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

Summary

Podcast Summary: ZOE Science & Nutrition Episode: Recap: What Time of Day Are Your Muscles Strongest? | Prof. Karyn Esser
Release Date: October 29, 2024
Host: Jonathan Wolf
Guest: Professor Karen Esser, Department of Physiology and Aging, University of Florida

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1. Introduction and Importance of Muscle Strength

In this episode of ZOE Recap, host Jonathan Wolf delves into the significance of muscle strength for overall health and quality of life. Welcoming Professor Karen Esser from the University of Florida, the discussion centers on the intriguing patterns of muscle strength throughout the day and the underlying physiological mechanisms.

Notable Quote:

Zoe [00:01]: "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."

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2. Circadian Rhythms and Peak Muscle Strength

Professor Esser reveals a fascinating aspect of human physiology: muscle strength peaks in the late afternoon. Her research indicates that individuals, regardless of gender or age, tend to be strongest between 4 to 5 PM, a phenomenon consistent across various muscle exercises.

Notable Quote:

Prof. Karen Esser [00:39]: "So 4 or 5 o'clock in the afternoon, you are going to be stronger... strength is better in the afternoon."

Wolf seeks clarification on the timing, acknowledging variability based on individual wake times.

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3. Genetic Regulation and Muscle Function

The conversation shifts to the genetic mechanisms governing this strength fluctuation. Professor Esser explains that our body's internal clock regulates the expression of over 1,000 genes in muscle cells, orchestrating metabolic processes that prepare muscles for optimal performance during specific times of the day.

Notable Quotes:

Prof. Karen Esser [03:10]: "The clock mechanism... regulates a set of genes at different times of day."

Prof. Karen Esser [03:53]: "There are some genes that are constant, but there are a number of genes... over 1,000 genes in a muscle cell are expressed in a pattern where they're higher at some times and lower at others."

Wolf paraphrases this, likening the process to muscles "waking up" and preparing for activity, akin to warming up a machine.

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4. Implications for Exercise Timing

Bridging research with practical advice, Wolf inquires about how individuals can apply this knowledge to their exercise routines. Professor Esser cautiously suggests that exercising in the afternoon aligns with the body's natural strength peaks, potentially enhancing performance and endurance.

Notable Quote:

Prof. Karen Esser [07:28]: "Exercising in the afternoon is probably when your body and when your muscles are best set for doing that... you're stronger."

However, she emphasizes the need for further randomized controlled trials to solidify these recommendations.

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5. Exercise as a Zeitgeber for Muscle Clocks

Exploring the concept of zeitgebers (time cues), Professor Esser highlights that exercise can serve as a powerful regulator of muscle clocks, much like light influences the brain's circadian rhythm. Timing workouts can thus adjust the muscle's internal clock, optimizing readiness and performance.

Notable Quotes:

Prof. Karen Esser [08:46]: "What time you exercise adjusts your muscle clocks."

Prof. Karen Esser [09:07]: "If you start exercising at 6 in the morning, the clocks in your muscles are going to shift more there... you're going to be better prepared."

Wolf connects this to practical scenarios like mitigating jet lag through timed exercise.

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6. Broader Effects on Body Clocks and Jet Lag

The discussion extends to the systemic impact of exercise on other peripheral clocks within the body. While not all body clocks adjust uniformly, evidence suggests that tissues like fat and lungs also respond to exercise timing, contributing to overall circadian alignment.

Notable Quotes:

Prof. Karen Esser [11:01]: "Clocks in your fat will change, the clocks in your lungs will change."

Prof. Karen Esser [11:26]: "It's obvious that if you were jet lagged, you should do exercise, it's going to help you to move."

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7. Gender Differences in Circadian Resilience

Professor Esser discusses observed differences between men and women regarding circadian rhythm resilience. Women exhibit more robust and adaptable circadian rhythms, enabling them to better handle disruptions such as jet lag or irregular sleep patterns.

Notable Quotes:

Prof. Karen Esser [11:39]: "Women tend to be more resilient... rhythms are more robust."

Prof. Karen Esser [12:57]: "Women better handle circadian disruptions."

This insight is illustrated through a personal anecdote from Wolf, highlighting the biological advantages women may have in maintaining circadian stability.

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8. Aging and the Decline of Circadian Efficiency

The conversation addresses how aging affects circadian rhythms. While the internal clock mechanism remains functional, the translation of these signals into physiological processes becomes less efficient due to factors likened to "gears rubbing off." This decline suggests that older adults might benefit from more structured daily routines to support their circadian health.

Notable Quotes:

Prof. Karen Esser [13:38]: "Clocks continue to work as we get older... just doesn't work as well as we get older."

Prof. Karen Esser [14:20]: "It becomes more important to maintain regular behaviors... to reinforce the clock function."

Wolf interprets this as a potential need for increased regularity in activities like eating and exercising to support diminishing circadian functions.

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9. Practical Takeaways

The episode concludes with actionable insights for listeners:

• Optimal Exercise Timing: Aim to schedule workouts in the afternoon when muscle strength peaks.
• Circadian Alignment: Utilize exercise as a tool to adjust muscle clocks, especially during disruptions like travel.
• Gender Considerations: Recognize that women may have more resilient circadian rhythms, influencing how they respond to lifestyle changes.
• Aging Strategies: Maintain consistent daily routines to support circadian health as you age, compensating for declining physiological responsiveness.

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Conclusion

Professor Karen Esser's research highlights the intricate relationship between our circadian rhythms and muscle strength, offering valuable guidance on optimizing physical performance through timed exercise. As our understanding of these biological clocks deepens, personalized approaches to health and fitness become increasingly attainable, reinforcing ZOE's mission to translate cutting-edge science into practical health advice.

Notable Quote:

Zoe [14:34]: "So it could be that actually you need to be more regimented because you need to support this."

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For a comprehensive exploration, listeners are encouraged to access the full episode through the links provided in the episode description. Embrace personalized strategies to enhance your health and well-being with ZOE Membership by taking the free quiz at ZOE.com/podcast.

Transcript

[Zoe]

Hello 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 Aging 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?

[Professor Karen Esser]

So 4 or 5 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 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, you're going to be stronger in the afternoon. Now, why? I don't, you know, 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, you know, the, you know, the mitochondria in the muscle cells, so the powerhouses, the things that make all the energy, they have a higher capacity in the afternoon.

[Host]

Just to make sure, I've got this. This is your body clot through 24 hours, changing the way that your muscles work. And interesting, 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 the day is.

[Professor Karen Esser]

Yeah, I don't want to be too precise here because you know it, but, but I'd say afternoon. So I'd say, let's just say from two on.

[Host]

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, that's really fascinating. Is that also constant as we age?

[Professor Karen Esser]

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 moved those studies into sort of the over 50 crowd.

[Host]

So 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?

[Professor Karen Esser]

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 second of genes at different times of day.

[Host]

Can you help us to understand that? Because 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?

[Professor Karen Esser]

So you have this timer that has sort of cog or 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 1,000 genes in a muscle cell are expressed in a pattern where they're higher at some times and lower at others.

[Host]

And does this mean like, because genes are sort of a bit like instructions, aren't they, to do something? So is this sort of saying you're basically, this muscle cell is being told, hey, at 4 in the afternoon, do all the things that are going to set you up to be the strongest you possibly can. But at three at, 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.

[Professor Karen Esser]

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 of day and that we do. And, and 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.

[Host]

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 warp them to school or whatever it is. You'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 over quite a long period. Right. You're not talking about just minutes here.

[Professor Karen Esser]

Correct. Your idea of the warmup is perfect. 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. And 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.

[Host]

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. What 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, like, 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.

[Professor Karen Esser]

Suboptimal with 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. Based on the mitochondrial measures, the endurance should be good. It's a very nuanced question. And so I'm struggling with trying to find the way. Not at all.

[Host]

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 a long way away from it, hasn't maybe done the research themselves. It's where they tend to make very strong statements. So I think we are used to the fact 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 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 controlled trials to sort of prove this yet. Would that be a.

[Professor Karen Esser]

That would be correct. And then the other part that we haven't talked about is what time you exercise actually feeds into the muscle clock.

[Host]

So talk about, help me to understand what you're saying.

[Professor Karen Esser]

So just like light adjusts the clock in the brain, Right. What time you exercise adjusts your muscle clocks.

[Host]

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. But you're saying that actually that might contribute to adjusting in the same way that the light is supposed to.

[Professor Karen Esser]

Absolutely. And feed.

[Host]

And again, I love that you say that like it's. If you, if you're on audio, you won't see Karen looking at me as 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.

[Professor Karen Esser]

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, I call it sort of toward the time of the exercise. What 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 6 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.

[Host]

And 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?

[Professor Karen Esser]

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.

[Host]

So it's definitely, it's not just the muscles. There is this, 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.

[Professor Karen Esser]

Absolutely, absolutely.

[Host]

Now, is there, 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?

[Professor Karen Esser]

To 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.

[Host]

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.

[Professor Karen Esser]

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. What we're learning with at least 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.

[Host]

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. Is I think what I'm hearing from.

[Professor Karen Esser]

You is that, yeah, it's just your biology. It's just your biology.

[Host]

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 a day?

[Professor Karen Esser]

Absolutely.

[Host]

Do you see that robustness continue later in life? Cause I think one of the things we see in a lot of the things that we study and Zoe's really interested in is personalization, is that often, as we get older, some of these different systems, maybe they're not as good as they were when you're 15. Do you see also that there's a difference between men and women over time in terms of how well these circadian systems continue?

[Professor Karen Esser]

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.

[Host]

And so does that mean that 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.

[Professor Karen Esser]

That's possible. Or 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 you leave.

[Host]

So it could be that actually you need to be more regimented because you need to support this.

[Zoe]

That's all for this week's recap episode. You can find a link to the full conversation in the episode description. If you want to make smarter food choices for your body and transform your health for life, why not try Zoe Membership? The first step is easy. Take our free quiz to find out what Zoe Membership could do for you, Simply go to Zoe.com podcast.