I'm making some assumptions, first that the reader is interested in improving his or her speed and performance. Second the reader is not an elite caliber endurance athlete, and finally that the reader probably has limited time available for training. My advice might be substantially for those who do not fit these assumptions.
Another Common Training Error
Following up on my post about the mistake of emphasizing volume over intensity, this post is about the error of running too often, which is closely related to the volume error. Like doing too much volume, running too often interferes with the quality of one's workouts resulting in junk mileage and possibly impeded improvement.
Most people, depending on a number of factors, are capable of between 2 and 4 hard runs per week. I'm defining a hard workout as a run that is intense enough to improve running performance by increasing one's speed, stamina or endurance. In other words, some type of speed work, tempo or long run. In between those hard workouts, most people will require between 24 and 48 hours of recovery before they are ready for another hard workout.
On recovery days, many people still feel obligated to run, and what most people will do is an "easy" run, to help fluff up their numbers. Unfortunately these easy runs do little or nothing to improve fitness or performance. At best, they are harmless and don't interfere with recovery. However, they will usually prevent one from recovering as quickly possible, resulting in less intense hard workouts, or more time between hard workouts. Either way, easy runs may impede progress and improvement.
Then what should I do?
In my experience, most people get better results by not running between hard runs. Generally recovery will be quicker, and so the next meaningful training run can take place sooner. At this point, lot of people will ask, "Do you mean I should just do nothing between hard runs?". Well, probably not, but this will be the subject of my next post on training errors.
CrossFit Endurance - http://www.crossfitendurance.com/