Low back pain is associated with spine, pelvis, and hip mobility impairments (Reis and Macedo, 2015; Nishimura and Miyachi, 2020) hypothesized to be caused by tight muscle contractions to protect sensitized lumbar tissues (Hodges and Tucker, 2011; Van Dieën et al., 2019). Fasciae are specialized connective tissue structures and exist of various phenotypes like the superficial fascia, deep fascia, myofascia, and arthrofascia (joint capsules and ligaments). Each fascia (single connective tissue sheet incl. expansions) has an important role in transmitting force toward muscles and bones in a three-dimensional fashion (Huijing, 2002; Maas, 2019). Pathophysiological lumbar fasciae adaptations (Langevin et al., 2011; Tesarz et al., 2011) can influence this force transmission resulting in painful asymmetric muscle contraction (Kim et al., 2013; van Dieën et al., 2017) and loss in joint mobility (Maas, 2019). Both painful muscle contraction and loss of mobility are treatment parameters (Staal et al., 2017; Shipton, 2018).

In physical therapy, “fascia tissue manipulation(s)” (FTM(s) are used in treating musculoskeletal pain, like low back pain. FTMs such as myofascial release techniques, myofascial trigger-point interventions, and elastic tape application methods have been applied and their effectiveness have been systematically reviewed (Liu et al., 2019; Zhang et al., 2019; Arumugam and Harikesavan, 2020). The effectiveness of lumbar FTMs have been demonstrated regarding pain relief and improvement of joint mobility (Vanti et al., 2015; Wu et al., 2021). However, the effects of lumbar FTMs do not unequivocally prove to be successful (Chen et al., 2021; van Amstel et al., 2021). The explanation for the inconclusive results can be the differences in type, intensity, location, and/or direction of the utilized lumbar FTM in the above-mentioned studies.

Optimization of FTMs requires a more detailed understanding of the underlying mechanisms of this type of treatment. It has been proposed that FTMs by displacement of the skin, the tension in the underlying fasciae will be modulated which alters the mechanical properties. In support of this rationale, mathematical geometric modeling has shown that forces exerted onto the skin can deform and displace the fasciae and as such change the mechanical properties of the underlying fasciae (Chaudhry et al., 2008; Chaudhry et al., 2014). As evidence for these working mechanisms is lacking, several theoretical models have been proposed.

Regarding the effectiveness of FTMs on pain and mobility, it has been proposed that this will depend on both location and direction of the applied skin displacement (SKD) (Noten, 2021). It has been proposed that SKD will affect fasciae stiffness and their relative positions to surrounding tissues (Huijing and Baan, 2003; Maas, 2019), which can be beneficial but may also “worsen” pain and decrease mobility (Noten, 2021). To indicate whether or not a patient would benefit from FTMs, a fascial diagnostic test has been proposed: The Dynamic ArthroMyofascial Translation^® Test. The test consists of 3 steps: 1) affirmation of the most painful movement from stance to either flexion or extension, as a reference test, 2) the same test with ongoing mediolateral directed SKD to the right at e.g., L3 or L5, and 3) the same reference test with ongoing SKD to the left. SKD leading to the largest mobility improvement and/or pain reduction can be utilized for FTMs at the tested location (Noten, 2021).

Several studies in which FTMs have been applied to healthy humans by elastic tape or myofascial release have shown that fasciae and muscles below the skin undergo deformations and are locally strained (Tu et al., 2016; Wong et al., 2017; de las Penas, 2019; Wang et al., 2019). Therefore, it is conceivable that variable effects in alterations in mobility (i.e., increase or decrease) due to FTMs by SKD are also expected to occur in healthy subjects, but could be less pronounced than in patients with limited mobility for instance in case of low back pain.

Although changes in joint mobility through SKD seem to be clinically effective, the basal effects of SKD on healthy subjects have not been tested objectively. Therefore, the aims of this study were: 1) to assess whether SKD at the lower back affects flexion- and extension range of motion of the spine, pelvis, and hip complex versus a sham skin-displacement, in healthy subjects, and 2) if present, to test the effects of SKD at different locations and directions, as well as 3) to assess intertester and intratester reliability of applying the SKD.

Participants were recruited from the student and employee population of the Vrije Universiteit Amsterdam using posters and flyers and via advertisements that were placed on social media platforms (Facebook and Linkedin). Inclusion criteria were: Healthy subjects (BMI range between 18.5 < 30, age 25 till 55 years, able to read and speak English). We have chosen this age category because disability due to low back pain is highest or most severe at the age of 25–65-year (Hartvigsen et al., 2018). Exclusion criteria were low back pain within the last 6 months and other injuries.

Each subject started standing on a custom-made station. The custom-made station was designed in such a way that the knees could only maximally flex 10° through a leg-support. The degree of knee flexion was measured with a BASELINE®BUBBLE®INCLINOMETER. Depending on the randomization, at first, a maximal spinal flexion or extension movement (index test) was performed at own comfortable speed to retrieve the baseline reference value (repeated 3 times). In addition, either an ongoing lumbodorsal SKD or sham displacement was carried out, conform the four conditions (combination: location and direction) of the test procedure (Figure 2). The four conditions consisted of: 1) a mediolateral directed SKD to the Right (R) or Left (L) direction with respect to the spine (Figure 3) at 2) the location L5 or L3 (RL5, LL5, RL3, LL3). The SKD intensity was beyond the skin and underlying fascia slack (grade 4) equivalent to Maitland’s passive tissue stretch grading scale (Lee, 2001; Chester et al., 2003). For sham, the hands were placed with a light touch at the same locations (L5 and L3) without movement of the skin. Per condition each end-flexion or extension position (attained at the end of the movement) had to be held for 4 s (400 frames). An a priori experiment demonstrated no carry-over effects of the index tests when a 30-s pause was held between every single test. All above-described tests were repeated three times (1^st, 2^nd, and 3^rd test). The whole procedure was repeated twice with ongoing SKD applied by two separate testers (both experienced physiotherapists) to determine the SKD reliability through the agreement between two testers (1^st vs. 2^nd) and a third time by tester 1 to determine the within tester consistency (1^st vs. 3^rd), see Supplementary Material.

Total seventy-five subjects were registered for the study. Twelve subjects were excluded for several reasons Figure 5. Sixty-three subjects, 26 women and 37 men, age 35 ± SD1.18 years were enrolled for the study. No significant differences in demographic characteristics between groups (SKD n = 33; Sham n = 30) were present Table 1.

For one subject the HROM and LROM data points were excluded since the sacrum cluster was touched during the flexion measurements. In addition, for two subjects the flexion data were excluded due to exceeding the large but still limited range of motion in the experimental set-up. The processed data consisted of a total of 3276 records (flexion, n = 1872; extension, n = 1,404). Thirty flexion and 46 extension data points were detected as extreme outliers and were excluded from analyses. The variables within each group had a normal distribution (p < 0.05). No significant carry-over effects were found regarding the order of testing (p < 0.05). The square root transformed data was back-transformed for interpretation.

This study shows that lumbodorsal mediolateral directed SKD affects thoracic, lumbar, and hip ROM. The effects of SKD are substantially direction -and location different as well as movement (flexion/extension) specific. In general, the mean flexion ROM decreased while mean extension ROM increased. However, based on the MDC_95% some individuals showed an increase in flexion ROM (n = 23, MDC_95% range = HROM:2.9- 21.3, LROM:1.5–6.5; TROM:0.9–7.0) and a decrease in extension ROM (n = 27, MDC_95% range = HROM: 1.7- 9.1, LROM: 1.4- 7.0, TROM: 1.6–5.2) due to SKD which was much greater than in the sham group. To the best of our knowledge, this is the first study showing that SKD affects the thoracic, lumbar, and hip ROM based on the SKD condition used. These findings support the hypothesis that skin and underlying fasciae are modulated by SKD. Consequently, this may have an impact on the structures that determine the thoracic, lumbar, and hip ROM. Whether this effect is due to altered tensions in underlying fasciae remains to be determined.

A strength of the study is the robust internal validity of the study because of several reasons: 1) the FDT consisted of a standardized procedure that was performed in a custom-made station in reducing the change of random errors (Gauvin et al., 1990), 2) the wrist instead of the finger-tip-floor distance was utilized to register FFD (Akaha et al., 2008), 3) SKD was performed by two trained physiotherapists, 4) sample size was sufficient (n = 63), 5) the order of SKD conditions per group was randomized, and 6) the increase or decrease of ROM per region was based on surpassing the MDC_95%.

A limitation could have been that the sham skin displacement chosen may have differed from the SKD conditions not only in the lack of horizontal shear stress (mediolateral displacement) but also in the much lower normal stress (posterior-anterior pressure) used in the sham group. Previous studies have shown that the amount of pressure experienced by patients may influence the treatment effects (Wilson et al., 2021) and also that posterior-anterior pressure on the skin without any mediolateral displacement influences joint mobility (Cagnie et al., 2013; Takamoto et al., 2015). It cannot be completely ruled out, that the observed mobility changes in the SKD group in this study were not only caused by the discussed effects of a mediolateral displacement but by the differences in the experienced pressure by the subjects in the SKD group versus the sham group. Another limitation could have been that the subjects were unfamiliar with performing the index tests in a fixed position on an elevated station (20.5 cm), which could have increased fear. Fear is associated with increasing myoelectric activity of the lumbar erector muscles in healthy subjects (Pool-Goudzwaard et al., 2018) influencing the thoracic, lumbar, and hip ROM (Colloca and Hinrichs, 2005). This might have affected the observed ROM. To diminish a possible activation of muscles, subjects were asked to stay in the end position for 4 s to stimulate muscle relaxation (McGorry and Lin, 2012). The thoracolumbar cluster T12-T8 that was used in our study was not fully in line with the more commonly used T12-L1 location (Vazirian et al., 2016). We have chosen this cluster marker since a pilot experiment showed that the markers of T12 could not be detected during the flexion- and extension movements. Finally, the second measurement was always performed by a different physiotherapist. Should an effect have occurred between measurements, the differences in thoracic, lumbar, and hip ROM outcome measures between the 1^st and 3^rd index tests would have been greater than the differences in measures between the 1^st and 2^nd index tests because repetition of movements increases ROM (Holzgreve et al., 2020). No carry-over effects were demonstrated, indicating no increase in thoracic, lumbar, and hip ROM during the 1^st, 2^nd, and 3^rd tests.

This study is the first step in investigating the Dynamic ArthroMyofascial Translation^® Test by evaluating the SKD effects on the spine, pelvis, and hip ROM (Noten, 2021). The next step will be to test whether SKD affects the spine, pelvis, and hip ROM in low back pain subjects and to test the implications for clinical application.

The initial SKD intensity aim was grade 4 (Lee, 2001; Chester et al., 2003). The question is whether both testers applied the SKD at a similar intensity. Since the intertester- and intratester reliability was good (resp. ICC_3,k = 0.81–0.93; ICC_3,1 = 0.70–0.84) it is likely that amplitude, displacement, and force applied to the skin were fairly similar for the two experienced physiotherapists. It remains to be determined whether a difference in intensity between less and more experienced physiotherapists exists. The SKD is increasingly used by physiotherapists during physical examination to determine whether or not a patient would benefit from FTMs. However, this needs to be assessed. It is conceivable that for clinical purposes fascial diagnostic testing needs to be adapted and optimized. Moreover, whether the same effects of SKD occur in people with low back pain needs to be investigated.

This study shows that lumbodorsal SKD affects the spine, pelvis, and hip range of motion in healthy subjects. Flexion ROM decreased by SKD whereas extension ROM increased. The range of motion change depended on the SKD location and direction. The reliability of the SKD was remarkably good. These results suggest that the SKD may be a promising interventional test to obtain an indication, whether or not, a patient would benefit from FTMs. Further research is warranted to obtain insight into the mechanisms by which SKD affects the spine, pelvis, and hip range of motion, muscle activation, force transmission, in healthy, asymptomatic, and low back pain subjects.