Exercise for bone: brisk walking, about 600 METs-minutes a week, and a plateau after that

Design

hierarchical Bayesian network meta-analysis with dose-response modelling, PROSPERO registered

Population

124 randomised trials, 18,429 adults aged 40 and over

Primary outcome

change in bone mineral density at lumbar spine, femoral neck and total hip

Effect

brisk walking or jogging: spine +0.013 g/cm2 (0.006-0.021), total hip +0.021 (0.005-0.038); benefit plateaus near 600 METs-minutes per week

A Bayesian network meta-analysis pooled 124 randomised trials of structured exercise in 18,429 adults aged 40 and over, ranking modalities against each other and against non-exercise control for bone mineral density at the lumbar spine, femoral neck and total hip, with fracture as a secondary outcome.

At the lumbar spine, brisk walking or jogging (mean difference 0.013 g/cm2, 95% credible interval 0.006 to 0.021) and combined aerobic-resistance training (0.013, 0.010 to 0.016) came out ahead. At the femoral neck, walking or jogging (0.009, 0.001 to 0.018) and mind-body exercise (0.007, 0.002 to 0.013) led. At the total hip only walking or jogging reached significance (0.021, 0.005 to 0.038). The dose-response curves were inverted U-shaped: the minimal clinically important difference was reached around 400 METs-minutes per week at the spine and around 600 at the hip and femoral neck, roughly two to three hours of brisk walking, with no further gain above that. In 26 trials reporting fractures, 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).

Certainty was rated low to moderate throughout, which the authors say plainly. But the shape of the advice is usable: the effective prescription is ordinary, achievable and has a ceiling, which is a more encouraging message than most exercise counselling manages to deliver.

• Prescribe about two to three hours of brisk walking a week as the bone-health dose, and say there is no bonus above it
• Add resistance work for the spine specifically - the combination outperformed either alone there
• Offer mind-body exercise to patients who will not walk briskly; it held up at the femoral neck and on fractures
• Do not promise fracture prevention on this evidence - certainty was low and the trials were not designed for it
• Record the dose in minutes rather than in a vague instruction to exercise more

Why it matters

It replaces exercise more with a dose and a ceiling, and identifies the plateau beyond which more effort buys no additional bone.

Don't overread it

These are bone density trials with fracture as a secondary outcome and low certainty - the fracture reductions are suggestive, not established.

The statistics, in plain English

Bone density differences of 0.007 to 0.021 g/cm2 are small - a few percent - and the credible intervals for several modalities nearly touch zero. Network meta-analysis also compares many treatments that were rarely tested head to head, so some rankings rest on indirect comparison rather than direct evidence, which is part of why certainty was graded low to moderate. The fracture odds ratio of 0.29 looks dramatic, but it comes from 26 trials with few events and a credible interval running from 0.11 to 0.78 - wide enough that the true effect could be modest.

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