Understanding Heart Rate and Effort

The Battery That Powers Your Run

When my colleague Praveen first suggested I should train based on heart rate rather than pace, I dismissed it with the confidence of someone who knew absolutely nothing. Heart rate zones? Training thresholds? It all sounded unnecessarily complicated when running felt so simple: just go out and push yourself as hard as possible every single day. Surely that was how you got faster, stronger, better.

I couldn’t have been more wrong.

The Body’s Battery

Think of your heart rate as your body’s battery indicator. The more controlled it performs, the longer and more efficiently you can run. This wasn’t just theory—it became visceral reality when I finally started paying attention to the numbers on my wrist. Running under the required heart rate kept me more motivated with fewer bouts of crushing fatigue. Those runs where I’d finish feeling destroyed, needing hours to recover? They were almost always runs where I’d let my heart rate spiral out of control.

The breakthrough came when I discovered Dr. Phil Maffetone’s method, a deceptively simple formula that would transform my understanding of aerobic training. Here’s how it works:

Start with 180 and subtract your age. I’m 40, so that gives me 140 beats per minute (BPM) as my baseline maximum aerobic heart rate. But the formula doesn’t stop there—it accounts for your training history and injury patterns.

If you’ve had more than a two-year gap in running due to injuries, subtract another 10 BPM. A gap without injuries? Subtract 5. If you’ve maintained 5-10% of your training during a gap without injuries, your number stays as is. With injuries during that sparse training? Subtract 5. Here’s where it gets interesting: if you’ve maintained 40-60% of your training over the past two years with no injuries, add 5 BPM. If you’ve been consistently training at 80-90% with no injuries, add 10.

Running the calculations on my own training history, my maximum heart rate came out to 155 BPM. My minimum aerobic heart rate—found by subtracting 10 from my baseline—sits at 130 BPM. So for my regular training sessions three to four days per week, I needed to keep my heart rate between 130 and 145 BPM.

The number felt absurdly low at first. Surely running that slowly wouldn’t make me faster?

The Revelation of Running Slow

When I started running, every run was an all-out effort. I believed that improvement came from pushing to your limit every single day. This approach didn’t just fail to improve my running—it made training feel like punishment. Every run left me stressed and in pain. I was stuck, unable to break through to the next level, confused about why harder work wasn’t translating to better performance.

The answer came when I started coaching with Chris Armstrong at Run2PB: it’s all about running slow and varying your training with consistency each week.

Here’s a test that changed everything: if I had to rate my runs from one to ten, with ten being maximum effort, I should be training most days at a five or six. This is what runners call “conversational pace”—you should be able to say a full sentence or even sing a song while running. Not gasping out single words between breaths, but actually maintaining a conversation.

This pace allows you to run with dramatically less fatigue. But achieving it required practice and, more importantly, a mental shift. I was too motivated, my brain refusing to accept that running slower meant training smarter rather than training less hard. The advantage, though, became undeniable: my joints and muscles felt stronger than they ever had when I was constantly redlining my effort.

The proof came in my marathon training. For six months, training on my own with constant high-intensity efforts, I couldn’t run further than 22 kilometers. My heart rate would spike, my body would rebel, and I’d hit a wall. Once I started running slower, building my aerobic base patiently within my target heart rate zones, everything changed. My endurance level built up steadily, injuries that had plagued me minimized or disappeared entirely, and speed—paradoxically—increased over time. Today, a half-marathon has become an easy run, and the full marathon feels achievable rather than insurmountable.

To measure all this, I use a Garmin Fenix 6x watch, whose wrist-based heart rate reading proves surprisingly accurate. For those seeking the most precise readings, the HRM-RUN chest strap syncs with most Garmin watches and provides real-time data that’s accurate to the second. Garmin isn’t your only option—Suunto, Polar, Apple Watch, and other brands offer similar capabilities based on your research and preferences.

For truly precise training effort, some runners use power meters like the STRYD. The distinction is important: a heart rate monitor shows what happened in the past (your heart’s response to effort), while a power meter tells you what’s happening now, at this exact fraction of a second. Running by feel has its place, but running with real-time data helps you make better decisions based on current conditions—your body’s state, the environment, the terrain.

The Fast Versus Slow Paradox

Every runner eventually confronts the same questions: How do I burn more calories? How do I set new personal records? How do I build better endurance? The answers all revolve around two fundamental substances: oxygen and glycogen, the twin pillars supporting the entire running game.

Running demands enormous amounts of oxygen. Building lung capacity reduces oxygen debt on your heart and cardiovascular muscles. When you feel fatigued during a run, that’s oxygen debt talking. The best workout for overcoming it? VO2max intervals that push your body to process oxygen more efficiently.

But oxygen is only half the equation. Fuel matters just as much, and this is where the fast-versus-slow debate becomes fascinating.

Glycogen—stored in your blood, liver, and muscles—provides approximately 20 minutes of running energy. Better glycogen utilization means more efficient running. Sprint athletes like Usain Bolt rely on creatine phosphate, which lasts 5-10 seconds at maximum effort before exhausting completely. That system works brilliantly for sprinting but proves disastrous for endurance running.

Now consider this: each pound of body fat contains 3,500 calories. You can check how many calories you burn during workouts using sports watches and apps, but here’s the crucial insight—it’s harder to burn fat than glycogen. The most effective way to burn fat is through consistent, regular running. Fast or sprint runs create stress and primarily burn glycogen. Long, slow runs enable fat burning by using fat as the primary fuel source at endurance speeds.

Here’s how the physiology works: your heart rate determines blood and oxygen delivery to working muscles. At high heart rates during fast runs, your body uses glycogen as quick fuel. The faster you run, the more fuel you burn, and primarily you’re burning glycogen, not fat. Your body simply can’t access fat stores quickly enough to fuel high-intensity efforts.

Long runs at endurance speed flip this equation. Running slowly causes fat to burn at a slower pace, yes, but it actually burns fat—and burning fat requires both oxygen and glycogen as catalysts. When you perform speed runs, you burn through oxygen and glycogen rapidly, leaving your body fatigued and stressed while fat remains largely untouched. The slow run theory releases oxygen and glycogen to your muscles more gradually, allowing your body to tap into fat stores. This is aerobic training in its truest form.

Looking at my weekend long runs planned by Chris Armstrong, they’re deliberately structured as slow run-walk combinations. This isn’t because I can’t run faster—it’s because running slower with walk breaks allows my body to become a more efficient fat-burning machine while building the aerobic base that paradoxically makes me faster when it counts.

The Whole-Body Transformation

The benefits of understanding and respecting heart rate extend far beyond running performance. Research by Hans and Ron documented how running at appropriate intensities transforms virtually every system in your body.

Your heart-lung system’s oxygen capacity improves dramatically. Your resting heart rate drops as your heart becomes stronger and more efficient—elite endurance athletes often have resting heart rates in the 40s or even 30s. Blood pressure normalizes, and blood vessels become more flexible, reducing cardiovascular disease risk. Your lungs grow stronger, capable of processing more air with each breath.

The muscular adaptations are equally profound. Leg muscles, heart muscles, and respiratory muscles all strengthen through consistent training. Your bones become denser, more resistant to osteoporosis. Joints stay agile and flexible rather than stiffening with age. Energy production in muscles becomes more efficient at the cellular level. You lose weight and become leaner as your body composition shifts. Your metabolism improves, and even bowel movements become more regular.

The disease prevention benefits read like a medical miracle: reduced risk of heart and coronary diseases, diabetes, osteoporosis, stroke, certain cancers including colon, uterus, and breast cancers, lung diseases like bronchitis, emphysema, and asthma, depression, fears, and stress, rheumatoid arthritis, cystic fibrosis, and even gout. Running addresses aging problems at their source and helps manage countless chronic conditions.

But perhaps the most remarkable changes are the ones you feel every day: better sleep quality, increased calmness and relaxation, improved physical performance, feeling younger and fitter, enhanced concentration and brain function with clearer ideas and thoughts, more sustained energy throughout the day, a sense of freedom, increased willpower, greater resistance to stress, and an overall improvement in life quality that extends into every corner of your existence.

The Patient Path

The lesson that took me years to learn can be summarized simply: your heart rate is your guide, your governor, and your teacher. Respect it, understand it, and train within its guidance, and running transforms from a constant battle against your body into a sustainable practice that delivers benefits for a lifetime.

That conversation with Praveen that I initially dismissed? It wasn’t just advice about training—it was an invitation to understand my body as a complex system that responds best to intelligent application of stress and recovery. Once you understand your heart rate and develop methods to control it, running becomes full of fun and motivation rather than fatigue and frustration.

The runner’s heart becomes, as cardiologist Dr. J. Wolffee noted, “a superior and more efficient organ.” But that superiority isn’t built through relentless intensity—it’s built through patient, consistent training at appropriate intensities, allowing your body’s remarkable adaptation mechanisms to work their magic over weeks, months, and years.

The battery that powers your run isn’t infinite, but charge it correctly, and it will carry you further than you ever imagined possible.