance running. I will begin the thread with my own basic attempt to mark large changes in training or define a decade's training style. Please add in! My knowledge, as you will see is somewhat limited but I believe this thread can draw from the knowledge lurking on the boards to fill in gaps and provide counter-methods to the ones I will highlight.
Pre-1900s: Pedestrian training. An area I know least of all, the true olden days of training. I do have some impression of training from reading a book on the history of the 4 minute mile and this book details an old pedestrian training routine that involves lots of walking, drinking beer, and eating steak.
1930s: Interval Training. The first real training innovation as I see it: intervals. The first notable example of high level interval training for middle distance running I find is Woldemar Gerschler when coaching Rudolf Harbig to world records in the 400 and 800, as well as a number of fantastic times for the era. Gerschler continued to be a prominent coach into the post-war years with athletes like Gordon Pirie and Roger Moens.
Post-war (1940s-1950s): Igloi and Stampfl. Siginificant enough for me to distinguish them from the general innovation of interval training because of their success. Both coaches were, of course, floating around the 4 minute mile barrier with their programs guiding Bannister and Tabori under the barrier. Both coaches would also continue their guidance beyond my listed timeframe and Igloi's influence particularly will be felt much throughout the later history. His terminology is also interesting to me, defining things like arm-carriage and stride to dictate the efforts in training.
Counterpoint: Percy Cerutty. Stampfl's rival and someone who I needed to mention but couldn't fit well. Cerutty's stotan philosophy goes beyond just the methods of training but is a whole lifestyle that produced the marvelous running of Herb Elliott. While interval training can be seen as mechanical and finely controlled, Cerutty took athletes through the dunes of Portsea and stressed the importance of whole body training to become a fuller athlete (both mind and body).
1960s: Lydiard. The great man and another huge innovator. While I am sure there were others advocating for high mileage before him, Lydiard's prominence with Peter Snell brought this idea to wider attention. He also, of course, influenced the likes of Bill Bowerman with the idea of "jogging" and created a running boom that would truly bloom in the later decade.
1970s: Jack Daniels. Exercise physiologist and someone closely aligned with great athletes like Jim Ryun, Daniels took the data he had accumulated on VO2 Max and developed his VDOT system. This defined a range of paces from easy to race that were based on hard data like heart rate to give a more holistic approach to what I believe were largely effort-based regulations in training before.
1980s: This is an era I am not sure how to define with a major training philosophy. Everything I have seen from top runners of the era has varied considerably, sometimes even varied between reports on athletes. I would almost call this era the era of the divide: quality vs quantity. I think this is best exemplified by Coe vs Ovett, as Coe's father famously preached for quality and explosive sessions in the gym while I have heard Ovett was a regular of 100 mile weeks. I know reports on Coe's training differ so this is an era I would love to hear more about!
1990s: Drugs. I am again not sure there is a singular training philosophy guiding top runners in this era but I think the influence of drugs at this time could not be ignored. The workouts reported from this time are often staggering to read and the proliferation of EPO with minimal to no testing can't be understated.
2000s: The internet age. As I write this, I am noticing that subsequent decades become harder to define cleanly but I can focus on other areas of innovation. For the 2000s, it is surely the advent of widely available internet access allowing training to be shared and training plans to be devised beyond just pen and paper. This informs other training trends as well, as things like the minimalist running movement would not have reached its massive reach in the running world if it hadn't been for internet discussion and dissemination of information. This feels especially relevant posting on the boards.
2010s: Elite training groups and post-race workouts. This is going to be more based on personal experience but I remember this was the era when the prominent training groups (NOP, Bowerman, OTC) really came to fore of world running and seemed to be more the major indentifier rather than a training philosophy. I will give special mention to Alberto's infamous post-race workouts that were heavily featured on FloTrack videos and seemed to be a staple for a brief moment.
2020s: Double threshold. The easiest recent decade to define, I don't think I've ever seen a training philosophy take off so much as double threshold has recently. While its practice isn't entirely new and has been incorporated into training long before now, its wide adoption has been a recent trend. I think the lactate testing is also something I am not aware of being widely used before recent times but now I see a lot of pros taking their rest intervals to prick their ears and check their mmol reading.
Again, please feel free to add, argue, or redefine my comments!