Let’s assume that you have been training for at least a couple of months, building your frequency up to an appropriate level. At that point in your training, it’s time to start changing duration in order to increase your fitness.
Frequency was easy to change; all you had to do was add a workout here and there. Duration is slightly more complicated, because it does not apply across every single workout. To be more precise: at this phase in your training, you will hold frequency steady, but start increasing the duration of 1-2 workouts per week. Your other workouts will remain as they were.
As a distance runner, one of your staple workouts is going to be a long run. Many runners do these long runs on a weekly basis, primarily because weekends work best. When designing the ideal workout regimen, I would probably advocate for a long run about once every 10 days, but since most of us have day jobs, that’s just not practical.
Creating your long run involves adding time, but not intensity, to one of your workouts per week. There is no set mathematical model for this, of course, but start by adding 5-10 minutes to one of your weekend runs each week for a month. If that’s too much, just back off a little. One other word of caution about long runs: you can’t build up duration infinitely. I recommend building up for 3 consecutive weeks, then dropping back down for a week before resuming the buildup. The duration of a long run for non-marathoners will build up until it's about 1:30 or 1:40 in length; marathoners will go longer, at least 2:00 and maybe up to 3:30. When I’ve finished all of these posts on training, I’ll create a sort of template workout plan that will illustrate all of the principles I've been writing about.
That takes care of the weekend long run, but it’s also a good idea to begin extending the duration of one of your weekly runs (logically, a mid-week run). Here you aren’t targeting the same duration as the weekend, but you want to gradually work your way up to a run of at least one hour (or up to 90 minutes if you are training for peak performance). Again, this should be accomplished gradually … try adding 5 minutes per week until you reach 60 minutes, then stay at that duration for at least three weeks before building up again.
Remember, at the core of endurance training is your body’s adaptation to stress. You adapt to stress when you rest, so make sure that you are recovering completely following each workout. If not, rest awhile. Be patient. How can you tell if you are not recovering completely? Several signs to look for:
- A sensation of "heavy legs" or "floppy legs"
- Afternoon sleepiness
- Weight loss or unusual weight fluctuations
- Dreading the next workout
- Loss of sexual drive or loss of motivation for things that normally excite you
- Breathing unusually heavily during low-intensity workouts
- Heart rate won’t go up during exercise, or a long lag before it does
- Muscle twitches or cramps during the day or night
- Unable to fall asleep, but then unable to wake up in the morning
If you have more than one of the "symptoms" described above, then you need rest, not workouts. Skip a day or two, and go to bed early each night. As soon as you feel refreshed and eager to get back at it, do so. If any of these symptoms drag on for more than a couple of weeks, I recommend you speak to your doctor about them.
Remember, during this phase you hold frequency steady and always keep intensity set at "low". Duration is built up over about 2-3 months, ideally (shorter if you are young and/or generally fit, longer if you are the opposite).
(On a personal note: I am still not running due to piriformis syndrome. I’ve now been off for almost 4 months, making this one of the longest layoffs of my 31 year running career. I am in biweekly sessions of physical therapy, and will see the doctor again in about 3 weeks. At this point, I’ve written off 2009 as a bad running year, and now just want to get back to some kind of running, ANY kind of running! I’m doing the recommended exercises daily, and trying to be patient. If there is a lesson to be learned through all of this, it is to see the big picture and to take care of the little things that will help me heal and then help keep me uninjured when I finally start running again.)