Recap: What time of day are your muscles strongest? | Prof. Karyn Esser

0:00Hello, and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today, we're discussing why muscle strength is so important to our health. And our guest shows us how it's possible to harness the power of your muscles to enhance your quality of life. Professor Karen Esser from the Department of Physiology and Ageing at the University of Florida. Let's kick off with a surprising quirk of human anatomy. Did you know that there's one time of day when we're all at our strongest?

0:38So four or five o 'clock in the afternoon, you are going to be stronger. And the impressive part about this, it's men, it's women, a variety of different ages. The exercises range from things like grip strength to sort of leg extension kinds of things. And it's tremendously consistent, which isn't always true in human research, that strength is better in the afternoon. And at this stage, people have, you know, looked at, is it the nerve? And there's no indication it's how the nervous system is recruiting the muscles. It seems to be something locally at the level of the muscle. And so that's one example where we have some evidence that likely the clock is playing a role and sort of, you know, under regular conditions, you are stronger.

1:29You're going to be stronger in the afternoon. Now, why? We don't have a why for that, but that's how it works. The other one that some of my colleagues from the Netherlands have shown is that the mitochondria in the muscle cells, so the powerhouses, the things that make all the energy, they have a higher capacity in the afternoon. Just to make sure I've got this, this is your body clock through 24 hours changing the way that your muscles work. And interestingly, you're saying, like across men and women, and it sounds like you said a lot of different studies, you can actually see that this strength is peaking surprisingly late in the day, you're saying sort of four to five in the afternoon, which I rather think is like sort of the day is sort of...

2:16Yeah, I don't want to be too precise here, because you know, but I'd say afternoon. So I'd say, let's just say from two on. Okay. Depends when you wake up, I guess is what you're saying is that when my afternoon and your afternoon might be different. But that's really fascinating. Is that also constant as we age? We don't know. If I had to make a prediction, I would say we'd lose our day-night difference based on what I understand with the timer. But that actually hasn't been tested. I mean, it's been looked at maybe up to about 30 years old. But again, I don't think we've actually move those studies into sort of the over 50 crowd.

3:00So in general, do we see circadian rhythms like become weaker as we age? What is it that makes you think that that's what's likely to be happening? We talked about the clock mechanism, which is the same in every single cell, right? So you have this timer where my research has been and where people don't really talk about it in terms of trying to apply it to the physiology is that beyond timekeeping, it has another job. All right. So it actually has a second job that from a physiological perspective is critically important. And that is to regulate a set of genes at different times of day. Can you help us to understand that?

3:41Because I think most people listening to this will be like, hang on, my genes are just this fixed thing. What does that mean to regulate a set of genes at a different time of day? Could you just help us to understand what you just said? So you have this timer that has sort of like gears on it, right? And those gears touch different parts, different sets of genes at different times of day. There are some genes that are constant, but there are a number of genes. So let's say over a thousand genes in a muscle cell are expressed in a pattern where they're higher at some times and lower at others. And does this mean like, because genes are sort of a bit like instructions, aren't they, to do something?

4:21So is this sort of saying you're basically this muscle cell is being told, hey, at four in the afternoon, do all the things that are going to set you up to be the strongest you possibly can. But at three in the morning, you should be working, switch on all the repair, switch off all of the special turbocharging stuff, switch on different functions that you want to be happening in this cell at different time of day. Absolutely. So one way to think about the clock or the way we, you know, is that it is a anticipatory timer. So it's based on, you know, the fact that we have these changes in what we do at different times a day.

5:03And so what you will see is before you wake up in your muscle, you will see sets of genes that are getting turned on and those will make for proteins. and those things are going to be involved in metabolism or breakdown of like fats and carbohydrates that will provide the energy for you to use your muscle. Your muscle is basically getting ready to be used. You know, you're still lying in bed, but it knows that you're going to be waking up in an hour and it's going to start doing these things so that it's ready because you're going to have to get up and you have to get the kids ready for school and you're going to walk them to school or whatever it is.

5:40You're going to start doing a bunch of stuff and it doesn't just get turned on instantly. It's not like we're a bit used to our phones can do anything instantly. But actually, this is more like these machines need to be warmed up and ready and with all the right things. And so this is doing that in over quite a long period, right? You're not talking about just minutes here. Correct. Your idea of the warm up is perfect, right? So what the clock is doing is it is changing things without you having to think about it. It's changing things in your muscle that get your muscle ready for once you get out of bed and do all those things you're going to do, right?

6:15And then at a different time of the day, it's going to be doing something different. And that will be related to storage of sugar, storage of replacement of proteins that may be damaged. So it knows you're going to be resting or, you know, it assumes you're going to be resting. and so it's getting those specific genes expressed to do the jobs it wants to be doing during that rest phase. So Karen, I'd love to like take that like very sort of cutting edge research that you're doing about, you know, literally what's going on inside our muscle cells and then step back and say, well, somebody's listening to this.

6:55What might it imply for how they think about their life and how they might think about doing exercise? There'll be a lot of people listening to this show who have become convinced, a bit like me, that they need to do more exercise, even if they don't necessarily really love it very much. But they're like, you know, it's a bit like brushing your teeth. You need to do this. So, I mean, why don't we start with me? I'm in my late 40s. What does this tell you about both what is good in terms of how I would think about the timing of my exercise or being physically active, but also, I guess, what would be suboptimal?

7:29With what we understand about the natural rhythms of the clocks in our muscles, then, you know, if you are able to, I mean, exercising in the afternoon is probably when your body and when your muscles are best set for doing that, right? You're stronger, you know, based on the mitochondrial measures, you know, the endurance should be good. It's a very nuanced question. And so I'm struggling with trying to find the way. Karen, one of the things I love about this show always is whenever you speak to the people who are like the absolute world experts in something, they're always much more cautious about the advice than when you talk to somebody who's like a long way away from it, hasn't maybe done the research themselves.

8:12It's where they tend to make very strong statements. So I think we are used to the fact that, you know, that this is cutting edge science, that the results may in fact be reinterpreted. And so I understand the caution. If I play it back, what I think you're saying is that, you know, right now the evidence is that there is a change during the day, that you are stronger starting from the afternoon and that that implies that that's a better time to exercise. And I think you're also saying that you haven't carried out all the randomized control trials to sort of prove this yet. Is it, would that be a - That would be correct.

8:47And then the other part that we haven't talked about is what time you exercise actually feeds into the muscle clock. So talk about, help me to understand what you're saying. So just like light adjusts the clock in the brain. Right. What time you exercise adjusts your muscle clocks. People often talk about the fact that if you do have jet lag, then sort of doing exercise in the place that you go to can be helpful. And I just assumed that that was something to do with like, you know, just being more active or something. But you're saying that actually that might contribute to adjusting in the same way that the light is supposed to help you adjust.

9:28And feed it. And again, I love that you say that. Like if you're on audio, you won't see Karen looking at me as though I'm a complete idiot because it's obvious that this is going to change the time zone. But I'm quite surprised. So to explain a little bit what happens, you're saying? You can perform exercise at different times of day. and depending on when you exercise, it will change the settings or the phase of the muscle clock independent. So the clock in the brain does not change, but the muscle clocks will shift sort of directionally toward, I call it sort of toward the time of the exercise.

10:10What we now understand is that there is information that's coming from that exercise at that particular time that's telling the muscle clock, hey, this might be something we're going to be doing more often. Let's adjust so we're going to be ready for this, right? So if we think about the clock being an anticipatory mechanism, if all of a sudden you start exercising at six in the morning, the clocks in your muscles are going to shift more there. It's learning. It's in training. It's adapting to that time. So you are going to be better prepared or your muscles are going to be better prepared to perform that activity at that time.

10:48And Karen, does that affect your body clocks elsewhere as well? So if I'm doing this exercise, does that start to drag all my other body clocks also in that direction? Well, it can. It's not a simple answer. It's not like all the other peripheral tissues come along. No. But we have evidence that the clocks in your fat will change. The clocks in your lungs will change. So it's definitely not just the muscles. There is this. Correct. Hence you saying like, it's obvious that if you were jet lagged, you should do exercise. It's going to help you to move. Absolutely. Absolutely. Now, is there anything, you know, if my wife was listening to this, is there any difference that you see between men and women in terms of these responses, either at particular times or over time periods?

11:39To be honest, I think everything we've seen sort of, at least I've looked at in terms of the circadian physiology and muscle, would say like a variety of things, women tend to be more resilient and their rhythmicity tends to be more resilient. When you say more resilient, I just want to make sure I understand. Does that mean that, help me to understand what you mean by that? Yeah, so what I mean by that is the rhythms are more robust. So you can kind of perturb them, but they stay on track a bit better. When we were talking about that sort of time of day differences in gene expression, they have a little bit stronger gene expression changes based on time of day.

12:16What we're learning with at least, you know, studies in women, studies in female animals is that they can handle a challenge, right? So they can handle whether it's a jet lag, whether it's something that interferes with the circadian clock or the timer function. The females handle that better than males. I wish you told me this five years ago because I remember when our little girl was really small, I felt that I was definitely struggling worse than Justine to deal with like all the interrupted nights. And now I'd be like, well, you know, science has proven that you're better able to cope with this.

12:55is I think what I'm hearing from you. It's just your biology. It's just your biology. But is that an example of what you're saying that that would potentially be more robust to these sorts of interruptions of, you know, the rhythm that you might get by being woken up by a small child sort of three times in the night? Absolutely. Do you see that robustness continue later in life? Because I think one of the things we see in a lot of the things that we study and Zoe's really interested in this personalization is that often, you know, as we get older, some of these different systems, maybe they're not as good as they were when you're 15.

13:31Do you see also that there's a difference between men and women over time in terms of how well these circadian systems continue? Yes. And so I think the challenge to understand right now is that the clocks continue to work as we get older. So the timer works, but it's like the gears have rubbed off. So it doesn't get translated into the sort of physiological output like it did when you were younger. And so it slips. It just doesn't, you know, just stuff just doesn't work as well as we get older is sort of the analogy, I think, in my head. So this is an area we're very interested in trying to identify.

14:07And so does that mean that, you know, at my age and as I get older, like the timing of the day doesn't necessarily matter so much because actually I'm not managing to switch the right things on and off in the same way? That's possible. Or, you know, the other side of it is it becomes more important to maintain regular behaviors like when you eat, when you exercise, to reinforce the clock function when we age. Oh, that's interesting. So it could be that actually you need to be more regimented because you need to support this.

14:41That's it for this week's recap. If you're listening to this, you're already on your way to living healthier through better nutrition. And at Zoe, we're doing everything we can to help you on your way. So we've developed Daily 30, a delicious dietary supplement to add to your meals. Because with Zoe, we ran a clinical trial testing Daily 30. The results were staggering. It's selling out in the UK and we're working hard to bring it to the US as soon as possible. Sign up to the wait list at zoe.com slash daily 30.

15:15Thank you.