Early on in my exploration of an ethical theory that incorporated both moral (other-directed) virtues and non-moral (self-directed) virtues (particularly those virtues related to physical fitness), I discussed the relationship between fitness and intelligence. In this previous piece, I presented several scientific studies which demonstrate that increased physical activity leads to improved cognitive performance. I also cited one study in which subjects increased their muscular strength simply by imagining they were moving particular muscles. Based on this body of research, I claimed a complementary relationship between the virtues of fitness and intelligence, although I noted that the assertion that greater cognitive ability could result in improved physical fitness would benefit from evidence “that higher levels of mental stimulation and intelligence are correlated with increased physical capabilities.”  Had I delved deeper into existing research when I wrote that piece, I would have found the evidence I had been seeking. Instead, I present it in this article.
In the study cited in that previous article, researchers at the Cleveland Clinic Foundation divided 30 subjects into four groups: eight subjects who were trained to perform mental contractions of little finger abduction, eight who were trained to perform mental contractions of elbow flexion, eight who performed no mental contractions, and the remaining six who performed physical training of little finger abduction. After 12 weeks of training, the mental abduction group improved finger abduction strength by 35%, the mental flexion group improved elbow flexion strength by 13.5% and the physical training group improved finger abduction strength by 53%. The control group showed no significant strength changes for either movement. 
This positive effect of mental imagery on physical action is well-documented. Researchers found that brain patterns activated when weightlifters lifted hundreds of pounds were also activated when they only imagined lifting.  A 2014 study compared 29 subjects who wore a rigid cast that immobilized their hands and wrists for four weeks against a control group of 15 subjects who did not wear a cast. 14 of the 29 subjects in the experimental group performed four weeks of mental exercise in which they imagined contracting the muscles in their wrists, while the other 15 experimental subjects performed no such exercises. After four weeks, all subjects with immobilized arms had lost strength in that arm in comparison to the control group. But those subjects who performed imaginary exercises lost only 24% of their initial strength compared to a 45% strength loss in the non-imaginative group. 
These three studies demonstrate a clear connection between mental imagery and physical performance. Imagining specific muscle contractions or physical movements can produce physical effects similar to those produced by actual physical activity. Yet the question still remains as to whether any such mental imagery, no matter its quality, can produce significant physical results. Is mental imagery a cognitive skill, like memory or vocabulary, which can be learned and improved to effect greater physical change?
In a 1985 study, 30 college students were separated into three groups of ten as follows: the first group was instructed to imagine putting a golf ball into the hole, the second group was instructed to imagine the ball just missing the hole, and the third group putted without any instruction. Each subject attempted ten putts on six consecutive days. Over the course of the experiment, the subjects who practiced positive imagery showed the greatest improvement, the control group showed less improvement, and the group who practiced negative imagery saw their performance get worse over the course of the trial. 
Finally, in a 1992 study, Anne Isaac classified 78 trampolinists as novice or experienced, and as high or low imagers based on an initial assessment of mental imagery ability. She then divided them into experimental and control groups, and had the experimental group practice a trampoline skill for 2:30 (two minutes, thirty seconds), mental imagery for 5:00, and then return to skill practice for an additional 2:30, while the control group practiced for 2:30, spent 5:00 on a mental task such as a math problem, and practiced the skills for another 2:30. The subjects were trained in this fashion in three skills over a six week period. As expected, the experimental group showed greater improvement in the skill than did the control group at the end of the experiment. Moreover, in both the novice and experienced group, the high imagers showed greater improvement than did the low imagers. 
Clearly, the quality of mental imagery does matter in the effectiveness of its translation to physical performance. Positive imagery encourages gains in physical performance while negative imagery translates to poor performance. Successful imagery would seem to require a certain level of focus to exclude negative impulses and concentrate on visualizations of success. Furthermore, mental imagery is a skill with different ability levels. Those who are more skilled at imaging will achieve better physical results. In other words, increased cognitive capabilities in the form of mental imaging skills are associated with improved physical performance.
In hindsight, my previous desire for “a demonstration that more intelligent subjects achieve greater physical improvements”  suffered from a poor choice of words. Individuals skilled at mental imagery are not necessarily more intelligent than others, but like those with good memories or large vocabularies, they possess a greater cognitive ability in this aspect of mental performance. My original goal was to show that physical virtues are related to mental virtues. Increased physical activity and fitness lead to improved cognitive function. And as the above studies demonstrate, greater cognitive capabilities translate to improved physical performance when appropriately focused.
1. Hickey, Greg. “Fitness and Intelligence.” KineSophy. 1 Jan. 2014. Online. 24 Sep. 2015. https://www.kinesophy.com//fitness-and-intelligence.
2. Ranganathan V, Siemionow V, Liu J, Sahgal V, Yue G. “From mental power to muscle power—gaining strength by using the mind.” Neuropsychologia, 2004, 42(7), p. 944-56. Online. PubMed.gov. 24 Sep 2015. http://www.ncbi.nlm.nih.gov/pubmed/14998709.
3. Cited in LeVann, AJ. “Seeing Is Believing: The Power of Visualization.” Psychology Today. Online. 24 Sep. 2015. https://www.psychologytoday.com/blog/flourish/200912/seeing-is-believing-the-power-visualization.
4. Brooks, Stacy. “Mind over Matter: Can You Think Your Way to Strength?” American Physiological Society Press Release. 31 Dec. 2014. Online. 24 Sep 2015. http://www.the-aps.org/mm/hp/Audiences/Public-Press/2014/30.html.
5. Woolfork R, Parrish M, Murphy S. “The effects of positive and negative imagery on motor skill performance.” Cognitive Therapy and Research, June 1985, 9(3), p. 335-341. Online. 24 Sep. 2015. http://link.springer.com/article/10.1007/BF01183852#page-1.
6. Isaac, Anne. “Mental Practice- Does it Work in the Field?” The Sport Psychologist, 1992, Issue 6, p. 192-198. Cited in Plessinger, Annie. “The Effects of Mental Imagery on Athletic Performance.” Vanderbilt University Psychology Department. Online. 24 Sep. 2015. http://www.vanderbilt.edu/AnS/psychology/health_psychology/mentalimagery.html.
7. Hickey, 2014. https://www.kinesophy.com//fitness-and-intelligence.