Excessive fat mass (FM) contributes to changes in the strength and endurance of skeletal muscles. Mid-thigh muscle mass is approximately 2.5 times that of fat mass, but individuals who are obese have increased intra- (fat within muscle cells) and intermuscular fat (fat between muscle cells), establishing a negative influence on strength generation capacity and functional independence. The functional capacity of a skeletal muscle can be assessed based on the muscle's ability to produce strength. The relevance of this study is to identify/analyze the changes in segmental body composition (BC) which might better determine the association between fat free mass (FFM) of the lower limbs and maximum voluntary contraction (MVC), 36 months after bariatric surgery. This study was elaborated and will be performed at the Clinical Hospital in the Medical School of the University of Sao Paulo (HCFMUSP). The patients involved will receive the Informed Consent Form. The sample, consists of 155 adults selected at the ambulatory of the Bariatric and Metabolic Surgery Unit of the Department of Gastroenterology of HCFMUSP in the periods: preoperative, 6 and 36 months after surgery. Patients of both sexes, above 18 years of age, will undergo bariatric surgery performed at the institution. Adult patients over 60 years old, undergoing revision surgery and other surgical techniques will be excluded. Anthropometric variables will be obtained on the same day as the evaluation of BC by trained evaluators. The BC will be measured by In Body 230. BMI (kg/m2) shall be determined by dividing body weight (kg) by height (m) squared. Evaluation of Body Composition and Muscle Strength will be held between 8:00 am and 10:00 am in the Laboratory of Exercise and Movement Studies at the Institute of Orthopedics and Traumatology of FMUSP. BC measurements as FM (% and kg), FFM (% and kg), will be obtained by the indirect noninvasive method of electrical bioimpedance. The dynamometer will be used to evaluate muscle strength extension (Ext) and flexion (Flex) MVC torques for both legs will be carried. The MVC assessed variables should be absolute Ext and Flex torques (Nm), Ext and Flex torques relative to the body weight (Nm/Bw) and Ext and Flex torques relative to FFM (Nm/FFM).

Anthropometric Assessment Anthropometric variables will be obtained on the same day as the evaluation of BC by trained evaluators. The body weight (kg) will be measured by In Body 230, 2.0, (Biospace Seoul, Korea). The patient should be in the orthostatic position, facing the display, in the center of the scale, barefoot, in light clothes. The height measurement (m) will be performed in a stadiometer coupled to the scale W 300, Class III, with a maximum capacity of 2m. The patient will be kept with his back to the meter, with the feet united, in an erect position, looking at horizon and arms extended to the side of the body. The reading will be made in the nearest centimeter when the horizontal rod of the vertical bar of the stature scale rests against the individual's head. BMI (kg/m2) will be determined by dividing body weight (kg) by height (m) squared.

Bioimpedance Body composition will be determined by bioelectrical impedance analysis (BIA) under constant conditions (with subjects appropriately hydrated and at the same time of day).The body composition analyzer (InBody230, Biospace Co., Gangnam-gu, Seoul, South Korea) was a segmental impedance device that uses a tetrapolar 8-point tactile electrode system, and the measured weight range was 10 to 250 kg. Impedance measurements were performed by utilizing 2 different frequencies (20 and 100 kHz) at each segment (the right arm, left arm, trunk, right leg, and left leg). The participant will be positioned in orthostatic position on a platform with lower electrodes for the feet and two brackets (the upper electrodes) gripped on hands. Data output was calculated in percentages (%) and included FM, FFM, trunk FFM, and appendicular FFM (the sum of the FFM values for the right arm, left arm, right leg, and left leg).

Isokinetic dynamometer The muscular strength evaluation will be performed on the isokinetic dynamometer, Biodex ® Multi-joint System 3 (Biodex Medical Systems Inc, Shirley, New York, USA). The dynamometer is calibrated thirty minutes before the start of the tests.

Participants are positioned for evaluation in the concentric / concentric mode of knee joint extension and flexion movements. Individuals remain seated with their hip at 90º of flexion, affixed to the chair with chest X-belts, a strap around the pelvic girdle, a strap over the distal third of the thigh and one at the distal third of the assessed leg, way to free the movements of the ankle.

All participants are instructed to perform four movements with submaximal force to familiarize themselves with the equipment. The test is performed first on the dominant limb and later on the non-dominant limb. The assessed limb is positioned with the lateral femoral condyle (axis of the knee joint movement) aligned to the mechanical axis of the dynamometer. The member that is not being evaluated will be aligned with the other member. The volunteers are instructed to perform two sets of 4 uninterrupted repetitions of knee extension and flexion with interval of 60 seconds. Throughout the period of the test, standardized and constant verbal encouragement is performed to obtain as much force as possible during contractions.

The tests are performed with concentric movements of flexion and extension of the knee, starting from 90º of flexion and reaching 20º of extension, with correction of the force of gravity.

The angular velocity used will be 60 degrees per second (60º / s).

The variables that will be obtained through the evaluation of muscular strength are:

Torque Peak (Nm): is the maximum force reached in each of the repetitions in which the test was performed. The peak torque represents the largest muscle contraction in the arc of movement and corresponds to the highest point of the force x distance curve.

Peak torque relative to body weight (Nm / kg): maximum force corrected for body weight, the result being expressed in percent newton-kilogram.

Inclusion Criteria:

• Body mass index (BMI) between 40 and 60 kg/m2.

Exclusion Criteria:

• Functional disability
• Treatment with steroid medication for any reason.
• Use of artificial devices such as an orthosis or a prosthesis.

Patients with severe obesity undergoing bariatric surgery in the Bariatric Metabolic Surgical Unit of the Hospital das Clínicas, University of São Paulo Medical School.