Design: hierarchical Bayesian network meta-analysis with multivariable dose-response modelling and CINeMA certainty assessment, PROSPERO registered
Population: 18,429 adults aged 40 and over across 124 randomised trials; 11,132 across 26 trials for the fracture outcome
Primary outcome: change in bone mineral density at lumbar spine, femoral neck and total hip, with fracture incidence as secondary
Effect: brisk walking or jogging 0.013 g/cm² at spine (95% CrI 0.006–0.021) and 0.021 at total hip (0.005–0.038); benefit plateau around 600 MET-min/week; fractures — mixed aerobic OR 0.29 (0.11–0.78), mind-body 0.58 (0.36–0.93)

Older patients are told to stay active for their bones without being told what to do or how much, which is a large part of why the advice is ignored. A hierarchical Bayesian network meta-analysis of 124 randomised trials covering 18,429 adults aged 40 and over compared exercise modalities against each other and against no exercise, for bone mineral density and for fractures.

Brisk walking or jogging came out best at every site measured: lumbar spine (mean difference 0.013 g/cm², 95% credible interval 0.006 to 0.021), femoral neck (0.009, 0.001 to 0.018) and total hip, where it was the only modality reaching benefit (0.021, 0.005 to 0.038). Combined aerobic-resistance exercise matched it at the spine (0.013, 0.010 to 0.016), and mind-body exercise helped at the femoral neck (0.007, 0.002 to 0.013) with moderate certainty — the highest certainty rating in the analysis. Dose-response was non-linear and inverted-U, with clinically meaningful benefit at around 400 metabolic equivalent minutes per week for the spine and around 600 for the femoral neck and total hip: roughly two to three hours of brisk walking. In the fracture analysis across 26 trials and 11,132 participants, mixed aerobic exercise gave an odds ratio of 0.29 (0.11 to 0.78) and mind-body exercise 0.58 (0.36 to 0.93).

For a geriatric clinic this is unusually actionable. The best-performing modality is the one that needs no equipment, no membership and no supervision, and the dose is a number a patient can hold. The inverted-U matters too: it means an older patient does not need to push, which removes the most common reason they stop. Mind-body exercise earning the only moderate-certainty rating and reducing fractures is the other practical point — for patients who cannot walk far, tai chi or yoga is not a consolation prize.

Prescribe about 150 minutes of brisk walking a week, built up gradually from the patient's current level.
Add resistance work where the lumbar spine is the concern.
Offer mind-body exercise where walking is limited; it helped the femoral neck and reduced fractures.
Do not push beyond the plateau — the dose-response was inverted-U, so more is not better.
Record the current activity level at the start so the increment can be reviewed rather than guessed at.

Why it matters

It converts 'keep active for your bones' into a modality, a number and a stopping point, for a patient who has been given the advice for years without any of the three.

The statistics, in plain English

The bone density differences are small in absolute terms — 0.013 g/cm² at the spine is a fraction of what drug therapy achieves — so this slows decline rather than reversing it, and it does not replace anti-osteoporosis treatment in someone who needs it. The fracture results matter more clinically and are the least certain: an odds ratio of 0.29 with a credible interval from 0.11 to 0.78 is wide, rated low certainty, and rests on 26 trials. The inverted-U shape means estimated benefit falls at the highest doses, but fewer trials studied those doses, so that tail is the least reliable part of the curve. Overall certainty was low to moderate, which is why the authors write 'cautious support' rather than a recommendation.