Objective To evaluate the effects of exercise on fall-related functional performance in postmenopausal women with osteoporosis or low bone mass and to explore whether intervention effects differed according to the reported consistency of the exercise prescription with American College of Sports Medicine (ACSM) recommendations. Methods Six electronic databases were searched from inception to 3 May 2026. Immediate post-intervention mean differences for the Timed Up and Go (TUG) test, Berg Balance Scale (BBS), and 30-second sit-to-stand test (30STS) were pooled using inverse-variance random-effects models with restricted maximum likelihood estimation, Hartung–Knapp inference, and prediction intervals. Prespecified exercise-prescription components were classified as meeting, unclear or unreported, or not meeting the ACSM criteria. Results Eighteen trials contributed 21 intervention arms. Exercise improved TUG performance (MD = −1.57 s, 95% CI −2.52 to −0.63; I² = 88.5%) and 30STS performance (MD = 3.88 repetitions, 95% CI 1.93 to 5.83; I² = 87.6%). The estimated effect on BBS was highly uncertain (MD = 3.37 points, 95% CI −2.68 to 9.43; I² = 83.6%). Formal tests found no evidence of a difference between the high and low/uncertain reported-consistency groups for TUG (p = 0.733), BBS (p = 0.985), or 30STS (p = 0.262). Prediction intervals crossed the null for all three outcomes. Certainty of evidence was low for TUG and 30STS and very low for BBS. Conclusion Exercise may improve functional mobility and repeated sit-to-stand performance, whereas the effect on BBS remains highly uncertain. The available analyses do not demonstrate superior effects for interventions with higher reported consistency with ACSM recommendations; the subgroup findings are exploratory. Systematic Review Registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420261353752 , identifier CRD420261353752.