We have recently shown, using transcranial magnetic stimulation (TMS) to assess voluntary activation (VA), that neural drive to back muscles is reduced in subjects with chronic low back pain. There is also evidence that central nervous system drive to abdominal muscles is altered in these subjects, however VA has not yet been assessed for these muscles in healthy subjects; this is the purpose of the present study. Twenty one healthy subjects (10M:11F) participated. Electromyographic activity was recorded from back and abdominal muscles and flexor torque was measured using a dynamometer. Subjects performed a series of isometric voluntary contractions (10%–100% MVC) of rectus abdominis during which TMS was applied to the motor cortex. The resulting superimposed twitches (SIT) were measured and VA was derived.Background:
Methods:
Characteristics of muscle activity, represented by surface electromyography (EMG), have shown differences between patients with low back pain and healthy adults; how they relate to functional/clinical scales remains unclear. The purpose of the current study was to examine the correlation between frequency characteristics of EMG and patients' self-rated score of disability using continuous wavelet transform (CWT) analysis. Fifteen patients with chronic mechanical low back pain (LBP) and 10 healthy adults were recruited. Patients completed the Roland-Morris Disability Questionnaire (RMDQ) and bilateral EMG activity was obtained from erector spinae at vertebral level L4 and T12. Subjects performed 3 brief maximal voluntary contractions (MVCs) of the back extensors and the torque was measured using a dynamometer. CWT was applied to the EMG signals of each muscle in a 200ms window centred around the peak torque obtained during the MVCs. The ratio (low/high frequencies) of the energy, the peak energy, and the frequency of the peak energy were calculated for each muscle and then averaged and correlated with the individual's RMDQ score. Patients had significantly lower peak power than the controls (p=0.04). Additionally, RMDQ positively correlated to the average ratio of energy (rho=0.71; p=0.01), meaning higher disability corresponded to a dominant distribution of energy in the lower-frequencies; but negatively correlated to the average frequency of peak energy (rho=-0.61; p=0.035), meaning lower frequency of peak energy corresponded to higher levels of disability.Purposes of the study and background
Methods and Results
