**3.4. Case n.4 low back pain 3D forward‐bending analysis and SEMG recording: the flexion‐relaxation phenomenon**

In this example, we introduce the analysis of the so‐called 'flexion‐relaxation phenomenon' (FRP) to show that the 'stop' of such phenomenon, that is, usually related to muscular spasms due to pain in LBP patient during acute phase, can exist even when the pain disappears. Movements in the lumbar spine, including flexion and extension, are governed by a complex neuromuscular system involving both active (muscle) and passive components (vertebral bones, inter‐vertebral disks, ligaments, tendons and fascia) [38]. There is evidence to suggest that EMG differences at paravertebral muscles exist between patients with back pain and healthy subjects during dynamic flexion tasks performed at peak flexion [38]. To this extent, several studies have examined the apparent myoelectric silencing of the low back extensor musculature during a standing to full trunk flexion manoeuvre named as FRP (**Figure 14**). The electrical signal reduction or silence that occurs in healthy subjects during lumbar spine flexion has been hypothesized to represent the extensor musculature being relieved of its moment‐supporting role by the passive tissues, particularly the posterior spinal ligaments

**Figure 13.** Upper panels: comparison between trunk unbalancing and spinal deformities induced by pain in LBP patient at acute phase and the postural improvement obtained after treatment (control evaluation). Lower panels: lateral bending tasks, revealing the patient's functional impairment of spinal mobility due to pain (left panels), compared with recovered range of movement after treatment (right panels).

A 3D Spine and Full Skeleton Model for Opto-Electronic Stereo-Photogrammetric Multi-Sensor... http://dx.doi.org/10.5772/intechopen.68633 37

after 1 month of treatment, when she recovered from acute phase (**Figure 13**). It is immediate to notice the improvement in both frontal and sagittal planes for orthostatic analysis as well as for spine mobility during lateral‐bending test. At acute phase, the patient was presenting spine deformities and trunk unbalancing induced by pain. In sagittal plane, the physiological lordosis was almost completely flattened. In addition, a severe functional impairment in the range of movement as well as blocked compensation curves is evident. After the treatment programme that removed pain, the compensation curves disappeared sagittal spine shape

**3.4. Case n.4 low back pain 3D forward‐bending analysis and SEMG recording: the** 

In this example, we introduce the analysis of the so‐called 'flexion‐relaxation phenomenon' (FRP) to show that the 'stop' of such phenomenon, that is, usually related to muscular spasms due to pain in LBP patient during acute phase, can exist even when the pain disappears. Movements in the lumbar spine, including flexion and extension, are governed by a complex neuromuscular system involving both active (muscle) and passive components (vertebral bones, inter‐vertebral disks, ligaments, tendons and fascia) [38]. There is evidence to suggest that EMG differences at paravertebral muscles exist between patients with back pain and healthy subjects during dynamic flexion tasks performed at peak flexion [38]. To this extent, several studies have examined the apparent myoelectric silencing of the low back extensor musculature during a standing to full trunk flexion manoeuvre named as FRP (**Figure 14**). The electrical signal reduction or silence that occurs in healthy subjects during lumbar spine flexion has been hypothesized to represent the extensor musculature being relieved of its moment‐supporting role by the passive tissues, particularly the posterior spinal ligaments

**Figure 13.** Upper panels: comparison between trunk unbalancing and spinal deformities induced by pain in LBP patient at acute phase and the postural improvement obtained after treatment (control evaluation). Lower panels: lateral bending tasks, revealing the patient's functional impairment of spinal mobility due to pain (left panels), compared with

recovered range of movement after treatment (right panels).

and the spine mobility really improved.

36 Innovations in Spinal Deformities and Postural Disorders

**flexion‐relaxation phenomenon**

**Figure 14.** The FRP (a) in the upper panel, the ranges of variation of spinal sagittal angles and of pelvis tilt for a healthy subject performing a forward‐bending manoeuvre are displayed. Full skeleton reconstructions (sagittal views) taken in the five most significant time events of the motor task are superimposed to graphs. (b) The lower panel represents paravertebral muscles activity recorded by SEMG, from which it can be emphasized that, in a healthy subject, a paravertebral muscles relaxation occurs when the maximum bending position is reached.

[41]. Likewise, a failure of the muscles to relax in patients with back problems is indicative of heightened erector spinae‐resting potentials or underlying back muscle spasticity. Similar phenomena have been documented also in neck pain [42].

In this section, we present a case study to show and analyse some new aspects about the FRP connected to LBP and impaired functional behaviour at lumbar level. The upper panels of **Figure 15** describe the outcomes of the analysis of the execution of a forward‐bending manoeuvre performed by a healthy subject and by LBP patient in acute phase and by the same patient at follow‐up, after recovering from acute phase. The graphs represent the measure‐ ment of SEMG activities recorded in the left and right MF and ESLD paravertebral muscles as explained above in Section 2 (SENIAM recommendations [37]). The 3D skeleton reconstruc‐ tion at maximum forward flexion and photos of the subjects are also shown. We remind here that the forward‐bending test is defined by the following sequence: from erect standing to maximum forward flexion maintained for a few seconds and then a final extension movement back to erect standing. For this test, the most significant kinematic information comes from sagittal plane ROMs (see **Figure 14**) measured along the execution of the full movement of spine angles (thoracic kyphosis and lumbar lordosis) and pelvis tilt (measured as the inclina‐ tion of the S1–S3 vertebral segment with respect to the vertical gravity line). By using the 3D skeleton model, the inter‐vertebral trunk torques (in the sagittal plane) are assessed as well, during the performance of the test. While there are large obvious differences between healthy and LBP subject in acute phase (this latter being not able to perform a complete forward bend‐ ing due to pain), more interesting is to focus the analysis on the differences that persist even after the LBP patient recovered from pain. **Figure 15** presents in the lower panels a com‐ parison between a healthy subject versus LBP patient (at follow‐up evaluation, when no more pain was present). As it can be noted, from the comparison of the time courses of both ROMs

**Figure 15.** Forward bending results for healthy subject and LBP patient. 3D skeleton reconstruction at maximum forward trunk flexion and measured SEMG activity during the forward‐bending test (upper‐row panels). Comparison healthy subject versus LBP patient on spine and pelvis measured sagittal ROMs (lower‐left panels) and flexion torques patterns (lower‐right panels), respectively.

(of spine and pelvis sagittal angles) and flexion torques, the healthy subject presents with respect to the pathological one, both a noticeably lower trunk torques (especially at S1–L5 low lumbar levels) and a wider range of spinal angles, with a different pattern showing different strategies in task execution.

In particular, the LBP patient shows a lower mobility in the lumbar spine with a decrease of the ROM quantified in more than 25° lordosis angle value at maximum forward flexion, compen‐ sated by a higher mobility in the pelvis that presents an increase of the ROM quantified in more than 10°at maximum forward flexion. Conversely, thoracic spine mobility ranges are compara‐ ble in the two subjects. Such a condition reveals a stiffer behaviour in the lumbar spine of the LBP subject that could be connected to the still persistent FRP stop. In fact, SEMG recordings show, in the healthy subject, a clear presence of FRP as expected, while LBP subject still shows a full contraction activity in all the considered paravertebral muscles, that is, FRP stop. Further studies are currently in progress to determine, on a larger LBP population, if such described FRP stop could relate to modified stiffer pattern and reduced lumbar mobility as observed in this case.
