Every run should have a purpose. Most experienced runners will describe to you the transformational moment in their training, when they learned to run their easy days easy and their hard days hard. The transition from junk miles – purposeless, always-moderate training – to polarized training allowed them to fully benefit from their runs. Junk miles are not “bad” but they are not optimal for performance.
The exact definition of junk mileage varies based on the coaching philosophy. Some view any run other than a quality session or long run as junk mileage; others believe no run is a junk run. Others view easy runs ran too hard or runs without a purpose as junk mileage. In my coaching philosophy, I adopt the latter view and believe that runs should have a purpose. However, I do believe that “junk miles” is too negative of a term; you still get some general benefits from a junk mileage run, even though you hinder long-term growth and risk injury. Ultimately, even a junk mile run is still a run.
How do you know if you are running junk miles? These criteria may illuminate some areas where you can improve your running – and see the full benefits of polarized running.
Are You Padding Mileage for the Sake of Mileage?
Increasing training volume benefits almost all runners; however, every runner has a point of diminishing returns. It may be 35 miles per week, 50 miles, or 75; and it will vary throughout an athlete’s career. Some athletes even get slower with high-mileage training and thrive off low-volume, high-intensity training or cross-training.
For most runners, an easy run will have diminishing returns after 75 minutes. Past 90-minutes, a run becomes a long run – with drastically different physiological effects and recovery timelines. Padding on mileage each day can change the physiological purpose of run. Furthermore, if you are running so far every day that you feel exhausted, irritable, or flat on your runs, you are likely junking out your miles and losing the benefits that come from stress, rest, and adaptation.
You may think “elite runners run 14 miles a day or 100 miles a week!” An elite typically splits their daily mileage into two runs, such as 8-10 miles in the morning and 3-4 miles in the afternoon. Training time matters also; this typically consists of a 60-75 minute run in the morning and a 30 minute run in the afternoon.
Doubles may sound like junk miles to some. However, a 60-minute morning run and a 30-minute evening run can be more beneficial than a 90-minute morning run. You accumulate less fatigue and glycogen depletion, so the two runs remain truly easy.
Are You Running in the Appropriate Training Intensity?
Surprisingly, during race training, junk miles often occur when your pace is moderate. Many runners fall into a pattern of running slightly too hard on their easy days – and therefore cannot push hard enough on their quality workout days. Every run becomes virtually the same. They see some improvements before plateauing. Polarized training – varying the intensity of your runs with easy days and quality hard workouts – produces sustainable growth and real results.
First, learn to slow down on your easy days (here’s how). Once your easy runs are truly easy, start pushing yourself more on your hard workouts.
A recent race or time trial can provide an accurate assessment of your fitness. Using that time, you can use a calculator (typically the McMillan or Jack Daniels VDOT) to calculate your training paces. Perceived exertion (if you are honest with yourself), breathing rate, and heart rate all serve as other gauges of intensity.
It is worth emphasizing that not all moderate-intensity runs are junk miles. When done deliberately, aerobic threshold runs are a fantastic (and often under-rated) quality session for half marathons, marathoners, and ultra runners. Deliberate is the key; these should be treated as quality sessions, including being preceded and followed by easy runs or recovery days.
Does Your Run Have a Purpose?
If you cannot name a specific purpose for a run, then you may be running junk miles. In a well-developed training plan, each run has a purpose. Easy runs are comfortable enough that they stimulate the aerobic system without accumulating fatigue.
I would argue that miles become junk miles when you push too hard for the intended purpose of the workout. Faster workouts are not better workouts. If you run too fast, you stress different energy systems. Oftentimes, that makes the workout too stressful (since volume and intensity are deliberately manipulated aspects of a workout) and hinders adaptation.
Let’s look at the example of a particular workout: cruise intervals. The prescribed workout is 8 x 800m at 10K pace, with a 1.5 minutes recovery jog. Instead of running at 10K pace – which will feel fast yet controlled for that duration – the runner pushes as hard as possible for each interval. The short recovery does not permit enough recovery for that high intensity, so one begins to flag and crashes by the end of the workout. You negate some of the desired adaptation and may increase your risk of overtraining.
Another example of purposeful runs comes in context of event-specific preparation. What may qualify as junk miles for even a marathon will not be the case for a 100-mile ultra runner, who needs to run through high levels of fatigue.
Finally, variety is a purpose. Imagine eating chicken, broccoli, and rice for every meal. It’s healthy enough, but you lack some key nutrients and it would become very boring very quick. If you ran the exact same 5-mile route each day, the same thing happens to your running. Sometimes, the purpose of a run can simply be to run a bit further or a bit less, even if it is still at an easy effort.
Recovery Runs are NOT Junk Miles
Many critics of high mileage training dismiss recovery runs as junk miles. In reality, they are quite the opposite. Recovery runs are purposefully very slow, often done the day after a quality session or long run. You cannot go too slow on recovery runs. If anything, running too fast negates their purpose.
Your Runs are Only as Good as Your Recovery
If you are running so much that you are unable to recover from your workouts, you may be running junk miles. Adaptation comes from a result from recovery from the stress of training. No recovery, no adaptation.
As mentioned above, mileage for the sake of mileage can lead to junk miles. If this is your situation, then honestly assess your training plan. Are you taking a rest day each week? How much time are you training each day? Is there day to day variation in both volume and intensity?
Know Your Why & Be Aware of Exercise Bulimia
What is your motivation for running that mileage? Performance, stress relief, and enjoyment are all worthy motivators. Be cautious, though, when disordered eating (fear of gaining weight, needing to “work off” what you ate, etc) drives you to run more.
A rising phenomenon in runners is exercise bulimia or binge exercising/compulsive exercise. Binge exercisers will run high mileage in order to stay thin and burn off calories from any “bad foods.” Many running and health professionals now consider exercise bulimia to be a type of eating disorder. It’s a fine line between high mileage for the good reasons of building an aerobic base and training for a long-distance race and high mileage for the sole sake of burning calories, so exercise bulimia cannot be generalized and must be diagnosed on an individual basis. One runner’s healthy high mileage can be higher than another runner’s binge exercising mileage, so a definitive marker cannot be set: some runners thrive on 80+ miles per week, while other runners can exhibit compulsive/binge behaviors on significantly lower mileage.
Burning extra calories does not count as a particular purpose related to training. Junk miles occur when you run an excessive amount of miles with very little training purpose: not base building, not a marathon PR, not an ultra marathon. In this case, junk miles should be the least of your concern in the face of overtraining, female athlete triad, stress fractures, and other serious issues. If you are worried that you suffer from exercise bulimia, please contact a sports medicine doctor or other health professional to help you, as this may be indicative of a health problem or mental health issue beyond the scope of your running coach.
(Please note that while I am a certified running coach, I am not your running coach, so I don’t know exactly what works best for you individually.)
Exceptions Always Exist:
Sometimes, running is about so much more than exercise and training. If you’ve just come off of a crappy day of work; if you want to run with a friend, family member, or pet; or you’re getting hit hard by the blues and need that boost which only running can offer, then these runs most certainly have a purpose. Sometimes you need to blow off some steam in the way that only running can provide. Running provides a huge social connection also, which can matter more than an exact training purpose.
How do you define junk miles?
Has polarizing your training led to improvement?