All the subjects in this group were informed of the procedure at the beginning of the intervention, which consisted of the following: in the first phase (the first week), all participants had to perform the same motor control exercises program than the control group, but previously, a mental practice based on kinesthetic mental motor imagery was performed. To reinforce the process of motor imagery, a video with the exercises was shown to the subjects before performing the mental practice. All subjects had to imagine that he/she was performing each exercise during 1 set of 12 repetitions prior to the real execution of this. During the second phase (the second and third week), subjects had to complete the set both imagining, with visual mental motor imagery, and actively performing the exercises.

All the subjects in this group were informed of the procedure at the beginning of the intervention, which consisted of the following: in the first phase (the first week), all participants had to perform the same motor control exercises program than the control group, but prior to the real execution, a video was shown in third-person perspective. All subjects watched one person performing each exercise during 1 set of 12 repetitions. During the second phase (the second and third week), subjects had to perform actively the exercises while they watched the video.

All the participants also received a booklet with written information about the indications and exercises to be practiced at home to ensure that the training program was performed properly. Each week, participants received messages to remind and motivate them to undertake the exercise program daily.

The subjects in this group received an intensive training program based on stabilization exercises of lumbo-pelvic region, which are common exercises used in rehabilitation of patients with chronic non-specific low back pain.

All subjects had to imagine that he/she was performing each exercise during 1 set of 12 repetitions prior to the real execution of this. During the second phase (the second and third week), subjects had to complete the set both imagining, with visual mental motor imagery, and actively performing the exercises.

Lumbar motor control will be measured by a pressure biofeedback called Stabilizer TM. The measurement protocol in the following procedure; The patient should be supine position with the Stabilizer TM placed in the lumbar region with an initial pressure of 70 mmHg. Then, the patient will be asked to flex the hip and knee at 90 ° with one leg and then with the opposite one. It is a validated and reliable protocol for motor control of the lumbar region

Lumbar motor control will be measured by a pressure biofeedback called Stabilizer TM. The measurement protocol in the following procedure; The patient should be supine position with the Stabilizer TM placed in the lumbar region with an initial pressure of 70 mmHg. Then, the patient will be asked to flex the hip and knee at 90 ° with one leg and then with the opposite one. It is a validated and reliable protocol for motor control of the lumbar region

Perceived fatigue will be measured with Visual Analogue Scale (VAS). The VAS consists of a 100-mm line, the left side of which represents "no fatigue" whereas the right side represents "maximal fatigue"