The most important result of this study is the confirmation of the beneficial effect of osteopathic MET techniques on changing the order of activation of GM and BF in relation to ES in the Janda test after MET therapy in patients with LBP. The relationship between changes in muscle activation and postural balance in patients was also confirmed. There are many studies in the literature stating the efficacy of MET [36, 4, 23, 11], however, most of them are based on subjective assessment of pain according to the VAS or ODI index. Furthermore, to our knowledge, there are no scientific publications evaluating the effectiveness of segmental muscle energy techniques in patients with LBP based on sEMG images. In our study, the applied therapy was proven to have a statistically significant effect on improving the activity of lower limb muscles and erector spinae muscles. In the studied group of LBP patients, before the therapy, there was a delayed activation of the gluteus maximus and biceps femoris muscles, compared to the erector spinae muscles. This confirms Levit and Chaitow's theory that, in individuals with normal motor control, lower limb muscles should activate before erector spinae muscles during hip extension movements [7, 17]. The therapy applied in the studied group resulted in faster activation of gluteus maximus and biceps femoris muscles during the PHE test. It should be noted that there is no consensus in the literature as to the order of muscle recruitment established by Janda. A study on an asymptomatic group and a group with LBP showed that there was a delay in gluteal muscle activation during the PHE test in individuals with pain [6, 5]. In our study, there was a delayed activation of the gluteal muscles during hip extension movement with simultaneous occurrence of LBP. Coopera also states that there is a decrease in gluteal muscle activity in LBP patients [9]. MET resulted in an increase in the activity of these muscles, relieving stress on the paraspinal muscles. It has been shown that equalising the tension of paraspinal muscles increases the activation of lower limb muscles. According to Bourdillon [3], muscle shortening may be an automatic mechanism resulting from an overreaction of the central system gamma. It is suspected that as long as this mechanism is operating, the muscle cannot return to its normal resting length. Pain occurs due to the inability of the muscle to return to the desired anatomical length. Thanks to the proposed research method, we know that affecting the distal muscles of the lower limb is possible by acting on the spinal joints through the short paraspinal muscles. Eliminating tension at the level of the lumbar spine affects the tension of the posterior myofascial chain. Spinal pain is relieved thanks to faster muscle activation. Furthermore, the active spinal stabilisers have been relieved by lower limb distal muscles.
The long work experience (over twenty years) of the studied men probably contributed to the pathological changes of the L1-S1 spinal segment diagnosed by the CT scan. The specificity of the work in this plant entails repetitive movements in the sagittal plane when reaching for construction elements. The flexion and extension movement of the lumbar spine with the load (i.e. the produced components) causes pressure change in the intervertebral disc and displacement of the nucleus pulposus to the back [25]. The radiation of pain to the left limb may be caused by the asymmetry of loading in the frontal and transverse planes in the course of performing assembly-line work. Before the treatment, a relationship between the order of muscle activation in the left limb and postural balance was observed. An increase in the reaction time of the erector muscles and a faster activation of the muscles of the left lower limb (BF) had a positive effect on the subjects' balance. After the therapy on the right limb, longer response time on the part of the erector spinae muscles resulted in improved postural balance parameters. Some researchers emphasise that the ability to maintain balance depends on muscle strength and the speed at which the muscle shortens [19, 30].
The right limb without pain symptoms responds better to therapy. When comparing pre-treatment reaction times for both gluteal muscles, a significant delay was observed on the right side. This is suspected to be related to the overloading of the right gluteal muscle. There was an instinctive reduction of strain on the lower limb which was hurting. In the case of the left limb, the stabilising function of the pelvis was taken over by the gluteus maximus muscle on the opposite side together with the other gluteal muscles and fascia. The most important function of the gluteus maximus muscle is to maintain a vertical posture while standing and walking. It is one of the stabilising (postural) muscles responsible for the correct posture of the entire body [2]. This is also confirmed by the above study: the reduction in GM work time achieved by MET translates into a reduction in the range of movement of the COP in the frontal plane. After the therapy, there was an equalisation of the tension of both gluteal muscles in relation to each other. Lumbar spine muscle manipulation improved pelvic stabilisation. This is particularly important for this occupational group, which performs most of its working time while standing with pelvic anteversion.
Jabłońska et al. [14] proposed evaluating the McKenzie therapy on the basis of sEMG as well. Muscle recruitment and pain intensity decreased following exercise according to the McKenzie method. A faster reaction time of the BF and GM muscles during the PHE test was observed. The therapy lasted only seven days, the patients performed it independently and unsupervised, and the results are presented for the right lower limb only. Muscle recruitment results are presented as a percentage. No data on the statistical significance of the results are available. In our study, with the use of MET, the improvement in BF and GM muscle activation was statistically significant when compared to the percentage of improvement in the McKenzie therapy. However, it should be noted that both the McKenzie therapy and MET have a statistically significant effect on pain reduction in patients with LBP. Jabłońska's paper [14] lacks data on the radiation of spinal pain to the lower limb. This is important information because, based on the results of our study in the lower limb without pain symptoms, the timing of muscle activation and muscle recruitment is significantly different from the limb with symptoms. The McKenzie therapy focuses on pathology within the intervertebral discs by mechanically applying pressure on the nerve root, thereby resulting in a significant reduction in pain [21]. MET, on the other hand, focuses on the myofascial system as a source of movement limitations and compensatory mechanisms of the musculoskeletal system. Better results of MET are due to the fact that, according to Schlenk et al. [31], neglecting muscles surrounding joints, especially spinal joints, in the treatment of joint dysfunctions is a mistake. Paying attention to the supporting function of muscles will normalise these muscles without excessive effort. Therefore, methods focusing on soft tissues, such as MET, allow the correction of both weaker and shortened muscles, often fibrous antagonistic muscles.
Szulc et al. [33] in their study proved that the use of MET in combination with the McKenzie therapy has a more beneficial effect on spinal mobility than the McKenzie therapy alone, thereby confirming that it is myofascial limitations that affect spinal mobility. They demonstrated that the use of MET is safe and does not adversely affect the amount of disc herniation on MRI. This confirms the validity of using these techniques in people with intervertebral disc pathology.