Exercise for bone: about two to three hours of brisk walking a week reached a meaningful effect

Design

Hierarchical Bayesian network and dose-response meta-analysis of RCTs

Population

18,429 adults aged ≥40 across 124 trials

Primary outcome

Change in lumbar spine, femoral neck and total hip BMD

Effect

Brisk walking/jogging total hip +0.021 g/cm² (CrI 0.005 to 0.038); fracture OR 0.29 for mixed aerobic (0.11 to 0.78)

A BMJ hierarchical network meta-analysis pooled 124 randomised trials, 18,429 adults aged 40 and over, comparing structured exercise with control or other exercise.

Brisk walking or jogging improved lumbar spine (mean difference 0.013 g/cm²), femoral neck (0.009) and total hip (0.021) bone density; combined aerobic-resistance training improved the spine (0.013), and mind-body exercise the femoral neck (0.007). The dose-response was an inverted U, with clinically meaningful change at about 400 MET-minutes a week for the spine and 600 for the hip — roughly two to three hours of brisk walking. In 26 trials reporting fractures, mixed aerobic exercise (OR 0.29) and mind-body exercise such as tai chi (OR 0.58) may reduce fractures.

Certainty was low to moderate, and fracture data are sparse. But the analysis turns 'exercise is good for bones' into a specific, achievable prescription for older patients.

• Prescribe a dose: about 150–180 minutes a week of brisk walking, in bouts the patient can manage.
• Add resistance training two days a week where feasible.
• Offer tai chi or similar for those at fall risk — it may reduce fractures as well.
• Build up gradually in frail patients; more is not always better.
• Combine with bone-protective drugs where indicated, not instead of them.

Why it matters

A concrete dose is more likely to be followed than general advice to stay active.

Don't overread it

Low-to-moderate certainty evidence; the fracture reductions in particular rest on few trials.

The statistics, in plain English

Credible intervals are the Bayesian equivalent of confidence intervals. The bone density gains are small in absolute terms, and the fracture estimates come from few trials with wide intervals, so they are low certainty.

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