An investigation into motor pattern differences used during prone hip extension between subjects with and without low back pain

Abstract

Summary Objective The objective of this study was to investigate whether any differences exist between subjects with and without low back pain (LBP) in the motor patterns of the gluteus maximus (GM), hamstring (HAM), contralateral erector spinae (CES), and ipsilateral erector spinae (IES) muscles during prone hip extension (PHE). Design Cross-sectional observational. Setting The Anglo-European College of Chiropractic. Subjects A convenience sample of 31 non-LBP subjects and 20 unilateral LBP subjects who met the exclusion criteria. Methods Each subject performed two sets of five repetitions of PHE. Surface electromyography recorded the activity within the four muscles and a pressure transducer was used to determine the onset of leg movement. For the non-LBP sample, only the right leg was tested. For the LBP sample, both legs were tested. This gave rise to three “groups” for comparison purposes: non-LBP (N), LBP-symptomatic leg (S), LBP-asymptomatic leg (A). Within-subject consistency was assessed by calculating the mean number of different activation orders used per set as well as the frequency with which the “average” activation orders of both sets agreed. The frequency with which each of the possible activation orders was used and the frequency with which each muscle became active first, second, third, and fourth in the activation order were calculated. The mean onset times of each muscle relative to the onset of leg movement as well as to the other muscles were also calculated. Results In general, the LBP sample demonstrated greater within-set and between-set consistencies in both legs compared to the non-LBP sample. No distinct differences were found between the samples in terms of the frequency with which the individual activation orders were used or the frequency with which each muscle became active at a particular rank. Although several statistically significant differences were noted in the relative onset times of the muscles, the one consistent pattern to emerge from the data is that the activation of the GM was delayed in both legs of the LBP sample. The magnitude of this delay relative to the onset of leg movement was 107.5 ms (95% CI = 78.3–136.7 ms) on the symptomatic side and 75.4 ms (95% CI = 47.8–103.0 ms) on the asymptomatic side. Conclusions Although the activation of the GM appears to be delayed in both legs during PHE in unilateral LBP subjects, there are several issues, that make the clinical significance of this finding debatable. Further research needs to be performed in order to better understand the importance of this apparent motor control alteration in the diagnosis and treatment of LBP.