Re: Effect of exercise on bone health in middle aged and older adults: hierarchical network meta-analysis of randomised trials

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Dear Editor

Lu and colleagues make a useful attempt to turn a complex literature into an exercise dose that clinicians can recognise.¹ I am less certain, however, that approximately 600 MET-min/week can be treated as a bone-specific target.

The difficulty lies in the unit used to define dose. MET-minutes estimate energy expenditure, whereas bone responds to mechanical loading.²˒³ A cycling session and a programme of jumping or heavy resistance exercise may produce similar metabolic totals while imposing very different strains on the skeleton. Current osteoporosis guidance likewise specifies resistance intensity, repetitions, and impact exposure rather than a single metabolic total.⁴ This distinction is particularly relevant in older adults, for whom activity-specific MET values have recently required separate calibration.²

The authors partly address heterogeneity by presenting modality-specific dose-response curves. Even within those categories, however, trial-level MET dose may track differences in supervision, adherence, progression, programme duration, and the amount of weight-bearing or impact activity. The apparent inverted U-shaped association could therefore reflect the mixture of programmes occupying each dose range rather than an optimum biological dose.

It would be useful to know whether the dose-response association persists within more mechanically coherent groups, such as weight-bearing aerobic exercise, impact exercise, and resistance training. If the original trials did not report enough loading detail for such an analysis, 600 MET-min/week would be better described as a summary metabolic volume across the included interventions rather than an osteogenic threshold. This distinction would not weaken the evidence that exercise benefits bone health. It would make the proposed target easier to interpret safely in clinical practice.

References
1.Lu C, Li L, Zhang L, et al. Effect of exercise on bone health in middle aged and older adults: hierarchical network meta-analysis of randomised trials. BMJ 2026;394. doi:10.1136/bmj-2026-100561.
2.Willis EA, Herrmann SD, Hastert M, et al. Older Adult Compendium of Physical Activities: energy costs of human activities in adults aged 60 and older. J Sport Health Sci 2024;13:13-17. doi:10.1016/j.jshs.2023.10.007.
3.Turner CH, Robling AG. Designing exercise regimens to increase bone strength. Exerc Sport Sci Rev 2003;31:45-50. doi:10.1097/00003677-200301000-00009.
4.Bae S, Lee S, Park H, et al. Position statement: exercise guidelines for osteoporosis management and fall prevention in osteoporosis patients. J Bone Metab 2023;30:149-65. doi:10.11005/jbm.2023.30.2.149.

No competing Interests: YesThe following competing Interests: Electronic Publication Date: Thursday, September 17, 2026 - 16:19AI use: No, I have not used AIHighwire Comment Subject:

Effect of exercise on bone health in middle aged and older adults: hierarchical network meta-analysis of randomised trials

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Re: Effect of exercise on bone health in middle aged and older adults: hierarchical network meta-analysis of randomised trials

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Effect of exercise on bone health in middle aged and older adults: hierarchical network meta-analysis of randomised trials

Check this box if you would like your letter to appear anonymously:: Last Name: WenjieFirst name and middle initial: LuEmail:

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Address: No. 641 Renmin Middle Road, Yuecheng District, Shaoxing City, Zhejiang ProvinceOccupation: ClinicianAffiliation: Shaoxing TCM Hospital Affiliated to Zhejiang Chinese Medical UniversityBMJ: Additional Article Info: Rapid response