A Surprising Link Between Muscle Mass, Strength, and Cognitive Function


Welcome to Better Brain Fitness, hosted by doctors Josh Turknett and Tommy Wood. In this podcast, we will explore the frontiers of how to keep our brain fit and healthy so that we can perform at our best and do the things we love for as long as possible. Let’s go. Hello and welcome to another episode of the Better Brain Fitness podcast. Today, as usual, I’m joined by my brawny cohost, doctor tommy Wood. Hello Tommy.

00:39 : So Tommy has recently published a paper on the connection between Braun and cognitive function along with some other authors, and he’s going to talk about it had some pretty interesting findings so I’m going to let Tommy tell us about what the paper showed and maybe what the implications are for those of us who are interested in long term brain health and fitness so Tommy, take it away thanks. So this paper I’ll just start by giving you the title is called Strength and multiple types of physical activity predicts cognitive function independent of low muscle mass in Haines 1999 to 2002 I just published in the journal Lifestyle Medicine and it actually started as me just digging into some data for a for a presentation that I gave at the metabolic health summit like 18 months.

01:43 : I was really interested in trying to understand how physical activity and muscle mass and strength are associated with cognitive function and taking into account other things that we know are important such as metabolic health say blood sugar regulation as measured by HBO and C blood pressure inflammation with measured by CRP home assisting we’ve talked about several times so some a measure of B vitamin status. You know trying to take these things into account and to do this I used data from enhance the National Health and Nutrition Examination Survey here in the US which would they do waves every year They just they invite people.

02:27 : It sort of creates a group that are supposedly representative of the of the US population and it’s a few thousand people every year and they do blood tests and a whole bunch of other different tests. And if you’re doing sort of large scale epidemiology with US based data, you’re often using this N Haynes data set and they’ve been doing this for several decades now. And in one or in a couple of waves of this they did a few things that then This is why I selected the 1999 to 2002 cohort, they had cognitive function tests in older adults so those sixty years or older, they did something called the digit symbol substitution test, which is a measure of processing speed in general and sort of it’s a nonspecific, that’s cognitive test but often associated with processing speed, how fast you can process information and what and what you do is you have a sort of a key that gives you a number and each number is associated with a symbol, like a random symbol of you know, various lines or something but fairly simple to draw.

03:40 : And then you just get a whole bunch of boxes and there’s a box that gives a number and then you’re supposed to write the associated symbol underneath and you get 2 minutes to do. I think it’s 133 symbols for numbers, so basically you have to very quickly associate each number with it if you want to do it and as many as possible you have to remember the symbol that associate with each number and like draw them continuously and quickly. And so we so we had a cognitive function test, but then they also had DEXA scan so we know how much muscle mass they have and they also had a strength metric, but it was leg strength.

04:18 : And in general these kinds of big epidemiology, epidemiological studies use grip strength and grip strength is fine, it’s easy to measure, but leg strength is probably much more important in terms of mobility strength, actual muscle mass, actual function, because it’s a much bigger muscle group and it’s probably going to be more related to, you know, other aspects of your health and physical activity so that that’s why I focused on this group because I think leg strength is probably going to be a better predictor and various health related things rather than grip strength. Although grip strength is okay if that’s what you have. And historically people have shown a few things like there was a UK biobank study that showed that the more muscle mass you had that was associated with a higher scores on a fluid intelligence test which is like a, it’s usually a nonverbal abstract reasoning kind of test.

05:14 : And then there was a Canadian study that recently showed that those who had low muscle mass and they used what they called the apendicular lean mass, which is basically how much muscle do you have on your limbs as a measure of muscle mass those who had low apendicular lean mass, they had fast the declines in executive function which they did with the range of different tests like the Stroop test over a three over a three-year period. But sort of what each of these different studies didn’t do was look at everything at the same time strength and muscle mass and physical activity and you know other health related metrics and so that was that was part of the reasoning why we did this analysis.

05:55 : And what we found to my surprise was that more muscle wasn’t better and I was very sad about this because I think that you know lifting weights is a is a favorite part style of mine and I think everybody should do it. So that was the first thing that we found was that and we actually focused on those who had. In general the literature has suggested that it’s not that more is better, it’s that you just need to have enough, right you just shouldn’t have low muscle mass.

06:29 : So we focused on low muscle mass and we did it two ways we did it with the limb muscle mass as they did in that previous Canadian paper but then we also use something which is slightly simpler to measure, called the F FM I the fat free mass index, which is basically you take how much you weigh, you remove your % of body fat, which is easy to estimate in a range of different ways.

06:51 : And then that’s the weight that you use and then you calculate an index like you would with BMI so you divide it by your height in meters squared and so those who are in the bottom 2020 %, you know did they have different cognitive function like performance of the cognitive test after accounting for things like strength and physical activity and the answer is no. So the muscle mass didn’t really play much of A role there.

07:19 : Strength and physical activity were much more important. Hey there. So if you like this podcast then I think you will enjoy the Brain Joe Connection newsletter. The Brain Joe Connection is a free newsletter sent out twice a month and is all about the science of how to keep our brain fit and healthy along with products, books, tools and resources for improving brain health and function that we use and recommend to subscribe.

07:47 : You can go to Brain Joe dot Academy forward slash connection or click the link in the podcast description. All right now back to the show some interesting other things that came out was that muscle mass was not correlated with physical activity. So those who are more physically active did not have higher muscle mass and in fact we saw some suggestion of the opposite. And this is really interesting, but it helps to explain some other things that we’ve started to see come out of the literature. So there was another UK biobank study that said that men in particular who had high amounts of muscle mass had a higher risk of cardiovascular disease. But in that same study they showed that those who had higher strength with grip strength had much lower risk and like the more the better like there’s there was no no cut off so just the stronger you were, the lower your risk of cardiovascular disease, but the higher, you know if you had a very high muscle mass, you had higher risk of cardiovascular disease.

08:51 : So what that starts to tell me is that muscle mass and strength are kind of disconnected in these in these population studies, particularly if muscle mass is not related to physical activity. And we saw something similar here, which is basically that if you had more muscle, it was just because you were, you were a bigger person in general and that’s probably because of a caloric surplus rather than because you were lifting a bunch of weights. So what really matters is muscle function. And muscle is functional if you gain it through physical activity, but it’s not as functional in the same way if you just gain it by just eating more.

09:27 : And if you gain mass, you get heavier some of that’s going to be muscle, and those who had more muscle mass actually had some worse indicators of they had more body fat and they had worse indicators of metabolic health. Like the men had a higher waist circumference, which suggests they probably had more visceral fat, which is the fat tissue that’s associated with cardiovascular disease and they also had worse blood sugar regulation, they had higher h b o n c ‘s. So the kind of the really interesting things that come out of this to me is the strength as sort of neuromuscular function is a really important predictor of cognitive function and we know that even in older adults, if they do a weight training program that is associated with improvements in strength and improvements in cognitive function.

10:18 : But just looking at muscle mass isn’t very helpful here because at the population level, people aren’t building muscle mass because they’re going to the gym, they’re building muscle mass just because they’re gaining total mass people just get heavier over time on average because they eat above their chloric requirements at the population level. So and in our sort of final analysis, we showed that we created this relative strength metric so how strong are you relative to your muscle mass And that was a very strong predictor of cognitive function.

10:48 : So you know I think that we can still take away that lifting weights is going to be good for your brain, but you know how you gained your muscle mass is really important factor as are all these other things related to physical activity so even if you don’t have a huge amount of muscle mass, if you’re physically active so that the way that we coded that was, were you doing some kind of resistance training once a week, were you doing some kind of vigorous physical activity in the past month that was a question that they asked and just say yes to doing at least one ten minute session where you increased your heart rate in your breathing very heavily in a month.

11:31 : That was associated with a significantly higher performance in the cognitive test so it’s really not that much. And then there was another question related to sort of daily activities and those who frequently took the stairs or carried light or heavy loads as part of their work or day or day-to-day activities that was also associated with significantly higher performance in the test. So all these different types of physical activity were beneficial, strength was beneficial, but if there was any factor of improved cognitive function associated with muscle mass, it we acted via improved strength. So you know muscle is only better if it’s also functional and stronger rather than you know, you just sort of gained it because you’ve gained weight overall.

12:19 : So those are kind of the main, the main takeaways and do you have any questions after any of that? So first of all, I know you were disappointed, but i’m pleased because my confirmation bias really likes this study because ultimately what it’s saying is that it’s our, if it’s strength is the thing then it’s our capabilities that matter, right. And so the people who have, who have, you know the stronger an individual is likely a reflection that they have been doing things to maintain a particular set of capabilities whereas like you say muscle mass doesn’t necessarily correlate to that, right there can be many other reasons why. But if someone is on the stronger side, then it means they’ve been doing things to keep up that which is a functional right metric, right it means they’re strong, they’re more capable And like we’ve talked about is that the, you know, how much you maintain capabilities should be the driving factor in your cognitive function so i like it as a very good supporting document for the demand coupling model of cognitive decline.

13:29 : So what after, you know, in light of this test is there, what would you pose to be maybe one of the best or a very good predictor if you could have one kind of test or a few tests, what would you think would be most predictive of cognitive function? As a physical test, As a physical test yeah. And I’ll just say that other things that popped up that we included and if people like fancy graphs, which I do, you can look at the paper and I made some very fancy graphs which shows how all the different factors interact. It’s called these graphical network models so you can kind of you generally when you do statistics you have one outcome and you have a bunch of things that predict the outcome and you adjust for some other factors whereas this essentially shows all of those relationships at the same time and takes them all into account together which I think is kind of cool so you can kind of take a look at that but the best predictor of cognitive performance was education, which we know you know lifelong cognitive stimulus and then there’s also some socioeconomic factors that get baked into that, but that was the best predictor in action and also sex was important so the in general the women performed better on the test, but in terms of physical predictors essentially any measure of strength seem to be seem to really important.

15:02 : But it’s all kind of I feel like it’s all sorts of proxies kind of for the same thing although they have an individual they have individual effects and another reason why I was interested in studying this is because you know, often when I say you know muscle mass is important for health, people say, what about reverse causality is it just that you’re healthy and therefore you have more muscle mass, right. Essentially saying that you just lose muscle mass because you’re sick and it’s like a it’s just an indicator of worse overall health. But that certainly doesn’t seem to be the case here. So what we kind of find is literally any regular physical activity is beneficial and this was just asking you know people questions about their physical activity.

15:48 : But then if you’re going to, if you’re going to try and test somebody. I think we have data from this and from other studies to suggest that any sort of test of baseline physical strength is probably going to be okay so group strength with a with a hand on and monitor that’s pretty good. What they did here is they use this isokinetic leg extension thing which basically means that you the speed, it’s like a leg extension machine which you sit at in the gym but the speed is held constant but the harder you push, the harder it pushes against you so it can it figure out, it figures out how hard you can push at that at that at that fixed speed.

16:30 : But nobody’s going to do that test right. But that’s just like that’s not a thing you’re going to have access to. So then if people are trying to apply this themselves, I think any measure of strength and i do think lower body strength is probably going to be more important that you know if we had to pick one just because that’s going to be associated with risk of falls and all these other things and also these are where the large muscles are, they’re important for glucose metabolism and metabolic health and all these other kinds of things.

17:04 : So then you know any kind of weighted squat, i personally like, I think my favorite is any kind of deadlift, you know anything that you have because I mean it’s a whole body exercise it also exercises your grip and you know you can do it with pretty much any kind, any kind of thing that you can pick up off the floor. And the reason why, you know now we’re kind of getting into what people can do for themselves and then and then you would just have some exercise that you could do and then you just see am I maintaining that over time or am I, am I improving, am I training it with the exercise that I’m doing, you know or am I, you know at best you know even as you get you know if you if you’re tracking it for several years not losing strength as you get into your forties fifties sixties and then particularly beyond that if you’re able to maintain some amount of strength that that’s a that’s a big deal because normally you would expect to lose strength that you know 2 or 3 % per year.

18:06 : So the real answer to your question is I don’t think there’s the perfect assessment but that also means that anybody can pick something that they have access to and then they can track it over time and hopefully do some kind of do some kind of training that helps maintain it and or if this is a new stimulus for you if you’ve never lifted weights before and you do happen to be able to get into a GM, you don’t have to do you know some people are worried about a deadlift it doesn’t have to be a deadlift you can use machines and that’s what they’ve done in some studies so like a leg press machine and some kind of bench press machine you know some kind of pull down machine you know just a just three or four exercises on the machines track your track your performance over time you know do you sort of improve initially we would expect to regardless of your age or training experience and then can you maintain performance in the years to come but those are going to be really important factors and would you say the most important metric is, would be not just not absolute strength but strength relative to size so in that regard like you know a body you know body weight, you know that could be a good way to determine for yourself like you know how many push ups, pull ups can you do that sort of thing would be a good easy metric to follow because it’s sort of normalized for size.

19:25 : Yeah that that’s that’s a great idea and a good point and there’s been lots of attempts to do this and they actually do it in things like powerlifting competitions where you have a coefficient based on your body weight which then allows you to compare individuals even though one may be much bigger than the other and stronger with that. You know what’s your what’s your relative strength that does those metrics do tend to favor lighter people that’s just a sort of how they work but yes, so I think you know strict pull ups and things like that very hard you know to do in general but if you had some kind of you can you can do them with bands or other assistance and so and then so it’s still.

20:12 : Normalized to your body weight and you can track that over time but yes push ups, body weight squats, things like that because relative strength and that’s what we looked at does seem to be, does seem to be really important so ways that you move your own body in space are probably a much fairer comparison across groups and there are some studies that look at you know how many push ups can you do and particularly cardiovascular disease and they do seem to be associable on other so the more push ups you can do to lower your risk of cardiovascular disease there are some studies that have looked at that so yes that that’s a great point and it’s it really is a case of if you’re getting bigger whatever the reason that is just make sure you’re getting stronger with that because if you’re increasing in mass whilst not increasing relative strength and that’s probably an indication that there’s a disconnect between the amount of muscle you haven’t and how functional is.

21:10 : And then that seems to directly relate to cognitive function as well right. To the extent that you’re increased muscle mass is improving your relative strength and it’s going to be likely beneficial for cognitive function given study findings. One other just point to make that you. Yeah, I think you allude to you mentioned it’s you know the strength is more of a neuromuscular assessment than it is bringing in more factors than just muscle mass right so to generate you know the muscle is only the size of the muscle is only one thing that’s determining how much you can lift of something or how much you can do it also requires you know the signal to get there and those signals to get there in a coordinated fashion which is as you’re looking then at processing speed and sort of timing of you know neural firings and all.

21:55 : So it’s bringing in a lot more parameters of neural function than just you know the size of the muscles so from that standpoint too, you could see why it might be more sensitive metric for nervous system function and brain function. Yeah and I guess there were also other things related to health so just cause you have more muscle, you also have the neuromuscular coordination associated with, you know, moving that muscle, but you also have the quality of that muscle itself and its ability to generate force which can be related to, you know, metabolic health and these other things as well.

22:30 : Yeah, Okay well, super interesting that’s a great study i’m glad it’s out there and thanks for sharing it with us and if you guys have any questions, follow up questions about it, feel free to send them our way¬† brainjo.academy/questions and we’ll be happy to answer. Thanks so much, Tommy. That’s great. Thank you. =