Arthur was doing what he called "Effort" runs in the 1950's, publishing his "Tables of Effort" in 1962.
Without getting all controversial I believe that he was probably the first. However, he had various levels of effort (possibly the controversial part and hardest to get your head around)
EG : If your 3 mile best was 15 minutes then he had your 3/4 effort at 15:30, 1/2 effort at 16mins,1/4 effort at 16:20.
Note these efforts were not "3/4" pace but an 'effort' or if you wanted to break it down a 'pace' to run at.
The idea was they were to be a 'steady' effort similar to what many of you now know as a "Tempo run" (I like those terms)
My own experience goes back over 35 years ago when I ran my first "effort' runs or "Timetrials" as they were also known with Bill Baillie. He decided we would do our 5k runs in 16:30 (I forget his reasoning). We ran them on a grass track at a very even pace and Bill would control that pace all the way.If you picked up the pace you were scolded if you started to lag you were encouraged. After 2 or 3 of these Time trails you found it was easy to maintain an even pace.
Some years later I would do the same thing as a student in the USA. I would run 6 mile 1/4 "efforts" in 36 minutes then work my way down to 35 minutes. All very "comfortable" but "working". That year I ran 4 miles in 19:20.
Once again as I have said on numerous occasions. What Arthur wrote down on paper was purely a guide. It was never intended to be the 'scripture' you were to run each workout by. You find or your Coach helps by finding what suits you.
Hope that explains the concept somewhat. Nobby, Glenn, HRE you may want to comment here.