The 80% rule in running—often called 80/20 running or polarized training—is a proven training approach used by many successful runners.

In simple terms:

Around 80% of your runs should be easy, and only 20% should be hard.

For runners using a Garmin watch, this rule is especially practical because intensity can be measured clearly using heart rate zones and post-run metrics.

What Does "80% Easy, 20% Hard" Mean on a Garmin Watch?

Easy Running (≈80%)

On a Garmin device, easy runs typically fall into:

Heart Rate Zone 2 (sometimes low Zone 3, depending on setup)
Comfortable, controlled effort
Able to hold a full conversation

These runs make up the bulk of your weekly distance and include recovery runs and most long runs.

Hard Running (≈20%)

Hard runs usually appear as time spent in:

Zone 4 and Zone 5
Intervals, tempo runs, hill repeats
Races or race-pace workouts

Garmin post-run summaries often make this split obvious by showing how much time was spent in each heart rate zone.

Where Did the 80/20 Running Rule Come From?

The 80% rule is strongly associated with research by Stephen Seiler, who studied elite endurance athletes across multiple sports.

His research found that top-performing athletes consistently:

Accumulated most training time at low intensity
Limited high-intensity work to a small portion of total volume

This pattern appeared regardless of event distance or sport.

Why the 80% Rule Works So Well for Garmin Runners

Builds Aerobic Fitness (What Garmin Calls "Base")

Easy Zone 2 running improves:

Aerobic efficiency
Fat utilisation
Endurance durability

Over time, Garmin metrics like Aerobic Training Effect and Training Status tend to stabilise and improve when most running stays easy.

Reduces Injury and Overtraining Risk

Garmin users often notice that running too hard too often leads to:

Consistently high Training Load
Poor recovery scores
Declining performance

Following the 80% rule helps balance load and recovery, allowing more consistent training.

Makes Hard Sessions Count

When easy runs are truly easy, hard workouts produce clearer benefits. This often shows up in Garmin data as:

Higher anaerobic training effect on workout days
Better recovery times
Improved race-day performance

A Common Garmin-Specific Mistake

Many runners see pace targets or personal records on their watch and unintentionally:

Push easy runs into Zone 3
Accumulate "moderate" effort day after day

This middle zone can feel productive but often leads to fatigue without meaningful gains. The 80% rule helps keep easy days easy—and hard days purposeful.

Is the 80% Rule Good for Beginner Garmin Runners?

Yes—especially for beginners.

Garmin users new to running benefit from:

Clear heart rate feedback
Better pacing discipline
Reduced injury risk

If most of your runs stay in Zone 2, fitness will improve even if the pace feels slow at first.

Does the 80% Rule Need to Be Exact?

No. Think of it as a long-term average, not a daily rule.

Some weeks may skew:

75% easy / 25% hard
85% easy / 15% hard

What matters is that, over time, the majority of your training remains low intensity.

How to Apply the 80% Rule Using Garmin Data

Keep most runs in Heart Rate Zone 2
Limit hard workouts to one or two sessions per week
Review weekly heart rate zone distribution
Watch trends in Training Load and Recovery, not single runs

Garmin makes it easy to spot when intensity creeps too high—use that feedback to slow down, not push harder.

Key Takeaway: 80/20 Running With Garmin

The 80% rule in running isn't about holding back. It's about using intensity strategically.

For Garmin runners, keeping most runs easy and limiting hard efforts helps:

Build aerobic fitness
Stay healthy
Train consistently
Improve race performance over time

Sources & Further Reading

Seiler, S. (2010). What Is Best Practice for Training Intensity Distribution in Endurance Athletes?
80/20 Running – Matt Fitzgerald
Runner's World – Easy running, heart rate zones, and endurance research
Outside Online – Polarized training and aerobic development