A number of studies have shown that aerobic exercise can lead to cognitive benefits. However, research had not directly examined the question of the specific degree of cognitive benefit associated with specific amounts of aerobic exercise. A recent article in PLoS One, describes a randomized controlled trial that examines how different amounts of exercise impact cognition.
This study assigned 101 sedentary or underactive older adults to one of four groups. The average age of the participants was 73. One group was a control group and the other three groups engaged in aerobic exercise 75, 150, and 225 minutes per week respectively. The American Heart Association and the American College of Sports Medicine recommend that older adults engage in 150 minutes of aerobic exercise per week, so this study examined how 50 percent, 100 percent, and 150 percent of that recommended dose of aerobic exercise impact cognition. Participants got their aerobic exercise on a treadmill or elliptical machine, and were asked not to otherwise modify other pre-existing physical activity for the duration of the study. In addition to giving participants cognitive tests at the start of the study and when the study ended 26 weeks later, the researchers also measured the change in participants’ cardiorespiratory fitness.
When analyzing the results, the researchers first looked at all participants, regardless of their degree of adherence to the prescribed amount of exercise. Overall, the 75-minute group completed 82 percent of the prescribed minutes of exercise, the 150-minute group completed 85 percent, and the 225-minute group completed 70 percent. Each of the three groups saw improvements in their cardiorespiratory fitness, with 7% percent improvement for the 75-minute group, 8 percent for the 150-minute group, and 10 percent for the 225-minute group. However, when they looked at cognitive changes in analyses that included all participants, the researchers did not see any statistically significant changes.
This changed when the researchers restricted their analysis to only 77 study participants who completed at least 80 percent of their prescribed exercise minutes. These participants averaged 95 percent completion of the prescribed minutes of exercise. These high compliance individuals in each aerobic exercise condition showed 6 percent, 9 percent, and 11 percent improvements in their cardiorespiratory performance respectively. When the researchers examined their cognitive performance, they found that attention and visuospatial processing improved compared to the study’s control group. Even those participants getting half of the recommended amount of aerobic exercise were showing statistically significant cognitive improvements. Interestingly, there was not a significant difference in improvement in attention across the three exercise groups. On the other hand, greater amounts of aerobic exercise resulted in greater amounts of visuospatial cognitive improvements. Here the 75- and 150-minute groups had similar levels of visuospatial improvement, while there was a more substantial improvement for the 225-minute group.
The researchers also examined how much of the observed cognitive changes were accounted for by cardiorespiratory performance, as opposed to resulting from some other aspect of aerobic activity. In this analysis they found that cardiorespiratory improvements fully mediated the relationship between aerobic exercise and visuospatial cognitive improvements. This finding suggests that cardiorespiratory improvement may be more appropriate goals for aerobic exercise than just exercise duration.
There are few key takeaways from this study. First, this study shows the importance of strict adherence to an aerobic exercise regime to produce measureable cognitive benefits. It was only among the high adherence participants that cognitive improvements were observed. Second, it suggests that even for older adults who are not able or willing to meet the recommended 150 minutes of aerobic exercise a week, there are still cardiorespiratory and cognitive benefits if they are only to do half the recommended amount of weekly exercise, if they strongly adhere to a regular regime. Third, the visuospatial cognition results show that greater amounts of exercise can lead to greater cognitive improvement. Achieving 150% of the recommended amount of aerobic exercise produced the greatest amount of visuospatial improvement. Lastly, the analysis of the relationship between cardiorespiratory fitness and cognitive improvement suggests that targeting cardiorespiratory improvements as a goal for an exercise regimen could be more effective than just targeting exercise duration. Exercise programs for older adults could be designed with the goal of maximizing cardiorespiratory gain, by varying frequency, type, time, and type of activity.