What’s Wrong with Chronic Cardio?

It feels good to go hard and go long…on occasion. However, the high-intensity aerobic sessions that are common in today’s “go hard or go home” fitness culture often do more harm than good.

This should be happy news to most people. However, hardcore fitness enthusiasts are addicted to chronic cardio. This involves a 45-minute to hour-long spin session, run, or aerobics class performed at continuous intensity several days a week. There is a healthier approach to lose weight. It is more fun and approachable. You can burn fat and also build and preserve lean muscle. We’ll show you how, but first, let’s get clear on what we mean by chronic cardio.

Chronic Cardio

What Is Chronic Cardio? Chronic cardio is long-duration, repetitive cardiovascular exercise that exceeds the aerobic threshold (80-85% of your maximum heart rate). Your aerobic threshold is personal, depending on your age, health status, and fitness level. It’s an effort between moderate and high intensity that doesn’t let up. It’s not so all-out that you couldn’t sustain it for 5-10 miles. However, it’s vigorous enough to put you in the sugar-burning zone. You’ll definitely feel it.

It’s “the black hole” that exercise scientist Stephen Seiler coined. It refers to that zone where it’s not painfully intense enough to make you feel like you’re about to collapse. Yet, it’s also not so easy that you feel like you’re barely breaking a sweat. It’s a brisk 30-minute cycle or run, pretty enjoyable, and easy to become addicted to.

That’s the “chronic” component of chronic cardio. An occasional fast-paced 10-mile run doesn’t qualify. Training 3-5 days a week for a marathon every month does. Beating your miles and RPMs at spin class 5 days a week is also considered chronic.

It doesn’t sound too bad, especially if you’re competitive by nature. Who doesn’t like to set new records? But your body would disagree. When we enter the black hole, we put near-constant stress on the body. This stress is not the kind that gives us the strength and endurance gains we’re after. Instead, it leaves us fatigued and weakens our systems.

Check in: Do you dread your cardio workout? Does it leave you feeling mentally exhausted and physically depleted? Is it torture throughout? If you answered “yes” to any of these questions, you may be in chronic cardio territory.

The Dangers of Chronic Cardio

When you exercise above your aerobic threshold, your body switches into sugar-burning mode because your muscles are screaming for glucose. It takes consuming a large amount of carbohydrates to meet this demand. Your muscles and liver can only hold 500-600 grams of glycogen (stored glucose) at a time. To replenish these stores before the next workout, you’d need to eat an additional 600 grams of carbs each day. This amount is far more glucose and insulin than your body needs. Adopting the chronic cardio habit can lead your body to start over-producing insulin, a condition known as hyperinsulinemia.

Continuous exercise at high levels stimulates the release of the stress hormone cortisol. It also increases the production of free radicals by a factor of 10 to 20 times the normal amount. This makes you vulnerable to injury and infection. It can reduce lean muscle mass and bone density. It also encourages your body to store more fat. And that’s just the beginning.

Inflammation That Doesn’t Quit

When it comes to building endurance or strength, oxidative stress is beneficial. Stress the body, break it down a bit, and it builds back stronger. The next time you encounter the stressor, you’re better equipped to handle it. This is basic exercise physiology.

If we don’t let up, and we keep adding stressor upon stressor without rest and recovery, systemic inflammation takes over. It damages healthy tissues, cells, and organs. It’s one of the root causes of many diseases, including heart disease, cancer, obesity, and type 2 diabetes.

Heart Troubles on the Horizon

The heart is a sensitive organ. It responds to even slight changes in blood chemistry, like increases in cortisol, insulin, or lactic acid. It adjusts its beat rate to meet the oxygen demands of your organs and muscles.

When we repeatedly subject the heart to this pressure over extended periods, the heart’s walls can enlarge. They can also thicken, a condition known as hypertrophy. This increases the risk for cardiac arrhythmias like atrial fibrillation. Such arrhythmias can further raise the risk of stroke and cognitive decline. Studies indicate that endurance athletes, including runners, are at a higher risk for atrial fibrillation. Explanations for this include increased fibrosis (scar tissue formation), myocardial injury, and excessive inflammation.

Chronic cardio is also associated with atherosclerosis, or hardening of the arteries. Studies have shown that marathoners have more calcified plaque in their coronary arteries. Recent research suggests that highly active endurance athletes also have elevated arterial plaque levels.

Endurance training is not off-limits. The key is to adjust the training method. Focus on occasional short bursts of “life-or-death” high-intensity exercises. Supplement this with resistance training, low-level cardio, and ample play, rest, and recovery.

Taking the Chronic Out of Cardio

By removing the chronic aspect from cardio, you’ll burn more fat. You will also improve your stamina and endurance. This approach does not tax your immune system or your adrenals.

Bonus: you’ll find that you don’t crave as many carbs, which will further contribute to weight loss.

Here’s how to do it:

Move Frequently: Go on long, brisk walks, enjoy lengthy weekend hikes, or jog with a buddy at an easy pace. Move as much as possible during the day to get those steps in!
Lift Heavy Things: Engage in resistance training two times a week for 10-30 minutes. The Primal Essential Movements—push-ups, pull-ups, squats, and planks—work the major muscle groups and are accessible to all fitness levels.
Sprint: Increase your oxygen uptake (VO2 max) with high-intensity intervals once or twice a week. Participate in a formal HIIT class. Alternatively, perform brief (20-40 seconds), explosive all-out sprints. Just follow the Primal Blueprint Fitness Pyramid.

Just follow the Primal Blueprint Fitness Pyramid

Supplement aerobic activities with strength training and high-intensity intervals. Include mobility and flexibility classes. Get massages. Play and have fun. Don’t forget to make time for sleep and relaxation; that’s where your body rejuvenates and rebuilds.

Let’s Talk Heart Rate

Keep your heart rate within your aerobic threshold during slow and steady cardio sessions. This helps you avoid the black hole. The easiest way to do this is by using a heart rate monitor. This ensures you don’t exceed the “180 minus age” heart rate. If you’re an endurance athlete, we strongly recommend using an HR strap to stay honest.

Check in: You can also gauge your heart rate with the “talk test.” If you can’t talk or sing while exercising, check your heart rate monitor. You’re likely out of the fat-burning zone. You may be over your aerobic threshold.

Wait for It

Start moving more (and more slowly), and you’ll reduce your dependency on carbs. You’ll be able to go longer without eating, potentially exploring intermittent fasting or a ketogenic diet. You’ll make room for resistance training, and you’re likely to go down some belt notches too. Indeed, one study showed significant results. People who swapped 20 minutes of cardio for 20 minutes of weight training saw the greatest reduction in waist circumference.

Be consistent and patient. Good things are happening, even when you can’t see them. Focus on how you feel, and stick with it!