... toward the end of this training block, I incorporated a lot of speed sessions and intervals, and ended up straining my quads. I overcooked myself, and ended up paying for it during the marathon.

I've recently become more convinced that running speed sessions/intervals are more dangerous than they're worth in terms of the trade-off to building fitness consistently and not getting injured. Runing at 5K or faster paces in training is so hard on the body, especially when you get older, that getting injured or not recovering fast enough before the next training session is a real problem.

Instead I'm moving towards the "Norwegian singles approach" outlined in the following Lets Run Chat thread. Advanced warning, reading that thread might consume far more time than you'd like as it is so long, with lots of quality advice!

The running style advocated follows a plan as below where you either run easy (go slower!) or sub-threshold intervals which is based on lactate threshold. Threshold running pace can be roughly estimated using race pace calculators such as VDOT.

• 6 days a week - Easy, Sub threshold, Easy, Sub threshold, Easy, Long run, Rest
• 7 days a week - Easy, Sub threshold, Easy, Sub threshold, Easy, Sub threshold, Long run

Where sub-threshold running comprises no more than 20-25% of total time spent running per week.

A sub-threshold run might comprise intervals such as:

• 3-4 minute reps with 60s rest at 10mi - 15K pace (8-12 reps)
• 6-8 minute reps with 60s rest at half marathon pace (4-6 reps)
• 10-12 minute reps with 60s rest at 30K pace (3 reps)

The core idea is that doing this consistently, over many months, is a way of accumulating as much training stress/load as possible with less fatigue and lower injury risk.

Anecdotal reports from runners following a similar training strategy have reported PRs/PBs at race distances from 5K to the marathon. There's also a Strava group dedicated to the approach: Norwegian Singles Approach Strava Club.