Proprioceptive Neuromuscular Facilitation (PNF) is a rehabilitation method used for many years by physiotherapists with the aim to facilitate upper limb function. However, there is little or no quantitative research investigating its underlying neural mechanisms and effectiveness. Our goal is to determine whether it is possible to facilitate movement in the right upper limb (RUL) using the isometric resistance of reciprocal isometric activity in the left upper limb (LUL), following the patterns of the crossed-extension reflex and whether the facilitation persists after training. The study I and II include 50 healthy subjects of both sexes, age between 18 and 27 years. In experiment III, 28 post-stroke patients, in the chronic stage (6 months after the stroke) and age range between 50-70 years old. All participants should have the motor preference for RUL. The subjects will be tested by a bilateral task in a virtual reality (VR) equipment and still, in experiment III, a robotic arm will be coupled to VR equipment. The LUL will be submitted to the extensor and flexor PNF diagonals, while the RUL will perform a movement with maximum speed in elbow extension to reach a virtual target. Magnetic sensors will be attached to the RUL to digitize the hand, forearm, and arm. Experiment 1 is composed of 3 groups. Participants in Group 1 will keep the LUL without any movement pattern (Zero Force), participants in Group 2 will perform flexion of the left elbow, and participants in Group 3 will perform elbow extension, using 75 % of the Maximum Voluntary Force (MVF). In experiment 2, the subjects will be previously trained to carry out the elbow extension at maximum speed for three days, performing 100 movements a day. In this experiment, we have 2 groups. Participants in Group 1 will receive no facilitation during training and participants in Group 2 will receive crossed-extension facilitation for the LUL by a 75% resistance of MVF. The evaluations will take place before, after the last training session and 2 weeks after the last training session. In Experiment III, we will have: group 1 where patients will maintain the LUL without any movement pattern (Zero Force) and in group 2, they will perform flexion and extension of the left elbow, using 75% of the MVF. The results will be analyzed by a two-way analysis of variance (ANOVA) and the post- test Holm-Sidack with significant P value set at < 0.05.
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