Moderate-to-Vigorous Exercise May Benefit Fluid Intelligence

Cardio workouts may help fluid thinking—but sitting has cognitive benefits, too.

Posted Oct 17, 2020

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In recent years, numerous studies have established that moderate-to-vigorous physical activity (MVPA)—a.k.a. aerobic exercise at an intensity that causes some huffing-and-puffing and results in breaking a sweat—can boost brainpower and improve cognitive functions. (See here, here, here, here.) 

However, until now, researchers haven't really zeroed in on how different intensities of physical activity affect various types of cognition. A recently published study (Burzynska et al., 2020) led by researchers from Colorado State University is one of the first clinical trials to investigate how light-intensity physical activity (LIPA) and MVPA compare to sedentariness in terms of older adults' fluid (processing speed, memory, and reasoning) abilities and crystallized (vocabulary knowledge) abilities.

These findings were published online ahead of print on September 24 in the journal Psychology and Aging. Aga Burzynska of CSU's Department of Human Development and Family Studies is the study's first author.

Interestingly, Burzynska et al. found that the daily amount of time spent doing moderate-to-vigorous physical activity was positively correlated with improved "fluid" abilities, whereas daily periods of sedentariness were associated with better "crystallized" abilities. "In contrast, time spent in light physical activity was not related to either fluid or crystallized abilities," the authors note. 

"Our results add to the previous literature by providing the first sensor-based evidence that crystallized and fluid abilities in older age may be associated with engagement in different intensities of daily activity," the authors write in the paper's abstract. "Moreover, our findings suggest that the behavior of moderate-to-vigorous physical activity is at least as important in relation to cognition as the desirable long-term physiological effects of higher intensity physical activity and exercise."

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"The Thinker" by Rodin
Source: Hung Chung Chih/Shutterstock

Although too much sitting isn't good for your brain (Siddarth et al., 2018), the latest research suggests that, in appropriate doses, sedentarism may benefit "book smarts" and help to optimize other types of thinking related to crystallized knowledge. (See "Too Much Crystallized Thinking Lowers Fluid Intelligence.")

Burzynska's latest study used the Virginia Cognitive Aging Battery, which tests 16 different cognitive tasks to assess fluid and crystallized abilities. They also monitored and adjusted their results based on several socio-economic, physical, and functional health factors such as aerobic fitness levels, mobility issues, blood pressure, employment status, and annual income. "Our study has pretty high-quality measures that cannot be done 'quick and dirty,'" Burzynska said in an October 16 news release

Because this study used hip-worn accelerometers to monitor sedentarism and daily physical activity intensities, the data is more accurate than results from studies that rely on self-reporting. 'We already know that people like to overestimate their daily movement and underestimate the time they spend sitting," Burzynska noted. "If you ask, 'How long did you sit today?' people will perhaps say two to three hours when the reality is more like six to eight hours."

"There's this big push within health and wellness that sitting is always bad for your body, that being a couch potato is not good," Burzynska added. "And although our earlier studies indicated that the brains of those who spend more time sitting may age faster, it seems that on the cognitive level, sitting time may also be meaningful."

Anecdotally, these research findings make sense to me as a writer who relies on MVPA to enhance my fluid intelligence. My daily blogging routine is purposely structured to absorb written crystallized knowledge by reading all the latest science news in the predawn hours while sitting still and drinking coffee. During this sedentary time, I also type out a skeletal draft of whatever I'm going to write about that day before lacing up my sneakers and heading out for a sunrise jog.

While running, my brain seems to connect the dots of miscellaneous science-based facts I've read thus far that day and my mind starts crafting sentences (or even full paragraphs). The minute I finish my workout and am seated at a computer keyboard, I always type out whatever ideas or written passages sprung to mind during my run. Based on road-tested life experience, I know that running improves my fluid thinking, but I need to be sitting still to take full advantage of my crystallized abilities.

Long before the latest (2020) research into how sedentariness and varying intensities of physical activity might influence fluid and crystallized abilities, Joyce Carol Oates described how a combination of running and sitting still to express her thoughts on paper in longhand was an integral part of her writing process. In a 1999 New York Times article, "To Invigorate Literary Mind, Start Moving Literary Feet," Oates wrote:

"Running! If there's any activity happier, more exhilarating, more nourishing to the imagination, I can't think what it might be. In running, the mind flies with the body; the mysterious efflorescence of language seems to pulse in the brain, in rhythm with our feet and the swinging of our arms. The structural problems I set for myself in writing, in a long, snarled, frustrating and sometimes despairing morning of work, for instance, I can usually unsnarl by running in the afternoon.

Running seems to allow me, ideally, an expanded consciousness in which I can envision what I'm writing as a film or a dream. I rarely invent at the typewriter but recall what I've experienced. I don't use a word processor but write in longhand, at considerable length.

By the time I come to type out my writing formally, I've envisioned it repeatedly. I've never thought of writing as the mere arrangement of words on the page but as the attempted embodiment of a vision: a complex of emotions, raw experience. Running is a meditation; more practicably it allows me to scroll through, in my mind's eye, the pages I've just written, proofreading for errors and improvements."

In the above passage, Joyce Carol Oates unwittingly corroborates the latest research findings by Burzynska et al. and offers practical advice on how to use daily bouts of moderate-to-vigorous activity to boost fluid cognitive abilities in a way that complements crystallized abilities and the use of verbal fluency during periods of sedentariness.  

"When you exercise, enjoy your exercise. Maybe sometimes think, 'Yeah I'm going to go sit now and enjoy a really good book," Burzynska concluded.

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Agnieszka Z. Burzynska, Michelle W. Voss, Jason Fanning, Elizabeth A. Salerno, Neha P. Gothe, Edward McAuley, Arthur F. Kramer. "Sensor-Measured Sedentariness and Physical Activity Are Differentially Related to Fluid and Crystallized Abilities in Aging." Psychology and Aging (First available online: September 24, 2020) DOI: 10.1037/pag0000580