- Isometric exercise using hand-grip. This exercise consists of two sets of 30 hand-grip contractions with the hand of the upper arm candidate for AVF (in case of doubts about the most appropriate arm for AVF the exercise will be performed with both arms). The patient will rest one minute every 10 contractions and 5 minutes between both sets. The patient will repeat this protocol twice a day, morning and night (Approximately 15 minutes each session). The contraction intensity will start with half of the maximum force obtained by dynamometry and will be increased or decreased to be placed on an effort intensity 2-3 in the Borg scale.