THE INFLUENCE OF CHRONIC BACK PAIN ON KINEMATIC RULES UNDERLYING MULTI- JOINT REACHING MOVEMENTS. J.S. Thomas, PhD, PT & Christopher R France, PhD* School of Physical Therapy, Department of Psychology*, Ohio University, Athens OH Introduction Reaching tasks such as ringing a doorbell, wiping a child’s face or retrieving the morning paper require the control and coordination of the trunk and limb segments in order to perform these tasks smoothly and effortlessly. Given the number of segments involved in these whole-body reaching tasks there are an infinite number of ways in which these tasks can be completed. Bernstein (1967) hypothesized that the CNS resolves the problem of kinematic redundancy by reducing the independent degrees of freedom required to complete the task. By imposing some rules by which coordinated movements are performed, complex multi-joint tasks are simplified. Using principal components analyses of time series segment motions we have shown that there are similar characteristics regarding the apportionment of motion to segments in a whole body reaching task that can be generalized across healthy individuals. The purpose of this research was to determine whether chronic low back pain leads to changes in the how motion is apportioned to various segments in a whole body reaching task. Methods The time-series changes in orientation of the forearm, humerus, trunk, pelvis, thigh, and shank were measured in 30 subjects (13 individuals with chronic low back pain and 17 healthy individuals) performing whole-body reaching tasks. In this paradigm the targets were located around a clock face such that the subject could, in theory, reach them by flexing the hips 20 , 40 , 60 , and 80  with the shoulder flexed 90  and the elbow extended (Figure 1). The target locations were chosen to create a task that progressively challenges the subject with larger excursions of the trunk. The segment orientation angles were measured in a counterclockwise direction as seen from the subjects right side, starting with horizontal equal to zero degrees. Subjects reached for the targets at two speeds (self-selected and fast-paced) and were given no instructions on the limb segment geometry to use while performing these reaching tasks. The time-series segment kinematics were analyzed by principal component (PC) analyses to determine if there was a commonality amongst the shapes of the waveforms across segments, across trials, and across subjects. Principal component analyses were also performed on the scaling of the kinematic waveforms across the experimental manipulations, to probe for any lawful relationships amongst their relative magnitudes. Results Comparison of waveform shapes: PC analyses of the time series segment motions revealed that the shape of the segment motion waveforms within a given trial were nearly identical for both healthy individuals and those with chronic LBP. The EigenCurve illustrated in figure 2B accounts for 99.86% of the total angular variance of the time series waveforms in figure 2A. These findings indicate that individuals with chronic LBP (at least confronters) use a similar shaped segment waveforms to perform these reaching tasks. Comparisons of scaling of waveforms: PC analyses of the scaling coefficients from each movement trial of every subject revealed that three principal components could account for greater than 95% of the total angular variance for these 6 DOF reaching tasks. This finding held for both healthy individuals and those with chronic low back pain. However, examination of the factor loadings for each group revealed important differences in these two groups. The factor loadings from the first movement component for healthy controls are as follows: shank=-.165, thigh=-.367, pelvis=.700, trunk=.893 humerus=.924, and forearm=.882. In contrast, the factor loadings for individuals with chronic back pain are: shank=.023, thigh= -.544, pelvis=.915, trunk=.829, humerus=.946, and forearm=.732. Conclusions Kinematic Rules: Based on the PC analyses of the segment kinematics of individuals with and without chronic low back pain performing reaching tasks that necessitate some forward bending of the trunk we have identified rules that are consistent across groups and have identified how movement strategies may be adapted with chronic back pain. Kinematic Rule 1a. Within any given movement trial of a multi-degree of freedom reaching task, the shapes of the sagittal plane segment orientation waveforms are nearly identical. Kinematic Rule 1b. There is one common waveform that describes the change in segment orientations in the sagittal plane amongst all the segments used in a multi-degree of freedom reaching task that is valid for all subjects across target locations, movement speeds. Kinematic Rule 2a. A relationship exists amongst the scaling coefficients of the kinematic waveforms for these 6-DOF reaching tasks (in individuals with and without chronic back pain) such that the scaling of these waveforms can be well described by only 3 principal components. Kinematic Rule 2b. While commonalities exists in motor coordination strategies across subject populations, chronic back pain leads to changes in how motion is apportioned to various limb and trunk segments in these multi-joint reaching tasks. Figure 1. Target locations were determined from the subject's on arm length, hip-to-shoulder length and hip height Subjects could reach the low target, in theory, by flexing their hips 60° (with the elbow extended and the shoulder flexed 90°) without any motion of the ankle, knee, or spine. Figure 2. A) Time series segment motions for an individual with chronic LBP and B) The EigenCurve and six scaling coefficients derived from time series data with PC analyses. Greater than 98% of the total angular variance from the time-series segment angle data can be accounted for by the first principal Eigencurve. Hip-to-shoulder length Hip Height Arm Length 60° Target Figure 3. The 24 time normalized first principal EigenCurves from this subjects movement trials are plotted. These waveforms and those from each movement trial of every subject were analyzed by PC analysis to determine the commonality of the shape of the waveforms. Consistent with our previous findings from healthy subjects, we were able to identify a common waveform in individuals with chronic back back pain. Figure 4. The change in segment orientation from initial posture to target contact ( i.e.  ) for the thigh, pelvis, and trunk are plotted for each trial of every subject. The data from the chronic low back pain group and from healthy normal subjects have each been been fit by a plane. Individuals with chronic back pain used increased pelvic flexion and reduced trunk flexion to perform these reaching tasks. They compensated for these changes at the humerus and forearm segments. These differences are consistent with the differences seen in the factor loadings of the 1 st principal component. Figure 5. Stick figures illustrating posture at contact with the 80  target in individual participants with and without low back pain. The individual with chronic pain tends to apportion motion to the limb and trunk segments such that the amount of lumbar flexion is reduced. A B This work was supported, in part, by a grant from the National Institutes of Health R01 HD , and an Ohio University Baker Award