Go Slow to Go Fast: The 80/20 Proof

Here's the toughest workout I'll ever ask you to do: slow down.

From the hockey rink and the ski hill to ultra trails and triathlons, I've spent my life as an athlete. Today I coach athletes across Canada, Europe and the US. The most common thing I fix isn't a lack of effort. It's too much effort, in the wrong places.

Where 80/20 Comes From

Dr. Stephen Seiler, an American-born exercise physiologist based at the University of Agder in Norway, spent decades studying how the world's best endurance athletes actually train. That's fitting research to come out of a nation famous for its endurance athletes. Rowers, cross-country skiers, cyclists and runners all showed the same pattern. About 80% of their training time was at low intensity, and about 20% was at moderate to high intensity. 80/20 Endurance built its entire training system on this research. As a certified 80/20 coach, I use it as the foundation of every plan I build for you.

The Data Keeps Agreeing

A recent analysis of 120,000 runners on Strava asked what best predicts marathon performance. The answer wasn't how hard people pushed. It was how much easy running they did each week. Controlled research with recreational runners points the same way: athletes who train closer to an 80/20 split improve more than those who spend their time at moderate effort.

What Easy Training Actually Builds

Easy miles are not junk miles. While the pace feels relaxed, your physiology is doing serious work:

Your mitochondria and capillaries multiply, so your muscles get better at using oxygen and fat. (Remember January's mitochondria issue? This is where it happens.)

Your plasma volume and stroke volume increase, so your cardiovascular system delivers more oxygen with every heartbeat.

Your tendons, ligaments and bones adapt to load at a pace they can actually keep up with.

Your autonomic nervous system recovers between sessions, so you arrive at your hard days ready to hit them.

The Grey Zone Trap

Here's where most athletes get stuck. The easy run creeps up to "comfortably hard," landing in 80/20 Zone 3 or Zone X, the moderate band between your first and second ventilatory thresholds. It feels productive. However, that effort is too hard to recover from quickly and too easy to drive real high-end adaptation. Stack enough of it and you get the classic pattern: always tired, performance stalls, and small aches turn into injuries. Your easy days get too hard, so your hard days end up too easy.

How to Find Your Easy

Stay in 80/20 Zones 1 and 2, below your first ventilatory threshold. Here's how to guide it, in order of priority:

Power: the most direct measure of the work you're doing, and it responds instantly to hills and wind.

Pace: reliable on flat ground. Expect it to slow on climbs, in heat and on rough terrain, and let it.

Heart rate: this is your vital sign. It lags behind effort, so it isn't what you steer by. However, it's never ignored. If your heart rate runs higher than normal at your usual easy power or pace, your body is flagging heat, dehydration, fatigue, stress or an oncoming illness. Listen to it.

Then, at the end of every session, rate your overall effort on a 0 to 10 scale. Rate the whole session, not just the last rep. Easy days should land around 2 to 3. This habit builds the internal awareness you need to train and race by feel, so you're not dependent on a device when a battery dies or race day gets messy.

One more rule: count your 80/20 by time, not by workouts. A 60-minute interval session with a warmup and cooldown may hold only 20 minutes of true intensity.

Why Now

With race season wrapping up for most of you, fall is the perfect time to reset. Pull up your last four weeks of training and look at your time in each zone. If your easy days are drifting into the grey zone, this is your window to rebuild the aerobic base that carries you through next season.

Slow down. Build deep.