Most runners are stuck in a weird kind of "purgatory" without even realizing it. They go out for a jog, get their heart rate up to that point where they can’t quite hold a full conversation but aren't exactly sprinting, and they stay there for forty-five minutes. This is what we call running at a medium pace. It feels productive. You're sweating, your lungs are working, and your fitness tracker says you burned a decent chunk of calories. But here is the kicker: staying in that middle zone is often the biggest reason people stop seeing progress.
It's tempting. Honestly, the medium pace feels like the "right" amount of effort for a workout. You aren't lazy, but you aren't dying. However, sports scientists like Stephen Seiler have spent years looking at how elite athletes actually train, and it turns out they almost never spend time in that middle ground. They follow something called polarized training. They go very, very slow, or they go incredibly fast. The middle is a "no man’s land" that generates a lot of fatigue without providing the specific physiological adaptations of the extremes.
The Physiology of the "Grey Zone"
When you decide to run at a medium pace, you’re typically hovering in Zone 3. In a five-zone heart rate model, Zone 3 is that awkward space between 70% and 80% of your maximum heart rate. It’s too fast to be a recovery run. It’s too slow to be a true threshold workout.
Why does this matter? Well, your body has different systems for energy.
When you run easy (Zone 1 or 2), you're teaching your body to burn fat efficiently and building out your capillary network. This is the "aerobic base" everyone talks about. When you run at a medium pace, you start recruiting more fast-twitch muscle fibers, but you aren't actually pushing them hard enough to make them more powerful. You end up in a state of "accumulated fatigue." You're tired the next day, so you can't go fast when you actually need to. This is how plateaus are born.
Dr. Seiler’s research famously showed that world-class endurance athletes—skiers, cyclists, runners—do about 80% of their training at a very low intensity. They only spend about 20% of their time at high intensity. The "medium" stuff? It's almost non-existent in their schedules because it doesn't offer a high enough return on investment for the recovery cost it demands.
Is It Ever Useful?
Look, I’m not saying you should never run at a medium pace. There’s a specific time for it, usually called "tempo" or "steady-state" runs. These are great for building mental toughness and getting used to the specific rhythm of a half-marathon or marathon.
But for the average person hitting the pavement three times a week? Doing every single run at that same "kinda hard" speed is a recipe for injury and burnout. You’re putting significant stress on your joints and tendons without giving them the low-impact aerobic work they need to strengthen.
How to Break the Cycle
The hardest part about fixing this isn't the physical effort. It's the ego.
Running slow feels embarrassing. You might see your pace on your watch and think, "I’m barely moving," or worry about what people think when they pass you on the trail. But that slow work is what allows your heart to grow larger and your mitochondria to become more numerous. If you want to get faster, you have to be willing to look slow.
- The Talk Test is your best friend. If you can't speak in full, rambling sentences while running, you've drifted into that medium pace. Pull back. Even if it feels like a fast walk.
- Monitor your recovery. If you wake up every morning with "heavy legs," you're likely spending too much time in the grey zone.
- Polarize your week. If you run three days a week, make two of them painfully slow. Make the third one a workout where you actually push your limits with intervals or hills.
The Science of Efficiency
Let’s talk about the heart. At lower intensities, the heart actually has more time to fill with blood between beats. This stretches the heart walls slightly, which over time increases your stroke volume—the amount of blood pumped per beat. When you push to a medium pace, the heart beats faster, and that filling time decreases. You lose that specific "stretching" benefit.
Essentially, by trying harder, you’re missing out on a specific type of cardiac remodeling that only happens when you’re relaxed. It sounds counterintuitive, but it's basic biology.
Most people who find themselves consistently running at a medium pace are also the ones who struggle with nagging injuries like shin splints or runner's knee. Because you're always "somewhat" tired, your form starts to break down. You stop lifting your feet properly. Your cadence drops. You start overstriding. Those little mechanical errors, repeated thousands of times at a moderate intensity, add up to a physical breakdown.
Actionable Steps for Better Training
To stop the "purgatory" of the medium pace, you need a plan that forces you out of your comfort zone—both the high and the low.
First, determine your true easy pace. For most people, this is about 90 seconds to 2 minutes per mile slower than their 5K race pace. It will feel ridiculously slow at first. Embrace it. Use this for the bulk of your miles.
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Second, schedule one "hard" day. This isn't just "running a bit faster." This is intervals. Maybe it's 400-meter repeats on a track or 3-minute hard efforts with 2 minutes of walking in between. The goal is to get your heart rate up into Zone 4 or 5, where you're actually challenging your VO2 max.
Third, pay attention to your "resting" heart rate. If it starts to climb over several weeks, you’re overtraining in that medium zone.
By separating your efforts, you allow your body to actually recover. You’ll find that when it’s time to go fast, you actually have the "pop" in your legs to do it. You won't just be grinding out miles; you'll be training your systems.
Stop settling for the middle. It’s the least effective place to be. Slow down your easy days so you can actually fly on your fast days. That’s how you actually get better.