Electromyographic analysis of the lumbar erector spinae muscles: Influence of position, a history of low back pain, gender and muscle location on fatigue and recovery

Epidemiological studies have shown correlations between the low endurance capacity of the erector spinae muscles and low back pain (LBP). The rate of decline in the median frequency (MF) of the surface electromyography (EMG) power spectrum has been evaluated for monitoring the fatigability of the erector spinae muscles during the performance of submaximal isometric contractions. In the majority of the previously reported studies, the EMG data has been collected while the lumbar spine was in a lordotic position with the extensor muscles shortened. However, in many daily activities, the erector spinae musculature function in a lengthened position. Therefore, it is of importance to investigate the fatigue behavior of the erector spinae in postures resembling those in which the muscles most commonly function. The intent of this study was to gain more information on how a change in the length of the back musculature affects two MF variables (MF fatigue and MF recovery). ^ Twenty-six college students (12 males and 14 females) between the ages of 18–25 voluntarily participated in the study. Sixteen (8 males and 8 females) had no history of LBP, while the remaining ten subjects had a history of a resolved LBP episode within the past year. Using surface electrodes, EMG data from the lumbar erector spinae muscles (bilaterally from L2 and L5 levels) was collected during a sustained (90-seconds) submaximal (70% maximal voluntary contraction) isometric contraction utilizing a Kin-Com dynamometer. A one-minute rest period was given followed by a 5-second recovery contraction. The subject performed the sustained isometric contraction and the recovery contraction with the lumbar spine in a neutral position (0 degrees) and in a 30-degree forward flexed position measured with an inclinometer. The data was analyzed to determine differences in the MF fatigue and MF recovery between two lumbar positions, between subjects with and without a history of LBP, between muscle location and between genders. Statistical analysis of the data described was carried out using two separate repeated measures analysis of variance for MF fatigue and MF recovery to detect statistical significance. Post-hoc testing was performed to discern any interactions. The alpha level was set at .05.