- Isometric exercise using elastic bands. At noon the patient will perform a slow contraction session using elastic band with 20 slow repetitions with the arm in flexion and 20 repetitions with the arm in extension. (Total duration: less than 10 minutes) Clinical follow-up of these patients will be fortnightly to ensure that they perform the exercises correctly and to measure the force acquired through dynamometry. Likewise, brachial diameter and bicipital and tricipital skinfolds will be measured. In addition, they will be contacted by telephone once a week to assess compliance. Doppler ultrasonography will be performed at the initial visit, and at 4 and 8 week-visits (visits 1, 2 and 3). In the doppler ultrasound performed at 8 weeks, the final surgical indication will be given depending on the caliber of the vessels in the chosen arm. At the initial visit and at the 8-week visit, biological samples will be obtained to assess the parameters of nutrition and muscle mass and a bioimpedanciometry will be performed.