Back extensor muscle strength and fatigability in female patients with idiopathic chronic low back pain

Strength and fatigability characteristics of back extensor muscles in female patients with chronic low back pain (CLBP) (mean age 47.3 yrs, n=9) and in age- and gender-matched healthy controls (45.6 yrs, n=10) were recorded in this study. Maximal isometric voluntary contraction (MVC) force of the back extensor muscles was measured by standard back dynamometer. Sorensen isometric back endurance test until exhaustion with the recording of electromyographic (EMG) power spectral changes was performed. MVC force was significantly (p<0.05) lower and endurance time was shorter in CLBP patients (24.1% and 24.4%, respectively) than in controls. EMG spectral median frequency (MF) declined (p<0.05) during Sorensen test as time of isometric contraction progressed, whereas no significant inside-group differences between right and left side were observed in CLBP patients and controls.