Patients complaining of nonspecific LBP without any structural or neuropsychological cause, for more than 3 months, were recruited from the rehabilitation outpatient-clinic. Exclusion criteria included a history of neurological, infectious, and systemic diseases, including cerebrovascular disease, spinal cord disease, spondylitis, cancer, rheumatologic disorders, and other chronic diseases that cause long-term immobilization. Patients who had undergone prior surgery for back pain, patients who were prescribed exercise therapy in the past, patients who seemed to have radicular pain due to nerve root involvement on physical examination, and patients with structural lesions, such as spondylolisthesis, vertebral bone fracture, scoliosis, and kyphosis on X-ray, were also excluded.
A total of 24 patients were enrolled in the study and randomly assigned to one of the two groups, a lumbar stabilization exercise group (n=12) and a conventional lumbar dynamic exercise group (n=12) by a computer-generated random number sequence. Two patients in the lumbar dynamic strengthening exercise group and one patient in the lumbar stabilization exercise group dropped out for personal reasons. The remaining 21 subjects completed the 8-week exercise program without incident.
Each exercise session lasted 60 minutes and was performed 2 days per week, for 8 weeks. All patients in both groups performed warm-up stretching exercises for 15 minutes before the main exercises and cool down exercises for 10 minutes after each session. All exercises were performed in the treatment room under the supervision of a physical therapist with technical knowledge. The therapist put each patient into the appropriate position to achieve the correct posture and muscle contraction.
Lumbar stabilization exercises consisted of 16 exercises, which were aimed to strengthen the deep lumbar stabilizing muscles: the transversus abdominis, lumbar multifidi, and internal obliques. All 16 stabilization exercises were performed once, consecutively, and in the same order (). Before each exercise, the physical therapist gave detailed verbal explanation and visual instructions (pictures), regarding the start and end positions. All exercises were conducted according to the following specific principles: breathe in and out, gently and slowly draw in your lower abdomen below your umbilicus without moving your upper stomach, back or pelvis" [14
]; resulting in a situation referred to as hollowing [15
]. Subjects practiced "hollowing" with a therapist providing verbal instruction and tactile feedback until they were able to perform the maneuver in a satisfactory manner. In addition, a "bulging" of the multifidus muscle should have been felt by the therapist when the fingers were placed on either side of the spinous processes of the L4 and L5 vertebrae, directly over the belly of this muscle [14
]. These feedback techniques provided by precise palpitation of the appropriate muscles, ensure effective muscle activation [11
Lumbar stabilization exercises.
Conventional lumbar dynamic strengthening exercises consisted of 14 exercises (), which activated the extensor (erector spinae) and flexor (rectus abdominis) muscle groups.
Lumbar dynamic strengthening exercises.
For all exercises in both groups, the final static position was held for 10 seconds, and each exercise was performed for 10 repetitions. There was a pause of 3 seconds between repetitions and a 60-second rest between each exercise. Exercise intensity (holding time and number of repetitions) was increased gradually, based on the tolerance of each patient.
Lumbar extension strength was assessed using a MedX (MedX Holdings Inc., Ocara, FL, USA) lumbar extension machine, which fixes the pelvis, thigh, and knee, to ensure complete stabilization allowing measurements of lumbar extension strength at flexion angles from 0° to 72° at intervals of 12° (0°, 12°, 24°, 36°, 48°, 60°, and 72°) [16
]. Strength tests were conducted at each angle with an approximately 10 seconds rest between tests. Differences in the maximal isometric strength at a given angle of flexion were compared between the groups, before and after the exercise. The percentage change in muscle strength (strength after exercise-strength before exercise/strength before exercise×100; Δ%) after the dynamic strengthening exercises and lumbar stabilization exercises was also compared.
All evaluations were conducted by an examiner who was not the treating therapist. The examiner was aware of the study design, but was blinded to the group assignments. The examiner and a clinical physical therapist with 10 years of experience in musculoskeletal rehabilitation, who had attended specialized stabilization exercise seminars and was very familiar with the application of these exercise interventions (about 2 years direct experience) before the initiation of the trial, were responsible for supervising all the exercise sessions.
The severity of LBP was evaluated using a visual analog scale (VAS), which ranged from 0 to 100 [17
]. The VAS consists of line (10 cm in length) with the left extremity indicating "no pain" and the right extremity indicating "unbearable pain." Participants were asked to mark the line to indicate their level of pain. Higher values suggest more intense pain. This instrument shows good reproducibility for assessing pain levels [18
]. The patients indicated the average severity of their LBP over the previous 3 days.
The modified Oswestry Low Back Pain Disability Questionnaire (ODQ; also known as the Oswestry Disability Index) was used to evaluate the functional disability and quality of life [19
]. This questionnaire was filled out before and after the 8-week exercise program.
This study was approved by the ethics committee of our institute and all subjects provided written informed consent.
Differences in general characteristics (e.g., male/female) between the two groups were analyzed using the Fisher's exact test. Differences in the baseline mean VAS, ODQ scores, and in the strength of the lumbar extensors between the two groups were analyzed using the Mann-Whitney U-test.
The baseline mean values were compared with the mean values after the treatment within groups using the Wilcoxon's test. The Mann-Whitney U-test was used to compare maximal isometric strength, VAS, and ODQ score between the two groups. Statistical significance was defined as a p-value <0.05. All statistical analysis were performed using SPSS ver. 18 (SPSS Inc., Chicago, IL, USA).