Weight training - specifically the pursuit of muscle building - make you stupid.This reckless knowledge bomb was dropped (like a fart in church) by Naudi Aguilar from the Functional Patterns YouTube channel. For reference, I have embedded the video below. After the video, you will find a recap of Naudi Aguilar's key quotes and statements.
Naudi Aguilar poses the question: Does weight lifting make you stupid?Aguilar goes on to speculate about the dangers of muscle building, and how it can distort and damper brain function and performance.
"25% of your metabolic demand is going straight ot the brain. The brain demands a great ton of energy. When you look at babies they have huge heads and a disproportionate body relative to what we are as grown adults.
If you look at this from an evolutionary perspective or an anthropological perspective, you're going to understand that the human being prioritizes brain function before muscles.
So when you start to think about doing something like bodybuilding, any kind of forms of weight lifting, heavy lifting that are geared and oriented around the development of muscle - for most of the time for arbitrary reasons like aesthetics that are percevied as relevant by our culture because of MTV and bodybuilding magazines - we begin to understand that, at some point, are we going to reach a point where by us having so much muscle are we going to start taking away the metabolic needs of the brain?
And are we going to start to develop distortions in our brain because we're so focused on ur muscles?"Before I move on to analyze the true impact of resistance training on the brain, here are a few brief notes on Aguilar's comment.
The brain demands a lot of energy. True.Is this number 25%? Well Scientific American recently stated that the brain uses up to 20% of our total energy resources, so Naudi was in the ball park. 
Babies have disproportionate head sizes. True.By 9 months old, a baby's head is 50% of its adult size. When a child reaches two years of age its brain reaches 75% of adult size.  This early brain development exists to facilitate and accommodate future physical growth. A disproportionate brain size is not so much a function of priority as it is of necessity. In fact, babies are born with more than twice the number of neurons that an average adult has. A newborn is born to run, you might say. After birth, synaptic pruning takes place and the stronger neurons survive. Unless you lift weights, apparently At least according to Naudi Aguilar.
The body prioritizes brain function. True.The body's hormonal reaction to starvation tells us all we need to know. During extreme periods of calorie restriction, insulin secretion drops while glucagon increases.  GLUT4, the glucose transport mechanism that drives energy into muscle and fat tissue, is dependent upon insulin. The bottom line here is easy to understand. The body is very efficient at protecting the brain. It is a priority. A decrease in insulin secretion during periods of limited calorie intake results in fewer glucose resources being used for muscle and fatty tissue, while the brain remains a priority. This begs an obvious question. If the brain is extremely efficient at protecting itself during taxing periods of starvation, would it really "flip a switch" and become extremely fragile when you add 10 to 20 pounds of muscle. Unlikely. The body can't be both hyper-protective of the brain and at the same time uncaring and fragile with brain protection because of muscle tissue addition. Logically and physiologically this makes no sense.
Muscle tissue robs the brain of resources, causing it harm. False.This is why Naudi Aguilar stumbles. His conclusion - or assumption - couldn't be further from the truth. In the section that follows we will analyze the true impact resistance training has upon the brain, and dismantle the nonsense and fear caused by such a reckless premise.
Resistance Training and the Brain
#1 - Muscle Building Improves AnxietyA 2010 meta-analysis by Patrick J. O'Connor, PhD, Matthew P. Herring, MS, and Amanda Caravalho analyzed the impact of resistance training on anxiety.  While this review called for deeper exploration into the impact of "the iron" upon this condition, meaningful connections were discovered. The researchers concluded that weight training provided a positive and worthwhile Impact (intervention method) for those suffering from anxiety. One of the interesting finds had to do with relative weight intensity, or how heavy you are training. Two of the studies found that lifters using weights below 80% of their one rep max experienced greater relief from anxiety. Keep in mind that all things are relative here. Heavy lifting still provided benefits. The good news is that moderate resistance training - which is what the vast majority of us engage in at the gym - is best. For me, this is an obvious conclusion. I've always felt better after a good workout, even when I entered the gym mentally or physically tired. Resistance training has given me improved confidence, and is an excellent stress reliever. It makes me feel like I can handle any task if I just work hard enough and remain consistent. Anyone that's dedicated a substantial amount of time to any form of exercise, including resistance training, has experienced an improvement in confidence, mental clarity, and as a result a general lessening of anxiety. Anxiety reduction or relief is brain and thought-enhancing. This needs to be stressed. The anxiolytic (anxiety reducing drug or intervention) benefits of weight lifting appear to impact women to a heightened degree.  In fact, there is a growing body of evidence revealing a robust reduction in anxiety for women who challenge themselves with resistance training.
"The majority of findings suggest that females may be more sensitive to the anxiolytic effects of resistance exercise than males." To wrap up this section, I want to leave you with an important point. While long-term resistance training has been established as a quality intervention procedure in the battle against anxiety, it takes only a single session to see benefits and anxiety relief.  A single session is good for the brain.
#2 - Resistance Training and Brain CognitionFirst, let's define cognition. It's the ability of the brain to acquire knowledge through thought, the senses, and from our personal experiences. Cognition is not just what we experience or think about, it's how well we process this information. You can bump into a low-hanging branch, but if your cognitive skills are nominal, it's likely you'll repeat this action over and over again. Thud. The brain not only has the task or storing memories, but also functions with a capacity to process these events and improve/refine how we tackle life, situations, and challenges. If we listen to Naudi Aguilar, it's very likely that resistance training will slowly turn us into tree branch-thudding Neanderthals. But this isn't what research tells us. The meta-analysis by O'Connor, Herring, and Carvalho (2010) noted that resistance training seemed to improve cognitive function in older adults.  One of the most noteworthy and profound benefits of this bodybuilding-style of training had to do with memory. Both memory and memory-related tasks were profoundly improved in older adults that challenged themselves with the iron. Moving away from the older crowd, it was also discovered that weight lifting sessions could improve executive functioning.  Executive functioning is a term used to describe the brain's ability to skillfully exhibit self-regulation and mental control. Simply stated, lifters are more adept at monitoring and controlling their thoughts and actions.
#3 - Resistance Training and Brain LesionsWe have established that resistance training is good for anxiety and cognitive function, but what about overall brain health and longevity? By late middle age our brains start to develop lesions. These lesions are age-related holes that appear in the white matter of our brains. White matter is very important because it's the information pipeline that allows the brain to pass along messages from region to region. Brain lesions usually appear long before an individual notices changes with critical thinking or memory. As the years go by, these brain holes widen and impact cognitive function to a much greater degree. Here's the good news: Resistance training helps in the battle against brain lesions. Sorry Naudi, but it's true. Dr. Liu-Ambrose, director of the Aging, Mobility, and Cognitive Neuroscience Laboratory at the University of British Columbia in Vancouver and a professor of physical therapy, took the initiative to study the impact of various forms of exercise on white brain health and lesion formation. Resistance training was a major focal point of this research. A large-scale study was performed on women ages 65 to 75 that had at least one recent brain scan. Of this group, 54 women had scans revealing existing lesions in the brain's white matter. Participants engaged in a supervised resistance training program. There were three total groups:
- The first group performed a single upper and lower body session per week.
- The second group performed the same routine, but twice a week.
- The third set of participants was a control group. They performed only stretching and balance training twice a week. No resistance training was involved.