Healthy bodies need healthy brains

By Betty Murray

If your brain is tired, your body will be too. A new study on mental fatigue found that mental exertion might play a role in lessening endurance, resulting in shortened workouts, even if the body has plenty of energy reserve left for a longer workout.

For years, scientists have studied the relationship between physical activity and cognitive function, though that research has been primarily one-sided. Research has proven that physical activity in small doses improves brain function, whereas long workout sessions may temporarily affect cognition.

But until recently, researchers have not paid much attention to the inverse relationship between exercise and the brain, that being how a tired brain might impact exercise. Fatigue is generally thought to be a physiological exhaustion, but fatigue can also apply to the mind.

A study published in May in Medicine & Science in Sports & Exercise looked at how tired brains impacted physical performance. Volunteers played a mentally demanding computer game for 90 minutes before exercising one of their legs. Muscle contraction of the leg was measured and the volunteers also verbally expressed how exhausted their leg felt throughout the exercise. In another visit to the lab, the volunteers watched a 90-minute calming documentary before exercising one leg.

What researchers found was that mental fatigue significantly impacted endurance — the volunteers grew tired about 13 percent faster following the 90-minute computer game than they did after watching the documentary.

What does this mean for you?

If you’re prepping for a marathon, don’t wear yourself out mentally the day before. But don’t make excuses not to exercise following a long day at work, either. Exercise is still tremendously beneficial and critical for your overall health, whether or not your mind is tired. However, you may find that a shortened workout following a mentally strenuous day is more efficient than a prolonged workout.

And as a side note, this research also suggests that training your brain to avoid mental fatigue can improve endurance during exercise.

Betty Murray, CN, HHC, RYT is a Certified Nutritionist & Holistic Health Counselor, founder of the Dallas-based integrative medical center, Wellness and founder of the Metabolic Blueprint wellness program. Betty’s nutrition counseling practice specializes in metabolic and digestive disorders and weight loss resistance. A master of the biochemistry of the body, Betty teaches her clients how to utilize nutritional interventions to improve their health. Betty is a member of the Institute of Functional Medicine and the National Association of Nutrition Professionals.


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