Professor Nicola Lautenschlager
A definition of physical activity would be any use of your skeletal muscles which needs energy. Research into the link between physical activity and cognition, in later life, is actually quite a new field. So we really only have increasing evidence in the last 20 to 30 years. However, the evidence we have so far is very promising. There are observational and longitudinal studies which have shown for quite a while that people who adhere to physical activity throughout their lifetime have a lower risk of developing cognitive decline when they get older. And more recently, there has also been an increasing number of randomised control trials with either healthy individuals or people in the community who are at higher risk. Especially for the randomised control trials, the evidence is not consistent. So some of the trials were negative but many were also positive. There is a clear indication we need more research done in this field to understand it better.
The positive studies have shown that regular physical activities are associated with improved cognitive performance. Interestingly, there seems to be evidence pointing towards not every type of cognitive performance benefiting in the same way. Currently, most positive studies show that the evidence is especially for executive function or frontal lobe functions, and anything having to do with speed, so for example, processing speed. Whereas for other cognitive areas such as memory, the findings are much more diverse and controversial.
The other interesting finding so far is that it is important to decide what type of physical activity or exercise is most beneficial when you want to maintain your cognitive health, and again the current evidence of the literature points towards aerobic exercise. Meaning it has to be a type of physical activity where there is enough expenditure of energy to have an increased heartbeat, have more intense breathing, basically an activity where the person can’t keep talking, for example, because they need their breath to do the exercise. To give you a practical idea, if you talk about walking which is the most commonly performed type of aerobic exercise, it has to be of a speed and intensity that is reached, that the person develops more laboured breathing and works up a sweat.
It also has been shown more recently that strength training, so specific training where you use, for example, weights to strengthen your muscles, is also beneficial for cognition, and it looks like a combination of both, physical activity with aerobic focus plus strength training, is probably the best combination, rather than doing only one of these types. Where the evidence is more limited is for exercise which is rather focusing on balance or relaxation, like yoga. We know there are lots of benefits for older people, like the reduction of risk for falls and having a better balance, but whether these more low-impact exercises also can help to contribute to cognitive health is not quite clear.
What is still unknown, and needs much more research in the future, is the question, “What is the right dose?” So how much physical activity do you have to do per week, at what level of intensity, to have the best benefits for your cognitive health? There seems to be emerging evidence that a combination of different types, as I mentioned, might be better than just doing one type, and there is also an emerging field which investigates whether combining physical activity with some cognitive tasks might have additional benefit. For example, it has been shown if you have a physical activity type, like dancing, where you also have to remember steps, or Tai Chi where you have to remember movements, this might give you additional benefit. Another area they’re investigating is what we call dual task exercise. That means someone is, for example, in the gym and does aerobic exercise and then in intervals between the physical activity, they try to do a cognitive task like solving a crossword puzzle or doing some arithmetic. So that’s also an interesting area of research.
Australia, like many other western countries, has official physical activity guidelines and we are also fortunate in our country that we have specific guidelines for older Australians. The recommendations for older people are actually very similar to the recommendations for younger people. So there is quite global agreement that the recommended physical activity level we all should try to adhere to is approximately 150 minutes per week. Now how these 150 minutes are spent across the week is very variable. The recommendation is that it shouldn’t be shorter than 10 minutes at a given time. Very often you read a recommendation that trying to do 30 minutes, most days of the week, is a good way to go about it. The recommendations further say the type of physical activity should be mainly moderate aerobic exercise. So that could be either fast walking, or it could be going into a gym program, or it could be bike riding, for example. So there are lots of options. It could be swimming. And then ideally that should be combined with, at least twice a week, some strength training, and obviously outside the benefit for cognition, some balance training to reduce the risk of falls in older people.
So the question, “[Does] it makes a difference if you have done lots of physical activity as a child or a younger person, in terms of the benefits to your cognitive health when you are older?” is a very interesting question. There are studies which have exactly shown that there is, sort of, a lifelong accumulation of your physical activity efforts throughout your lifespan, and the more you have done throughout your life, the better the chances that you have good cognitive health when you’re older. However, there is also research showing that it’s never too late to get started. Looking, for example, at older participants or people who never have done physical activity in their life, who have had a more or less sedentary life and then only started doing physical activity at an older age, even that group can experience some quite impressive benefit with regards to their cognitive health.
The largest amount of evidence in this field we do have for cognitively healthy people, when it comes, for example, to randomise control trials, there is a small but increasing number of studies which focused on people who already experience some cognitive impairment. A classic example would be studies with either older people who have subjective memory decline or, what we call, mild cognitive impairment. Both of these clinical groups have been identified as being at increased risk of later on developing some more pronounced cognitive decline, such as dementia. The study results are less clear in those clinical groups, compared to healthy participants, but there have been a number of trials now which have shown that, also in these clinical groups, there is benefit to cognitive performance, and a few of these studies even have shown that the right type of physical activity program might help to delay the progression of the cognitive impairment.