High-intensity progressive resistance training has the potential to slightly increase bone mineral density (BMD) of the lumbar spine in older adults over 1 year, but moderate-intensity training did not lead to any changes in BMD, according to preliminary findings from the randomized controlled FORTIFY Bones trial presented at the American Society for Bone and Mineral Research (ASBMR) 2026 Annual Meeting in Boston.

“What we found is that progressive resistance training may not improve lumbar spine [BMD] unless it’s performed at high intensity, and the changes were small,” Lora Giangregorio, PhD, a professor of kinesiology and health sciences at the University of Waterloo in Waterloo, Ontario, Canada, told Medscape Medical News. Minor expected adverse events occurred, but no fractures occurred that were directly attributable to the exercises.

Mary L. Bouxsein, PhD, a professor of orthopedic surgery at Harvard Medical School in Boston, and former president of the ASBMR. who saw the presentation, said this was an interesting and important study.

“I was encouraged that high-intensity resistance training can improve spine [BMD] in these older adults with low bone density and that the exercise intervention was safe, with few to no injuries,” Bouxsein told Medscape Medical News. “At the same time, it was disappointing that the intervention did not improve hip [BMD]. I think the important takeaway is that if patients are doing resistance training with the goal of improving their bone health, intensity matters, and that benefits may not be seen at all skeletal sites.”

Addressing Gaps in the Medical Literature

Giangregorio explained that the trial was designed specifically to address some of the gaps in the literature in understanding what kind of training has what kind of effect on BMD.

“There’s mixed messages when it comes to what we know about exercise and its effect on [BMD], especially in people with low bone mass, because a lot of the studies have been done in postmenopausal females, but they’re not always people with low [BMD],” Giangregorio said.

A commonly cited study, she said, is the LIFTMOR trial, which showed increase in lumbar spine BMD after 8 months of training, but that trial used both resistance and impact training.

“So we don’t know if resistance training alone is effective, and a lot of people want to know because they don’t want to do high-impact training,” Giangregorio said. “The unanswered questions that we were trying to answer were: Is resistance training alone effective for improving bone density without impact exercise, and does resistance training intensity matter?”

Trial Aimed to Be ‘as Pragmatic as Possible’

The researchers designed a 12-month trial with three groups: a control group doing home posture and balance exercises, a moderate-intensity resistance training group, and a high-intensity resistance training group.

The 324 participants were mostly White (81%-87%%) and female (90%-95%). They had an average age of 67 years, an average BMI of 22.1-27.2, and a mean lumbar spine T-score of -1.9. Most were in the low-risk range for FRAX 10-year major osteoporotic fracture risk (72%-81%), with about 15% in the moderate risk range and 13% in the high-risk range.

Participants were excluded if they were already resistance training at moderate or high intensity, had contraindications to heavy lifting, had recent fractures or joint replacement, had dementia, had cancer in the past 2 years, weighed over 450 lb, were taking medication or had a health condition affecting bone, or had upcoming surgery or travel of more than 6 weeks. Those with arthritis or other health problems could still participate as long as they could do the exercises.

“We wanted to be as pragmatic as possible because that means the results are more broadly applicable,” Giangregorio said.

All participants received two one-on-one sessions to learn the exercises. The control group did posture and balance exercises twice a week that were unlikely to affect bone density. The resistance training groups participated in small group sessions for up to 6 weeks before ongoing training twice a week with exercises that included squats, dead lifts, step-ups, hip thrusts, bench press, landmine presses for the shoulders, and either bent-over or standing rows. The moderate-intensity group used a weight that they could do for 12 repetitions without failure, and the high-intensity group used a weight they could only repeat six times before failure.

The primary outcome was lumbar spine BMD, but the researchers also assessed total hip and femoral neck BMD. They compared the control group to all the resistance training participants combined and then to each intensity group separately as well as comparing the moderate- and high-intensity groups to each other.

The study had 91% retention, which refers to those who returned for assessments, though not all of them necessarily may have completed the exercise. Median adherence to the exercises was 92% in the moderate-intensity group and 86% in the high-intensity group. The researchers conducted an intent-to-treat analysis, so their results reflect “the most conservative estimates of effect” because adherence was not calculated into the findings, Giangregorio said.

When the control group was compared to the combined-intensity groups, there was no effect on lumbar spine, total hip, or femoral neck BMD. There were, however, modest but statistically significant effects on lumbar spine BMD when comparing high-intensity resistance training to the control group and to moderate intensity. 

It will require further analysis to confirm the precise effect size of the quantitative differences, but the preliminary analyses suggest that high-intensity resistance training resulted in lumbar spine BMD that was approximately 1% greater than that of the other two groups (P < .04). No effects emerged for high intensity for total hip or femoral neck BMD.

“Our preliminary results suggest that resistance training by itself at moderate intensity may not move the dial on lumbar spine [BMD],” Giangregorio said, but high-intensity progressive resistance training may lead to small changes, albeit not as high as seen with medication, she added.

“I think people think they can replace medication with exercise,” she said, “but I don’t think it would be fair to say you can reverse osteoporosis with exercise, based on our results.” It’s possible that the researchers may learn about factors that influence effectiveness, such as adherence or nutrition, after they analyze variability between participants.

When they examined adverse events deemed to be related or possibly related to the intervention, they included things expected with exercise, such as muscle strain, muscle or joint pain, tendonitis, and exacerbation of preexisting conditions. These were reported more often in people who attended in-person resistance training than in those who exercised at home. One person developed bladder prolapse that was possibly related to intervention. One person developed vertebral fractures that were possibly related, though it was discovered that they were fractures related to metastatic cancer that the person had developed during the course of the trial that affected their spine.

Additional Analyses Planned

The researchers have several additional analyses planned for the data, including sensitivity analyses to look at potential differences in effect when taking adherence into consideration and when looking at diet, particularly protein, calcium, and vitamin D intake. Giangregorio said that participants were screened at baseline for nutrition, and those with any protein, calcium, or vitamin D intake below the recommended daily allowance received a nutrition consult. Her team also plans to do analyses to explore effects on physical functioning, mobility, and quality of life.

“The presentation did not show the impact of the resistance training on muscle strength and other functional outcomes that may reduce the risk of falls and improve overall quality of life,” Bouxsein noted. “The vast majority of fractures in older adults result from a fall, so even if [BMD] does not change, reducing one’s risk of falling can reduce the risk of suffering a fracture.”

Bouxsein added that she would like to see in future research whether impact loading, such as jumping, is safe and can improve BMD in those with low BMD.

“I think it is also important to remember that this study was conducted in older adults and may not be applicable to women going through the menopause transition, when bone loss is most rapid,” Bouxsein said. “We need further studies in these women to understand what interventions, besides menopausal hormone therapy, could be effective at slowing bone loss during this critical period.”

This study was supported by a grant from the Canadian Institutes of Health Research and in part by funding from the Canada Research Chairs Program. Giangregorio has received honoraria to create continuing education materials on exercise and rehabilitation for osteoporosis for physical therapists by Allina Health, TrustMe - Ed, and Physio Network. Bouxsein had no disclosures.

Tara Haelle has been an independent science/health journalist for over 15 years, with work appearing in over two dozen trade and consumer publications. She is the author of Vaccination Investigation: The History and Science of Vaccines and The Informed Parent: A Science-Based Resource for Your Child’s First Four Years. Tara is the Public Health Beat Leader for the Association of Health Care Journalists, where she develops resources to help other journalists report on medical studies and public health. She is based in Dallas.