Lift heavy for your bones? A new trial says intensity matters.

If you’ve ever wondered whether the weights you lift are heavy enough to matter for your bones, a new Canadian trial has a first answer. It’s called FORTIFY Bones, short for “Finding the Optimal Resistance Training Intensity for Your Bones,” and it was led by Professor Lora Giangregorio at the University of Waterloo. The early results were presented in October at the American Society for Bone and Mineral Research meeting in Boston.

The team followed 324 adults with low bone density for a year. Their average age was 67, and about nine in ten were women. None were taking bone medication. Everyone trained twice a week in one of three groups: posture and balance exercises at home, moderate supervised lifting (about 12 reps, not to failure), or heavy supervised lifting (a weight they could lift only about 6 times). The lifting groups did squats, deadlifts, step-ups, hip thrusts, presses and rows.

The good news

The heavy-lifting group ended the year with spine bone density about 1% higher than both the moderate group and the balance group. That’s a small number, but in a year-long randomized trial in older adults with low bone density, it’s a real signal.

Just as important, heavy lifting was safe in this group. There were some minor, expected aches, but no fractures caused by the exercise. People also stuck with it: 91% came back for their final scans, and attendance ran around 86–92%.

Bone responds to load, not effort. Moderate weights felt like work, but they didn’t move the needle.

Harvard’s Mary Bouxsein, a past president of the bone research society who saw the talk, summed it up: if you’re training for your bones, intensity matters, and the benefits may not show up at every site in the skeleton.

The catches

A note on where these numbers come from: the full results aren’t public yet. We read the trial’s registration and its published protocol ourselves. The result figures come from Medscape’s report of the conference presentation.

What to do with this

If you’re training for bone, the load has to be genuinely challenging, and it should be built up gradually with good coaching. Moderate work still has value for strength, balance and confidence, which help prevent falls. But this trial suggests it may not be enough on its own to change bone density. And exercise isn’t a substitute for medication when your doctor recommends it. The effects seen here are smaller than what bone drugs typically produce.