Dear Mark: Decline in Mental Energy

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Updated on June 11, 2009

Fatigued Dear Mark,

Have you noticed a decline in mental energy or focus since not doing “cardio”? I have read several reports that indicate that aerobic exercise is best for mental performance. Any thoughts?

Thanks to reader Phillip for his question on the comment boards. I’ve talked a lot over the course of the last few months about chronic cardio and the very real disadvantages of this type of training (higher cortisol levels, oxidative damage, systemic inflammation, depressed immune system and decreased fat metabolism, etc.). However, just because I don’t do chronic cardio anymore doesn’t mean I don’t get huge cardio benefits from the high intensity sprints and other interval exercises I do. This high intensity part of my workout is short compared with the hours I used to used to spend training. I choose to consider efficiency as a factor in my training program, and (as I’ve said on a number of occasions) I’ve never felt better than I do now.

Personally, I haven’t felt any decline in mental energy or focus since I dropped out of the chronic cardio race. I used to feel like napping mid-afternoon, but these days I’ve found that my energy levels are more even throughout the day. A big part of that, I’m sure, is not experiencing the rundown and recovery phases. Because I now skip the extra cardio, I have more energy and more time for the other important and healthy things in my life. I feel a lot less stressed physiologically and psychologically because of the changes I’ve made to my routine.

There are a slew of studies out there that confirm the benefits of exercise for mental clarity, concentration, stress, anxiety, you name it. Rigorous exercise (before you get to the law of diminishing returns) stimulates the central nervous system and the activity of neurotransmitters like serotonin, which enhances mental clarity and focus. But it doesn’t need to be traditional cardio of long duration. In fact, if your routine gets the blood pumping and healthily stresses the heart, you’re getting cardio benefits (and all the other associated advantages like improved mental clarity). I’m not familiar with any study that specifically compares the impact of interval training with traditional cardio on mental clarity/function/fatigue. I’d love to see them if there are any floating around out there.

When it comes to mental as well as physical function, the Primal Blueprint works with our primal design. The exercise model is meant to healthily stress the body without exhausting it. When we perform any kind of rigorous exercise that doesn’t exceed, say, 45 minutes or so, we never deplete our glycogen store to the point of descending into muscle breakdown, and we never starve the brain as we can when we train hours a day.

As always, thanks for your questions!

Graham Binns Flickr Photo (CC)

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.