Most of us think about muscle in fairly simple terms: you either have enough of it, or you don’t. But a significant piece of research published in Radiology back in June 2023 suggests the picture is more nuanced – and genuinely more interesting – than that.

The study, in brief

Researchers led by Maxime Nachit followed nearly 9,000 adults for close to nine years, using AI-assisted CT scanning to measure body composition in detail – not just how much muscle people had, but what condition that muscle was actually in.

One measurement stood out above the rest: myosteatosis, which is the medical term for fat infiltrating muscle tissue itself. Rather than fat sitting around the muscle, it’s fat marbled through it, a bit like the streaks running through a well-marbled steak.

The results were striking. Myosteatosis turned out to be one of the strongest predictors of mortality in the entire study – a stronger signal, in fact, than obesity itself. Even after accounting for other factors, people with higher levels of fat infiltration in their muscle carried a meaningfully higher risk of dying during the follow-up period.

Why this matters more than the number on the scale

This is a useful reminder that muscle isn’t simply a cosmetic feature, or even just a strength number. It behaves more like an organ in its own right – one that influences metabolism, inflammation, and overall resilience. And the quality of that tissue seems to matter every bit as much as the quantity.

It also explains something a lot of us have probably noticed anecdotally: two people can look broadly similar, or have a similar build, and yet have very different health outcomes. Muscle quality, invisible from the outside, may be a big part of that difference.

The encouraging part

Unlike a lot of health metrics, myosteatosis isn’t fixed. It responds to the same things we already know help: regular resistance training, adequate protein, staying physically active day to day, and avoiding long periods of inactivity. Fat infiltration in muscle tends to increase with a sedentary lifestyle – and tends to improve when muscle is used regularly and properly fuelled.

In other words, the very things I bang on about at Power of One Fitness – consistent strength training, sensible nutrition, staying active outside of formal workouts – appear to be directly protective against exactly the kind of hidden risk this study identified.

You don’t need a CT scanner to benefit from that. You just need to keep training the muscle you’ve got.

So, if there’s one takeaway from this newsletter today it is this: muscle isn’t just about how much you can lift, or how you look. What’s happening inside that tissue may matter just as much as the tissue itself.

If you’d like some support building a strength routine that keeps your muscle – and not just your muscle mass – in good condition, get in touch with me at Power of One Fitness. Let’s build something that works from the inside out.