High-intensity progressive resistance training has the potential to modestly increase lumbar spine bone mineral density (BMD) in older adults over 1 year, but moderate-intensity training resulted in no change in BMD, according to preliminary results from the FORTIFY Bones randomized controlled trial presented at the 2026 American Society for Bone and Mineral Research (ASBMR) annual meeting in Boston.
“What we found is that progressive resistance training may not improve lumbar spine (BMD) unless it is done at high intensity and the changes are minimal,” said Lora Giangregorio, PhD, professor of kinesiology and health sciences at the University of Waterloo, in Waterloo, Ontario, Canada. Medscape Medical News. Expected minor adverse events occurred, but no fractures directly attributable to the exercises occurred.
Mary L. Bouxsein, PhD, professor of orthopedic surgery at Harvard Medical School in Boston and past president of the ASBMR. who saw the presentation, said it 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 physical intervention was safe, with little or no injury,” Bouxsein said. Medscape Medical News. “At the same time, it was disappointing that the procedure did not improve hip (BMD). I think the takeaway is that if patients are doing resistance training with the goal of improving their bone health, intensity matters and the benefits may not be seen at all skeletal sites.”
Filling gaps in the medical literature
Giangregorio explained that the trial was designed specifically to fill some of the gaps in the literature in understanding what type of training has what type of effect on BMD.
“There are mixed messages when it comes to what we know about exercise and its effects on BMD, especially in people with low bone mass, because a lot of studies have been done on postmenopausal women, but it’s not always people with low BMD,” Giangregorio said.
A frequently cited study, she said, is the LIFTMOR trial, which showed an increase in lumbar spine BMD after 8 months of training, but that trial used both resistance training 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 we were trying to answer were: Is resistance training alone effective in improving bone density without impact exercise, and does the intensity of resistance training matter?”
The trial aims to be “as pragmatic as possible”
The researchers designed a 12-month trial with three groups: a control group performing posture and balance exercises at home, a moderate-intensity resistance training group, and a high-intensity resistance training group.
The 324 participants were predominantly white (81 to 87%) and female (90 to 95%). They had a mean age of 67 years, a mean BMI of 22.1 to 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% to 81%), with approximately 15% in the moderate risk range and 13% in the high risk range.
Participants were excluded if they were already engaged in moderate or high-intensity resistance training, had contraindications to heavy lifting, had recent fractures or joint replacement, had dementia, had cancer within the past 2 years, weighed more than 450 lb, were taking medications or had a health problem affecting the bones, or were undergoing surgery or travel lasting more than 6 weeks. People with arthritis or other health conditions 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 applicable more broadly,” Giangregorio said.
All participants received two individual sessions to learn the exercises. The control group performed posture and balance exercises twice a week that were not likely to affect bone density. Resistance training groups participated in small group sessions for up to 6 weeks before continuous training twice per week with exercises including squats, deadlifts, step-ups, hip thrusts, bench press, shoulder landmine presses, and bent-over or standing rows. The moderate-intensity group used a weight they could repeat 12 times 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 researchers also assessed total hip and femoral neck BMD. They compared the control group to all resistance training participants combined, then to each intensity group separately and compared the moderate and high intensity groups to each other.
The study recorded a 91% retention rate, which refers to those who returned for assessments, although not all necessarily completed the exercise. Median exercise adherence was 92% in the moderate-intensity group and 86% in the high-intensity group. The researchers performed an intention-to-treat analysis, so their results reflect “the most conservative effect estimates” because adherence was not accounted for in the results, Giangregorio said.
When the control group was compared to the combined intensity groups, there was no effect on BMD of the lumbar spine, total hip, or femoral neck. 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.
Further analysis will be required to confirm the precise magnitude of the effect of quantitative differences, but preliminary analyzes suggest that high-intensity resistance training resulted in approximately 1% higher lumbar spine BMD than the other two groups (P. <0.04). No effect appeared at high intensity on total BMD of the hip or femoral neck.
“Our preliminary results suggest that resistance training alone at moderate intensity may not move the lumbar spine dial (BMD),” Giangregorio said, but progressive, high-intensity resistance training may lead to small changes, but not as large as those seen with medications, she added.
“I think people think they can replace medications 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 is possible that researchers will discover the factors that influence effectiveness, such as adherence or nutrition, after analyzing the variability between participants.
When they looked at adverse events deemed related or possibly related to the intervention, they included things expected during exercise, such as muscle strains, muscle or joint pain, tendinitis, and exacerbation of pre-existing conditions. These were reported more often in people who did resistance training in person than in those who exercised at home. One person developed a bladder prolapse possibly related to the procedure. One person developed vertebral fractures that were possibly related, although they were found to be fractures related to metastatic cancer that the person had developed during the trial that was affecting their spine.
Additional analyzes planned
The researchers planned several additional analyzes for the data, including sensitivity analyzes to examine potential differences in effect when accounting for adherence and when examining diet, particularly intake of protein, calcium and vitamin D. Giangregorio said participants were screened at baseline for their nutrition and those whose protein, calcium or vitamin D intake was below the recommended daily allowance received a nutrition consultation. His team also plans to conduct analyzes to explore the effects on physical functioning, mobility and quality of life.
“The presentation did not show the impact of resistance training on muscle strength and other functional outcomes that could reduce fall risk 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 the risk of falling can reduce the risk of sustaining a fracture.”
Bouxsein added that she would like to see in future research whether impact loads, such as jumping, are safe and can improve BMD in people with low BMD.
“I think it’s also important to remember that this study was conducted in older adults and might not apply to women transitioning to menopause, when bone loss is most rapid,” Bouxsein said. “We need further studies in these women to understand what interventions, besides menopausal hormone therapy, might be effective in 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 from Allina Health, TrustMe – Ed, and Physio Network. Bouxsein had no disclosures.
Tara Haelle has been a freelance science and health journalist for more than 15 years, with work published in more than two dozen trade and consumer publications. She is the author of Vaccination Survey: The History and Science of Vaccines And The informed parent: a scientific resource for your child’s first four years. Tara is the public health manager 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.
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