Trunk Extensor Muscle Activity during Exercises in Patients after Lumbar Fusion Surgery
Authors: Tarnanen S. , Neva M. , Häkkinen K. , Häkkinen A. 
Published: June 2012

Introduction The goal of postoperative rehabilitation after lumbar spine fusion (LSF) is to decrease pain and disability; however, back function should also be taken into account. Low trunk muscle strength has been reported in patients after LSF and it correlates with poor disability1. To increase the trunk muscle strength after fusion surgery the training should also include more intensive exercises. Exercises that are performed lumbar spine in a neutral position allow loading without the strain of fused segment. The purpose of present study was to determine trunk extensor muscle activity during different exercises and evaluate association between pain during loading and muscle activation in patients after LSF. Materials and Methods A total of 22 patients (50%women) with mean (SD) age of 59 (17) years who had undergone LSF 3 to 11 months earlier participated in the study. The indications for surgery were spondylolysis, degenerative olisthesis, spinal stenosis, and degenerative disk disease. Bilateral surface electromyography (EMG) activity of trunk extensor muscles (longissimus at the L1 level and multifidus at L5) was measured during dynamic upper limb exercise (bilateral shoulder flexion in the standing position). The load was individually adjusted using a pull machine so that each subject was able to perform 10 repetitions per set. In addition, lower limb exercise (right hip extension in the four-point kneeling position) with 10 repetitions and static back extension exercise (in the Biering-Sorensen test position) were studied. The starting and finishing points of the fifth repetition in the upper and lower limb exercises were determined from simultaneous EMG and video analysis, and this period was used for analysis. In static trunk extension exercise, the first 3 seconds were taken to analysis. The raw EMG signal was rectified and averaged. Then, the reference EMG activities obtained from maximal isometric trunk extension strength measurement (reference value) were used to normalize the EMG-activation levels collected for trunk muscle exercises. The intensity of back and leg pain during the past week and during the exercises was assessed by visual analogue scale (VAS, 0–100). Results The mean (SD) trunk extension strength was 341 (204) N. The highest activation in the longissimus was measured during the static back extension exercise. The activity on the right side was 104% and on the left side 83% when compared with the reference values. The corresponding values during bilateral shoulder flexion were 65 and 62%. The highest activity levels of the multifidus (62% on the right side and 64% on the left side) were also measured during the static back extension exercise. Activity levels of multifidus were 55% on the right side and 52% on the left side during bilateral shoulder flexion and 34% and 27% during right hip extension exercise. EMG activities of longissimus ( p < 0.005) and left multifidus ( p < 0.009) were higher during the static back extension than during the bilateral shoulder flexion exercise. The activation of longissimus and multifidus muscles was higher in the upper limb than in lower limb exercise (both p < 0.003). The average intensities of back and leg pain during past week were 19 (19) mm and 15 (20) mm, respectively. In all participants during the reference and exercises measurements, back pain was less than 16 mm and leg pain was less than 9 mm. No significant correlation was found between strength and pain in back or leg during measurements. Back pain correlated only with right side multifidus activity during static back extension exercise ( r = −0.45, p < 0.04). Conclusion Static back extension exercise elicited the highest longissimus and multifidus muscle activity. Bilateral shoulder flexion exercise in the standing position also elicited muscle activity that may be high enough to develop muscle endurance and strength characteristics. All studied exercises are feasible in the postoperative rehabilitation after lumbar fusion surgery because pain intensity remained at relatively low level. All studied exercises are performed in the lumbar spine in the neutral position, thus strain of fused segment is minimized. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Tarnanen SP, et al. 2012, Submitted