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Today’s Health Upgrade

• Can muscle turn to fat?

• Why some red light devices work (and others don’t)

• Beyond the headline: Diet soda and brain health

• Adam’s Corner: Skip to the end

Reader Question
Does Muscle Turn Into Fat When You Stop Lifting?

Your muscles can get smaller when you stop lifting. Fat can increase. When both happen together, it’s easy to see how the idea that one becomes the other got started.

But muscle and fat are different tissues. Taking a break from training can change how much of each you have. It does not turn one into the other.

Your body constantly repairs and replaces muscle protein. Lifting helps you build and maintain that muscle. Without enough work to keep it, your muscles can (and will) gradually shrink.

Meanwhile, skipping workouts means burning fewer calories. If your portions stay the same while your activity drops, you can start storing more fat.

Losing muscle contributes to the drop in calorie burning, but less than you might think. A pound of muscle uses about 6 calories a day at rest. Missing the workouts and moving less throughout the day can make a much bigger difference than losing a little muscle.

Fat can also collect between muscles during prolonged inactivity. In one small study, young adults who kept weight off one leg for four weeks lost muscle while fat increased between the muscles. The muscle cells shrank, and the fat between them grew. One tissue didn’t turn into the other.

That doesn’t mean a week away from the gym will noticeably change your body. And looking smaller doesn’t automatically mean you’ve lost muscle.

Stored carbohydrate and water in your muscles can also shift their size by a few percent. Those stores change with your diet and training, so the mirror can’t tell you how much muscle you’ve lost.

Even when you lose some muscle, a short break doesn’t necessarily set back your long-term progress.

Researchers randomly assigned young men to 24 weeks of either continuous bench-press training or a program that included two three-week breaks. The break group lost about 3% of their triceps size during each pause, then regained it after returning.

By the end, triceps size had increased about 19% in the break group versus 21% in the continuous group. Strength gains were 50% versus 51%, even though the break group did 25% fewer workouts. It was a small study of previously untrained men doing one exercise. 

But it suggests that a few weeks off, as long as you’re consistent overall, doesn’t derail months of progress.

You can also train far less and still hold onto your gains. In one trial, young adults maintained muscle size and strength for roughly eight months with one challenging set of each lower-body exercise, once a week. Adults ages 60 to 75 kept their strength but lost some size, even with three sets once a week, suggesting they need more training to preserve muscle. Strength proved sticky overall: even people who stopped training entirely kept most of their strength gains.

An injury or illness that prevents normal movement needs a different approach. In small studies, two weeks in a knee brace without putting weight on the leg reduced the size of the front thigh muscles by about 8% to 10%. Older adults on 10 days of bed rest lost nearly a kilogram of lean tissue from their legs. In those situations, muscle is lost faster than when you miss workouts but keep up your everyday activities.

For a busy stretch or vacation, don’t stress. You can take off and enjoy.

If you want to hold onto as much as possible, aim for one challenging workout a week that hits your major muscle groups as a temporary way to help maintain your progress. If you’re over 60, plan for a bit more than that to maintain your muscle mass.

Together With Celluma
Why Do Some Red Light Devices Work Better Than Others?

Two red light panels can look identical and deliver very different doses. That’s why one may help while another does little.

Red light works more like a medicine than a gadget: the benefit depends on the dose. 

Wavelength decides how deep the light reaches (red for skin, near-infrared for deeper tissue). Power determines how much reaches your skin. Session time decides how much adds up. And more isn’t automatically better: research suggests too much light can blunt the effect, just like too little. 

In a review of 22 trials of laser treatment for knee arthritis, recommended doses meaningfully reduced pain, while off-target doses did little.

Here’s the catch. The wattage on the box usually means electricity drawn, not light delivered. And the dose drops as you sit farther back. Independent testing also shows some brands’ power claims don’t match what the device actually outputs.

Can LED light therapy help? Yes, but not for every claim. And, before you buy, look for these numbers: wavelength (nm), power density (mW/cm²), protocol duration, and — most importantly — the fluence (Joules/cm²). This is delivered energy and should be between 2-10 J/cm². The range is known as the Bi-Phasic Dose Response of low-level light therapy (where therapeutic effects begin to occur in your cells).

And watch out for claims on short treatment times (like "10 minutes"). Treatment times are just one session out of many. It's more about the full protocol: how often to treat and for how many weeks to see visible results.

Then ask two questions: was the power independently measured, and which study is the protocol based on? If the brand can’t answer, you can’t know whether you’re getting the dose that worked in research.

That’s why we first check FDA clearance. It means the FDA reviewed the device for specific uses, so you don't have to take the brand’s word for it. Plenty of panels can’t say that.

The Celluma PRO PLUS is FDA-cleared for skin health, acne, wrinkles, pain, and body contouring. So you get more options in one device. It's patented, and the flexible panel bends around your face, back, or knee, so the light energy stays consistent across the treatment area instead of falling off the curves, which research shows is needed for results. 

We tested multiple red light devices, and most aren’t FDA-cleared or match the frequencies used in studies. Celluma Pro Plus is used by clinics and licensed professionals in 100+ countries, and Celluma is the most credentialed LED brand on the market. But keep your expectations realistic: light therapy can work, but you should expect smoother skin and less stiffness over weeks, not overnight.

Red light devices that actually work are an investment, but as an APC reader, Celluma is covering the financing: 0% APR for up to 12 months with Shop Pay Installments through October 31st. Pump Club readers can also save up to $1,000 on select devices with code PUMPED. 

Get the PRO PLUS here. Financing ends Saturday at midnight.

Beyond The Headline
Does Diet Soda Age Your Brain?

There’s a study out there suggesting artificial sweeteners are linked to faster declines in memory and thinking. It keeps getting sent to us, even though it’s not new. So we reviewed it in depth to help you understand what it found, what it can’t tell us, and what the rest of the research says.

This study doesn’t show that diet soda ages your brain. It found a link between sweetener intake and declining test scores, but it couldn’t establish that sweeteners caused the decline or isolate the effects of diet soda.

The researchers followed more than 12,000 Brazilian adults for about eight years. Participants answered diet questions at the start, then took memory and thinking tests over time. 

Researchers estimated their intake of seven sweeteners across foods and drinks. Sorbitol, a type of sugar alcohol, was the biggest contributor. The “one can of diet soda” comparison came from the press release, which used it to help explain the amount of sweetener consumed.

People in the highest third of sweetener intake had faster declines in overall thinking scores than those in the lowest third. Researchers estimated the difference at about 1.6 extra years of cognitive aging over eight years. The middle group also declined somewhat faster. 

When researchers looked at different age groups separately, they found the link in adults under 60, but not in those 60 and older, which surprised the researchers.

The overall findings deserve more research, but several features of the study make it hard to pin down cause and effect. 

Diet was measured with a single questionnaire at the start, then not again for eight years. Unfortunately, that makes it very hard to assess how much of a role the sweeteners play. Two data points over 8 years aren’t very helpful. 

The amounts involved were tiny, averaging about 92 milligrams a day, with some sweeteners measured at just a few milligrams or less. At those levels, sweeteners are more likely a marker of eating habits than the cause of anything. The authors’ own earlier research linked ultra-processed foods, where many of these sweeteners show up, to faster cognitive decline.

The bigger issue could be the association between soda drinkers and overall health. In the Framingham Heart Study, adults over 60 who drank at least one diet soda a day had higher rates of dementia over 10 years.

But diet-soda drinkers there also had more diabetes and heart disease, and the authors noted that people at higher risk may switch to diet drinks. 

In a UK Biobank study of about 178,000 adults, heavy intake of both diet and sugary drinks was linked to higher dementia risk. 

And then there’s the fact that controlled trials find the opposite results, though they’ve been short. 

In one study, healthy adults consumed high doses of aspartame (far more than anyone in the Brazil study) for 20 days, with no effect on cognitive tests. But no trial has tested sweeteners and brain health over years.

For anyone considering switching back to sugary soda, there’s other evidence to weigh. 

A review of 17 randomized trials, mostly short studies in younger adults with overweight, found that replacing sugary drinks with diet versions led to about 2 pounds more weight loss. A second review, including 29 trials comparing low-calorie sweeteners with sugar, found a similar benefit. 

Some observational studies suggest a link between sweeteners and brain health, but none can rule out that people who use more sweeteners differ in other ways that matter. We don’t have long-term trials to settle it. Sugary drinks don’t look better for the brain in the same research, and they come with clear downsides for weight. 

Water is the simplest everyday choice. If diet soda helps you cut back on sugary soda, this study (and the other evidence) doesn’t seem like a strong enough reason to switch back.

Adam’s Corner
Skip To The End

I've been getting paid to write for 25 years, which means I've spent 25 years being told I'm wrong.

That's what happens when you get edited. You hand over something you're proud of, and someone you trust or respect shows you everything that isn't working. You fix it. They find more that’s wrong, and you do it all over again. 

My job as a writer is to be told I'm wrong until I get it right.

So when feedback comes in, I take it seriously. A reader recently told me this column should be shorter. That's fair, and it's something that’s probably correct.

But that wasn't what bothered me. They told me specifically they didn't like reading about me “figuring it out.” They wanted me to skip to the end. Cut the details, and just give the takeaways.

That's a problem when it happens too often, and with the wrong information.

Editing is important. Hemingway built a career on economy of words, on the idea that a sentence has to earn its spot on the page, and he was right. But great writing doesn't mean shorter. It means real.

We do plenty of skip to the end and just tell me what works in this newsletter, and we love it. 

When you want to know how much protein you need or why your knees ache, you should get the answer fast. 

But when we avoid the reality of the process and the journey, I’m worried it does far more harm than good.

Look at Arnold. People romanticize his Hollywood career. But they don't talk about the five years between his Golden Globe role in Stay Hungry and Conan the Barbarian. He wanted to be a leading man, so he took acting classes. He invested in real estate. He did the things that let him be patient and keep investing in himself until he earned leading roles, which eventually led to The Terminator.

Nobody makes a highlight reel out of acting class.

We don't talk about this enough, and maybe we should.

Are You Editing Too Much Of Your Life?

Most of us already live this way, and not just with newsletters.

We want the before-and-after photo without the fourteen months between them. 

We want the founder who "came out of nowhere," minus the nine years nobody saw. 

We watch morning routines filmed in perfect light that somehow never include the kid who threw up at 5:40 a.m. or the email that wrecked your mood before the coffee finished brewing.

People call it a microwave society, and that's part of it. We want things faster. But I think the bigger cost is harder to spot.

When everything we consume has the mess edited out, we start holding our own lives to the edited version. Then we look at the unedited footage of our week (the missed workout, the argument in the car, the plan that fell apart by Wednesday) and assume something is wrong with us.

Nothing is wrong with you. You're just watching your own raw footage next to everyone else's trailer.

A column about making sense of life works the same way. Cut the complications out, and you also cut the part that helps you see clearly.

There's a difference between editing for brevity and editing for honesty.

One makes a story easier to read. The other makes it easier to believe something that isn't true.

The Messy Middle Never Ends

In business, there's a popular idea called the messy middle. 

Scott Belsky wrote a whole book about it. The gist is that every project has a long, ugly stretch between the exciting start and the satisfying finish, and the people who make it are the ones who learn to endure that stretch.

I believe that. Building The Pump Club has been three years of messy middle with some amazing moments sprinkled on top. The community is incredible, the app is a source of pride, the events are memorable, and the newsletter is a beacon of pride. 

But that doesn’t mean it’s easy or pretty. We make mistakes, we get things wrong, we build and rebuild…and rebuild again.

The business version of “the messy middle” comes with a promise attached. Endure the mess, and eventually you grow out of it. You scale. You stabilize. You arrive.

I used to believe that about life, too. I don't anymore.

I’m convinced the mess never ends; it just changes shape. And I think that reality can be freeing. 

At 25, the mess was figuring out what job I wanted. Now it's figuring out how to raise three kids, build resilience in a body that files complaints it never used to, build the Pump Club into a community that helps millions, and manage a family calendar that some weeks looks like a ransom note. 

I didn't graduate from the messy middle. I just got better at recognizing when I'm standing in it.

Weirdly, that's been a relief.

If the mess is permanent, then it isn't evidence you're failing. It's evidence you're in the middle of something, living and learning your way toward whatever comes next. 

The frustrating moments don't disappear, but they stop feeling like a verdict. There's no one way this is supposed to look.

It's also why I think we'd benefit from showing more of the mess. 

I don't mean a performative "here's my vulnerable post" moment. I mean the ordinary stuff, like telling a friend the diet fell apart last week, or letting your kids watch you get something wrong and try it again. Mess is where most of us actually live. When someone else names theirs, it calms the part of you that was about to freak out over your own.

If someone's life looks too clean to be true, it's probably because it is.

So, to the reader who asked for less: I hear you, and I mean that. A shorter column might be an easier read.

It would also be less honest. 

Love it or hate it, these words will be real, with the wrong turns left in, because that's where most of the figuring out happens.

All of us have parts of life we’d rather gloss over. The stretch where nothing made sense, or the years that looked nothing like the plan. The season you couldn’t explain to anyone, including yourself. 

It’s tempting to treat those moments like detours, something to rush through so you can get to the good part.

But the people who stop skipping to the end tend to find something the rest of us miss. 

They’re more present in the moments that feel like nothing is happening. They appreciate the outcome more when it arrives, because they watched it get built. And they’re usually more satisfied with where they end up, even when it isn’t where they planned.

The end is coming either way.

The only question is whether you were there for the middle.

Because the middle isn’t what stands between you and your life. It’s where you become the person who gets to enjoy it. -AB

-Adam Bornstein is the co-founder and co-editor-in-chief of Arnold’s Pump Club

The Positive Corner of The Internet
About Arnold’s Pump Club Editorial Standards

We do things a bit differently here, starting with transparency.

1. The Content: All APC emails are researched, written, and fact-checked by the APC editors (see bottom of the email), with written contributions from Arnold (noted with “Arnold’s Corner”). Links take you to original studies (not second-hand sources).

2. Does AI play a role? Not for the primary content, but we use it in two ways. The main items are original content written by the APC team. The summaries at the end are AI-generated based on the human-written content above. We also use an AI tool to edit and review our interpretations of the research, ensuring scientific accuracy. We don’t assume AI is right, but we use technology to hold ourselves accountable.

3. Yes, we have partners (all clearly noted by “Together With”). Why? Because it allows us to keep the APC emails free. We first test products, and then reach out to potential partners who offer ways to help you improve every day. The bar is set high, and to date, we have turned down millions in ad deals. (Example: we will not partner with any non-certified supplements or those without evidence in human trials). If we won’t buy the product, we won’t recommend it to you. And if there’s no evidence it works, then there’s no place for it here.

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Publisher: Arnold Schwarzenegger​

Editors-in-chief: Adam Bornstein and Daniel Ketchell