The 80/20 rule: Balancing easy and hard runs for maximum results
When it comes to training, more intensity doesn’t necessarily mean better results. In fact, running too hard all the time might be holding you back.
If you’ve ever plateaued despite increasing your efforts, or if you’ve struggled with persistent fatigue or injuries, it’s time to re-evaluate your training balance. One of the most powerful and well-researched methods for endurance athletes is the 80/20 rule: running at low intensity 80% of the time and at moderate to high intensity for the remaining 20%.
It sounds simple, but it can transform your training.
What is the 80/20 rule?
The 80/20 rule, also known as polarised training, means that around 80% of your weekly training should be at a low aerobic intensity. The remaining 20% can consist of harder sessions such as tempo runs, intervals, or races.
This approach is used by elite endurance athletes in a variety of sports. Yet it is just as effective for everyday runners, especially those training for longer distances such as half marathons and marathons.
Although the principle was popularised by coach and author Matt Fitzgerald, it is rooted in decades of sports science. The magic of the 80/20 rule lies in achieving the right balance between stress and recovery. Easy running builds endurance and aerobic capacity. Hard workouts develop speed, strength, and efficiency. But if the ratio leans too heavily towards “hard”, the body doesn't have enough time or energy to adapt.
Note: It’s less about sticking rigidly to an exact 80/20 split and more about the principle: most runs should be easy, so your harder sessions feel sharper and recovery comes quicker. For new or low-volume runners, the ratio can be too rigid - at that stage, almost any consistent training brings progress. But as you build fitness and increase mileage, the 80/20 approach becomes increasingly more valuable.
Why getting the balance right makes all the difference
Many runners start with great intentions, but their training isn’t always optimally balanced. It’s easy to think, “I’m not aiming for the Olympics, so shouldn’t I be pushing myself more often?” But actually, that mindset can hold you back.
Here’s what often happens:
Easy runs are run too fast because you want to feel productive or match your 'watch pace'.
Conversely, hard runs aren’t hard enough because you’re carrying fatigue from all those medium-effort days.
The result? You spend most of your time in the grey zone, working harder than necessary but not hard enough to improve.
This 'moderate every day' approach leads to stagnation, stress, and injury. The irony? Slowing down often helps you speed up.
Note: Moderate runs can play a role in a well-structured training plan, as long as you keep in mind that they add more hard effort than a typical easy run.
What counts as easy or hard?
Easy running
Conversational pace
Relaxed breathing
60-75% of max HR
Feels manageable even on tired legs
Effort 3-4 out of 10
Examples: base runs, recovery runs, long runs (if run in zones 1-2)
Hard running
Noticeably elevated breathing
80-100% of max HR
Shorter in duration, focused on quality
Effort 6-10 out of 10
Examples: intervals, hill repeats, tempo runs, races
Note: “Hard” doesn’t have to mean all-out sprinting. It means a structured, purposeful effort where your body is pushed beyond its comfort zone for a reason. And in an easy run, brief harder segments or tougher conditions can make the overall effort score feel higher.
How KULG helps you get the balance right
Understanding the 80/20 rule is one thing. Applying it to your own training is a whole different challenge. That’s where most runners need help. And that’s exactly where KULG comes in.
KULG provides a clear visual breakdown of your training intensity over time. You can:
Filter your runs by run type (easy, tempo, interval, race, fartlek, long, etc)
See weekly, monthly, quarterly or annual breakdown of effort
Track the high-intensity distance and see its proportion compared to easy runs
Identify when you’re tipping too far into the “hard” zone with the help of insights
Reflect on whether your training load supports your goals
This helps you to shift your focus from chasing daily pace metrics to seeing the bigger picture. Am I training smartly, recovering well, and making consistent progress?
Here’s a simple cheat sheet on how to categorise easy and harder runs in KULG:
Tips for applying the 80/20 rule
Start by slowing down your easy runs. If you can't hold a conversation, you're running too fast.
Don’t try to squeeze in intensity on every run. Let workouts be workouts and recovery be recovery.
Don’t stress about perfection. It's OK if some weeks aren't split 80/20 exactly. Aim for trends, not absolutes.
Use a tool like KULG App to track patterns and make small adjustments over time.
Remember that your body gets stronger when it’s given both a challenge and time to recover. Most gains come from consistency, not heroic efforts.
Train smarter, not harder
The 80/20 rule may feel counterintuitive, especially in a world that celebrates hustle and speed. But for endurance athletes, it’s not laziness, but a smart training strategy.
It’s how you build the foundation to go farther and faster while staying healthy.
Want to see if your training is balanced? Try KULG free and start training with perspective.
