Assessment of the pathology involving injury and dysfunctions of the spine has led to numerous philosophies and methodologies of assessment and treatment intervention to improve clinical outcomes. Varying the exercise protocols and prescriptions is a common method to influence muscle stabilization of the spine. Trunk extensor endurance tests are one method of objectifying low back function. The purpose of this study was to examine the effects of three different endurance exercise protocols on isometric holding time of the trunk extensor muscles in a normal group of subjects. The null hypothesis was that there will be no significant differences in the mechanical endurance of the trunk extensor muscles in the experimental groups compared to the control group. The methods included 52 healthy volunteer subjects who were randomly assigned to one of the four groups comprised of active individuals without a recent history of low back pain or pathology. There was 1 control group and 3 exercise groups targeting various trunk and lower extremity muscles groups and combinations at specific exercise frequencies and intensities. The self-directed home exercise training was performed at a frequency of three times per week, ranging fro 35 to 90 minutes for each exercise session, depending upon group assignment. The exercise prescription emphasized relative perceived exertion (RPE) grading of muscle contractions during exercises in an effort to optimize muscle recruitment. Tests were performed every two weeks for 8 weeks and emphasis was placed on an EMG monitored trunk extensor test to failure. The RPE scale was also used to determine perceptual fatigue during testing, as well as to rate the intensity of each muscle contraction during home exercises. Results of this study indicate that 8 weeks of training in all three trunk exercise protocols promoted statistically signifiant changes in trunk extensor endurance. Gender and somatotoype were found to be statistically significant in association with the modified Sorensen Test scores. Most of the endurance gains by the exercise groups were acquired in weeks 2-8. No significant differences were observed when the 3 exercise protocols were compared with each other. Group #1 exercised the extensors of the hip and spine, group #2 added the abdominals and quadratus lumborum and group #3 added a resistance exercise in standing to integrate trunk and lower extremity extensor muscles. Expressed as a percentage, the changes in mean holding time via the modified Sorensen Test indicated the control group improved .55%, exercise group #1 improved by 22.7%, exercise group #2 improved by 24.8%, and exercise group #3 improved by 26.4%. The exercise protocol and prescription used in this study was observed to significantly increase spine extensor endurance. Further studies regarding modifications of the protocol or exercise prescription may be appropriate.
