Healthy, post-menopausal elderly women without other conditions restricting them from completing an exercise intervention. Inclusion criteria will be: Aged 60-80 and postmenopausal for at least 5 years, not taking/eligible for osteoporosis medication. Exclusion criteria will be: regular (\>once per week) participation in high impact or high load resistance training, any disease or medication that contraindicates exercise or affects bone metabolism, meet UK criteria for pharmaceutical treatment of osteoporosis (will be referred to GP for treatment). The primary outcome measure will be AP lumbar spine (L1-4) BMD, measured by DXA using a GE Lunar iDXA densitometer. Secondary outcomes will include: BMD at femoral neck and lateral BMD of vertebra and hip structural parameters by DXA. Vertebral morphometry and dimensions, and total and regional body composition (bone, fat and lean masses), spinal curvature will be assessed from lateral DXA scans using statistical shape modelling (SSM) and the Cobb angle will be calculated as a measure of kyphosis, previous and current bone relevant physical activity will be assessed using a validated questionnaire, physical performance will be assessed using the Short Physical Performance Battery and functional mobility will be assessed using the Senior Fitness Test (SFT), peak force developed during exercises will be assessed by performing exercise using a resistance band of the current weight instrumented using a spring balance, postural sway will be assessed by measuring the movement of the centre of mass (COM), centre of foot pressure (COP), body segment through force platforms.

The intervention group will be asked to take up a six-month programme of muscle strengthening exercises using resistance bands. Exercises will be introduced through group sessions run three times per week, some of which could be substituted by home exercise supported by an exercise booklet and video. The intervention will consist of initial spinal extension and core strengthening exercises to ensure good posture and form (e.g. thoracic spine extension and abdominal exercise avoiding spinal flexion). Exercises that increased BMD will be adapted for resistance bands, initially at low intensity to allow development of good technique. Intensity will be increased gradually by employing bands of greater stiffness until participants can only complete 8 repetitions without a break. Once participants can attain 12 repetitions, intensity will be progressed by using a higher strength band. Participants will be advised in technique and progression at group sessions, to support transition to independent exercise by the end of the study.

The intervention will include a behaviour change component that considers capability, opportunity and motivation using the Behaviour Change Wheel framework by using the taxonomy of behaviour change interventions to identify the most appropriate strategies for facilitating behaviour change. The nature of the intervention considers the social and physical limitations to opportunity to exercise, and physical and psychological capability as identified in the qualitative phase by incorporating a group component to exercise and avoiding settings such as a gym. To accord with the practical and environmental factors identified, sessions will be offered at a variety of times of day. Explanations of safety of exercise with low BMD and purpose of the exercises in the group class and booklet/video will underpin knowledge aspects. Participants will be encouraged to be involved in goal setting and action planning. This will be supported using text reminders and motivational messages or other support strategies. Feedback in group sessions will also reinforce reflective motivation. Support and implementation strategies will be continuously reviewed based upon findings in initial participants. The control group will be asked to continue their usual exercise and dietary habits as if they were not participating in the study.