Exercise and fluid intelligence — a tale of questions and more questions
After I published my first article a couple weeks ago, a friend of mine asked me if I could write an article on the links between exercise and fluid intelligence. He’d said that he looked but couldn’t find much evidence on the topic. So, I set out to have a look at what I could find, but much to my surprise, there wasn’t a whole lot, or at least not exactly what I was looking for. Nevertheless, I did find a few interesting bits, so let’s have a look at those!
What is intelligence?
Intelligence is one of those topics in psychology where everyone has their own opinion, and can spin the existing evidence in a way that corroborates said opinion. One only needs to think of the infamous book ‘The Bell Curve’ by Hernstein and Murray[1] and the fallout that followed its publication, and the contentiousness of intelligence becomes clear as day.
Similarly, there isn’t really any agreement on what the types of intelligence are, if there are any at all, but one typology that has received a decent amount of attention in particular is Cattell’s theory of fluid and crystallised intelligence[2]. Within this theory, crystallised intelligence encompasses the things that we already know and the skills that we already have, as well as our past experiences — this roughly equates to long-term memory, by the way. Fluid intelligence, on the other hand, refers to our capacity to learn new skills and acquire new knowledge, as well as our problem-solving and thinking skills — what others may call working memory, or even executive functioning.
Fluid intelligence, therefore, is not really knowledge or even logic, per se, but rather, our ability to improve knowledge and logic,
It would be difficult to conceptualise the effect exercise has on crystallised intelligence, understandably: exercising will likely not increase our lexical knowledge out of the blue, unless it has to do with learning sport-specific skills and movement sequences, such as how to do proper jumping jacks or a parry-riposte in fencing. But fluid intelligence, that’s a hot topic. If we exercise, will that improve our thinking skills and problem-solving? Will we be able to learn faster and more efficiently?
The answer is… perhaps?
There aren’t a whole lot of studies that explicitly measure fluid intelligence and exercise. Instead, there are plenty of studies in children that look at cognitive ability (I.e. thinking skills, more or less) and its relation to physical activity, which although not a direct measure, gives us an idea of what might happen in the brain with physical activity. In most of these studies, the researchers will take a few classes of schoolchildren, mostly in primary schools, and for some of them, they will introduce a physical activity intervention. They will either instruct the kids to do something active during breaks, or they will train the teachers to deliver ‘active lessons,’ like incorporating a ‘run to the correct corner’ type task during Maths classes. This then continues for a few months or even an entire academic year, and at the end of it all, researchers will compare the two groups — those who had the activity intervention and those who didn’t, on some measure of academic achievement or intelligence.
Overall, these studies have shown some pretty compelling findings: for example, in Reed and colleagues’ intervention study, the 3rd graders who did 30 minutes of physical activity 3 days a week for 3 months had higher scores on a fluid intelligence task at a 1-year follow-up than those who didn’t[3]. Similarly, a review of a whole bunch of studies by Donelly and colleagues concluded that physical activity was beneficial for the cognitive functioning of children aged 5–13, but couldn’t provide specific recommendations for duration or frequency[4].
Interestingly, a lot of studies in this area find that the physical activity intervention was beneficial in terms of Maths or English marks, but not always in fluid intelligence.
This suggests that for children, perhaps the real benefit of active lessons and activity breaks is an increased interest in Maths and English classes, rather than an increase in the ability to acquire new knowledge.
How about adults?
We can learn a lot from studies on children, but there are huge differences in cognitive ability between different age groups, so for us sitting here, reading this article, it might be more interesting to see what the literature has on adults.
Most studies in adults focus specifically on middle-aged and older adults, and examine intelligence and exercise from an aging point of view. This means that most research doesn’t really look at whether intelligence improves fluid intelligence per se, but rather, whether it stops the decline of fluid intelligence as we get older. The findings in this are pretty promising, at least: studies consistently show that older adults who engage in regular physical activity lose their working memory function slower — for example, Powell and Pohndorf followed older men who were either active exercisers, inactive, or had an unknown activity status, and found that physical measures of health were associated with fluid intelligence, meaning that those who were fitter had better cognitive functioning[5]. In another study, Gard and colleagues examined elderly yoga practitioners, and found that fluid intelligence declined slower than it did in non-active participants[6].
This is great, because what this suggests is that even modest exercise may be helpful in reducing the cognitive decline that comes with aging.
What it doesn’t tell us, though, is whether exercise can improve fluid intelligence.
There are some studies out there investigating this question, but it’s worth noting that in a lot of cases, studies won’t explicitly refer to what they’re measuring as ‘fluid intelligence.’ For example, Masley and colleagues did a 10-week intervention of low, medium, and high frequency physical activity, where previously inactive participants exercised for 30–45 minutes either 0–2, 3–4, or 5–6 times a week, and found that the more active groups had increased cognitive flexibility by the end of the programme[7]. Cognitive flexibility is our ability to adapt our way of thinking to a changing environment, which is kind of related to fluid intelligence, but it would be a stretch to say they are the same thing, so the evidence is promising, but not authoritative.
Similarly, a review by Ratey and Loehr proposed that both single exercise sessions and long-term exercise routines can improve executive functioning, working memory, and information processing[8], but again, these aren’t exactly the same as fluid intelligence. Information processing probably comes closest, because it’s all about how much information we can take on at any given moment, but it’s not quite there yet.
The most convincing piece of evidence I found was a prospective study by Singh-Manoux and colleagues[9]. What this means is that the researchers followed a slew of participants for 10 years and looked at their physical activity and fluid intelligence at regular intervals. This study did find an association between activity levels and fluid intelligence specifically, which is good news for us, but there’s a caveat: being a naturalistic study, we can’t be sure that this association really is due to physical activity, and not something else. There is a host of things that could have changed in the 10 years of the study, from lifestyle changes to illness, so I’d be cautious to rejoice just yet. Besides, a later intervention study by Daugherty and colleagues found that fitness training alone didn’t achieve significant changes in participants’ fluid intelligence — only fitness training in conjunction with cognitive practice did[10].
So, it may be that to boost our smarts, we need to train our brains as well as our muscles.
What’s the conclusion?
That’s a tough one to answer, chief. It certainly seems that physical activity has some beneficial effects in children, and we can also probably accept that if we keep exercising even in later life, it will help to slow down the decline of our fluid intelligence. But as to whether exercise can actually increase fluid intelligence in healthy adults, well, we’ve got a big question mark hanging over our heads. It’s likely that whatever effects exercise would have are contingent on things like our diet, our job, our family situation, and so forth. There’s also a couple of things worth noting about the studies themselves:
- Many studies are not very specific about the exercise they used as an intervention, so it could be that jogging outdoors is more beneficial than plugging in a home cardio video (the benefits of exercising outdoors is actually a popular area of research nowadays, so this is not entirely a random example).
- One of the biggest issues in psychology research is publication bias, meaning that studies that seemingly ‘confirm’ what we want to know are more likely to see the light of day in a journal.
- Most studies only look at white, middle-class people from Western countries. This is also a wider-reaching problem in psychology, but worth keeping in mind nevertheless.
That said, even if exercise doesn’t make you a genius all of a sudden, it still has all sorts of benefits. Exercise improves your mood on the long run, and you feel more energetic afterwards. It’s also a good way to socialise, whether you’re doing organised sports or running on your own (think Strava!).
And if you feel better, you learn better.
References:
- Herrnstein, R., & Murray, C. (1994): The Bell Curve: Intelligence and Class Structure in America. Freepress.
- Cattell, R. B. (1963). Theory of fluid and crystallized intelligence: A critical experiment. Journal of Educational Psychology, 54(1), 1.
- Reed, J. A., Einstein, G., Hahn, E., Hooker, S. P., Gross, V. P., & Kravitz, J. (2010). Examining the impact of integrating physical activity on fluid intelligence and academic performance in an elementary school setting: a preliminary investigation. Journal of Physical Activity and Health, 7(3), 343–351.
- Donnelly, J. E., Hillman, C. H., Castelli, D., Etnier, J. L., Lee, S., Tomporowski, P., … & Szabo-Reed, A. N. (2016). Physical activity, fitness, cognitive function, and academic achievement in children: a systematic review. Medicine and Science in Sports and Exercise, 48(6), 1197.
- Powell, R. R., & Pohndorf, R. H. (1971). Comparison of adult exercisers and nonexercisers on fluid intelligence and selected physiological variables. Research Quarterly. American Association for Health, Physical Education and Recreation, 42(1), 70–77.
- Gard, T., Taquet, M., Dixit, R., Hölzel, B. K., de Montjoye, Y. A., Brach, N., … & Lazar, S. W. (2014). Fluid intelligence and brain functional organization in aging yoga and meditation practitioners. Frontiers in Aging Neuroscience, 6, 76.
- Masley, S., Roetzheim, R., & Gualtieri, T. (2009). Aerobic exercise enhances cognitive flexibility. Journal of Clinical Psychology in Medical Settings, 16(2), 186–193.
- Ratey, J. J., & Loehr, J. E. (2011). The Positive Impact of Physical Activity on Cognition During Adulthood: A Review of Underlying Mechanisms, Evidence and Recommendations. Reviews in the Neurosciences, 22(2), 171–185.
- Singh-Manoux, A., Hillsdon, M., Brunner, E., & Marmot, M. (2005). Effects of physical activity on cognitive functioning in middle age: evidence from the Whitehall II prospective cohort study. American Journal of Public Health, 95(12), 2252–2258.
- Daugherty, A. M., Zwilling, C., Paul, E. J., Sherepa, N., Allen, C., Kramer, A. F., … & Barbey, A. K. (2018). Multi-modal fitness and cognitive training to enhance fluid intelligence. Intelligence, 66, 32–43.
