If you’re a runner, cyclist, or triathlete, chances are you’ve heard the term “junk miles” thrown around in training conversations. It’s one of those phrases that seems to mean different things to different people, and it can leave you wondering whether you’re doing yourself a favour or just wasting your time. Let’s break it down…

What Are Junk Miles?

Junk miles refer to those miles in your training that don’t have a specific purpose. They’re the ones you rack up without really thinking about what they’re doing for your overall fitness. Often, junk miles are done at a moderate pace—too fast to be easy, yet too slow to significantly improve speed or strength.

In essence, junk miles are the miles that don’t contribute directly to your training goals. They’re not part of a speed session, a long run, or a recovery ride. They’re just…there.

When Junk Miles Can Be Good

Despite their name, junk miles aren’t all bad. In fact, there are times when they can actually be beneficial:

Building Fitness: When you’re in the early stages of a training plan, just getting miles in can help build a solid aerobic base. These miles might not be at a specific intensity, but they help your body get used to regular exercise.
Mental Breaks: Not every workout needs to be laser-focused on improvement. Sometimes, a run or ride without an agenda can be a mental reset. It’s a chance to enjoy the sport without worrying about times, distances, or goals.
Social Time or Just Having Fun: Training doesn’t always have to be serious. Junk miles can be a great way to catch up with friends who might not be on the same training plan as you. These miles might not push your limits, but they can contribute to your overall enjoyment of the sport.

Why Junk Miles Can Be Bad

On the flip side, junk miles can become a problem if they start to dominate your training. Here’s why:

Increased Risk of Injury: Unfocused training can lead to overuse injuries, especially if you’re adding miles without considering their impact on your body. Running or cycling extra miles when your body needs rest can cause strain and injury.
Reduced Quality of Key Workouts: Junk miles can tire you out, making it harder to give your best effort in the workouts that really matter. If you’re fatigued from too many easy miles for example, your speed sessions or long rides might suffer.
Lack of Progress: If your training is full of junk miles, you might not see the progress you’re aiming for. Without targeted sessions focused on speed, endurance, or strength, your fitness levels can plateau.
Burnout: Training without a purpose can lead to mental burnout. If every session feels the same and you’re not seeing improvement, it’s easy to lose motivation. Junk miles can make your training feel monotonous and leave you questioning why you’re even putting in the effort.

The Verdict: To Junk or Not to Junk?

Like many things in life, the key to junk miles is moderation. A few here and there won’t derail your training, and they can even be beneficial in certain contexts. However, if your training is becoming a never-ending string of junk miles, it might be time to reassess.

The best approach is to have a clear purpose for each workout. Whether you’re building endurance, working on speed, or taking it easy to recover, knowing why you’re doing what you’re doing is crucial. This way, you can avoid the pitfalls of junk miles and make every session count.

Cited Papers on Why Junk Miles Don’t Work

Bosch, A. N., & Noakes, T. D. (2006). “Scientific evidence for the effects of endurance training on performance at various intensities.” Sports Medicine, 36(9), 795-809.
Laursen, P. B., & Jenkins, D. G. (2002). “The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes.” Sports Medicine, 32(1), 53-73.
Seiler, S., & Tønnessen, E. (2009). “Intervals, thresholds, and long slow distance: the role of intensity and duration in endurance training.” Sports Science, 27(1), 45-53.
Foster, C., et al. (2001). “A new approach to monitoring exercise training.” Journal of Strength and Conditioning Research, 15(1), 109-115.
Neal, C. M., et al. (2013). “Effect of high-intensity interval training on markers of aerobic and anaerobic capacity in competitive cyclists.” Journal of Sports Science, 31(1), 1-9.

These papers outline how targeted, purposeful training leads to better outcomes compared to unfocused, moderate-intensity exercise. They make it clear that while junk miles might have their place, they shouldn’t be the backbone of your training plan.