The evidence points the other way. In a randomized trial of 101 postmenopausal women (mean age 65, low bone density), high-intensity strength training improved bone density without vertebral fractures.[1] A meta-analysis of 40 studies confirms the benefit of exercise for bone density.[2] The studies, however, examined groups older than 40 to 55.
What does the LIFTMOR trial show?
LIFTMOR examined 101 postmenopausal women with osteopenia or osteoporosis over 8 months. The training group did high-intensity resistance and impact training.
Lumbar spine bone density rose by 2.9%, while it fell by 1.2% in the control group. At the femoral neck the result was +0.3% versus −1.9%. Cortical thickness at the femoral neck rose by 13.6%, in the control group by 6.3%. The only adverse event in the training group was a mild back spasm, and there were no vertebral fractures during the study.[1]
What do larger overviews say?
A meta-analysis of 40 studies with 2,230 women aged 50 to 60 found that all forms of exercise significantly improve bone density. Combined endurance and strength training showed the most consistent effects at the lumbar spine and hip.[2]
Another meta-analysis of randomized trials looked at impact training with ground reaction forces at least at running level. Effects were site-specific: trabecular density improved at the distal tibia of postmenopausal women, among other sites, and cortical thickness at the radius. Training therefore works mainly where the bone is loaded.[3]
Does this apply to you at 40 or 45?
The studies mostly examined postmenopausal women, partly with low bone density. Studies directly in healthy 40- to 55-year-olds are rarer. That loading is also useful and bone-friendly for you is a plausible assumption, not direct evidence.
How do you train safely?
Warm up in two steps and increase load step by step.[4][5] Learn the technique before you train heavy. If you have been diagnosed with osteopenia or osteoporosis, plan your training with medical or physiotherapy support.
In short
- High-intensity strength training improved bone density in an RCT, without vertebral fractures.
- A meta-analysis of 40 studies sees benefits for bone density from all forms of exercise.
- Effects are site-specific: bone responds where it is loaded.
- With diagnosed osteoporosis, training belongs in medically supervised hands.
Frequently asked questions
Is running enough for my bones?
The meta-analysis on impact training found site-specific effects for loads at least at running level.[3] It does not allow the conclusion that running alone is enough.
How long does it take for bone density to improve?
The LIFTMOR trial ran for 8 months and showed measurable changes in that time.[1]
Does the trial apply to me?
Only to a limited extent. It examined postmenopausal women with low bone density, mean age 65.[1] For 40- to 55-year-olds, transfer is a plausible assumption.
What should I consider with osteoporosis?
Have a doctor or physiotherapist support your training before you go high-intensity. The trial provides no basis for training on your own with diagnosed osteoporosis.
Sources
- Watson, S. L., Weeks, B. K., Weis, L. J., Harding, A. T., Horan, S. A., & Beck, B. R. (2018). High-Intensity Resistance and Impact Training Improves Bone Mineral Density and Physical Function in Postmenopausal Women With Osteopenia and Osteoporosis: The LIFTMOR Randomized Controlled Trial. Journal of Bone and Mineral Research, 33(2), 211–220. doi:10.1002/jbmr.3284Study type: Randomized controlled trial, n = 101 postmenopausal women (mean age 65), 8 months
- Hejazi, K., Mohammad Rahimi, G. R., & Hofmeister, M. (2025). Impact of exercise modalities on bone health: a meta-analysis of aerobic, resistance, and combined training on bone mineral density in postmenopausal women. Archives of Osteoporosis. doi:10.1007/s11657-025-01594-5Study type: Meta-analysis, 40 studies, n = 2,230 women aged 50–60
- Ng, C.-A., Gandham, A., Mesinovic, J., Owen, P. J., Ebeling, P. R., & Scott, D. (2023). Effects of Moderate- to High-Impact Exercise Training on Bone Structure Across the Lifespan: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Bone and Mineral Research, 38(11). doi:10.1002/jbmr.4899Study type: Systematic review and meta-analysis of randomized trials
- Neves, P. P., Alves, A. R., Marinho, D. A., & Neiva, H. P. (2021). Warming-up for Resistance Training and Muscular Performance: A Narrative Review. In: Contemporary Advances in Sports Science, IntechOpen. doi:10.5772/intechopen.96075Study type: Narrative review
- Chodzko-Zajko, W. J., Proctor, D. N., Fiatarone Singh, M. A., et al. (2009). Exercise and Physical Activity for Older Adults (ACSM Position Stand). Medicine & Science in Sports & Exercise. doi:10.1249/MSS.0b013e3181a0c95cStudy type: Position stand of the American College of Sports Medicine
Limits of these statements: The studies measure bone density and structure, not fracture rates over decades. Participants were mostly older and partly had low bone density. The results are no substitute for a medical assessment.
Note: This article is for general information and does not replace medical advice, diagnosis or treatment. Talk to your doctor before you start training, especially if you have pre-existing conditions.