People always talks about slowing down your recovery runs so that you can run more mileage and be better rested for the harder workouts. My question is: say, your normal "recovery day" in between tuesday and thursday interval workouts is 12 in the morning and 6 at night. This adds up to 16 miles of running, and, at one's usual pace, 2 hrs of running. You decide that you want to follow the aforementioned advice by slowing down your easy day pace and increasing the miles. So you slow down to an 8 minute pace and run 14-16 in the morning in about 1hr50 to 2hrs and then another 6 in the evening in about 48-50 minutes. So, my question is, when does slowing down the pace prove detrimental because you're out there on your feet for so much longer? The nearly 2hr run is upping the mileage, but, even with the slower pace is still kicking your ass too much to perform well in harder workouts on tuesday and thursday. is there some sort of cut-off for time on easy days?