Interference During Motor Learning of Different Degrees of Freedom in the Paretic Upper Extremity of People With Stroke

Post-stroke rehabilitation of the upper extremity is a challenge in neurorehabilitation. Selective training of different degrees of freedom (training of specific monoarticular movements and in one plane of movement of the upper extremity) to achieve true recovery could be a good approach. However, it is not known how the training should be structured to avoid interference between the different movements trained, hindering the motor learning process during neurorehabilitation.

The objective is to determine the effect on performance and kinematic control of a selective movement control task during training of 2 different degrees of freedom, close or distant in cortical representation, of the upper extremity in persons with early (within the 5 first weeks and between 9 to 12 weeks) and chronic subacute stroke.

The hypothesis is that in the upper extremity of subacute or chronic phase stroke survivors, learning 1 target DoF is interfered by training another DoF of the same joint. In contrast, learning 1 DoF from a different, distant joint does not interfere with learning the target DoF in a training session. Likewise, this interference is diminished when multiple training sessions are performed. On the other hand, in early post-stroke stages, within the first 5 weeks, the gain in kinematic control of each controlled DoF is greater than in later post-stroke stages (between 9 to 12 weeks of evolution or chronic stages).

An experimental design of 4 days of training, of approximately 60 minutes per day, which are distributed in 3 days of training (days 1, 2, and 3) and 2 days of evaluation (days 2 and 4) will be carried out in people who are within the first 3 months after a stroke or in a chronic stage. Each group of different evolution times will have 3 intervention groups where they will train the movement of different DoF of the affected upper extremity or with another effector to maintain the practice dose among all groups. A randomization will be performed to distribute the participants in the different intervention groups.

The DoF of interest (DoF target) is shoulder flexo-extension. The first group, the control group: will train the DoF target and DoF dorsi-ankle flexion of the contralateral lower extremity. The second group, the proximal interference group, will train the DoF target and the shoulder abduction-adduction DoF. The third group, the distal interference group, will train the DoF target and the wrist flexo-extension DoF.

The training will be performed by a videogame, which is controlled by the acceleration signal of an inertial sensor. The person by selective movement of each DoF must follow the trajectory of a sinusoid.

To achieve the objective of this study, performance and kinematic variables of the movement obtained during the training (days 1, 2, and 3 of the protocol) and in the retention tests (days 2 and 4 of the protocol) will be analyzed.

The recruitment will be carried out in the Acquired Brain Injury Unit of the Hospital General from Valencia and in the Physiotherapy Faculty at the Universitat de Valencia.

In order to answer the study hypothesis, two variables will be examined:

1. Changes in performance associated with the error in the trajectory: based on the expected trajectory and the realized trajectory, the difference between the expected trajectory and the one realized will be calculated to be able to compare the changes between the beginning of training, the end of training and the retention tests of each trained DoF.
2. Kinematics: based on the acceleration data that are delivered by the inertial sensor, an analysis of the smoothness of the movement will be carried out, understanding it as a quality related to the continuity or intermittency of the movement to determine the specific changes associated with the kinematic control of each trained DoF.

For both the performance and kinematic control data, an analysis of the variance of repeated measures of 2 factors (time and intervention) is expected to be performed, if the data have a normal distribution. The sphericity and homogeneity of the data will be analyzed, and the effect size will be reported. Then, a post hoc analysis will be performed using the Bonferroni test. The level of statistical significance will have a p-value of 0.05.