One of the strangest and most confusing terms in the lexicon of distance running is “junk miles.” Despite the connotations of the word “junk,” this term is not always used as a negative designation. But often it is. That’s what’s so confusing about it.
When used neutrally, “junk miles” refers to all of the moderate-pace running that a runner does over the course of a week to reach a certain total mileage target. In this usage, the only running that is not junk mileage is the higher-intensity stuff (tempo runs, hill repeats, track intervals) the runner does once or twice a week and perhaps also the endurance-building weekend long run. When used negatively, “junk miles” refers to wasteful extra running that a runner may do in excess of what is needed to develop peak fitness.
Runners who use the term “junk miles” tend to subscribe to the high-mileage philosophy of training. They believe that a high training volume is the most important characteristic of an effective training program. “The more miles you run, the better”—within reason—is their motto. By contrast, runners who use the term “junk miles” negatively typically subscribe to a quality-over-quantity philosophy. They believe that fast-paced running should be the first priority in training, and that the point of diminishing returns in mileage is reached much sooner than high-volume advocates believe it is.
So who’s right? Science offers no clear answer. On the one hand, studies that have looked at various training variables in groups of runners competing in the same race and compared these variables against their finishing times have found that weekly running mileage is usually the best predictor of performance. In other words, those who run the most tend to achieve the lowest finishing times in races.
On the other hand, numerous prospective studies have shown that runners can achieve large improvements in performance without increasing their mileage by replacing some of their slow running with faster running. For example, in a 1998 Dutch study, 36 recreational runners were divided into three groups. One group performed only moderate-intensity running. A second group did an equal amount of running in the form of long, high-intensity intervals. A third group did an equal amount of running in the form of short sprints. The researchers found that VO2max and running speed at VO2max increased the most in the long intervals group.
Evidence from the real world also does not clearly favor either the quality-first or the quantity-first philosophy. In his book, Run Faster from the 5K to the Marathon, elite coach Brad Hudson observes that runners representing both philosophies have found the highest level of success. For example, in the late 1970s and early 1980s Alberto Salazar leveraged a very high-mileage training program (routinely exceeding 150 miles per week) to win the New York City Marathon three times and the Boston Marathon once. Then, in the mid-1980s, Steve Jones of Wales used a comparatively low-mileage (80 miles per week), high-intensity training program to set a new marathon world record.
Hudson himself advocates a balanced approach where mileage and faster running are given equal weight. He recommends that runners do two challenging high-intensity runs each week (typically a threshold run and an interval run). These workouts are your highest-priority of the week, which means you must be relatively rested for these workouts so you can perform well. This requires that you avoid running so much on the other days that you are left depleted for your “quality” days. But because mileage is equally important, Hudson believes that you should run as much as you can on these other days without hampering your performance in your quality workouts.
Finding this balance requires a little experimentation. And the right balance is different for individual runners. Even among runners of the same ability level, some can handle more mileage than others, and some thrive on a level of high-intensity training that breaks others down. Let personal experience settle the quality vs. quantity question for you, however you may choose to define “junk miles.”