A lot of talk about the marathon in this thread at the moment, which makes sense, but I will add my two cents about the other end of the intensity distribution. I ran a disappointing 3:31 marathon in mid-March, then took the next two months pretty easy, training in the spirit of this thread but with 600km total across all of March, April, and May (so including the end of the marathon block and the marathon itself). Started being really consistent in mid-May, so this is the 12th week of me really training like this, weekly mileage slowly ramping up from 53km to 70km, nothing crazy but really consistent (haven't taken a day off in 50 days). I ran a 19:57 parkrun on a pretty good if not amazing course on the 7th of June and then stalled out, messaged sirpoc recently to ask him what he thought since all the parkruns since then were in the 20-low range with no real signs of improvement (or so I thought). He encouraged me to stick with it, and so I did.
Four days ago I jumped into a local mile road relay and ran a 5:28, which is a 19 second PB. Apart from two sessions I did with my old running club for old times' sake (10th June - 13x370m @ 3:39/km avg, 15th July - 11x370m @ 3:36/km avg), and the aforementioned parkruns (5 in total since that 19:57), all my training was slower than 4:10/km for the fastest reps, and as slow as 4:40-4:50/km for the 10 minute reps depending on the conditions, and I raced at 3:24/km while feeling unaccountably amazing throughout. My easy runs are even more comically slow, I never go faster than 6:00/km and often shuffle around at close to 7:00/km. I did do strides here and there, though, cos my turnover sucks, and I also do strength training once or twice a week, and I played football a few times, so it's not 100% strict NSA, but it's still pretty amazing to me that on unspectacular mileage and pretty much no X-factor training whatsoever I could go that fast over that short a distance. I've been running for 8 years, as well, so these aren't really newbie gains.