Weight trainers often espouse the “mind-muscle connection”. But what actually happens to the brain during strength training? Surprisingly, even a few weeks of weight training alter the nervous system, and long-term lifting can result in cognitive and neurological benefits.
A recent primate study in The Journal of Neuroscience showed that neurological changes produced by strength training accompany muscle changes (Glover & Baker, 2020). As muscles increase in strength, so may connections between neurons in parts of the brain’s motor system.
Measurable behavioral effects may accompany these invisible changes: resistance training can have substantial impacts on cognition, with neural changes improving cognitive impairment and even cognitive decline. In a 2016 study from Mavros et al., even a 6-month resistance training program led to significant global cognitive performance improvements in people with mild cognitive impairment, improving scores on an extensive cognitive battery of tasks such as memory recall and verbal comprehension. According to the authors, strength gains specifically played a role in this effect. Similar cognitive improvements in younger adults with mild cognitive impairment have been demonstrated, suggesting that strength training has benefits distinct from other forms of exercise (Tsai et al., 2014). Faster response times and greater brain response to a cognitive task have also been seen in healthy young adults after resistance training, similar to improvements elicited by movement without weights (Vonk et al, 2019).
“Resistance training can have substantial impacts on cognition, with neural changes improving cognitive impairment and even cognitive decline. “
Astoundingly, weight training has been shown to protect subregions of the hippocampus—a brain region involved in cognition and long-term memory—from degeneration in populations at risk for Alzheimer’s Disease (e.g., Broadhouse et al, 2020). This neuroprotective effect helps explain the cognitive and memory benefits of resistance exercise. Age-related degeneration in the hippocampus is common in aging populations (Leal & Yassa 2015); according to recent research, weight training may offer a way to help combat this decline. While studies suggest that resistance training may be neuroprotective, it is not yet known how long these cognitive changes last, and whether resistance training can robustly delay or even halt age-related cognitive impairments.
A 2019 study from Kelty et al. demonstrated that, not only can weight training reduce mild cognitive impairment, but it can even reverse memory loss in rodents. Following experimentally-induced cognitive deficits, as few as three resistance-exercise workouts over the course of a week activated a cascade of neural changes accompanied by increased memory performance. After weight training, higher concentrations of proteins involved in DNA replication and synaptic plasticity were detected in brain regions associated with memory. The authors postulate that these changes are part of a mechanism by which resistance training contributes to improved cognition.
Beyond these molecular changes, does weight lifting alter brain function? Resistance training leads to substantial changes in brain function, particularly in frontal regions, and improvement in cognitive performance (Herold et al., 2019). This includes increased activation of prefrontal areas during cognitive testing. Resistance training has also been associated with fewer structural brain abnormalities that have previously been linked to dementia. The changes in brain activation in response to resistance training is likely related to neurobiological mechanisms distinct from those induced by aerobic exercises.
“The changes in brain activation in response to resistance training is likely related to neurobiological mechanisms distinct from those induced by aerobic exercises.”
What more is known so far about the neural changes underlying strength gains? Neural adaptations following weight training are supported by evidence of motor unit adaptations. Motor units—motor neurons and their accompanying muscle fibers—take movement instructions from the brain and convert them into muscle actions (Heckman & Enoka, 2012). Adaptations occur within motor units in even the first few weeks of training; in the early stages of strength gains, greater strength of electric signals has been linked to increase in the capacity at motor units to generate muscle force (Häkkinen, Kallinen, & Izquierdo 1998; Moritani & DeVries, 1979).
These findings, however, should be interpreted with caution. Researchers are still investigating the dose-response effect of strength training and, given the paucity of research on the neural effects of weight training, it is unclear exactly if and how much strength training is necessary to induce meaningful and lasting neurological changes. Thought must be given to how strength training is measured experimentally, accounting for the volume of weight and individual-specific biological markers such as metabolic stress and tissue damage (Schoenfeld et al. 2014; 2017).
Resistance training may offer a supplement or alternative to other forms of exercise with distinct neural and physiological mechanisms. While more research is needed to determine the extent and longevity of these effects as well as their molecular and large-scale neural mechanisms, current findings show that strength training may be a worthwhile investment for achieving cognitive gains or staving off cognitive decline. As lead author of the 2019 strength training rodent study, Taylor Kelty, told the New York Times, “I think it’s safe to say that people should look into doing some resistance training. It’s good for you for all kinds of other reasons, and it appears to be neuroprotective. And who doesn’t want a healthy brain?
Written by Carolyn Amir
Illustrated by Carolyn Amir
Edited by Lauren Wagner and Chris Gabriel.
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