This is an observational study. Measurements were made during two different motor tasks: trunk tilts without and with the tension of the abdominal muscles in the sitting position and walking in a place with high knee lifting. It was checked how the intervention (active tension of the muscles stabilizing the core) changes the parameters of the motor coordination of the trunk and lower limbs.

Surface electrodes (single-use 55 and 40 mm; ECG Electrodes; Sorimex, Poland) were glued to the subject's body according to the SENIAM (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles) procedure for the transverse abdominal, multifidus, and supraspinal muscles, and a laser rangefinder was attached to the dorsal side at chest height. Before each exercise, the subject was instructed on how the exercise should be done.

The examination involved two motor exercises. In the first one, the subject was seated on the therapeutic table (with their upper extremities crossed over their chest) and instructed to lean forward as far as possible (ideally to place their torso on their thighs) and then quickly return to their starting position. The movement was repeated three times. Then the subject performed three more repetitions of the movement with their core engaged (i.e., their abdominal muscles contracted or "stabilized"). The range of trunk inclination in the sagittal plane (mm) and in the frontal plane (m), and the reaction of the multifidus, transverse abdominal, and supraspinatus muscles (tension values reported in microvolts [µV]) were measured using a millimeter board, laser pointer, rangefinder (measurement/angle of inclination accuracy of ± 1.5 mm), electrode, and a device for measuring the voltage of selected muscle groups, Luna EMG (accuracy of measurement [-1-+1V+/-1mV]).

The second exercise was a march-in-place with a high elevation of the knees. This exercise was also done as quickly as possible (time measured for 20 steps in place in seconds [s]). The exercise was done in duplicate. On the second occasion, subjects were instructed to do the exercise with their core engaged (i.e., their abdominal muscles contracted or "stabilized"). The exercise was performed in duplicate. The duration of the march and the elevation of the feet were measured, as well as the activity of the multifidus, transverse abdominal, and supraspinatus muscles.

Main criteria for stroke group inclusion: 1) patients with ischemic stroke; 2) patients with hemiparesis after 5 to 7 week after stroke; 3) subjects with stable trunk (the Trunk Control Test 70-100 points); 4) subjects who were in a functional state allowing walking (Rankin Scale ≤ 3); 5) no severe deficits in communication, memory, or understanding what can impede proper measurement performance; 6) at least 22 years of age; maximum 83 years of age.

Main criteria for stroke group exclusion: 1) stroke up to five weeks after the episode, 2) epilepsy, 3) lack of trunk stability, 4) lack of independent walking, 5) high or very low blood pressure, dizziness, malaise.

Main criteria for control group inclusion: 1) the control group consisted of subjects with stable trunk (TCT 100 points); correct muscle tension (MAS 0), independent walking; 2) at least 22 years of age; maximum 83 years of age.

Criteria for control group exclusion: 1) a history of neurologic or musculoskeletal disorders such as stroke or brain injury or other conditions that could affect their ability to active movement the trunk and the legs; 2) back pain; 3) no severe deficits in communication, memory, or understanding what can impede proper measurement performance; 4) high or very low blood pressure, dizziness, malaise.