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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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May 19, 2008

Dear Mark: Decline in Mental Energy

By Mark Sisson

FatiguedDear 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)

Further Reading:

More Chronic Cardio Talk

Dear Mark: Weightlifting Weary

The 7 Habits of Thin (Healthy) People

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5 Comments on "Dear Mark: Decline in Mental Energy"


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9 years 2 months ago

Since I switched to a high intensity exercise modality 2 years ago my standing heart rate dropped from low 70’s to mid to upper 50’s and I don’t do any low intensity cardio work. I also probably lowered my stress levels by not worrying about scheduling in the hour or so (3-4 days/wk) I used to need for my workout.

Mike OD - IF Life
9 years 2 months ago

They say the best workouts leave you feeling great afterwards, and I find that to be true. Unless one is severely overtraining, mental energy should remain high. That lots of good quality fats in the diet also help!

simon fellows
simon fellows
9 years 2 months ago
I’d wager my left nad you won’t go wrong(i.e getting the aerobic benefits and being devoid of excessive thinking, feeling energized and basically just feeling grand to be alive) with oodles of walking and some brief intense weight work outs..whether chucking tyres around, doing some Turkish get-ups, just a bit o variety, randomnly performed, not being rampantly obsessed with having very low body fat (i actually think rightly or wrongly that the obsessiveness that some lads(and lasses) have about low body fat is likely a symptom OF low body fat and a kind of obsessive-compulsive disorder whereby the body is… Read more »
9 years 2 months ago

Thanks Mark
I new there had to be a better way than tearing your joints up through excessive cardio.

9 years 2 months ago

Thanks Mark for addressing the question. I agree.

The biggest adjustment I have faced has been volume of exercise. As a runner, I bought into the more is better theory. When I switched to kettlebells and intervals, I tried to do too much. Inevitable burnout ensued.

I was quick to blame the type of exercise for decreased mental and energy levels. However, once the volume was reduced, I was feeling better than I had when running. I certainly appreciate your thoughtful insight into chronic cardio and primal fitness.