A comparison of pain level and entropy changes following core stability exercise intervention

Abstract

Background: As reported in our previous studies, the complexity of physiologic time series is a sensitive measure of muscle fatigability. This study compared the differences between 2 different analyses following 4 weeks of core stability exercises (CSE) in subjects with and without chronic low back pain (LBP). We examined whether the observed Shannon (information) entropy, as compared with median frequency (MF), was able to differentiate fatigability of the thoracic and lumbar parts of the erector spinae (ES) muscles following the intervention.

Material/methods: In total, 32 subjects participated in this study. There were 13 subjects in the CSE intervention group (average age 50.4 ± 9.1 years) and 19 subjects in the control group (average age 46.6 ± 9.1 years). The CSE group performed the specific exercise intervention, but the control group was asked to maintain their current activity and/or exercise levels. The endurance of the back muscles was determined by using a modified version of the isometric fatigue test as originally introduced by Sorensen.

Results: Pain level decreased significantly for all subjects (F=25.29, p=0.001), but there was no difference between groups (F=0.42, p=0.52). The MF was not different between groups following treatment (F=0.81, p=0.37). Although there was no entropy level changes following treatment (F=0.01, p=0.93), the interactions between muscles and groups following treatment were significant (F=7.25, p=0.01). The entropy level decreased in both thoracic ES muscles following intervention in the exercise group, while remaining the same in the control group.

Conclusions: Although the change in pain level was not different between groups, the Shannon entropy measure more sensitively differentiated the exercise intervention than did MF. In addition, the results also suggested that complexity is related to muscle fatigue, which corresponds to the values of entropy between groups. Further studies are needed to investigate the effectiveness of nonlinear time series of EMG data for fatigability.

Figure 1

Modified Sorensen test for fatigue measure. The subject is shown with EMG electrodes attached over the thoracic and lumbar erector spinae (ES) muscles of the low back. During this test, subjects lay prone and lift their trunks off the table for one minute.

Figure 2

Pain changes based on million visual analogue scale (MVAS) following intervention. Pain in the low back was measured using a horizontal analogue scale, with options ranging from 0 to 100 mm, in which 100 mm reflected the worst pain imaginable. The pain level decreased significantly (F=25.29, p=0.001), but there was no difference between groups (F=0.42, p=0.52).

Figure 3

Shannon entropy measurement for thoracic and lumbar ES muscles. Although there was no entropy level change following treatment (F=0.01, p=0.93), the interactions between muscles and intervention following treatment were significant (F=7.25, p=0.01). The entropy levels of the ES muscles decreased following intervention in the exercise group, but remained the same in the control group. (R: right, L: left, TES: thoracic erector spinae muscle, LES: lumbar erector spinae muscle).

Figure 4

The median frequency (MF) measurements for thoracic and lumbar ES muscles. There was no change in the MF following treatment (F=0.81, p=0.37); however, there were significant differences among the muscles (F=39.36, p=0.0001). Both sides of the LES muscles revealed significantly higher MF values compared with the other muscles. (R: right, L: left, TES: thoracic erector spinae muscle, LES: lumbar erector spinae muscle).