Every Bit Counts

by Women's Brain Health Initiative:It is widely understood that physical activity is important for both physical and cognitive health. But, just how much physical activity, and at what intensity level, is enough to reap the benefits?The Canadian Physical Activity Guidelines, published jointly by the Canadian Society for Exercise Physiology (CSEP) and ParticipACTION in January 2011, recommend that adults (aged 18 to 64) should aim for at least 150 minutes of moderate- to vigorous- intensity aerobic physical activity (MVPA) each week, in bouts of ten minutes or more, as well as muscle and bone strengthening exercises at least twice per week.For older adults (aged 65 and over), the recommendations are the same, but the guidelines also note that those with poor mobility should perform physical activities to enhance balance and prevent falls. While there is no reference to light-intensity aerobic physical activity, the guidelines emphasize that engaging in "more physical activity provides greater health benefits."The 2018 Physical Activity Guidelines for Americans, published by the U.S. Department of Health and Human Services, provide slightly different recommendations for adults, with a broader approach to exercise intensity and duration. The U.S. guidelines recommend a minimum of 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic physical activity each week for “substantial health benefits.”They, too, recommend at least twice per week muscle-strengthening activities, but add that this exercise should be of moderate or greater intensity. Although the U.S. guidelines also mention that engaging in more physical activity is better, they emphasize the value of reducing sedentary time and note that engaging in "some physical activity is better than none." Their recommendations for older adults are the same as for adults, with a few additions:

1. add balance training each week;
2. adapt level of effort to level of fitness;
3. take any chronic conditions into consideration to choose physical activity that can be done safely; and
4. if 150 minutes of moderate-intensity aerobic activity is not possible due to chronic conditions, just do as much as abilities and conditions allow.

Both sets of guidelines stress the various health benefits of engaging in moderate and vigorous exercise, and there is a plethora of research to support these recommendations. Research is also beginning to demonstrate that there are benefits of engaging in light-intensity exercise as well, even for short periods of time, and the U.S. guidelines reflect this new understanding.The Canadian guidelines, however, are quite a bit older than their American counterpart, so perhaps the next version will incorporate similar recommendations in this regard. CSEP announced in June 2019 that it is working on developing the world’s first 24-Hour Movement Guidelines for Adults and Older Adults, which will recommend the appropriate amounts of physical activity, sleep, and sedentary time for a healthy day.Light-intensity Physical Activity Provides Physical and Cognitive Benefits for Older AdultsResearchers from Hong Kong conducted a systematic review of the research on the effectiveness of low-intensity exercise on the physical and cognitive health of older adults, and shared their findings in 2015 in Sports Medicine. After reviewing 15 studies conducted from January 1994 to February 2015, Dr. Andy C.Y.Tse and colleagues concluded that there was “strong evidence” that low-intensity exercise improves physical and cognitive health for older adults. Specific to cognitive health, the researchers noted significant reductions in depression symptoms and improved cognitive function.Light-intensity Physical Activity Reduces Risk of Cognitive Decline in Older AdultsIn 2017, Experimental Gerontology published the findings from research conducted by Dr. Brendon Stubbs and colleagues examining the effect of light-intensity physical activity on cognitive decline. Rather than use self-reported measures of physical activity, which are known to be unreliable because they depend on an individual’s recall ability, these researchers used accelerometers to measure the physical activity of over 270 older adults in Taiwan.Light-intensity physical activity and MVPA were each considered separately, rather than as a combined measure of overall physical activity. The resulting data suggest that a higher amount of light-intensity physical activity, independent of MVPA, is linked with a reduced rate of cognitive decline. MVPA on its own was also associated with a lower decline in cognitive ability.“Our data suggest that light-intensity physical activity may offer protection of future cognitive ability in older adults,” said Dr. Brendon Stubbs, a National Institute for Health Research (NIHR) Clinical Lecturer at King's College in London, U.K., and lead author of the study. “We should not overlook the importance of promoting light-intensity physical activity, such as walking, to help older adults maintain their cognitive ability as they age.”Light-intensity Physical Activity Associated with Larger Brain Volume and Healthy Brain AgingDr. Nicole Spartano and colleagues analyzed data from over 2,350 participants (with an average age of 53 years) who were part of the Framingham Heart Study. Using accelerometer measurements and magnetic resonance imaging (MRI) brain scans, the researchers looked at the effects of physical activity on total cerebral brain volume.They found that higher levels of light-intensity physical activity were associated with larger total cerebral brain volume. Each additional hour of light-intensity physical activity was associated with an estimated 1.1 years less brain aging. Total cerebral brain volume is known to shrink as a part ofnormal aging at an average rate of 0.2% per year once you are over the age of 60.Given the emphasis on MVPA in both the Canadian and U.S. physical activity guidelines, it is surprising that these researchers found that MVPA was not significantly associated with brain volume after adjusting for light-intensity physical activity (i.e. in their analysis of MVPA, the researchers stripped away the effect of light-intensity physical activity and were able to examine the impact of MVPA individually).Their observation that MVPA in and of itself was not significantly associated with brain volume suggests that it is unclear whether one can expect additional benefits for the brain with higher-intensity activity. These findings were published in April 2019 in JAMA Network Open.Even a Short Burst of Light-intensity Physical Activity Provides a Brain BoostResearchers at the University of California, Irvine, and Japan’s University of Tsukuba conducted a study involving 36 healthy young adults to learn about the impact of mild exercise on neurocognitive function, including hippocampus-dependent episodic memory.The participants engaged in a single ten-minute session of very light-intensity exercise on a recumbent bicycle and then completed a memory test. They each also underwent a high-resolution MRI brain scan shortly after the exercise session. The findings were published in October 2018 in PNAS.The MRI scans revealed that, after just ten minutes of light exercise, participants’ brains showed better connectivity between the hippocampal dentate gyrus and cortical areas linked with detailed memory processing. The hippocampus is important for the creation and storage of new memories and is one of the first regions of the brain to deteriorate with age, particularly severely in cases of Alzheimer’s disease. And, the higher the level of connectivity observed in the brain, the better the participants performed on the memory test.“This study demonstrates the immediate impact of light-intensity exercise,” said Dr. Michael Yassa, a professor at University of California, Irvine, and co-leader of the research, “and it’s exciting to know that just a small amount of light-intensity physical activity can make a difference." Dr. Yassa further noted that even short walking breaks throughout the day could help considerably with improving memory and cognition. That’s a very realistic goal for many older adults.The Importance of these Findings about Light-intensity ExerciseThe reality is that, despite widespread efforts to promote the various benefits of physical activity, most people are not meeting the MVPA recommendations set out in the physical activity guidelines. In the U.S., for example, one study estimated that only 9.6% of U.S. adults met the minimum recommendations based on accelerometer measurements (or 62%, based on self-reported data).Of course, for some individuals, not meeting the MVPA recommendations is a matter of lack of time or motivation. But, for many older adults, it is a matter of physical limitation and lack of energy, and these are likely not variables that are within their control to change.For some older adults, then, no amount of physical activity promotion is going to make them participate in moderate- to vigorous-intensity physical activity, particularly for the recommended duration. But many of these individuals are still capable of participating in light-intensity activities, particularly in short sessions at a time.Making the general public – and older individuals in particular – aware that there are brain benefits to engaging in even small amounts of light-intensity physical activity could provide motivation for people to get moving more. Knowing that even a little bit can go a long way might be surprising, and very welcome, information. Promoting light-intensity physical activity to older adults might also help with better compliance (i.e. people are more likely to engage in this level of activity because it is the right fit for their fitness level and is enjoyable), while at the same time potentially lowering the risk of injuries.Of course, if you are physically capable of engaging in moderate-to-vigorous activity, then certainly you should aim to meet the minimum guidelines. However, if MVPA is not realistic for you for any reason, these research findings should provide reassurance that if you move as much as you can (even if that is just at an easy pace and for a short period of time), your brain will thank you.What is “moderate” intensity?The Canadian Physical Activity Guidelines describe moderate-intensity physical activities as those that will cause you to sweat a little and breathe harder. Such activities would be rated 5 or 6 on a scale of 0 (at rest) to 10 (absolute maximum effort).What is “vigorous” intensity?The Canadian Physical Activity Guidelines describe vigorous-intensity physical activities as those that will cause you to sweat and be out of breath. Such activities would be rated 7 or 8 out of 10.What is light-intensity physical activity?Examples of light-intensity physical activity include walking at a slow pace, tai chi, gentle yoga or stretching, and lifting light hand weights. Certain household tasks also provide light-intensity exercise, including gardening and cleaning.Source: MIND OVER MATTER V9