Does Resistance Training Protect Bone Density After 40?

A reader wrote to me last month, not about herself at first. Her mother, 71, had just gotten a bone density scan back with the word "osteopenia" printed near the top, and the reader wanted two things explained: what that word actually meant, and whether it was something she should be thinking about for herself already, at 46, carrying nothing heavier most days than grocery bags and the occasional sack of compost for the garden.

Osteopenia isn't a disease so much as a label for where a bone scan falls on a chart, lower than average peak bone mass but not low enough to be called osteoporosis. It's common, more common the longer someone has been past menopause, and it happens to be exactly the population most of the strongest bone research has been built around, which is its own kind of problem for a woman writing in from her mid-forties, wondering what any of it means for her.

What the LIFTMOR trial found

The most cited trial connecting resistance training to bone density is still LIFTMOR, a randomized controlled trial published in 2018 in the Journal of Bone and Mineral Research. Researchers randomly assigned 101 postmenopausal women, 49 to a supervised, high-intensity resistance and impact program and 52 to a lighter home-based routine, and followed them for eight months. Every woman entering the trial already had a diagnosed low bone density, either osteopenia or osteoporosis. The high-intensity group came out ahead on lumbar spine bone density, gaining an average of 2.9% compared with a 1.2% loss in the comparison group, along with better scores on physical function tests like rising quickly from a chair.

It's a carefully run trial, and it's worth being precise about who it studied. The average participant was 65, close to 20 years past the reader who wrote to me, and every single one of them already had a bone density diagnosis before the trial began. Whether the same kind of training changes bone density in a 46-year-old with ordinary, undiagnosed bones isn't a question LIFTMOR can answer, because it never tested that population.

What the larger reviews add

LIFTMOR is one trial. For the wider picture, I looked at reviews that pool many trials at once, which is usually where sturdier evidence lives. A network meta-analysis published in 2025 in Scientific Reports pooled 49 studies and 3,360 postmenopausal women, average age just under 61, comparing resistance training against aerobic exercise, combined training, and no exercise at all. Resistance training on its own produced a significant improvement in lumbar spine bone density, and pairing it with aerobic exercise did better still. It's a genuinely large body of evidence, and it still describes the same kind of population LIFTMOR did: women well past menopause, not the perimenopausal years most of my readers are actually living through.

A still larger systematic review, published in 2023 in Osteoporosis International, pooled 80 intervention studies and 5,581 women across a range of exercise types, not resistance training alone, and found a smaller but real effect on bone density at the lumbar spine, femoral neck, and hip. The researchers also checked something useful here: whether being newly postmenopausal versus many years past it changed how much a woman's bones responded. In this pooled data, it didn't. That's mildly reassuring, but it isn't the same question as whether resistance training changes bone density before menopause arrives at all, and the studies feeding this review, spanning roughly ages 50 to 79, weren't built to answer that either.

Where the research doesn't reach yet

Here's the gap, named plainly rather than smoothed over: I could not find a well-designed randomized trial testing resistance training and bone density specifically in women aged 40 to 55 who don't already have a bone density diagnosis. The research exists almost entirely in two forms: postmenopausal women averaging somewhere in their sixties, or postmenopausal women who already have osteopenia or osteoporosis on record. Whether lifting weights in your forties, well before anything shows up on a scan, changes the path your bones are already on is a real, open question. Nobody has dressed it up to sound settled when it isn't. Researchers are still exploring it. Nobody has yet run the large, prevention-focused trial that would answer it directly.

What this has looked like in practice

None of the trials above tested one universal program, and none of them were run on my reader, or on you. What LIFTMOR and the two reviews had loosely in common was structured resistance training using real external weight instead of bodyweight alone. Each program lasted months, and it was done at a meaningful intensity throughout. That's a description of what the women in these specific trials did. Your spine, your joints, and whatever your own doctor already knows about your bones from a scan a research summary will never see are a separate matter. A conversation with your own doctor, along with a bone density scan if you're at the age when that starts being routine, is the actual next step here. This article isn't.

I gathered the fuller research trail behind resistance training, including the bone density question above alongside the muscle and training-frequency questions I've written about elsewhere, into a workbook called Strength After 40. It's on Etsy for $17, in case having the whole trail in one place is useful while you're sitting with your own version of this question.

What's worth skipping

Skip assuming a word like osteopenia is a countdown to something inevitable. It's a point on a chart, not a verdict. Skip treating any of the trials above as proof that lifting alone will fix a bone density problem you already have. That's a conversation for you and whoever ordered your scan, and an article can't have it for you. The fear-marketing version of this, the "your bones are disappearing, act now" kind, I'd skip too. Bone remodels slowly, over years, and panic has never been anyone's training program.