Hassan Chahdi, 8th in Boston, 2:09:46, just behind Kipchoge hates running long runs and hates double days and keeps his training mostly to around 80 km per week most of the year which is around 50 miles per week with quality. If he has to do a double day he prefers getting on the bicycle. This guy might be an anomaly as a world-class runner. I think Coach J.S. from Sweden would love coaching this guy. Minimalist.
For marathons, Hassan’s build up of around 120 km per week, for about 10 weeks, which is 75 miles per week. On those occasions he does 2 double days. He hates running long and prefers to do a good solid 20 km which is 12 miles progressive run. Specificity is the key for this lightweight.
Most of his long runs don’t go further than 20 km which is 12 miles. It’s all about quality and specificity. He probably does only half or less mileage compared to the famous Frenchman Nic Navarro, 2:06 mini monster.
Disclaimer: my source includes numerous articles about this runner over the years and if things have changed recently then I will update you.