Experimental low back pain decreased trunk muscle activity in currently asymptomatic recurrent low back pain patients during step tasks

Low back pain (LBP) patients demonstrate reorganized trunk muscle activity but if similar changes are manifest in recurrent LBP patients (R-LBP) during asymptomatic periods remains unknown. In 26 healthy and 27 currently asymptomatic R-LBP participants electromyographic activity (EMG) was recorded from trunk and gluteal muscles during series of stepping up and down on a step bench before and during experimentally intramuscular induced unilateral and bilateral LBP. Pain intensity was assessed by numeric rating scale (NRS) scores. Root-mean-square EMG (RMS-EMG) normalized to maximal voluntary contraction EMG and pain-evoked differences from baseline (Delta-RMS-EMG) were analyzed. Step task duration was calculated from foot sensors. R-LBP compared with controls showed higher baseline RMS-EMG and NRS scores of experimental pain (P<0.05). In both groups, bilateral compared with unilateral experimental NRS scores were higher (P<0.001) and patients compared with controls reported higher NRS scores during both pain conditions (P<0.04). In patients, unilateral pain decreased Delta-RMS-EMG in m. iliocostalis and bilateral pain decreased Delta-RMS-EMG in all back and gluteal muscles during step tasks (P<0.05) compared with controls. In controls, bilateral versus unilateral experimental pain induced increased step task duration and trunk RMS-EMG while both pain conditions decreased step task duration and trunk RMS-EMG in R-LBP patients compared with controls (P<0.05).

PERSPECTIVES: Task duration and trunk muscle activity increased in controls and decreased in R-LBP patients during experimental muscle LBP. These results indicate protective strategies in controls during acute pain while R-LBP patients showed higher pain intensity and altered strategies that may be caused by the higher pain intensity, but the long-term consequence remains unknown.