The investigators will recruit healthy pre-menopausal, Caucasian female participants 25-40 years and divide them into two groups, obese and lean according to their Body Mass Index. Participants will be identified and approached from a study group of obese and lean participants previously recruited for the 'The Effects of Obesity on Bone Structure and Strength - Fat and Bone Study (FAB)' study (REC ref 10/H1308/61) conducted at the Academic Unit of Bone Metabolism (AUBM) in Sheffield. Participants from this study have been selected as some of the scan and neuromuscular function data generated from this study will be reused as explained below. Body Mass Index ≥30 kg/m2 will be used to define obesity with BMI for lean participants defined as 18.5-24.9 kg/m2. Thirty participants will be recruited, 15 obese and 15 lean. Participants will be matched for age, and where possible height.