I’m experimenting with twice-a-day running. My main purpose in running twice a day on some days rather than once is to raise my overall mileage, but I’m convinced there are merits of running twice a day, even if the overall mileage is the same.
Some coaches and physiologists believe that running twice a day will make you a "stronger" runner, while running the same distance once a day carries purely aerobic benefits not gotten in a pair of shorter runs. They feel that distributing a given number of miles among more runs reduces the likelihood of injuries, since most running injuries befall runners toward the end of their runs.
The marathon training plan I’m following suggests several optional recovery runs of 20-60 minutes as a second workout 3-4 times a week. I’m beginning cautiously, so I've added a pair of easy three-mile runs for a few weeks, then I’ll progress to three of them, building on the length and frequency as much as my time and energy allow.
I ran twice on Monday and Thursday this week. As the training plan suggested, I did each of these runs as a second workout. What I found was that in each of these runs, I felt like the earlier running in the day had somehow primed me to perform better, and I had to force myself to maintain “recovery” pace. This has left me wondering if I shouldn’t try running the easy three-milers in the morning, followed by a harder workout at the end of the day. In fact, this is what I will try.