Muscle Strength Now Predicts Heart Attack Risk
The Signal, Twice
Two studies landed five days apart this week, from different teams, using completely different methods. Both found the same thing: strong muscles track with a healthier heart, independent of anything else going on in the body. A paper published June 25 in JACC (the Journal of the American College of Cardiology, one of the field's top journals) followed 117,025 women for nearly two decades, from 2002 to 2020, as part of two long-running studies, the Nurses' Health Study and NHS II. Tianyue Zhang and colleagues at Zhejiang University and Harvard's Chan School found that women doing at least two hours of resistance training a week had a 44 percent lower risk of heart attack than women doing none. Every extra weekly hour of lifting added another 14 percent reduction on top of that. Then, on June 30, a University of Edinburgh team led by Michelle Williams, part-funded by the British Heart Foundation, published a different kind of study in Radiology. They ran an AI tool over 1,722 chest CT scans, the imaging routinely used to check hearts and lungs, and measured the density of the muscle around the chest and back. For every 10-point rise in that muscle density, heart attack risk dropped 31 percent, and ten-year mortality dropped 39 percent. Neither paper can explain why muscle and heart health move together. They just agree, independently, that they do.
What The Scans Miss
Here's the catch: both studies are observational. That means researchers watched what people already did and tracked what happened to them, rather than randomly assigning some people to build muscle and others not to. That design can show you a pattern. It cannot tell you what caused it. The Edinburgh study has an extra wrinkle that makes this even harder to untangle. Those patients weren't a random sample of the public, they'd already been referred for chest pain, so the group was tilted toward sicker hearts before anyone ever measured a muscle score. That's a selection problem, and it means the study can't tell 'lifting weights protects your heart' apart from 'a body that holds onto muscle is a body whose metabolism was already working well.' This is the reverse-causation problem that haunts almost all fitness research: you can't always tell if the healthy habit caused the good outcome, or just came along for the ride with it. What the Edinburgh tool actually delivers, and this part is real, is speed. It grades muscle density from a scan that's already been taken, in about a minute, a read that would otherwise take a radiologist hours by hand. But the bigger question, whether building muscle actually protects the heart or is just a marker of a body that's already healthy, is still open in both papers. The Regeneron trial reporting later this year is the next place to look for an answer.
That answer may come soon. Regeneron has a drug in trials that blocks myostatin, a protein that limits muscle growth, and the trial is testing whether preserving muscle during GLP-1 weight loss (the mechanism behind drugs like Ozempic and Wegovy) protects the heart beyond whatever benefit comes from the weight loss itself. If it works, that turns into a pricing story: a muscle-preserving drug sold alongside a weight-loss drug, not instead of one. If it doesn't, the JACC and Radiology findings stay exactly what they are today, a strong correlation nobody has yet explained. Either way, the trial reports before the year is out.