Tag: aging

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Sarcopenia redux: running preserves “motor units”

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- Alex Hutchinson (@sweatscience)

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I posted a few thoughts last week about an article on sarcopenia — the gradual loss of muscle with age — and new attempts to find drugs that will slow it down. I’d be remiss if I didn’t point out some of the research on the obvious drug-free ways to avoid withering away to nothingness. For instance, I just noticed an article in the current issue of Medicine & Science in Sports & Exercise that compares the number of “motor units” in the muscles of masters runners (average age 65) with age-matched controls, and with a younger group (average age 25). The news is good.

First off, a motor unit is “a single alpha-motor neuron and all of the corresponding muscle fibers it innervates.” Losing motor units is one of the several mechanisms that combine to produce the muscle loss grouped as sarcopenia. In this case, it’s not the muscle fibres themselves that die; rather, it’s the motor neurons that control them. When you’re young, the orphaned neurons often sprout new axons that connect them to other motor neurons — so the number of motor units decreases, but the amount of muscle you can use stays the same. This can hide the problem until your 60s or 70s, at which point you’re no longer able to reinnervate orphaned fibres as well, and motor unit loss becomes a serious issue.

Anyway, the study itself was quite simple. Testing the tibialis anterior (shin) muscle, they found that the masters runners had 140 motor units on average, compared with 150 for the young group but just 91 for the old non-runner group. So there it is: consistent training preserves muscle — not the muscle fibres, in this case, but the motor neurons that control them. As the researchers put it:

The significance of the (…) findings centers on providing an improved understanding of the neuromuscular system through ‘‘elite aging’’ and provides support into the favorable value of long-term physical activity and exercise for protecting neural function.

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Sarcopenia: muscle loss is the new bone loss?

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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For an article I’m working on, I’ve been digging through the literature on sarcopenia, the age-related loss of muscle mass that most of us face starting in our 30s. I’ve found several conflicting estimates of how much muscle you can expect to lose, with a high end of 1-2% per year starting in your fourth decade (from this paper). That’s a lot more aggressive than I’d expected. I get the sense that it’s one of those problems whose implications we’re just now beginning to grasp — so I was interested to see this article by Andrew Pollack in the New York Times, which offers a good introduction to the topic:

Bears emerge from months of hibernation with their muscles largely intact. Not so for people, who, if bedridden that long, would lose so much muscle they would have trouble standing.

(Nice lede!)

Why muscles wither with age is captivating a growing number of scientists, drug and food companies, let alone aging baby boomers who, despite having spent years sweating in the gym, are confronting the body’s natural loss of muscle tone over time.

Comparisons between age groups underline the muscle disparity: An 80-year-old might have 30 percent less muscle mass than a 20-year-old. And strength declines even more than mass…

Much of the article focuses on attempts to agree on a clinical definition of the condition — which would then make it possible for drugmakers to win approval from regulators for drugs to treat it. But the key point for me is:

Researchers involved in the effort say doctors and patients need to be more aware that muscle deterioration is a major reason the elderly lose mobility and cannot live independently.

In other words, I need to start doing my push-ups again. Soon.

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Exercise vs. calorie restriction for brain aging

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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One of the clearest signs that you’re getting older, microscopically speaking, is that your synapses start to degenerate. This means that signals from your brain have a harder time getting through to your muscles (for neuromuscular synapses) and to other parts of the brain (for brain synapses). Harvard researchers decided to investigate how exercise and calorie restriction — “among the most effective anti-aging treatments known” — affect the age-related changes in mouse neuromuscular synapses (PNAS abstract here, press release here). The results:

“With calorie restriction, we saw reversal of all aspects of the synapse disassembly. With exercise, we saw a reversal of most, but not all,” [lead researcher Joshua] Sanes says.

Score one for calorie restriction? Not so fast…

Because of the study’s structure — mice were on calorie-restricted diets for their whole lives, while those that exercised did so for just a month late in life — Sanes cautions against drawing conclusions about the effectiveness of exercise versus calorie restriction. He notes that longer periods of exercise might have more profound effects, a possibility he and [Jeff] Lichtman are now testing.

That makes me hope that, with longer and more consistent exercise, we might one day discover that all the benefits of calorie restriction are in fact available from consistent and vigorous exercise. (That being said, a month in a mouse’s life does correspond to a considerably longer period in human terms. The “old” mice were about two years old.)

On a somewhat related note, another just-published study found a correlation between how much blood your heart can pump and how quickly your brain ages. The study didn’t include anyone with heart disease, so it applies to people with normally functioning hearts: the more blood you can pump, the more blood gets to your brain, and the less the brain shrinks. The study can only measure correlation, not causation — but it sounds like more confirmation that aerobic exercise is the best “brain training” around.

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How calorie restriction extends lifespan

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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British researchers are presenting some new research on how calorie restriction works at a conference on aging research this week. In a mouse experiment, they found that it reduces cell senescence (the point at which a cell can no longer replicate) and helps protect telomeres (which exercise does too, researchers have recently found). Interestingly, the effects seems to be significant even if if it’s only started later in life and maintained for a relatively short period of time.

As I blogged about recently, I’m a little ambivalent about this whole calorie restriction thing. I just can’t see a happy ending — if it works, you feel guilty about eating for the rest of your life, and if it doesn’t, you die! Ultimately, I respect that we want to know how the body works, and this line of research is part of that. But I was happy to see some of this ambivalence reflected in the quotes from the press release describing the research:

Professor Thomas von Zglinicki, who oversaw the research, said: “It’s particularly exciting that our experiments found this effect on age-related senescent cells and loss of telomeres, even when food restriction was applied to animals in later life. We don’t yet know if food restriction delays ageing in humans, and maybe we wouldn’t want it. But at least we now know that interventions can work if started later.

And a recognition that extra years aren’t the only thing that counts:

Prof Douglas Kell, BBSRC Chief Executive and keynote speaker at the BSRA Conference, said: “As lifespan continues to extend in the developed world we face the challenge of increasing our ‘healthspan‘, that is the years of our lives when we can expect to be healthy and free from serious or chronic illness.

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Caloric restriction extends your life, but may make you stupider

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Okay, that’s not really a fair headline or a good summary of the research I’m describing (which is a neat study by researchers at Princeton, explained in an excellent and detailed press release). But I have to admit, I’m not always perfectly neutral — like everyone, I prefer to see some results more than others. And research into caloric restriction is a good example: there’s been plenty of evidence over the past few years of the age-defying benefits of starving yourself:

To date, caloric restriction has been observed to extend lifespan in every organism tested, including worms, mice and monkeys, [Princeton prof Coleen] Murphy said. While the reasons for this are still under investigation, scientists generally believe that the benefits of caloric restriction go well beyond preventing diseases associated with obesity, such as heart disease and diabetes, Murphy added. It appears that limiting food intake actually slows the aging process.

In general, I’m used to leafing through studies and press releases that give me a nice pat on the back. Aerobic exercise is good? Super, I do tons of it! Eating lots of fruits and vegetables is good? Fantastic, I do pretty well on that front. But caloric restriction? That’s the antithesis of everything I stand for, which is doing ridiculous amounts of exercise and consequently being able to eat more or less until I get bored with no ill effects — or at least, no ill effects that I knew of until the emergence of this idea that eating less slows down aging.

So you should read the press release for yourself, and judge its merits in an unbiased manner… but here’s what I took from it:

Young worms whose calories were restricted had normal short-term memories, but their long-term memories were severely impaired; the memories faded within 24 hours, as opposed to 40 hours in normal worms.

(40 hours in worm time corresponds to about 15 people years.)

Now, the study has a lot more to say. While caloric restriction impaired long-term memory, the (impaired) memory abilities didn’t decline as much with old age as they normally do. The study also investigates how insulin-signalling pathways affect longevity and cognitive function (this appears to operate independently of the calorie-restriction effects). So there’s a lot of on-the-one-hand-this, on-the-other-hand-that going on. But it’s the first sign I’ve seen that caloric restriction, even if it extends life, may have some significant downsides:

“The assumption in the field of longevity research has been that organisms able to live longer will function longer as well,” said [Murphy]. “It seems we need to revisit that.”