How do you train for a race? If you're like many endurance athletes, you set a mileage goal at the beginning of the week, divide that total by the number of days you plan to run, then try to complete those miles in as little time as possible.
Despite your dedication, this strategy won't help you run faster. If your goal is to bring down your average per-mile pace, follow one of the most important rules in long-distance running: avoid junk miles.
Here's what they are and how you can cut them out of your training program.
What Are Junk Miles and What Aren't?
Junk miles are the ones you run that don't produce a specific physiological benefit.
It could be argued that tempo runs—middle-distance training runs at a "comfortably hard" pace—are junk miles. However, most good training plans only include a tempo run every 10 to 14 days, as a "check in" to see whether you're on track for race day. These runs can also be valuable for mental conditioning, since they require both discipline and patience to complete. A training calendar filled with these types of runs will not produce the results you're looking for.
Slow miles, run at a conversational pace, have the physiological benefit of building your aerobic base and training your body to favor fat as a fuel source over glycogen. These are not junk miles. Hard miles, run near, at or above the acidosis threshold, have the physiological benefit of pushing that threshold up a bit higher, meaning you'll be able to run faster for longer.
These, along with hill runs, speed intervals and form drills aren't junk miles either. Junk miles are less about the way you run, and more about when and how often you do it.
Improper Training Translates to Junk Miles
How many times have you set out for a long run at conversational pace, got bored, and sped up in the middle of it? You finish the miles faster than planned and pat yourself on the back, but what you've really done is sabotaged your training plan. Your body needs those slow miles to make the physiological changes that will help you finish strong on race day.
The same thing goes for hard runs: If you ease up and bring your effort level down, you're reinforcing what your body already knows how to do rather than pushing it to the next level of performance.
Any miles run with poor form are considered junk miles. Logging any amount of these per week teaches your body to run with less-than-optimal form. Cut them out by slowing down to maintain your best form.