Dynamics of Changes in Isometric Strength and Muscle Imbalance in the Treatment of Women with Low back Pain

The aim of the study was to evaluate the dynamics of isometric changes in strength and muscular lumbar-pelvic imbalances in the treatment of women with low back pain. Forty-one women, nineteen in the study group (A) and twenty-two in the control group (B), participated in the study. Magnetic resonance imaging (MRI) was performed to assess the degree of degenerative changes in the lumbar spine. The diagnosis of isometric muscle strength and their imbalances was performed with the Tergumed 700 device. After six weeks of therapy in the study group (A), there was a significant improvement in the strength of all the examined muscle groups. However, in the control group (B), significant improvement occurred only in the strength of the lumbar flexor muscles and the flexor muscles on the left side. Furthermore, there was a significant intensification of the imbalance of left flexor muscle strength compared to right flexor strength in group B. Significant differences in favour of the study group (A) concerned the strength of the rotator muscles to the left, the strength of the extensor muscles of the lumbar spine, the strength of the flexors of the lumbar spine to the right, and the balance of the strength of the lumbar spine flexors to the left compared to the strength of the flexor muscles to the right. Therapy with the Tergumed 700 system leads to an increase in the muscle strength of the lumbar and pelvic complex, compensating for its imbalance, bringing beneficial effects in the treatment of low back pain.


Introduction
Low back pain is one of the most commonly diagnosed diseases of the osteoarticular system [1]. It is also the most frequently reported ailment [2] and the second main cause of sickness absence [3]. It is the most common cause of the inability to perform work [4] and is one of the main causes of physical disability of people below the age of 45 [5]. Pain syndromes can be divided into specific and nonspecific [6,7]. Myofascial overloads, ligament injuries, and psychogenic factors are considered to be the causes of those nonspecific [8,9]. Specific pains are most often caused by a herniated nucleus, spondylolisthesis, spinal canal stenosis, degenerative changes of the interappendix joints, vertebral fractures, spinal tumours, or inflammatory diseases [10,11]. Pain sensations may be dull and diffuse but may also be shooting, stabbing, causing a burning or stinging sensation [12,13]. In the population, nonspecific back pain is the most common, that is, the basis for which the specific pathology that causes the pain cannot be found [14,15]. In acute pain, appearing for the first time in life, only 2% of patients can determine its cause [16,17]. e incidence of this disease entity causes a significant burden on the state budget. e largest direct costs are generated by diagnostics, treatment, and rehabilitation, while indirect costs are disability pensions, benefits, and sick leaves at work [18,19].
ere are many suggestions in the available literature for conservative treatment of low back pain [20,21]. Properly targeted kinesiotherapy plays a dominant role [22,23]. In recent years, various devices have been developed to create optimal conditions for conducting isolated exercises regarding the lumbar region of the spine [24]. Tergumed is one such system used in the diagnosis and therapy of low back pain.
Research conducted using this system, however, generally took the short duration of therapy into account, which hindered its objective assessment.
ere is also a lack of research on the dynamics of changes in strength and muscle imbalance at individual periods of therapy, or comparison of results with the control group. erefore, there was a need to conduct a comprehensive, objective, and controlled clinical study as well as a thorough analysis of the dynamics of changes in muscle activity and their imbalances [25].
For stabilization, the spine needs both muscle strength and stiffness, to which the muscles contribute. Due to the recognition of the close relationship between muscle function and low back pain, a new paradigm has been developed regarding the function and dysfunction of the deep muscle system. Moreover, the characteristics of exercises necessary for the rehabilitation of patients with low back pain have also been determined. is model has contributed to the modification of programmes for the rehabilitation of patients with this type of ailment by introducing rotation and extension exercises [26][27][28]. Basically, there are two main modes of action aimed at improving the protective function of muscles in relation to the spine joints. e first of them utilises the principle of minimising the forces affecting the lumbar spine during basic motor activity, and the second the optimal control of the lumbar-pelvic complex. Patients suffering from low back pain may demonstrate a lack of muscle tone normalization even after the pain subsides [29,30]. erefore, in this study, the authors focused on the assessment of isometric muscle strength and muscle balance [31]. e aim of the study was to assess the dynamics of changes in isometric strength and muscular imbalances of the lumbar and pelvic complex in the treatment of women with low back pain. e authors assumed that this therapy, by developing muscle strength and improving balance, improves the stabilization of the lumbar-pelvic complex and demonstrates beneficial effects in the treatment of people with low back pain.

Materials and Methods
Forty-one women aged 60-75 took part in the study (X � 65.3; SD � 6.5). ey were patients of the Rehabilitation Clinic who were diagnosed with low back pain. e inclusion criteria were low back pain, degenerative changes of the lumbar spine visible in magnetic resonance imaging, age 60-75 years, patient's consent to participate in the study, and not undergoing lumbar spine rehabilitation with a different kinesiotherapy method than the one applied in the study at the time of research. e exclusion criteria were less than 3 months from the onset of the acute discopathy phase, fresh fractures, short remission intervals in the course of rheumatic diseases, inflammatory diseases at the stage of exacerbation, for example, ankylosing spondylitis, hernia (abdominal, inguinal), osteoporosis with mineral density of bones up to 80% of the average for a given age, cancer, and spinal deformities.
Magnetic resonance imaging (MRI) was performed to assess the degree of degenerative changes in the lumbar spine. Randomly tested using a computer number generator, the subjects were assigned to two groups. e study group (A) comprised nineteen participants, while the control group (B) totalled twenty-two subjects.
In the study group (A), central stabilization exercises and therapy using the Tergumed 700 system were performed. In the control group (B), only central stabilization exercises were performed. e therapy lasted 6 weeks. All research procedures were carried out in accordance with the 1964 Declaration of Helsinki and with the consent of the Bioethics Committee at the Regional Medical Chamber in Kraków (Poland) No. 73/KBL/OIL/2016 from May 4, 2016.

Assessment of the Dynamics of Isometric Changes in Muscular Strength and Muscular Imbalances of the Lumbar-Pelvic Hip Complex.
e muscle strength test of the lumbarpelvic hip complex was performed using the Tergumed 700 system. is system was TÜV Süd 0123 certified and met the requirements of Directive 93/42 EEC [32].
e test was performed in flexion, extension, lateral flexion (left/right), and rotation (left/right). e test took place in a seated position. Each device was adapted to the patient. e authors made sure that the axis of motion was correct and that the subject was well stabilized. Isometric strength of the muscles was tested. e measurement was carried out using a built-in dynamometer (Nm). On each of the four Tergumed devices, a strength and muscle imbalance test was performed. One test repetition and two research repetitions were carried out, from which the average value was calculated. e examination was performed four times: before and after two, four, and six weeks of therapy.

Central Stabilization Training.
Central stabilization training was conducted on the basis of a scheme developed by Richardson et al. [33]. It consisted of three stages: training of local segmental control, of segmental control in a closed chain, and of segmental control in an open chain. A warmup using cycloergometers and deep muscle activation in low positions was also performed. e ability to properly activate muscles was palpated, enabling the transition during training to exercises in higher positions. Coordination and balance exercises were carried out with the use of Swiss balls, aerodynamic discs, sphere segments, and elastic bands. In addition, exercises for stretching and relaxing contracted muscles were used. Central stabilization training in both groups (A and B) was conducted equally by the same physiotherapist and was applied for 30 minutes, 5 days a week, and for 6 weeks from May 2016 to March 2017.

erapy Using the Tergumed 700 System.
Tergumed 700 is a line of 4 devices for diagnosis and therapy of the lumbar spine. Each device was responsible for 4 main directions of spinal movement (extension, flexion, lateral bend, and rotation). Before therapy, a maximum muscle strength test was performed on each device. Based on the test, an individual therapy plan using feedback was generated. e therapy was aimed at improving strength and compensating for muscular imbalances. e test also allowed for painless treatment. anks to programming the therapy based on the patient's current-condition test, it was a therapy that met the criteria of evidence-based medicine. e therapy followed the instructions given by Stevens [25,34]. In the case of extension and flexion, 30-40% of maximum muscle work was used to activate the appropriate muscle groups. However, in terms of flexion and lateral flexion, this increased up to 60% of maximum muscle work. e loads gradually increased by 5% every 3 days. Patients initially performed 3 sets of exercises of 10 repetitions on each device. e number of repetitions was also gradually increased to 18 in the series. erapy with the Tergumed 700 system was only carried out in the study group (A), for 1 hour a day, 5 days a week, and for 6 weeks, from May 2016 to March 2017.

Applied Statistical Methods.
Analysis of variance (ANOVA) was used to assess the dynamics of isometric changes in strength and muscular imbalances. e above calculations were performed using the Statistica StatSoft computer program and the Microsoft Office Excel spreadsheet. Statistically significant differences were assumed for p < 0.05.

Dynamics of Changes in Muscular Strength and Muscular Imbalances of the Lumbar-Pelvic Hip Complex in the Study Group (A).
In the study group (A), the greatest absolute differentiation occurred for the strength of the extensor muscles of the lumbar spine, examined after 2 weeks of therapy (SD � 51.25), while the relative differentiation for rotator muscle strength to the left in the preliminary study was (V � 50.02 Nm) ( Table 1). e largest absolute and relative differences in muscle balance concerned the ratio of flexor muscle strength to the left to flexor muscle strength to the right after 2 weeks of therapy (SD � 0.47, V � 42.21) ( Table 1).
In the study group (A), there was a significant (p < 0.005) improvement in all examined muscle groups. After 6 weeks of therapy, the strength of the lumbar flexor muscles improved significantly (p � 0.018) from an initial value of 61.54 Nm to 86.61 Nm (Table 2). e strength of the lumbar spine extensor muscles improved significantly (p � 0.001) from an initial value of 105.85 Nm to 159.59 Nm (Table 2). Also, the rotation force to the left improved significantly (p � 0.001), from the initial value of 26.65 Nm to the value of 46.005 Nm (Table 2). e strength of the muscles rotating the lumbar spine to the right improved significantly (p � 0.001) from the initial value of 28.10 Nm to 46.5 Nm (Table 2). ere was also a significant improvement in the strength of the lumbar flexor muscles to the left (p � 0.039), from an initial value of 36.72 Nm to 53.71 Nm (Table 2). e right flexor muscles of the lumbar spine also improved significantly (p � 0.049) from an initial value of 37.7 Nm to 52.07 Nm after 6 weeks of therapy (Table 2). e balance of all tested lumbar-pelvic complex muscles was correct at individual measurement periods (Table 2). e strength of the antagonistic muscle groups was balanced.

Dynamics of Changes in Muscle Strength and Muscular
Imbalances of the Lumbar-Pelvic Hip Complex in the Control Group (B). In the control group (B), the greatest absolute differentiation was demonstrated by the strength of the lumbar extensor muscles examined after 2 weeks of therapy (SD � 53.69), while relative differentiation, rotator muscle strength to the right of the lumbar region, and preliminary examination totalled (V � 62.23) ( Table 3).
e greatest absolute differentiation of muscle balance concerned the ratio of rotator muscle strength to the left compared with rotator muscle strength to the right, examined after 6 weeks (SD � 1.84). Relative differentiation, however, concerned the ratio of rotator muscle strength to the left compared to the strength of rotator muscle to the right, examined after 4 weeks of therapy (V � 395.18) ( Table 3).
Flexor muscle strength improved significantly (p � 0.002) from an initial value of 50.37 Nm to 74.06 Nm after 4 weeks, only to slightly deteriorate after 6 weeks of therapy to 73.83 Nm (Table 2). e strength of the flexor muscles to the left improved significantly (p � 0.030) from 29.27 Nm to 46.8 Nm after 6 weeks of therapy (Table 2).
ere was a significant (p � 0.010) worsening of the left flexor muscle balance compared to right flexor strength after 6 weeks of therapy. e strength of both of these muscle groups did not balance (Table 2).

Comparison of the Dynamics of Changes in Muscle Strength and Muscular Imbalances of the Lumbar-Pelvic Hip
Complex in Groups A and B. Before therapy, muscle strength and their imbalance did not show significant differences between groups A and B.
After 2 weeks of therapy, there were significant (p � 0.03) differences in the strength of the rotator muscles to the left of the lumbar region (Nm). In group A, there was greater improvement in muscle strength responsible for spinal rotation to the left (40.2 Nm) compared to the control group (28.28 Nm) ( Table 4).  (Table 4). In addition, a significantly (p � 0.01) better result was observed in the strength of the muscles rotating the lumbar spine to the right in group A. In the study group (A), this force was 45.43 Nm and in the control group (B), 31.82 Nm (Table 4).  (Table 4).
is also applies to extensor muscle strength (p � 0.02), which in the study group (A) increased to 159.6 Nm compared to the result in the control group (B) of 121.68 Nm (Table 4).
ere was also a significant  (Table 4). A significant (p � 0.03) difference was also observed in the balance of lumbar flexor muscle strength to the left compared with the right flexor muscle strength. Imbalance in the study group (A) remained within normal limits (1.05 Table 2: Differences in muscle strength and imbalance before and after 6 weeks of therapy in the study group (A) and the control group (B) demonstrated by analysis of variance (ANOVA).

Discussion
In the treatment of low back pain, it is of key importance to know the cause of the ailment and focus therapy on the problem occurring in a given patient. In developed societies, we are increasingly dealing with people who work long hours every day in a seated position [35]. In the case of weakening of the lumbar-pelvic hip complex muscles or their large imbalance, the rapid onset or asymmetrical lifting of a small weight can result in unilateral overload, muscle spasm, and trauma to the spine. is is because a sedentary lifestyle results in a loss of muscle mass and a gradual, systematic decrease in strength and flexibility.  Most studies available in the literature regarding physiotherapy in low back pain assessing individual methods or therapies are based on the evaluation of the training programme. Patients are examined before and after therapy, and in some cases, additionally in the middle of the therapy [36]. In this study, the authors evaluated the dynamics of changes in the strength of the lumbar-pelvic hip complex muscles and the equalization of their imbalances 4 times: before therapy, and after 2, 4, and 6 weeks of its duration.
Many authors have evaluated the effects of treating low back pain similarly as in the authors' research. Pranata et al. [37] investigated the coordination of lumbar extensor muscle work in patients with low back pain. Biofeedback was used in the form of a sinusoid, on which the indicator of the isometric force with which the patient exercised moved. Maximum values during the exercise oscillated between 20% and 50% of the patient's maximum isometric strength. A much smaller degree of sinusoid mapping (both voltage increase and relaxation) was observed in comparison to the control group without low back pain.
ere were also correlations between the increase in sinusoidal mapping during the return to the starting position and the increase in disability measured by the Oswestry questionnaire. In these studies, it has been shown that the control of extensor muscles in the lumbar region is impaired among patients with low back pain. Training using the Tergumed 700 system applied by the authors of this study was also based on biofeedback in the form of a sinusoid, which, as it has been shown in studies, has a positive effect on impaired muscle coordination.
França et al. [29] compared central stabilization training with strength training in fighting back pain, reducing disability and activating the transverse abdominal muscle. Both types of training gave satisfactory results, but central stabilization training proved to be more effective, mainly in the area of transverse abdominal muscle activation. However, as stated by Stevens et al. [38], strength-coordination training with the use of the Tergumed 700 system also activates the multifunctional muscle, especially when loaded with 30% of the maximum extension force. In these studies, it has been shown that strength training also affects deep muscle activity. In the research conducted by Parkkola et al. [39], it was also indicated that patients with low back pain had weakened muscles compared to the control group, as demonstrated by the isometric force test. Ruas and Viera [40] conducted a study on muscle strength and imbalance in low back pain, the results of which demonstrated that imbalance, mainly of flexor muscle strength relative to extensor muscle strength, may be associated with chronic lumbar spine pain.
Although pain syndromes are a complex and multifactorial problem, many authors associate them with muscle weakness [41]. As reported by Rossi et al. [42], therapy of back pain syndromes should include training of the efficiency and strength of muscles, mainly of the extensors. As reported by Steele et al. [43], such training should be conducted with the pelvis stabilized so as to exclude the involvement of other muscles, for example, the hip extensors. From the research by Catala et al. [44], it may be assumed that dorsal muscle training is beneficial in reducing lumbar pain among patients with low back pain. Patients who experience lumbar pain due to lumbar pain syndrome have reduced strength in their trunk muscles, mainly the extensors [44]. e legitimacy of the authors' research is also confirmed by other authors. Wang et al. [45] conducted a study regarding the impact of a 12-week standardized training programme on patients with low back pain. e results of the study showed significant improvement in muscular strength as well as compensation of flexion and extensor muscles of the lumbar region. In this study, the positive effect of training using the Tergumed system on muscle strength has been exhibited. However, a disadvantage of this study was the lack of precise specification of the group of subjects. Haag et al. [46] used the Tergumed system in their research to assess the strength of the dorsal muscles in athletes complaining of and not reporting pain in the lumbar spine. In the second group without pain, significantly higher isometric strength of the trunk muscles was observed. Nitera-Kowalik et al. [47] conducted studies on the impact of comprehensive therapy using the Tergumed system on improving coordination, compensating for muscular imbalances, the degree of disability caused by low back pain, and reducing pain sensations in patients treated at sanatoriums. Improvement in muscle imbalances was observed here for all of the examined muscle groups. However, this study did not include a control group.
In this study, in group A, in which the Tergumed 700 system was additionally used, there was a significant improvement in the strength of all the examined muscle groups after 6 weeks of therapy. Increased muscle strength responsible for extension of the lumbar spine and rotation to the left occurred after 2 weeks. is maintained after 4 and 6 weeks of therapy. e strength of the muscles rotating clockwise improved after 4 weeks and was maintained after 6 weeks of therapy. On the other hand, the strength of the trunk flexor muscles and those responsible for lateral flexion improved in the final measurement period.
is suggests that the 6-week training programme is optimal for achieving strength improvement in all of the examined muscle groups. e definitely worse results obtained in muscle strength in the control group (B) suggest that traditional central stabilization training has less of an effect on muscle strength. e differences between groups A and B became apparent after 2 weeks of therapy in terms of the force of rotation to the left. en, after 4 and 6 weeks of therapy, the difference concerned the strength of both-sided rotation, extension, and flexion to the right. Muscle imbalance of the lumbarpelvis-hip complex in the study group (A) remained within normal limits (1.05 on average), while in the control group (B), an abnormal increase in the strength of the flexor muscles to the left compared with the flexors to the right (average 1.21) was observed. erapy using the Tergumed system, through its programming based on objective patient examination, is effective in treating low back pain. Its use is also supported by economic considerations because one therapist can simultaneously rehabilitate 4 patients according to individual programmes. It is also important that objective examination before and after therapy allows verification of the applied therapeutic programme.

Conclusions
After 6 weeks of therapy in the study group (A), there was a significant improvement in the strength of all examined muscle groups. However, in the control group (B), significant improvement only occurred in the strength of the lumbar flexor and flexor muscles on the left side. In addition, in group B, there was significant deterioration of imbalance regarding the left flexor muscle strength compared to the right flexor strength. Significant differences in favour of the study group (A) concerned the strength of the rotator muscles to the left, the strength of the extensor muscles of the lumbar spine, the strength of the flexors of the lumbar spine to the right, and the balance of strength of the flexors of the lumbar spine to the left compared with the strength of the flexor muscles to the right. erapy with the Tergumed 700 system leads to an increase in the muscle strength of the lumbar-pelvic complex and compensation for its imbalance, which provides beneficial effects in the treatment of low back pain.
Data Availability e data and materials supporting the conclusions of this article are included within the article.

Conflicts of Interest
e authors declare no conflicts of interest regarding the publication of this paper.