Objective: Animal data has shown that loads inducing large strains and/or rates of strain in bone are required to stimulate a notable adaptive response. High intensity resistance and impact training (HiRIT) can be employed to generate such strains, but have not previously been recommended for individuals with osteoporosis owing to a perceived high risk of fracture. The aim of the LIFTMOR trial was to determine the safety and efficacy of HiRIT to improve parameters of risk for fracture in postmenopausal women with low to very bone mass. Material and Methods: Women over 60 with osteopenia or osteoporosis (T-score < −1.0 at hip or spine), free of conditions or medications that influence bone and physical function, were randomised to either 8 months of twice-weekly, 30- min, supervised HiRIT (>85% 1 repetition maximum) or a home-based, low intensity exercise program (CON). Testing at baseline and follow-up included anthropometrics, posture, whole body, lumbar spine and proximal femur BMD, proximal femur geometry, and indices of functional performance related to risk of falling (timed up-and-go, functional reach, 5 times sit-to-stand, back and leg strength). Results: 101 eligible women (65 ± 5 years, 161.8 ± 5.9 cm, 63.1 ± 10.4 kg) were recruited. HiRIT (n = 49) improved height (0.2 ± 0.5 cm vs. -0.2 ± 0.5 cm, p = 0.004), LS BMD (2.9 ± 2.8% vs. -1.2 ± 2.8%, p< 0.001), FN BMD (0.3 ± 2.6% vs. -1.9 ± 2.6%, p = 0.004), FN cortical thickness (6.3 ± 16.4% vs. 13.6 ± 16.4%, p= 0.014), WB BMC (−1.6 ± 3.2% vs. -2.2 ± 3.2%, p < 0.014), and all functional measures (p < 0.001), relative to CON (n = 52). Compliance was high in both groups (HiRIT, 92 ± 11%; CON 85 ± 24%). Only one adverse event was reported (HiRIT: minor lower back spasm). Conclusion: Our novel, brief HiRIT programme enhanced bone, posture, and functional performance in postmenopausal women with low bone mass. Contrary to conventional wisdom, HiRIT is a safe, feasible and efficacious therapy for this demographic at high risk of osteoporotic fracture.