The Effect of Initial Posture on The Performance of Multi-Joint Reaching Tasks: A Comparison of Joint Excursions Between Individuals With and Without Chronic Low Back Pain Erica Johnson and James S. Thomas. School of Physical Therapy, Ohio University, Athens, OH Introduction Low back pain (LBP) is a prevalent and costly health concern. Approximately 90% of adults will suffer from an episode of LBP at some time in their lives, 50% will have a recurrent episode and 5-10% will develop chronic and potentially disabling LBP 1-3. However, there is no clear consensus on the best treatment for this condition. Conservative treatment may include manipulation, myofascial release, exercise, modalities, and a number of other treatment options. Conservative treatment often includes flexibility exercises, especially of the hamstrings. Many clinicians support this practice on the theory that normal hamstring length will prevent excessive lumbar flexion during postures that place the hamstrings in a lengthened position such as forward bending 4-6. McGill has shown that increased lumbar flexion during forward bending tasks increases anterior shearing forces on the spine and increases risk of injury. However, there are few studies that have examined the influence of hamstring flexibility on hip and lumbar spine joint excursions during forward reaching or bending tasks. Therefore, we performed a retrospective examination of data from our lab to evaluate the influence of hamstring flexibility as measured by hip flexion with the knee extended (i.e. straight leg raise) on hip and lumbar spine joint excursions. Methods Data from participants of two prior investigations were analyzed for this study. Study 1 consisted of one group of participants: Recovered - currently pain free after an acute episode of low back pain (n= 48 men, 52 women)8. Study 2 consisted of two groups of participants: Healthy- no history of low back pain (n= 8 men, 10 women) and Chronic Low Back Pain- back pain greater than 3 months duration (n=8 men, 10 women) (Unpublished findings). In these two prior studies, hamstring flexibility was assessed with the knee straight (SLR) using a bubble goniometer following standard methods 9. Hip flexion range of motion was also assessed with the knee bent to evaluate the full flexion range available. No movement restrictions were found with hip flexion in any of the participants that would limit evaluation of hamstring flexibility. In both studies, participants performed reaching tasks to two target locations based on their individual anthropometric characteristics. Specifically, the high and low targets were positioned in the mid- sagittal plane such that target contact could be made, in theory, with 90° of shoulder flexion and 15° and 60° of hip flexion, respectively. These target heights were chosen to vary the amount of flexion of the hip and spine needed to reach the target. Participants in Study 1 then performed a maximum forward bending task (FBT) by starting in a standing position and bending forward as far as possible as if to touch the toes while keeping the legs and arms straight. Joint motions were measured using The Motion Monitor™, a magnetic based kinematic system. The change in joint angle from initial to final posture (i.e. target contact or end range flexion) was extracted using custom software. To assess the influence of hamstring flexibility on joint excursions, separate bivariate correlation analyses were performed between SLR measures and hip and lumbar spine joint excursions used during the standardized reaching tasks and the FBT. These analyses were performed separately for the right and left sides. Data Analysis Separate bivariate correlation analyses were performed between SLR measures and hip and lumbar spine joint excursions used during the standardized reaching tasks and the FBT to assess the influence of hamstring flexibility on joint excursions. These analysis were performed separately for the right and left sides. Results Excursions of the lumbar spine and hip during the reaching tasks and FBT were not significantly correlated with SLR for the Recovered or LBP groups. A significant negative correlation was found in the Healthy group between SLR and lumbar spine excursions only during the forward reaching task to the low target (Table 1). For the Recovered group, mean (SD) SLR for the right side was 56.8° (±9.1) and 61.7° (±10.0) for the left side. For the LBP group, mean SLR was 72.3° (±10.5) for the right side and 68.2° (±12.2) for the left side. Mean SLR for the Healthy group was 80.7° (12.3) for the right side and 77.2° (±13.7) for the left side. Mean SLR in the Healthy group was significantly greater than the mean SLR in the Recovered and LBP groups p<.05. However, there was no corresponding significant difference between the Healthy and LBP group for amount of lumbar excursion during the forward reaching tasks. Conclusions The results of this study show that there was a significant negative correlation between hamstring flexibility and lumbar excursions in healthy individuals indicating that with greater hamstring flexibility less lumbar flexion excursion is employed to complete forward reaching tasks. However, in individuals with LBP or who have recovered from an episode of LBP flexibility of the hamstrings, as typically measured clinically, correlates poorly with hip and lumbar spine excursions during forward bending and reaching tasks. These results indicate that hamstring flexibility is not strongly related to the amount of lumbar flexion used to perform these tasks in these individuals. These results support the findings of a study by Li et al in which the amount of lumbar motion during partial and full forward bending was not significantly affected after a stretching intervention to increase hamstring extensibility in spite of the fact SLR and active knee extension increased significantly(Li, McClure et al. 1996). These findings refute the assumed relationship between hip flexibility and lumbar motion during various tasks 4, 5. It appears unlikely that increasing hamstring flexibility will translate into changes in movement patterns in individuals with LBP or those recovered from LBP. Moreover, a recent study showed that a daily stretching protocol increases hamstring stretch tolerance, but does not result in lasting changes in muscle extensibility. It is possible that there is a lower limit to the amount of hamstring flexibility required to complete forward reaching and bending tasks while maintaining optimal posture of the lumbar spine, but that is outside of the scope of this study. More research needs to be conducted to examine the influence of hip flexibility on observed movement patterns to further evaluate the efficacy of flexibility training in the rehabilitation of patients with low back pain. This research was supported by The National Institutes of Health Grant R01-HD to J.S. Thomas