Running Twice Per Day
Only the most serious runners habitually run more than seven times per week, which necessarily entails a certain amount of doubling, or running twice a day. Personally, I think more runners should consider it, as some magical things can happen when you push your running volume beyond the amount you can practically squeeze into one run a day.
There’s a simple rule that runners can use to decide whether or not they should double: If you plan to consistently run more than 70 miles per week, double at least once or twice a week. The rationale behind this rule is that every runner’s training schedule must include some easy runs, and if you try to pack more than 70 miles into just six or seven runs each week, none of those runs can be very easy. You can double if you want to on a schedule of fewer than 70 miles per week, but it only really becomes necessary when you run more.
As you continue to add mileage to your weekly schedule, continue to add doubles as necessary to keep your average run distance from creeping above 10 miles. So, for example, if you run 100 miles a week you should run at least 10 times.
Ease into doubling by inserting one or two very short, easy runs into your schedule. Gradually increase the distance of these runs and add more doubles until you reach your weekly mileage target, but keep the pace easy in all of these extra runs. Never try to perform two hard runs in a single day.
Some runners do an easy run in the morning and a longer and/or faster run in the evening. Others do the opposite. It’s a matter of personal preference.