Long-distance running remains wildly popular. In 2024, a survey of just 190 half-marathon races worldwide recorded more than 1.5 million finishers – a staggering 21% increase over the previous year.

All these amateur athletes think they’re getting really healthy as they work themselves up to full marathons.

But what they don’t realize is that those grueling miles are doing more harm to their bodies than good…

And shaving years off their lives.

I’m not exaggerating. It happens every time.

Let me show you what I mean…

A few years ago in London, 31-year-old Army captain David Seath collapsed three miles from the finish line. He died a few hours later.

A couple years before that, two runners — ages 31 and 35 — died during a marathon in Raleigh, North Carolina.

I was unfortunate enough to witness this pattern firsthand.

About 30 years ago, I provided emergency care for marathon runners.

At one race, I saw a thin, young man fall to the ground just feet from our emergency aid station. His heart was beating erratically as we placed an oxygen mask over his blue lips.

Seconds later, another runner arrived at our station and keeled over. He was dizzy, weak and scared. He had a dangerously erratic heartbeat. This man was only in his early 20s.

The sad part is that marathon runners think they’re getting healthy by training for these long-distance runs. But the truth is, this kind of cardio is hurting your health.

I once asked a long-distance runner I knew why he dragged himself out of bed at 5 a.m. every morning, laced up his running shoes and pounded away on the treadmill for 45 minutes.

He told me he was tired of being overweight for years and never wanted to be fat again.
I admire his dedication. But here’s the thing…

Long-duration cardio exercise encourages your body to store fat.

The exercise industry has been lying to us for years. They still promote the idea that cardio workouts lead to fat loss.

But they’ve got it all wrong.

Sure, cardio will help you burn fat for a while. You’ll even lose weight in the short term.

But long-duration exercise tells your body to make more fat the next time you exercise. And after a while, your body adapts and it gets very good at making and storing fat.

Fat is a starvation survival strategy. You put on and store fat because your body thinks it’s under duress. When you do 45 minutes of cardio, your body believes that having fat is a good thing… And it starts to adapt to gaining fat.

The next time you eat, you convert even more of your food into fat.

In the Western world, we’ve also mimicked this “starvation mode” with the nutrient content of our food.

When you eat starch-heavy foods from a bag or box — things like cereal, crackers and bread — your body goes into insulin overdrive. Insulin not only increases your body’s storage of fat, it decreases your body’s ability to burn fat.

I call this Environmental Lipogenic Syndrome. Lipogenic means the creation of fat.

As we get fatter and fatter, our bodies are deprived of the energy needed to do routine maintenance and fight disease and infection.

This is the root of all chronic diseases like diabetes.

It’s scary. But it’s preventable — and even reversible.

You have to exercise to beat this epidemic.

But not any old workout will do. You need to work out for short periods at high exertion. I’ll tell you exactly how, but first I want to bust the 3 biggest workout myths of today.

Fact: Nothing could be further from the truth! Long-duration, medium intensity workouts decrease your cardiac output and put more stress on your heart. Sadly, marathon runners have a 50% higher chance of having a heart attack.

It’s time to face the facts: Cardio does not build heart health and does not provide what our heart needs.

A better option: Engage in a high-intensity training program — involving short bursts of intense, constantly varying exercises that gradually increase your heart rate to near maximum levels — buffered by short periods of rest.

While there can be a place for strength training and for incorporating light weights into boosting your PACE routine, weight lifting, as it is done by most people, is not good for us.

Weight training, or weight lifting, is unnatural, ineffective and misnamed. Far from “training” anything, practicing these isolated tensing movements “un-trains” your muscles.

Instead of producing real strength that you can use in real situations, it produces bloated muscle fibers that become dysfunctional, prone to injury and uncoupled from our nerves.

The concept of “aerobics” is built on a flawed and incomplete science that falls apart under scrutiny.

If we only exercise within our current aerobic limits, we do so without improving our aerobic capacity. In other words, we never push hard enough to stop to catch our breath!

While this type of exercise trains your body for endurance and efficiency, this system causes “shrinkage.” I’m talking about smaller muscles, a smaller heart and smaller lungs. Even worse, it wipes out our heart’s reserve capacity.

Now that you know the awful truth — and myths — about conventional cardio, let me show you how they got it wrong from the beginning…

Your Body Mass Index (BMI) is a measurement of your body fat percentage. And based on the results, you are labeled normal, overweight or obese.

But BMI can give you some crazy results. Using this measurement, I’m considered obese.

And so is NBA superstar LeBron James.

You see, BMI only compares your height against your weight. It doesn’t distinguish between fat and muscle. But here’s the thing…

Muscle is much denser than fat. So if you have a lot of muscle, you can have a high BMI but still be lean. There’s a much more reliable test to measure your body’s composition of fat and muscle. It’s called dual-energy X-ray absorptiometry (DXA or DEXA).

In my clinic, it’s one of the first tests I give to my patients.

You probably know the DEXA test as the gold standard for measuring bone density. But new research shows it can also give you a detailed snapshot of your body’s composition of bone, muscle and fat.

In a recent study of 50 women, doctors compared BMI with DEXA results. They found that some women who were told they were overweight based on their BMI actually had normal fat levels on their DEXA.¹

And 18.5% of the women with normal BMI actually had a lot of excess fat based on their DEXA. In other words, they were “skinny fat” people.

You see, the BMI also can’t measure deadly visceral fat. This type of fat collects in your abdominal cavity. It surrounds your organs and restricts them. Visceral fat is also a haven for toxins that can’t be cleaned by the liver. They contribute to heart disease, diabetes and cancer.²

I advise all my patients to stop obsessing over the scale and start monitoring their body composition.

DEXA scans are the best way to do that. The scan takes just a few minutes. Afterward you receive a report detailing the mass of your bones, fat, muscle and organs broken out individually. It’s great for tracking your progress in building muscle and losing fat from your diet and workouts. You do get a small amount of radiation from the scan. But it’s less than 10 microsieverts or just a fraction of a chest x-ray or mammogram.

Our ancestors lived in a world where our food fought back. Predators attacked without notice.

They had to run or fight – fast and hard. These short bursts of high-output activity fine-tuned our ancient ancestors and kept them fit.

You may not think we have much in common with our ancient ancestors.

But genetically speaking, we’re 99.998% identical.

Cavemen never exercised for 45 minutes like we’ve been taught to do. And they never lifted weights to build muscle. They did it naturally.

And intensity is one of the keys.

When a caveman was hunting, his day was punctuated by periods of high-intensity exertion followed by longer periods of rest.

This is the kind of activity that’s natural for a human body.

Not long, boring workouts that last forever.

We still have the same physiology of our ancestors, but we have lost that kind of challenge.

To “reactivate” your native fitness, and stay as lean as your ancient ancestors, a few simple techniques will ensure your success.

That’s where my PACE principle comes in.

PACE – which stands for Progressively Accelerating Cardiopulmonary Exertion – is the antidote to traditional aerobic exercise.

It flips a “metabolic switch” in your body and puts you in fat-burning mode for up to 24 hours.

I realized long ago the value of increment increases of intensity in exercise. That’s why I created PACE. What makes PACE so unique is that your goal is to hit a peak of intensity in a short timeframe and then rest.

One of the core features of PACE is your body’s adaptive response to a new challenge.

This adaptive response sets changes in your body in motion every time it’s confronted with a unique physical challenge.

Notice I said, unique.

This is where 99% of all other exercise routines fail.

If you repeat the same challenge, the same routine, over and over, you’ll never make real progress.

If you apply the right intensity to a new challenge, your body will react to that challenge by triggering of biochemical changes that will produce a result of some kind.

And when you give it the right challenge, you’ll get a desired result – like fat loss.

But give it the wrong challenge – like traditional cardio – and you’ll wind up fat without ever realizing what you set in motion.

And in return, your body will adapt by storing more fat, not less.

What’s more, your body will stop adapting if you continue the same routine month after month, year after year.

That’s why making small changes in your routine is critical. It allows your body to make new adaptive responses over time. This is your key to long-term success.

This is the basic principle behind PACE: You alternate between exertion and recovery, while making progressive changes.

I’m often asked what makes PACE different from High Intensity Interval Training (HIIT). People often think that PACE is just a more intense way of doing interval training.

It’s not.

It’s true that like PACE, HIIT uses high exertion over short intervals.

But high intensity training is not the right starting point for everyone. And it is not PACE.

Interval training was formalized in the late 1930s when German coach Woldemar Gerschler teamed up with Dr. Hans Reindell.

Together they created the first interval training program: Multiple sets of 200-meter sprints with intervals of rest in between.

They called it “interval” training because each burst of exertion was followed by rest. To them it was the most valuable part of the workout.

They understood it was during the rest period that the bodies of their athletes made adaptive responses.

Did they get results? You bet.

The athletes they trained broke world records.

The first athlete to set a world record using interval training was Roger Bannister. In 1954, after incorporating the techniques of interval training into his daily one-hour training program he became the first man in history to run a mile in under four minutes.

The problem with HIIT is that the typical out-of-shape American can’t run eight 100-yard wind sprints. They probably can’t run one 100-yard sprint.

I designed PACE to work for someone at any fitness level.

No matter your current conditioning, PACE still works.

The P in PACE stands for Progressively. You progressively challenge yourself through exertion.

Let me explain…

I had a female patient who weighed 250 pounds. Her name is Terri Lyttle. Terri’s starting point for becoming fit and lean was walking for 45 seconds.

That’s all she could do. That took her to her maximum exertion and she was out of breath and panting. So she would rest, and then do it again.

Walking for 45 seconds is not exactly High Intensity Interval Training.

But it did progressively challenge her output bit by bit. 45 seconds turned into one minute. Before long, she was “power walking” up steep hills. Today, she runs and does calisthenics.

After two years, Terri:
• Was 98 pounds lighter
• Lost 66 pounds of fat
• Built 14 pounds of new muscle

The second component of PACE is acceleration.

As you increase your maximum output you want to accelerate the time it takes you to get there.

In other words, if it takes five minutes to get out of breath and panting, you want to accelerate that time.

Try to reach that level in four minutes then 3 and a half minutes. You do that by accelerating your exertion.

Or, if it normally takes your heart two minutes to return to normal after a workout set, shorten that time.

When you give your body the signal that it has to adapt, it will.

New research shows that working out at a high intensity in a short time frame is best for reversing insulin resistance.³

In fact, insulin sensitivity can improve 23 to 58% with high intensity in in just weeks.

In one study, 40 sedentary adult women at risk for diabetes worked out using this kind of program for 10 weeks.

The women with the worst insulin resistance got the biggest benefits from this type of workout in terms of sugar and insulin in their blood.

The study found that exercising for a short time at a high intensity makes your body more sensitive to insulin so blood sugar levels stay low and glucose can get inside your cells to produce energy.

Another study showed that exercise intensity was a stronger predictor of improved blood sugar control when compared to steady exercise without bursts of intensity.

And a brand-new study just found that high intensity workouts even work to improve insulin sensitivity in your brain.⁴

Researchers in Finland looked at middle-aged men and women with insulin resistance. They divided them into two groups.

One group did high intensity workouts on exercise bikes. They did 30-second intense training sessions followed by 4-minute recoveries.

The other group did long-duration cycling.

The brains in the HIIT group were much better at taking up glucose and using it for energy. In other words, their insulin resistance improved.

I’ve seen similar results in my own practice.

After only a few weeks implying my PACE principles, my patients reported lower blood sugar levels and better insulin sensitivity.

Here’s how it works…

During intense exercise, your body burns glucose as a muscle fuel, therefore preventing it from being stored as fat.

PACE also lets your body store less energy as fat, but more as something called ATP, the most readily available source of energy.

PACE exercise uses carbs as fuel. By using carbs as fuel, you train your body to store energy as ATP, creatine and glycogen – making muscle the main energy storage.

But your supply is limited. After two to three minutes, your body switches to carbs stored in muscle tissue. This lasts 10 to 20 minutes before you switch to fat.

As you can see from the chart, during low intensity activity your body derives most of its energy from carbohydrates and only 15% from fat.

When you look at the lifestyle of our ancient ancestors, this makes sense. Low intensity activity, like walking long distances, was natural for hunter-gatherers.

But when you step up your activity level to moderate, you increase the percentage of the energy burned from fat to 55% of the total.

Now notice that if you increase your activity to high intensity you dramatically reduce your dependency on fat and derive nearly all your energy from carbs.

This relationship has led many to advise that you should exercise at moderate intensity because that’s how you burn the most fat.

Although this seems logical, it turns out to be completely the wrong advice for getting lean.

To fight diabetes, you need an exercise routine that mimics our native ancestors, who were naturally fit and healthy.

They didn’t rest or live sedentary lifestyles like we do today.

They had to adapt to survive.

They pushed themselves to exertion, rested then pushed again.

A good workout for people with diabetes is one that works the leg muscles. These are your biggest muscles. Working them demands more energy, which helps to lower your blood sugar.

Plan your workouts to last about 12 minutes and then switch between periods of rest and periods of high-intensity bursts.

Remember, intensity is subjective. If an activity gets your heart rate up – making it difficult to breathe and speak at the same time – then you’re working at a high intensity pace.

Try walking, cycling, sprinting, or any other activity that you want.

If you’re new to the idea, your first PACE workout will be a single period of exertion followed by recovery. And it takes just 12 minutes a day.

Before you start PACE, you want to establish a baseline so you can track your progress. Here are 4 easy ways:

As you’ve learned, the most accurate way to measure your body fat percentage is with a DEXA scan. But if you don’t have access to this machine, the next best way is with skinfold calipers. It’s fast, inexpensive and easy.

They come with simple instruction manuals that will show you how to get a good read on how much fat you’re carrying. It’s best to measure at three different body sites. Then average the measurements to get an accurate body fat percentage. Most men carry between 15-17% body fat. For women, the average is between 18-22%.

Body Fat Percentage

You can buy skinfold calipers at most sports and fitness equipment stores.

Take all of the measurements on the right side of your body. Gently pinch and fold your skin between your thumb and forefinger. Don’t grab any muscle. Hold the calipers to the fold and measure. I recommend repeating the measurements three times to get an accurate reading.

Men, measure skinfold at your:

Women, measure skinfold at you:

Record the final measurement in a body composition log, which I’ve included in the back of this article. Then, add them all together. Use this number to look up your body fat percentage using an online calculator.

Simply google “body fat percentage calculator for men and women.”

Body Fat in Pounds

Calculating your body fat in pounds is easy. Take your total body weight - what you weighed when you hopped on the scale. And multiply it by your body fat percentage - the number you got from the body fat calculator.

Lean Body Mass

Figuring out your lean body mass is even simpler. Subtract your body fat in pounds - the number you just calculated - from your total body weight.

Circumference Measurements

I recommend using a MyoTape to get fast, accurate measurements. All you do is wrap the tape around your body, hook the end into the slot of the MyoTape, and read the tape.

You can find MyoTapes at any sporting goods store

Both men and women should take the same three measurements:

The key is consistency. Measure yourself at the same place each time, and you will get an accurate view of your progress.

Now you should be ready for your first PACE workout. Here’s a basic one to get you started.

Here’s how it works:

You start at a speed and level of intensity that feels comfortable. Then you gradually increase your level of intensity until you are panting. When you reach this level of exertion you will stop and recover. That’s it.

Here’s an example of your first workout. It’s a period of exertion followed by recovery.

That’s it for the first time. Tomorrow, do this again, with a focus on slightly increasing the challenge each time. Then, every session, incrementally accelerate your exertion or recovery.

Here are three tips to get yourself ready for your first PACE routine:

And don’t look at the scale every day! We are working toward life-long results and it takes a different amount of time for everyone.

Plan your weigh-in day once a week to keep your log and do your measurements. That’s all.

Here’s a sample PACE 8-week program:

Here you have a basic 4-set workout. Every two weeks the exertion period decreases. To make it more challenging, you’ll increase the intensity every time the exertion period gets smaller.

I also recommend switching your workouts up to avoid getting bored with the same thing day after day and adding in calisthenics strength training.

And here’s a strength training log I use.

Now that we’ve busted the biggest cardio myths, you can stop killing yourself at the gym and start getting truly healthy with PACE.

Like I said earlier, you don’t have to be in great shape to get started.

The important thing is to gradually, progressively increase your exertion over time. Check out a free PACE class online by just clicking here.

To Your Good Health,

Al Sears, MD, CNS