Thanks for the message and I'm happy to help. Are you from Portsmouth? I've since moved to Dorset, but am still relatively local! Coming from a long course triathlon background and having trained 'a lot' to get to 5 x Kona qualifications, I was coming into this with a background of a lot of volume (aiming for ~1,000 TSS a week).
I turned 40 last year and, with work, family, life commitments, decided to try and run some decent masters times—as running takes a lot less time than triathlon if you want to be competitive. Prior to 2025 I would typically be in the boom or bust cycle of battling niggles and not being as consistent as I'd like.
I've ran PBs at all distances from the mile to the marathon this past year, following a version of the NSM, but I have doubled plenty of easy days and also tend to increase the easy volume to ensure the balance of easy is appropriate as I scale towards the marathon. Peak week was 90 miles.
For context, I ran a 2:37 in 2017 at London Marathon prior to carbon plated shoes. I used a plan by Steve Way. It worked well, but the two big days a week and aims of 100 mpw were much more risky. I was also 32 at the time and now 8 years on, to have run 2:34 at Valencia and 2:32 at Seville, shows the training is working, as whilst the shoes are undoubtedly worth a minute or two, I'm battling age and will be 41 this year. I feel the trend will continue as I'm aiming to run 2:29 or faster this year at London or Berlin.
I use Intervals.icu and hit a fitness score of 78 before Valencia and 76 before Seville, but have seen a gradual improvement in my threshold pace. I haven't really done any speedwork outside of strides before sessions and the odd race for a hard VO2 stimulus.
I think the consistent load and spreading the load is the key. I never felt totally fried in the build up and certainly didn't need a 3 week taper. I would have no concerns training like this for another marathon and just gradually adding a little more load here and there to nudge up the fitness to another level.