For someone aged 18-35 yrs +5ys/-3yrs the answer is yes their bodies could possibly handle the workloads required to make it to 100 miles in 9-10 weeks. Most good to elite distance runners do doubles throughout the week, but not everyday. Out of shape morons like me don't do doubles but instead like to mix tempo and easy in a continuous run followed by some intervals.Â
remember the median age for this is about 27yrs of age to do this.
Here is an example for a 40 mile/week person to start on a 9-10 week base building phase of what I would setup for someone.
Monday 1.5 miles AM hard, 4 miles PM easy
Tuesday 5 miles AM easy, 1.5 miles PM hard
Wednesday 4 miles easy AM, race specific workout of 3x1k or 2x1 mile, etc.. in PM with 2 mile warmup and cooldown
Thursday 6 miles easy PM
Friday 2 mile @ 5k tempo AM, 6 miles easy PM
Saturday 5 mile fartlek PM
Sunday - some form of active rest
then add 1 mile each week to each easy run, .25 miles to each hard run every other week and slowly increase race specific work to 10K pace @ 10k worth of distance or to 10K tempo and you get 100 miles a week in 9-10 weeks. Basically that person is increasing their training time by 30-40 minutes per week. It's not easy, but it is not exactly impossible for the serious 800m and above runner to do.
I like to build through the week in a progression on mileage with wed being my peak performance day of the week, then start to wind it down a bit with Friday being a rebound test day and let the body start recovering for the next wednesday. For someone who is in the military I would alter the training a bit, to make mileage heavier on weekends, while I was in the USMC and training at 80-100 miles per week for marathons it was easier to do back to back days of 6-8, 12 and 15 or 6-8, 10 and 18 with a tempo run mixed in on friday PM, saturday, and sunday and veg out afterwards when in garrison. I personally tended to overtrain if I stacked the weekdays with to high a workload, because I would plan on not resting on the weekends when I should have been and those long mileage days were always followed by a couple of beers in my barracks room playing tecmo football, before falling asleep. I went thru a lot of trial and error to make myself a succesful distance runner for a period of 2 years and it never panned out the way I wanted to. Mainly because I thought at 19-20 yrs old I could make myself into a succesful marathoner at that age and for that age I wasn't bad, but I needed about 5-6 more years of mileage to know for sure, the answer was probably doubtful. I am certain I would have broken 3 hrs if I stuck to it, but another runner/coach showed me the light after my 2nd unsuccesful attempt at a marathon and were my true talents lied and that my friends is another story.