Surprise! wrote:
I never understood this "you have to run this much in singles before starting to double"
If you want to be your best, run twice a day. Don't overthink it.
The idea is this:
If you're running 14 times per week (daily doubles) and only hitting 30 mpw - then you are not benefiting from the actual doubles in any traditional sense. You're better off running 7 times per week (singles) in terms of traditional aerobic development.
The same general logic likely applies to many weekly mileages: perhaps all of them under 40 mpw, probably most of them from 40-60 mpw, and maybe even some from 60-80 mpw.
30 mpw in 7 runs = 4.3 mi per run
30 mpw in 14 runs = 2.15 mi per run
40 mpw in 7 runs = 5.7 mi per run
40 mpw in 14 runs = 2.85 mi per run
60 mpw in 7 runs = 8.6 mi per run
60 mpw in 14 runs = 4.3 mi per run
80 mpw in 7 runs = 11.4 mi per run
80 mpw in 14 runs = 5.7 mi per run
Of course every person is different, it depends on what the individual's goals are, and no one is splitting their weekly mileage evenly amongst their runs as I indicated in the math above. But the point is still valid.