The investigators main goal is to determine if an Exercise-Training Intervention program (ETI) tailored to improve bone health, strength and balance, is effective in preventing Roux-en-Y gastric bypass (RYGB) induced fracture risk. To achieve this the investigators will perform a randomized clinical trial (RCT) on volunteer obese patients (BMI\>35 Kg.m-2) undergoing RYGB that will be followed for 13-months (Figure 1). The patients will be recruited, operated and will receive follow-up medical care in the Department of General Surgery from the Centro Hospitalar de São João E.P.E (DSHSJ). After being elected for RYGB and if inclusion and exclusion criteria are met, patients who decide to join the study will be randomly assigned to either i) participate in a 11 months duration ETI tailored to improve bone health and reduce fall risk in addition to the standard follow-up medical care (MFU) (ETI+MFU group), or ii) will receive only MFU (control group). Recruiting patients from only one institution will increase the likelihood of all patients receiving the same surgical and MFU care, reducing the bias related to the use of different clinical protocols. The option to include only RYGB is also to reduce the bias associated with the surgical technique. Participants allocated to the ETI+MFU group will undergo an exercise-training program of 11 months duration, 3 sessions/week, and 60 minutes/session, starting one month after the surgery. Each exercise session will be supervised and will include 5 major components: i) warm-up, ii) multidirectional jumps, iii) balance, iv) strength and, v) cool down. This structure is planned to meet two main objectives: i) enhance bone formation and, ii) reduce fall risk by improving muscle strength, cardiorespiratory fitness and balance. The ETI will last almost 1 year because the effects of BS on bone metabolism have been shown to be greatest during the first postoperative year (1). As the investigators main objective is to understand, in a broad perspective, the possible therapeutic benefits that an ETI has on the BS patient bone health and fracture risk, the plan is to investigate several variables in this study (bone turnover markers, bone mineral content (BMC) and density (BMD), body composition, body mass index (BMI), nutritional intake, static balance, dynamic balance, muscle strength of the lower limbs and trunk, daily physical activity, cardiorespiratory fitness, bone derived hormones, hormones involved in phosphate and calcium metabolism, adipokines, gastrointestinal and energy-metabolism hormones and gonadal hormones). These will enable the investigators to comprehensively understand the metabolic changes following BS that might affect bone health, and how can exercise influence those changes potentially preventing fracture risk increases.

Each patient will be assessed 4 times during the study (Figure 1). Each assay will match the monitoring protocols already scheduled by the DSHSJ for all patients undergoing BS. The 1st evaluation will occur prior to BS, to gather pre-surgical state. The 2nd, 3rd and 4th evaluations will occur in the 1st (before the beginning of the exercise-training program for the patients allocated to the exercise intervention group), 6th and 12th months after bariatric surgery, respectively. The variables analyzed at each time point fit into four major categories: i) bone quality surrogates (BTM, BMD, bone biomechanical properties); ii) anthropometry (weight, height, body composition, nutritional intake; iii) fall risk (static and dynamic balance, muscle strength, cardiorespiratory fitness, daily physical activity), iv) hormones involved in calcium, bone and gastro-intestinal metabolism. Biochemical analysis will be performed in blood samples collected during follow up hospital visits. Biochemical markers of bone turnover (BTM) reflect the degree of bone remodeling and the balance between formation and resorption and are therefore surrogates of fracture risk. As BS profoundly affects body composition, gastrointestinal and energy-regulation physiology, and because adipose tissue and gut-associated hormones also influence bone metabolism, the investigators will determine how these hormones are affected by RYGB and exercise. By monitoring these variables the investigators will gain insight on the etiological mechanisms associated with BS induced bone loss and the therapeutic effects of exercise. BS also leads to a reduction in calcium and vitamin D absorption, which may result in increased bone resorption. The investigators will therefore also monitor Vitamin D, Parathyroid Hormone (PTH), calcium and phosphorous concentrations to determine how they are influenced by the ETI. Despite mechanical unloading due to the weight loss may contribute to bone loss following BS, there is no data supporting this mechanism. To investigate this relation, the investigators will also monitor serum sclerostin, a protein released by osteocytes in response to mechanical unloading that negatively regulates bone formation. To determine the effects of BS and exercise on skeletal muscle and adipose tissue mass, the investigators will measure body composition and BMI in all patients. As one of the investigators main goal is to investigate the effects of the ETI on fall risk, they also plan to determine the cardiorespiratory fitness and muscle strength in these patients since these variables have been previously shown to influence fall risk. Daily physical activity and nutritional intake will also be determined by accelerometer and food diary, respectively, in order to control for confounding variables. Despite the several caveats associated with the determination of BMD by DXA, the investigators plan to analyze this variable, as it will provide data that will enable them to compare their results with the results from previous studies. Nevertheless, the investigators plan to complement this information with the direct assessment of bone biomechanical properties, which until recently was only available in in vitro studies due to the invasive nature of the procedure. Bone micro-indentation is a newer technique that allows measuring bone tissue mechanical properties in the clinical setting, which reflects with higher accuracy the bone resistance to fracture (6). One of the main outcomes in this research is to investigate the effects of BS on fall risk, as there is almost no data on this issue. This will be accomplished by direct determination of static and dynamic balance by means of using a forces platform. By analyzing this broad set of parameters the investigators plan to contribute with a more thorough understanding of the effects of BS on bone metabolism and, most importantly, how can an exercise training program, specifically tailored to improve bone health and balance, can reduce the risk of bone fractures in these patients. Only by analyzing this broad number of parameters will the investigators be able to control the several confounding variables and gain deeper insight into the effects of BS and exercise on the bone metabolism of these patients, thereby contributing with a potently useful strategy for the management of skeletal health in BS patients.