Run Slow to Run Fast; When It Helps and When It Doesn’t

“Run slow to run fast” has become one of the most popular phrases in running. Alongside ideas like Zone 2 training, it’s often presented as the missing piece that will unlock better performance, faster race times, and fewer injuries. While the concept in genuinely useful, it’s also commonly misunderstood. Taken without context, it can leave runners slowing down too much, overthinking every run, and sometimes just… running slow to, well, run slow…

A big part of this comes from the rise of GPS watches, heart rate data, and running content online. Easy running has finally had its moment in the spotlight, which is a good thing. Plenty of runners do train too hard, too often. The problem is that simplified advice doesn’t always tell the full story. Not everyone needs the same approach, and what works well for one person can hold another back.

At its simplest, “run slow to run fast” just means that easy runs should actually feel easy. The idea comes from the polarised training model, which is well researched and widely used in endurance sports. It’s often explained using the 80/20 rule: roughly 80% of your running is done at an easy intensity, with the remaining 20% made up of harder work like intervals, tempos, or progression runs.

Easy running is what builds your aerobic system. This is your body’s ability to take in oxygen and deliver it to working muscles. Over time, this improves efficiency and strengthens your endurance “engine”. Through easy running, you develop more mitochondria, which means you can produce more energy with less effort. Easy running also improves how well you use fat as a fuel source, helping preserve glycogen (your limited card stores) for harder sessions and longer efforts.

Keeping most runs easy also makes recovery possible, and recovery is where your fitness actually improves. When intensity is managed well, you’re less likely to break down, get sick, or burn out. Overtraining isn’t always caused by running too much, it often comes from doing too much intensity too often, without enough easy running to balance it out.

Here’s the part that often gets missed: this advice assumes a certain level of training volume and consistency. “Run slow to run fast” generally works best for runners training four to five days per week (or more) and running relatively high milage for their level. It also assumes you’ve already built a solid aerobic base and need to preserve energy for quality sessions. At that point, running hard most days simply isn’t sustainable.

For beginners, that context often disappears.

If you’re only running two or three times per week, you already have plenty of recovery days built in. Add to that the internet’s obsessions with heart rate zones, and many beginners become afraid they’re running too fast. The issue is that many new runners haven’t yet build the aerobic base needed to comfortable run in zone 2. For them, zone 2 might mean jogging painfully slowly, or even walking, which can lead to frustration and the feeling that fitness just isn’t improving.

In those early stages, the “run slow to run fast” mantra often needs to be parked.

The main goal isn’t recovering from hard workouts, it’s simply getting your body used to running in the first place. At this point, running a little faster can actually be beneficial, as long as you’re recovering well. That doesn’t mean every run should be an all-out or painful effort, but it does mean you don’t need to be scared of moderate effort if you’re training a couple times per week and bouncing back fine.

For beginners, consistency matters more than anything else. Gradually increasing volume over time, staying healthy, and avoiding injury will do far more for long-term progress than hitting perfect paces or heart rate zones. Early on, learning what effort feels like is far more valuable than starting at numbers on a watch.

As fitness improves, easy pace naturally starts to get quicker. Pace calculators based on race results can be useful reference points, but they don’t account for fatigue, stress, or life outside of running. During heaver training periods, easy runs may need to slow down. Weather, terrain, sleep, nutrition, and stress all affect how easy a run feels on any given day.

This is why perceived effort is often the simplest and most reliable guide. On a scale of 1 to 10, easy running should generally feel like a 3-4: relaxed, controlled, and sustainable. You should feel like you could keep going without having to dig deep.

When easy runs start creeping too fast, training drifts into what’s often called the “grey zone”. This is where runs are too hard to allow proper recovery, but not hard enough to drive meaningful adaptation. Over time, that middle ground can lead to fatigue, injury, illness, plateaus, and burnout.

Zone 2 is often described as roughly 60-70% of max heart rate, but heart rate zones are only useful if they’re set correctly. Many watches rely on generic formulas, and wrist-based sensors can be inaccurate. For most runners, especially beginners, it’s far more useful to base easy pace on perceived effort. If heart rate data is being used, an external chest straps or arm bands are usually more reliable. Even then, heart rate should support decision-making, not override how the run actually feels.

“Run slow to run fast” is a valuable principle, but it’s not a one-size-fits-all rule. For higher milage runners, easy running is essential for recovery, aerobic development, and long-term progress. For beginners, the priority is consistency, gradual progression and learning how different efforts actually feel. The key is understanding where you are in your running journey, and applying the advice in a way that genuinely helps your training, rather than holding you back.