Lets take a look at the effects of exercise on human subjects. In a very large study following more than 18,000 women aged 70 to 81 for 8 to 15 years, it was found that higher levels of long term regular physical exercise was strongly associated with higher levels of cognitive function.
The women who exercised regularly, behaved as if they were three years younger on average. And they had a 20% lower risk of having cognitive impairment. The benefits derived from physical exercise were not limited to women who did heavy, vigorous exercise. Women who walked more than or equal to an hour and a half per week, the equivalent of walking two times around a standard track in ten minutes per day. Also saw protective benefits against cognitive decline.
In another study, a hypothesis was tested, that aerobic fitness training enhances the cognitive vitality of healthy but sedentary older adults. 18 studies published between 1966 and 2001, were entered into the analysis. Several theoretic and practically important results were obtained. Fitness training was found to have robust, but selective benefits for cognition, with the largest fitness induced benefits occurring for executive functions. Such as planning, decision making and multitasking. Exercise also showed positive effects on spatial recognition and speed. These studies showed a larger effect in women and the effect was the same on healthy and cognitively impaired adults.
Let's explore specific studies looking at the effects of aerobic exercise on cognition, brain function and brain structure in older adults. In a six-month study, one group was randomized to walk three times a week, and the other to stretch and perform relaxation techniques. All subjects then had their cognitive and executive functions measured. The walking group had, on average, a higher brain volume compared to the stretching group. This increase was seen more in the anterior cingulate area, which is the seat of emotional control, as well as the weight matter connecting both hemispheres. Possibly showing a more efficient communication between the hemispheres. From a neuropsychological standpoint, the walking group showed better attention and better memory. And this was thought to be correlated to those areas in the brain that increased in volume.
The same study was done, but the observation time was increased to a year. Subjects were randomized two or three times a week, walking program versus relaxation. Their cognition was measured and their brain volume evaluated.
Results showed that the hippocampus volume increased by 2%. You may think that this increase is not significant, but actually that increase corresponds to a reversal in age-related loss in volume by two years.
What about strength and resistance training? How does that affect the brain?
We know it has a lot of non-brain benefits, such as promoting bone health and reversing osteoporosis and sarcopenia, or loss of bone tissue. We also know its effects on muscles, but does it affect the brain?
In a study comparing the effect of moderate versus high intensity resistance training in two groups of subjects aged between the ages of 65 and 75. The group performing high intensity resistance training showed improvement in verbal and spatial memory compared to the group with moderate intensity training. In another study, resistance training versus balance exercises, three groups of subjects were randomized to once a week versus twice a week of resistance training. Versus twice a week of balanced exercises.
This group of subjects were all women between the ages of 65 and 75 who had not partaken in resistance training before. These participates were all community dwelling women with no history of brain disease like stroke or a neurodegenerative disease. The resistance training group did 60 minutes of classes, including 40 minutes of resistance training with sets of eight reps, versus the group of balance, which also exercised for 60 minutes. More details on the exercises done can be found in the supplemental reading provided. The resistance training group showed significant improvements in executive functions at 12 months of training. And this was the case for both the once and twice a week groups.
And in a most recent study published just in 2018, a Swedish group published findings that moderate to high physical fitness in women was associated with a 90% decrease in risk of dementia. And even when dementia did occur, it happened on average 11 years later than expected. How about yoga? We know yoga is a great exercise for the mind body connection because it's itself a sort of moving meditation, and because it often includes a portion of meditation as well. It's well known that yoga decreases hypertension, stress, depression, and anxiety.
In a study, first-time yoga participants were enrolled in a 12 week program. Their brain physiology was measured through EEG measurements. And the subjects who went through the yoga training showed a higher activity of the left hemisphere, compared to the control group. That is typically associated with good and positive moods. The study also showed an increase in blood flow in the prefrontal cortex, which is the seat of executive function, including judgment, planning and such. The yoga practitioners also had changes in their amygdala and sensory motor cortex, which is where sensory phenomena and emotions get processed.
Another study compared age related gray matter decline in yoga practitioner and in a control group. In this study, they found that the control group displayed the well-documented age-related grey matter decline, while yogis did not, suggesting that yoga contributes to protecting the brain against age related decline. Also, the more time spent practicing yoga, the higher the effect on brain volumes. The number of years spent practicing yoga also correlated with gray matter volume differences in the left hemisphere, insula, frontal lobes, and orbitofrontal cortex. The results also suggested that yoga tunes the brain towards more positive states. Study analyses indicated that the combination of postures in meditation contributed the most to the size of the hippocampus and parietal lobe. While the combination of meditation and breathing exercises contributed the most to visual cortex volume. Yoga's potential neuro-protective effects may provide a neural basis for some of its beneficial effects.