I grew up playing soccer. Every practice was hard. “No pain, no gain,” and all of that. By tenth grade, I was burned out and quit.
I started rock climbing. Every day at the crag was about pushing your limits. This was before indoor gyms or any concept of training other than doing as many pull ups as possible. I plateaued, got frustrated, and quit.
Then I had a go at running. I read some books, but skipped the training methodology parts and cherry picked the workouts. Every run was hard. Every interval was done to exhaustion. I plateaued, got frustrated, and quit.
Then I got into cycling. I began to hear of “easy” rides. I knew pros who rode around for four or five hours at such a pedestrian pace that they were talking the whole time. ‘How insanely boring!’ I thought. ‘Where’s the fun in that?’ So I went hard every time because it’s more fun. And guess what? I plateaued, got frustrated, and quit.
Fortunately, I didn’t learn my lessons the really hard way – through injury – but I still learned them the really stupid way – by throwing away any potential I might have had.
You can’t go hard all of the time. It’s as simple as that (at least on paper).
The Basics of Polarized Training
Make your easy days easy and your hard days hard.
That is the backbone of a Polarized Training model. I had no problem making my hard days hard–they were all hard days after all. Full gas. Gun to tape. But in hindsight, I realize how depleted and chronically fatigued I was. I thought that was the desired effect, but it meant my training became less and less productive.
It’s the easy days that are actually the hard part.
First: I hear your inner dialogue. “Who wants to go easy? It’s unproductive. It’s a waste of precious time. It looks lame on Strava.” But the science says everyone should want to go easy. Metabolic efficiency is the name of the game.
If hard workouts train the engine to create more horsepower, then the easy sessions improve the gas mileage.
Secondly: let’s define easy. Training intensity is commonly split into five zones. (Some systems use three and others use seven, but I’ll be referring to a five zone system.) Zones 1, and especially 2, define the ranges of easy. Heart rate is the typical metric, especially for cross country skiers and runners, while cyclists typically use power.
Identifying Your Easy Zones
The theoretically simple method for establishing heart rate zones is to work backwards from your maximum heart rate where each zone represents a percentage of the max. The challenge is that there’s very little agreement on how to best calculate one’s max heart rate without actually experiencing it.
A more accurate method is to undergo a lactate threshold test, where heart rate zones are calculated based on the amount of lactate measured in the bloodstream. More accurate, but more difficult to conduct, and not universally accessible.
So how can we determine what is easy and what is too hard?
In an effort to keep easy easy, I’m going to define it as conversational pace. You should be able to talk in complete sentences without having to… pause… to take in… more air… to finish your sentence. This is mediocre science and not especially objective, but with some practice, it’s not difficult to find that upper limit of talkability.
If you’re a numbers person, you can likely conduct your own ramp test where – after a warm up period – you progressively increase speed/effort while reciting poetry or singing along to what’s in your AirPods. Mark the heart rate where you lose the rhythm, and that’s a decent estimate of your upper limit for Zone 2.
Your new goal on easy days will be to keep your heart rate below this threshold, not necessarily at this level. For those accustomed to pushing the pace on every session, slowing down enough to keep your heart rate in the appropriate zones might feel like a big adjustment. There’s no real way around it – you’ll need to buy in, and trust the process/science. Maybe use it as an excuse to get out with a training buddy who is generally slower than you and give the whole “pedestrian pace, talking the whole time” thing a go.
Worst comes to worst, you give it an honest try and decide you prefer to just go hammer, then go back to your old ways. That’s the beauty of being a recreational athlete – at the end of the day, we’re just pursuing hobbies we find rewarding and enjoyable.
* A note for Strava users: don’t rely too much on the Relative Effort number. As a metric of intensity over time, it seems optimized to capture long, hard efforts like an hour-long tempo run where your heart rate stays high for the entire hour. It doesn’t handle intervals very well since the rest periods sort of cancel out the high intensity efforts.
For example, Strava gave 60 points to a 55 minute tempo run with an average heart rate of 158; however, an 57 minute interval session (9x600m on the track) with an average heart rate of 147 only got 35 points. To me, both sessions were equally hard, but the tempo run scored 25 points higher.
Strava does allow you to use your perceived exertion in place of heart rate for calculating Relative Effort. When I enabled this override, the tempo run scored an 87 while the track workout got a 147. (My easy efforts aren’t affected much.) Personally, I’ve found the Relative Effort score, along with the weekly log and Fitness and Freshness, far more useful (and accurate?) with this tweak. Here’s a deeper dive into that black hole.
The Purpose of Polarized Training
Now we can talk about why the easy is important.
Stress + rest = growth/adaptation/strength/speed. That is the basic formula. Our bodies are designed to adapt to load, but we have to give ourselves the opportunity to make those adaptations. Too much volume or intensity and the body will stop absorbing. Not enough recovery and the body will stop adapting. Best case, your performance plateaus. Worst case, you get injured.
The Krebs Cycle. The stuff of High School nightmares. But the essence of the endurance athlete. The Krebs Cycle is the pathway by which our bodies put gas in the tank. It is the process by which our mitochondria – magical little intracellular thingies – convert carbohydrates, fats, and proteins into the specific energy required by muscles to contract. In oversimplified terms, the more efficient the mitochondria are, the faster and longer we can go. And it appears that the best way to train mitochondrial efficiency is with training in Zone 2. (If you want to seriously nerd out, this podcast with Dr Iñigo San Millán, perhaps the Father of Zone 2, is a deep dive in a submarine to depths of the ocean.)
The easy/Zone 2 is considered so important that it typically makes up 70-80% of elite athletes’ training volume. The other 20-30% is hard (high Zone 3, Zone 4, and rarely into Zone 5). For the athlete who doesn’t have all day, every day to train, that means you only get a couple of hard sessions per week. Keep the rest easy.
Some that’s hard, lots that’s easy – that’s the essence of putting Polarized Training into practice.
Example Training Plan Template
| Monday | Easy short or Rest if needed |
| Tuesday | Hard long |
| Wednesday | Strength/core maintenance |
| Thursday | Hard short (intervals) |
| Friday | Easy short or Rest if needed |
| Saturday | Easy long OR Hard long AND Sunday is Easy |
| Sunday | AM: Hard short (intervals) + PM strength/core maintenance |
My training template is based on my work schedule and typical life obligations. I’ve given myself a max of three hard sessions a week with one of them longer (2-3 hrs ride or mountain run–the fun stuff!) and the others around an hour of intervals. My strength/core maintenance sessions typically fall into the easy category and don’t require much recovery (no delayed onset muscle soreness). But my schedule is also very flexible. If I’m tired, I can move a hard session to another day or skip it that week. If I get too busy or stressed, then I can modify the program without too much frustration.
I’m fortunate that I can train/play seven days a week, as long as I’m recovering adequately. However if your schedule only allows for training three days a week, you can still apply the basic formula and have one hard day and two easy days.
For some of you, this may be common sense and describe how you’ve been training for years. For others, this is quite a departure from your norm and will take a concerted effort to implement. But whether your goal is optimal performance or staying healthy for years to come, investing in a polarized plan, and especially leaning into the Zone 2 work, will pay dividends.
Lastly, I think any discussion about training principles/plans needs to have the overriding theme of ‘push yourself, but be kind to yourself’.
Be flexible. Training plans aren’t written in stone. Don’t beat yourself up if work, family, weather, fatigue, or lack of motivation keeps you from your intended workout. Take a walk, play with the kids, lie down on the sofa—whatever it takes to reset and be ready for another day. One workout will not make or break, but constant self-criticism will sink the ship.
